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A STUDY OF COLD-WORKED
LOWBGABBON STEEL
and
AN INVESTIGATION
or TUBE EAILUBE I]

moo 1b. 301m

. Ihesie
submitted.To The Faculty
of
Michigan State College
of Agriculture and.Applled Science
in Partial Fulfillment
of the
Requirements For A.Degree
of

Mae§eerf Science‘

-—.._.——-

f 4
”1

C. Le 0mm}.
June 1937

I wish to thank and acknowledge my in-

debtedness to Professor H. Pnblow, Dept.

of Chemical Engineering, Michigan State

College. for the help and advice he so

willingly gave me in the writing of
this thesis.

d!.\. ‘1
5i);!u}fi§¥

INDEX

SECTION I. - A STUDY OF GOLD-WORKED LOW-CARBON

STEEL.

SECTION II - LN INVESTIGATION Ol' TUBE FAILURE

IN 11:00 lb. 301m.

SECTION I.

A STUDY Ol' COLD-WEED
LOW-CARBON STEEL.

 

 

 

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INTRODUCTION

One of the chief difficulties confronting the steel manufacturer
is his endeavor to supply'the steel fabricator with material which will
not only meet all of’the physical requirements, but also satisfactorily
withstand the deformation required to produce the fabricated part.

Failures are particularly'noticeable where the steel must have ductility,
that is, low-carbon steel. This is indeed unfortunate as the physical and
mechanical pr0perties of this type of steel has increased the volume of its
use until it is now well-defined.by many as the ”steel of commerce.I

The use of tremendous pressure upon dies to deform flat, strip steel
naturally'demands a certain degree of ductility. Steel of this type is
‘usually first formsd.into strips by'hot-rolling the original ingot. By
hot-rolling is meant the working of the metal above the recrystallisation
range to retain certain desireable properties such as small grain size and
toughness.

The particular steel under observance in these pages is what is termed
"killed steel"; that is, ”Molten;steel which has been.held in the ladle,
furnace, or crucible (and usually treated with Aluminum, Silica, or Manganese)
until no more gas is evolved and.the ladle is perfectly quiet.“ Figure No. 1
illustrates the effect of this "killing“ {

of the steel is to decarburise the outer

  

sections of the ingot. The ingot or

'CAKBURt 2.,

casting is then hot-rolled in several ; *“‘~

 

reducing Operations until the thin or ~—*
FIGURE NO. 1
strip steel is obtained. The strip

steel is then subjected to cold, working at the place where the fabrication

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is to take place, the great force of the dies forming the shape desired.

For the metal used in the Terraplane Clutch Plate made by the Motor
Wheel Corporation, Lansing, Michigan, the description in the above para-
graphs adequately pictures the preliminary steps in its manufacture.
However, there are five distinct pressing Operations whereby the strip
metal is prOgressively shaped into the final or finished product. It has v
often been the failure of a certain shipment of this steel to withstand
this progressive deformation that has been the source of many tons of
scrap metal and the loss of much money to both the steel manufacturer and
the consumer.

It is the purpose of this paper to investigate the structure and
various preperties exhibited by various sections of the clutch plate after
being subjected to one or more of the pressing operations. This will entail
a discussion of such items as cold-working theory, plagic and elastic
deformation, structure of grain boundaries, reduction of area by working,
and grain movements.

The paper will be divided into three parts, viz., (l) The analysis
of the various sections of the clutch plate; (2) The advancement of various
theories relative to the cold—work phenomena exhibited in part one; and (3)

A summary and conclusion involving cold-worked metal as found by the author.

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METHOD OF CUTTING SECTIONS

Sections were cut from the clutch plate as follows: Section A.was
cut from a plate that had undergone the first pressing operation; Section
B, from one involving two pressing Operations: and Section E, after all
five Operations had.been performed, or in other words, the finished.product
as far as the shaping of the piece was concerned. Sketches of the three
sections are shown in figure NO. 2, giving the actual sizes and shapes
of each from a cross-sectional view. Each section will be discussed sep-
arately. It is to be understood that each section is in itself a different
piece of metal, and not the same piece at different stages of pressing.
There will also be fOund, at the end.of this section, tables showing the

data collected, and an index to the photomicrographs shown.

§DCTION "A“

This section was shown to be a ”killed steel", with the carbon seemingly
concentrated in the center of the specimens of A2, 13, Au, and.16,(for loc-
ation of specimens in section, see Figure No. 2) with the edges composed of
larger ferrite grains which hays little or no pearlite intermingled with them.
That is, the outer edge of each specimen has been decarburized due to the
"killing" of the steel. “Ghost linestare in evidence in the specimens named
above, the photomicrographs of those depicting the typical structure of the
center portion of the strip of metal. "Ghost lines are long bands of ferrite
grains in the direction of the working“, and in which the carbon.has seemingly
been pushed to one side to give a white line effect due to the ferrite grains.

The phenomena of Specimen 11 and.Specimen A5 being uniform in grain size
through out can be well explained.in Figure No. 3. With Figure No. l in mind,

and.looking along the plane EDFG, it can be seen that the carbon would be more

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Figure No. it Figure No. 5
Specimen NO. A Specimen No. A
1 2
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concentrated in the encircled area. With the plane EDFG representing the
cross-sectional view of the section before being pressed into the form
exhibited in Figure No. 2, it can be seen that a certain portion of this
section will have the edges decarburized and the center containing carbon
to a much greater degree, while the portion on the one end would tend

to be somewhat decarburized throughout the entire cross-section. With

specimen ‘1 appearing

 

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plane, the latter

would thus exhibit a

decarburized area only on the two narrow edges. Thus specimen A1 would

tend to have uniform grain size throughout, due to the uniformity of structure
exhibited.

Photomicrographs were taken at 100x, 2501, 5001, and 10001. Figures
No. h to 13 inclusive are photomicrographs taken at 1001, in which the essentials
outlined above are clearly exhibited. Figures No. N and.NO. 13 clearly exhibit
the uniform structure typical of Specimens A1 and.ts.

The photomicrographs at 2501, rigures No. in to 19, inclusive, were taken
to get the average shape Of the grains. The grains were found.to be polyhedral
and.undistorted.

In the pictures of‘higher magnification fOr this section, white strips
appeared in many instances in the Junctions of grain boundaries. sometimes
near pearlite grains, but not necessarily so. Cementite is supposed to have
the chemical formula 3e36, the hardest iron compound.in steel. Sometimes,

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being lmown as "divorced” cementite. When etching a specimen of steel.

the solution will attack or ”eat-out” all the constituents to a barked degree
except cementite, which remins unnattacked. Thus the ferrite grains will

be at a lower plane than the cementite. If, when focusing upon a strip of
what appears to be cementite, by moving the objective nearer the specimen

on the stage, the white strip comes into focus as a dark line, then sufficient
evidence has been advanced that the white Space is due to a deeper etching

at this point. 'lherefore cementite is not present, but ferrite or some

other metal or inclusion. But supposing en the other hand that by moving

the objective away from the specimen the effect is to make the black line
come into focus. This is sufficient proof that cementite is present.

This condition was found to be true in several instances when viewing Section
A under a high powered microscope. Photomicrographs No. 20 to 27, inclusive,
exhibit possible cementite inclusion in grain boundaries and around penrflitic
areas. in. location of these areas are clearly defined upon the tissue used
to identify each figure.

Since the steel in question is low-carbon steel. (.05 to .10$ carbon).
and is normally thought to be an aggregate of Pearlite and Icrrite, plus
various impurities, it is necessary to explain the presence of csmentite,
that is, free cementite. By free cementite is meant in this instance, cement-

ite other than that combined with ferrite to for: pearlite. Figure No. 28

is a portion of the a
i l
iron-carbon diagram i M

 

 

 

 

 

 

 

necessary for the i I/
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l
interpretation of this I 'X'
phenomena. i new IO. 28

Figure No. 20. Specimen No.

(edge). 10001. Large
grain in center apparently
fractured. White strip in
grain boundary in lower cen-
tral portion. Other white
stripe present in grain
boundaries.

Figure No. 21. Specimen No.

(center). lOOOX. Long
grain at left apparently
fractured. Also grain in
upper left hand corner.
Distortion and cementite
present.

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ls the low-carbon steel, IX' cools, individual ferrite grains or a solid
solution of alpha iron plus carbon crystallizes. If any of these ferrite
pains contain less than .06$ carbon, then at the point A, cementite is
precipi tated out.

w means of micrometer measurements, the average diameter of each
specimen was obtained, that is the cross-sectional distance of each narrow
strip. 'Ihese diameters are indicated in Table No.1. Specimen ‘1 measured
.1323 inches, while at the other end of the section, A2 measured .1126 inches,
or a reduction in cross-sectional area of 15$. Next, the average number of
grains were counted across the diameter of the specimen at four different
places, and the average number thus determined. This was pdcomplished by
placing the specimen under the microscope and passing it across the field
of view.

The average count of grains across ‘1 was found to be 123. Specimen
12 at the opposite end of the section has been shown to be reduced in area
by 15%. Therefore, if there has not been a formation of new gains poduced
in some manner by the cold working, and if there has been no deformation or
elcnation in the direction of the working, then the grains across the diam-
eter of Specimen 12 should be:

1;; 3 J or 104.5 grains.

 

l .85
This may be shown by means of the sketch in figure Ho. 29:
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HOUR! F0. 29.

However, from Table No. l, the average count across 12 was 167 gains.
Therefore, since there was no evidence of distortion in Figures No. 11! to 19,

and since these were typical structures of the specimens, then there must have

-6-

been a movement of the grains or crystals of metal accompanied by a formation
of new grains, possibly caused by a breaking up of the larger grains into
several smaller ones. Photomicrographs Nos 21 and 22 seem to indicate that
some of the larger grains have been broken up. With the bending or stretching
of the metal by the tremendous pressure of the dies, it would seem that
elongation might take place before fragmentation of the crystalline structure
which is supposedly quite ductile.

From Table No. 1 can be seen that in the other specimens of Section A,
there has been approximately the same reduction in average grain size for
correspondingly less reduction in areilthan the 15% experienced in Specimensng.
Therefore, for this section, the grain size reduction has been independent of
the extent of reduction of area to with 5 or 10%..

Pertinent questions involving the phenomena above are now listed. 3:
what force or mechanism should the grains break down or new grains be produced
as the steel is rethiced in area? The entire spcimen or section was cold-worked
at room temperature and therefore there could be no recrystallization of ferrite
or pearlite grains. Gold work is supposed to elongate or distort the grains,
yet there was no evidence of this phenomena in Section A. What prevented the
elongation or distortion of this ductile metal so strenously cold-worked at
room temperature? Also the question of hardness which is supposed to aocoqany
reduction in area in cold working; has it exhibited itself in this section?
Cold-working is supposed to decrease ductility and increase hardness. Therefore,
the hardness of specimen A1 would seem to be less than for 12 or L5.

If there is a movement of grains in this cold-working, then how can the
grains move to exhibit the characteristics exhibited in part (a) of Figure lo. 30
rather than in part (b).

I'}.
11*». 22. Speci-
my: (center). 5001.
(gem its in grain

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Figure lo. 26. Speci-
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Figure No. 23e Speci-

men 11. 1000):. Divorced

cementite around pearl-
its grain.

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Iigure lo. 27. Speci-
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with figure No. 26.

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(a) (b)
HGURE NO. 30

   

In figure lo. 30, part (a). the larger sketch of cross sectioning represents
the grains in Section 11, while the smaller gains are shown in the smaller
sketch, supposedly representing Specimen A3. The grains are drawn in squares
_to sshow that in both cases they are undistorted. How did these larger grains
'get into this smaller size by the accompanying movement of metal and stretching
involved? In part (b), the grains of Section A3 appear smaller in diameter,
but elongated in the direction of the working, as might be expected, yet not
exhibited in Section A.

To better study the shape and distribution of the grains across sections
or specimens 11 and L3, photomicrographe were taken in series completely
across the diameter of each section at 5001. he resulting pictures of each
section whre then pieced together to give a continuous exhibit of annular
structure, each conposite picture when pieced together being about four inches
wide and better than five feet in length. from table He. 2, it will be seen
that the number of grains were counted for sections 12 inches in from the end
of each picture, and the umber of grains per inch times 500 determined for
the distance measured. The reduction in grain size was then figured and found
to be 31.2% and 23.0%, thus closely checking the results obtained in Table No. 1.
There was, however, some evidences of distortion or elongation of the grains in
Specimen 13, but not to any great extent or regularity.

Table No. 5 indicates the hardness values as determined with the Rockwell
Hardness Tester for Sections A,B, and 3. The points upon the various sections

where the readings were taken are shown in Figure lo. 2a. The following items

were noted concerning Section: (1) The hardness 'aI 61'0“.“ in the region

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where the bending of the metal took place, than disagreeing with the theory

in this instance that hardness increases with reduction in area: (2) The hardness
otherwise throughout the section was about the same, from 65 to 75 RoekIell '3";
and (3) For hardness readings in the region near the edge of the metal where
decarbnrisation had taken place, the hardness reading were considerable be,

from 50 to 60 Rockwell '3", possibly also due to the fact that the ball point

of the tester penetrated too near the edge of the metal.

SECTION "B"

This section was analyzed in about the same general manner as Section ”A”.
Photomicrographs were taken at 1001, 2501, and 1000!. Figures No. 31 to 36,
inclusive, taken at 1001, show this section (see Figure No. 2) to be somewhat
uniform in grain size, with no evidences of the "killed" steel exhibited in
Section "1", due to the fact that this strip was out from a different section
of the ingot and possibly from a different ingot entirely.

Figures Nos. 37 to 1&2, inclusive, show the gains to be in general
of polyhedral structure, with very little distortion in evidence. Even at this
magnification, there seems to be some white stripe (possibly cementite) in
the grain boundaries, this phenomena being present in each of the figures named.
more seemed to ‘be more cdmentite in the grain boundaries than in Specimen “1".
Figures No. It} to its, inclusive,(taken at 10001: ) indicating this fact.

Again the cementite appeared in the grain boundaries and also in the form of
”divorced" cementite. he location of these white strips is clearly defined
upon the tissue identifying the photomicrographs.

In the photomicrographs at 2501: and lOOOX, there appeared several indications
that larger grains had been fragmented into two or more smaller gains, but

the number fragmented appeared to be less than in Section ”A".

 

 

Figure ’0. “3e
Specimen No. )1.
Thick white strip
*1! gain boundary.
' 10001.

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Specimen No. 32.
Abundance of white
strips in grain
boundaries. 10001.

 

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Figure No. 141$.

Specimen No.

More white str ps

in grain bound-
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Figure le. #6.

Specimen lo. 3 .
Divorced cemengo
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lite.

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lOOOX. Notice predominance of
white strips in grain boundaries.
Seems to surround Pearlite and then
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Specimen 31 (see Table No. 3) measured .1153 inches in diameter,
as compared with .1106 inches for Specimen B}, a reduction in cross-
sectional area of 18%. For this reduction of area, there was an
accompanying reduction in gain size of only 8.1% as compared with 369%

in Section ”A“. Furthermore, specimen 3 showed an increase in grain

2
size over B}, rather than a reduction, there being a. 1.7% increase.

However, by counting the number of grains in Figures 1&2 and 10+, there

was found to be 111$ grains in the photomicrograph of 232, and 96 in

B . This would indicate a reduction of 167% in grain size in 3 relative

3

to the size exhibited in 33.

Again referring to Table No. 5 and Figure No. 2a, the hardness values

2

for this section will be found to agree quite closely with that of Section "A",
with increased hardness indicated at the places in the steel where a bending
occurred.

Summarizing, Section 'B", after undergoing the second cold-working
Operation, exhibited practically the same generallz characteristics as Section
”A”, though the two sections are two different pieces of metal. The grain
size of the two sections were in the san range and but little more reduction
in area had taken place. The cementite areas seemed to be more numerous
than in Section ”A”. Another section, that of the final pressing Operation,
will next be investigated, and should this section agree appreciably with
the two Just analyzed, is is then thought that for this type of steel, the

pr0perties exhibited may be termed characteristic for cold-worked metal

Of this type.

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SECTION "E"

Figure No. #9 showed.at 100X that E1 was a very fine grained metal with
"ghost” lines present. Figure No. 50 of the same specimen showed that the
grains near the edge of the specimen were larger, again indicating the presence
of a “killed" steel. Figures No. 51, 52, and 53 show somewhat uniform structures
but larger grainsd.than Specimen E1. The first real evidence of distortion to
any'marksd degree is exhibited in the photomicrOgraph of the edge of Specimen
m} (Figure No. 51+), this picture being taken at the point of the bend in this
piece. It is quite evident that the cold working at this point has elongated
the grains, due of course to the fact that the elastic point of the metal has
been exceeded in the tending operation.

Figure No. 55 shows a composite picture taken across Specimen.F3 at the
point of bending and distortion is in evidence at both edges of the metal.

These pictures were taken at lOOX and.in a series across the specimen.

In the photomicrographs taken at 250x, Figures No. 55 to GB, inclusive,
the structure is noted as polyhedral, generally undistorted, and gave evidence
of grain fragmentation. In Figures No. 54 and.No. 55, (of Specimen E1) distortion
was present in a more advanced degree than any other specimen analyzed except

that shown in the bent section of Specimen E Figure Ho. 62, taken across

3.
the bent section of’E3 shows some distortion and.a noticeable amount of'grain
fragmentation, while Figure No. 63 clearly shows the elongation of the grains
in this same specimen.

semantite again appeared in the grain boundaries as indicated in Figures
No. 69 to 7k, inclusive. It occurred.in the same manner as in the previous
sections, that is, in grain boundaries and surrounding Pearlitic grains.
Grain fragmentation was especially'noticeable in Figures No. 71 to 7h, inclusive.
These photomicrographs were taken at 10001.

From Table No. M, it will be seen that Specimen E1 had.an average diameter
of .0922 inches as compared,w1th .1359 inches for Specimen E3, a reduction in

-10-

 

 

Figure No. 60.

Specimen No. E I
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(center). 25

 

 

 

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Figure Ho. 6”. Specimen No. Fl.
10001. Cementite predominantly
present. Small carrot shaped grain
apparently fractured.

”we NOe 65e Specimen NOe Ea
IOOOXy~ Divorced cementite and
white strips in grain boundaries.

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area of 32.2%, practically double that Of the first two pressing Operations.
For this reduction in area, an accompanying reduction in grain size of 37.2%
was determined, this being about the same reduction in grain size exhibited

‘by Section A. Distortion was beginning to be noticeable in the thinned out

Specimen E1, where this reduction took place. In counting grains across the
distorted or bent section of I}, it was noticed that the number was greater

than for any other specimen in this section, indicating that the grains had

been elongated in the direction of the length of the piece.

From Table No. 5, the hardness values for this section (see Figure No. 2a)
were found somewhat uniform through out, except at the point of bends where
the hardness was generally greater. The hardness values agreed to within five
or ten points Rockwell with Section A, thus showing that the average hardness of
Section I had not increased appreciably with the reduction in area and colde
working. However, it must be remembered again that Section A.is an entirely
different piece of metal than Spctiunan, and therefOre cannot be taken as
absolute proof that the hardness has not increased, even though such seems

to be the indication.

pggg

Table No. 1 shows the count of grains, average diameter, number of
grains per 0.1 inch, reduction in area, reduction in grain size, and number
of grains if there had not been a reduction in grain size with reduction in
area; these being determined from Section.L.

Table No. 3 and No. It show the same properties for Sections 13 and F,
respectively.

Iable No. 2 indicates the results obtained from counting the grains
upon the composite pictures of Specimens A1 and A3, taken at 5001, and then
noting the reduction in grain size as compared.with Table No. 1.

Table No. 5 exhibits the hardness readings as taken it the points

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Specimen Fe. Fe. Figure No. 66.
10001. Fotice long white strips in
grain boundaries in central portion
of picture.

 

 

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Specimen No. . Figure lo. 67.
10001. Notice long white strip
which is apparently severing
grain.

 

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Figure No. 68. Specimen NO. 32.
10001. Divorced cementite present.

Grain boundaries at various points
contain irregular strips of white.

Figure No. 69. Specimen No. I .
iooox. Cementite predominant in
grain boundaries.

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indicated in Figure No. 2a.

Table No. 6 is an index to the photomicrographs included in the thesis.

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'Figure No. 70. Specimen NO. E .
10001. Rectangular Pearlite grain
surrounded by divorced cementite.

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Figure No. 71. Specimen NO. E .
lOOOX. Thru.distorted sectiofi.
Grain fracture in evidence. Cement-
ite present in grain boundaries.

Filhre No. 72. Specimen no. 13.
1006i; Thru distorted section.
Grain in center fractured and
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Figure No. 73. Specimen IO. 13.
10001. Thru distorted section.

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of picture apparently cut in tic
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TABLE no. 5
ROCKWELL HARDNESS DETEPMINATIONS"

 

 

Reading Section Section Section
- No. ”1" “B” '1'
1 76 77 .89
2 79 73 90
2 62 68 7h
77 66 77
5 80 77 - 87
6 EB _ 71 79
7 s1 32
s an 83 35
9 sh 33 so
10 sh s1 79
11 76 so 36
12 7o 76 37
13 75 73 79
1h 70 7o 60
15 63 7h 60
16 71 7o 53
17 75 70 52
18 73 71 75
19 80 7h 77
20 78 :3 79
21 79 87
22 75 82 35
:3 so so :3
s3 32 sh
25 82 77
26 62 77 32
27 57 79 so
as 67 79 so
29 7“ so
30 77 83
31 73

 

” - See figure No. 29. for points upon each nation
where hardness readings taken. All readingu
in Rockwell '3' .0910.

new no. 6
INDEX so Pmmmcnomss

 

 

figure Specimen he Object. 53110" Napifi- Remarks
No. lo. Piece ive Length cation
(an) (I)
1} A1 7.5 16 mm 27 100 Grains uniform - no evidence
or kill-Gd. ItOOIe
5 12 7.5 16 mm 27 100 “Ghost 11:..." throughout
center picture.
6 A3 7.5 16 mm 27 100 ' Larger grains near bottom
e 3e are at edge of specimen.
”Killed“ steel shown here.
7 1.3 7.5 16 m 27 100 Killed steel and mu lines
go in evidence. Decarburized
area at bottom of picture.
8 A} 7.5 16 m 27 100 ”Ghost lines“ thronfiont.
c nter
9 ‘3 7.5 16 m 27 100 "(most lines“ and larger
e ge grains at edge of specimen.
10 7.5 16 m 27 100 “float 11:..." throughout.
center
11 :8. 7.5 16 m 27 100 Larger grains at edge of
. specimen.
12 g 7.5 16 m 27 100 Ghost lines present.
nter
13 ‘6 7.5 16 m 27 100 Grains uniform - no evidence
. Of ”.1106. Ital-e
1h 11 7.5 s m 311.5 250 Grains polymer-.1. Some ind-
center ications of larger grains beg-
inning to break up.
15 1 7.5 s m 94.5 250 Same as 1156:. No. 1!». In
else these figures. notice white
strips in grain boundaries.
16 7.5 8 mm 3h.5 250 Smaller grain. hagnentation
center present. 'maost lines” present.
17 7.5 s 317.5 250 Polyhedral grain structure.

21..

-16..

White strips in grain bound-
aries and in pearlite. White
strips in places appear to
sever portion from large grain.

men: NO. 6
(Continued)

 

figure Specinen he

Ho.

Ho.

Object- 732110.. Magnifi-
Piece ive Length
(cm)

cation

(1)

Bourke

 

18

19

21

22

23

26

center

23..
25..

center

center

7-5

7.5

7.5

12.5

7.5

12.5

12.5

12.5

8 I. 31h5
8 mm 3M5

Lem 317.5

1.3mm 3,-1.5

5.5mm 31.0
Lam 317.5

6-! U.Y. 70.0

, 1.7 U.'. 32.0

5.5m 58.0

6m U. V. 70.0

-17..

250

250

1000

1000

500

1000

1000

1000

1000

1000

“most lines” present. Notice
grain fragmentation.

Grain fragmentation present.
Polyhedral structure.

Notice how small parts apparent-
1y severed from larger grain.
Cementite in Junction of grain

boundary and also partially
surrounding pearlite grain.

Grain fragmentation present.
Some cementite present in
grain boundary. Notice one
large grain in center which
has apparently been elongated
and broken into two parts.

Gemsntite in grain boundaries.
Notice grain fragmentation.
Some distortion present.

Divorced cementite almost

completely encirclsing long
pearlite(black) can.

Taken in Ultra Violet Light-
exposure time x 1‘05 minutes.
Divorced cementite around
pearlite grain and narrow

strip of cementite extending

in grain boundary from pearlite.

Taken in Ultra Violet Light .-
exposure tine : 50 minutes.
Notice shite strip in upper
portion of picture. Other less
noticeable cementite present.

lhite strips in grain boundaries.
Divorced cementite in center

of picture. What is the nature
of strip between grains?

Photographed in Ultra Violet -
Exposure tine: 515 minutes.
Compare with Figure 26.

Here resolution.

A—

TABLE'NO. 6

 

 

(Continued)
Figure Specimen Nye Object- Bellows Magnifi- Remarks

No. No. Piece ive Length cation

(cm) (X)

31 7.5 16 m 27.0 100 Typical low carbon steel with

center uniform gain structure.

32 B 7.5 16 mm 27.0 100 Uniform structure.

edge ‘

33 7.5 16 mm 27.0 100 Notice small white stripe

center around and near pearlite (black)
gains.

3"" Big 7e5 16 m 27.0 100 3830 &. um. IOe 33e

e e

35 B3 7.5 16 mm 27.0 100 Uniform structure. White strips

center in few instances in Pearlite.

35 h“ 7.5 16 m 27.0 100 Uniform structure. White strips
in gain boundaries in several
instances.

37 7.5 8 mm 3h.5 25o Grains polyhedral. Notice long

age white strip in center of picture
located in gain boundaries.

38 7.5 8 mm 3h.5 250 Many white strips in grain

center boundaries. No distortion.

39 1%; 7.5 3 mm. 3k.5 250 No distortion present. nor.

e e white stripe visible in gain
boundaries. 8m gain frag-
mentation.

1&0 32 7.5 8 m 31h5 250 Apparent gain fragmentation.

center In some instances shite strips
almost entirely surround ferrite
WEQe

1+1 31‘. 7.5 8 mm 3&5 250 Grain fragentation present.

e Divorced cementite apparently
in pearlite gains.

1+2 Bin 7.5 8 mm 3’45 250 Cementite in gain boundaries.

0 ter Divorced cementite present.

Bone gains apprently fragmented.

It} Bl 7.5 1.8m EMS 1000 laminated pearlite surrounded by

-18-

divorced cementite. Notice

strip or channel of cementite

in gain boundaries at various
points. Notice small gain appar-

ently cut in two parts.

TABLE NO. 6
(Continued)

 

figure Specimen

No.

No.

Eye

Piece

Object-

ive

 

an

#6

1+7

to

51

52

53

5h

B1

center

also

I
cgnter

E

.52.
fighter

33..

7-5

7.5

7.5

7.5

7.5

7.5

7.5

7.5

7.5

7.5

7.5

1.8mm

1.8mm

1.8mm

1.8mm

1.8mm

16 mm

16 am

16 mm

16 mm

16 mm

16 mm

311.5

3“.5

39-5

Sh-S

27.0

27.0

27.0

27.0

27.0

27.0

- 19 -

Bellows Magnifi-

Length cation

)

1000

1000

1000

1000

1000

100

100

100

100

100

100

Remarks

Divorced cementite in pearlite
grain. Just above pearlite,
notice apparent grain fragment-
ation. Notice white strip

of cementite in grain boundary
on Opposite end of picture.

Notice abundance of irregular
white strips in grain boundaries.
White strips seem to out large
grains into several smaller ones.

Divorced cementite around Pearl-
ite. Two white stripe of
cementite touching each other

in grain boundary away from
Pearlitic grains.

Cementite in grain boundaries

in irregular strips. Will seem
to surround Pearlite and then
shoot out along grain boundary
away from Pearlite. White globe
seen some distance from Pearlite.

Celentite in same form as
above. Notice white strip
connecting two pearlite grains
and apparently cutting large
grain in half.

Shows very fine structure.
"Ghost" lines present.

Portion with larger grains
are the edge of the specimen.
Shows "killed“ steel qualities.

Larger and more uniform grain
structure than E1 and no
"Ghost" lines present.

Uniform grain structure. No
evidence of “killed" steel.

Uniform structure with apparent-
ly lower carbon content than

11 or E2e

Taken at portion of 90° bend.
Distortion and elongation in

direction of bend noticeable.
Some grains appear fragmented.

TABLE NO. 6
(Continued)

 

Object- Bellows Magnifi- Remarks

Length cat ion
(cm) (X)

Figure Specimen Eye
No. No. Piece ive

55

56

57

58

59

61

62

53

65

E
agross

center

52...

E2
center

36..
in...

33..

E
center

edge

El

7.5

7.5

7.5

7.5

7-5

7-5

7-5

7.5

7.5

7.5

16 mm

8 mm

1.8mm

1.8mm

27.0

3“-5
BM-S

BuoS

311.5

314.5

3M-5

3W5

3h.5

3h.5

Bu-S

100

250

250

250

250

250

250

250

250

1000

1000

A series of five pictures
pieced tOgether to give a
continuous grain structure
across distorted section.
Distortion in evidence at both

edges.

Dirty steel.
elongated.

Grains somewhat

Elongation present. Grain
fragmentation apparent.

Ibtice
Polyhedral

”Ghost lines" evident.
grain fragmentation.
grain structure.

Notice little grains, usually
occurring in pairs, which seem
to have been torn apart from
larger grains.

Taken asay from distorted
section. White areas in grain
boundaries. Some fragmentation
of grains.

Same as above.

Some distortion present.
Notice apparent grain frag-
mentation. Taken at point
of 90° bend.

Taken at point of severe dist-
ortion. White areas in grain

boundaries at several places.

Some grain fragmentation.

Cementite in grain boundaries.
Notice small, long grain which
has apparently been fragmented
in half (in center of picture).
Some "Divorced” cementite.
Little white strips,far apart

from pearlite, in grain bound-
aries.

Notice ”divorced" cementite,
and white strip of cementite
shooting out from pearlite to

form grain boundaries. Are
grain boundaries more or less

made up of cementite?

TABLE NO. 6
(Continued)

 

Figure Specimen Eye

No.

66

67

68

7O

71

72

73

Piece

7-5

7.5

7-5

7.5

7.5

7.5

7.5

7.5

Object- Bellows Magnifi-
cation

ive

1.8mm

1.8mm

1.8mm

1.8mm

1.8mm

1.8mm

1.8mm

leg m

Length

(cm)
3165

31+.5

31+.5

3u-5

Bu-5

3u.5

(X)

1000

1000

1000

1000

1000

1000

1000

1000

Remarks

Notice long white strips in
grain boundaries in center of
picture. Notice at same point
the large grain which has
apparently'broken up into three
smaller grains. Divorced
cementite present.

Notice long, irregular strip

of cementite which is apparently
cutting off end of grain.
Divorced cementite present.

More divorced cementite present.
Grain boundaries at various
points contain irregular strips
of cementite. Grain fragment-
ation noticeable.

lhite strips predominant in
grain boundaries. Does this
mean that the grain boundaries
contain principally cementite
or as much cementite as there
is ”free” cementite present!

Notice rectangular pearlite
grain surrounded by divorced
cementite. Notice several
broad strips of white material
in grain boundaries.

Taken through distorted section.
Notice elongation of grains.
The long, thin grain in center
of picture has been cut into
two parts. Notice irregular
strips of cementite present in
grain boundaries.

Taken through distorted section.
In upper center of picture, notice
white strip where long grain has
been severed in half.

Taken through distorted section.
Long ”carrot shaped" grain
apparently cut in half by long
distorted grain. which was in

turn, fractured. Cementite pres-
ent.

 

I 21..

TABLE N0. 6

 

 

(Continued)
rigure Specimen Eye Object- Bellows Magnifi- Remarks
No. No. Piece ive Length cation
(cm) (X)
7n n 7.5 1.8mm 3h.5 1000 Taken through distorted
3 section. Notice white strips

in grain boundaries. Divorced
cementite present. Notice
large grain in uppper right
hand corner which has been

 

 

 

 

 

fragmented.
CALCULATIONS INVOLVED IN DATA
(From Table No. 1)
Number of Graing£pgr Oglfinch:
.Lverage Diameter of Specimen A2 (measured) -------------------- .1126"
Average Count of Grains across Specimen - —-—— ----------- - 167
Number of Grains/0.1” : ( 167/.1126) : _— —— ------- - lbs
Reduction in.Area (fl):
Diameter of A1 taken as 100% ----—---------------~----- .1323 in.
.1126

 

Diameter of A2 __— — —-_ — _ -_ =_ — —:_
Reduction in Area : ( 1 - .1126/.1323)1100--- ........... ....

Reduction in Grain Size (i): (of A2)

No. grains across specimen if no decrease in size
(.85 x 123 ) — -——- - —-4* — ~-—--

 

No. grains actually counted.(average) across specimen -----—--
Reduction in Grain Size : ( 100 - 105/167 ) -.......-----------
Number of Grains Across Specimen if No Decrease in Grain Size:
Number Of grains across unity’specimen A1 (1005) -- -------- -..
Relation Of Diameter of £2 to 100% Diameter of 11 ---—---------

Number of Grains Across Specimen : ( .85 x 123 ) ..---.-----..

19%

105
167
37.3%

123

85%
10h.5

CALCULATIONS INVOLVED IN DATA: (con'td)

(From Table No. 2 - Left Hand Edge of’Photomicrograph)

Number of Graggp;per ingh29f Photomicroggggg:
Average number of grains counted ---------- -----------—---— 25.25
Distance on Photomicrograph over which grains counted -------- 12 in.
Number of Grains per inch : ( 25.25 / 12 ) -------- -------- 2.10

Reduction in Grain Size:

 

Number of Grains per inch of Specimen A =—— — 4 — —~ —- 2.10

Number of Grains per inch of Specimen A3 ------—----------- 2.73

 

Reduction in Grain Size : ( 1007- 2.10 / 2.73) — -— A —— 23.0%

(Calculations fer Tables No. 3 and no. M involve same outline as Table No. l.)

-23..

The fellowing discussion of coldpwork phenomena, grain movements,
plastic deformation, elastic deformation, possible structure of grain
boundaries, effect of reduction of area upon hardness, and.the amorphous
cement theory are a compilation of theories and Observed facts by'recoge
nized authorities in the field of metallurgy and metallography. They will
be presented almost entirely verbatim. It is thought that this will accomp-
lish a ready reference upon the above mentioned subjects without making it
necessary to locate the bodks from.which they are taken. In the conclusion
and summary of the thesis, the facts and theories enumerated in this section

will as much as possible be correlated.with the Observed facts taken from

the research work discussed in Part one.

"Cold Working", as defined by the Metals Handbook}, ”is the permanent
deformation of a metal below its recrystallization temperature“. Since the
lowest limit of the recrystallization temperature is about “50° Cent., some
have stated that this definition does not really define coldpworking. A
definition suggested by some states that it is a deformation of a metal at
room or surrounding temperature.

Sauvsuru. in his book of Metallograpfifand Heat Treatment of Iron and Steel,
states of cold-working: "By cold.working of steel is meant in these pages,
working it while its temperature is below its critical range. The effect of
cold working upon the properties of the metal is very different from that
of hot working. This should.not be a cause for surprise if it be borne in mind
that steel above its critical range is in a condition totally different from
its condition below it. Above the critical range, we have an aggregate of
pearlite and ferrite (or cementite). The solid solution existing above the

range will crystallize if allowed to cool undisturbedly and it has been shown

that working in this range, i.e., hot working, is effective in preventing or

- 2b.-

at least retarding this crystallization, thus imparting a smaller grain to
the metal. The aggregate existing below the range, on the contrary. enhibits
no tendency to crystallize during slow and undisturbed cooling, because this
aggregate was formed and fully deveIOped while passing through the range, the
size of its elements, that is its coarseness, depending (1) upon the coarsness
of the solid solution immediately before its transformation and (2) upon the
time occupied in cooling through the range. Working this aggregate, therefore,
as it cools to room temperature, or working it while at room temperature, i.e.,
cold.working it, results in distortion the existing structure, chiefly through
the stretching or elongation of its crystalline elements (free ferrite, free
cementite, or pearlite) in the direction of the forging, and.auch distortion
in turn means decreased ductility and eventually extreme brittleness. The
ferrite present in the aggregate, distorted by work below the critical range,
may recrystallize provided the cold.work ceases above its recrystallization
temperature, the lowest limit of which is at about 150 deg. c. The distorted
pearlite particles, however, remain distorted. While the structural distortion
caused by cold working is very slight near the critical range of the metal,
it rapidly increases as the temperature decreases, becoming very pronounced at
room temperature. The manufacture of wire by'coldpdrawing affords a familiar
instance of the effect of work performed.at atmospheric temperature both on the stru
structure and preperties of the metal. It is well known that after the wire
has been passed through several dies it becomes so brittle that annealing is
necessary in order to make further reduction in size possible, the annealing
Operation removing the structural distortion and brittleness produced by working
at room temperature."

Sauveur further states that "the elastic limit, tensile strength, and
hardness are increased in a marked degree'by coldpworking, while the ductility

as represented both by elongation and reduction of area is reduced, brittleness

-25...

at least retarding this crystallization, thus imparting a smaller grain to
the metal. The aggregate existing below the range, on the contrary, exhibits
no tendency to crystallize during slow and undisturbed cooling, because this
aggregate was formed and fully develOped.while passing through the range, the
size of its elements, that is its coarseness, depending (1) upon the coarsness
of the solid solution immediately before its transformation and (2) upon the
time occupied in cooling'through the range. Working this aggregate, therefore,
as it cools to room temperature, or working it while at room temperature, i.e.,
cold working it, results in distortion the existing structure, chiefly through
the stretching or elongation of its crystalline elements (free ferrite, free
cementite, or pearlite) in the direction of the fOrging, and.such distortion
in turn means decreased ductility and eventually extreme brittleness. The
ferrite present in the aggregate, distorted by work below the critical range,
may recrystallize provided the cold.work ceases above its recrystallization
temperature, the lowest limit of which is at about #50 deg. c. The distorted
pearlite particles, however, remain distorted. While the structural distortion
caused.by cold working is very slight near the critical range of the metal,
it rapidly increases as the temperature decreases, becoming very pronounced.at
room temperature. The manufacture of wire by coldpdrawing affords a familiar
instance of the effect of work performed at atmospheric temperature both on the stru
structure and properties of the metal. It is well known that after the wire
has been passed through several dies it becomes so brittle that annealing is
necessary in order to make further reduction in size possible, the annealing
Operation removing the structural distortion and.britt1eness produced'by working
at room temperature."

Sauveur further states that "the elastic limit, tensile strength, and
hardness are increased in a marked degree by coldpworking, while the ductility

as represented both by elongation and reduction of area is reduced, brittleness

-25...

being eventually produceio'

A further disucssion on the effects of cold working is entered by Jeffries
and Archers: "It is now known that cold deformation produces refinement of grain
in‘ the sense that one original grain, after cold work, exhibits a mixture of
orientations. This type of grain refinement is not the same as the refinement
of grain produced by annealing at low temperatures. For exwple, a metal may be
obtained with the same hardness by moderately cold working a coarse-grained
piece or by annealing a severely worked piece at a temperature which will produce
small unstrained grains. Even though there is refinement of grain by cold
working, the directional prOperties of the crystals are never obliterated, and,
in fact, extreme conditions of cold work actually produce directional character-
istics, namely a tendency for the crystal units to be oriented in a certain manner
with reference to the direction of deformation.“

"The general effect of cold deformation is to increase hardness and decrease
plasticity. Impurities also affect the shape of grains. Non-metallic impurities
generally obstruct grain growth and, because of their distribution in worked
metals, the obstruction to growth at right angle to the direction of working
is greater than the destruction to growth in the direction of working."

'ith reference to increased hardness resulting from cold working, Sauver6
remarks: “The increased hardness resulting from cold work deformation has been
ascribed to (1) grain deformation and fragmentation increasing resistance to
slip, (2) distorted space lattice and (3) presence of amorphous cement at the
slip planes. Rosehains modified theory postulates the existence of what he
terms irregular material instead ofamorphous material, the former having its
atoms arranged otherwise than in the regular fashion of the crystal lattice. He
further believes that the presence of this irregular material plays only an

indirect role in the hardening phenomenon. The material is itself incapable of

-26..

crystalline slip and its location at the places where slips have occurred in
cold working prevents the distorted lattice to return to its original shape
after release of stress, hence the resulting hardness. Rosenhain considers
lattice distortion to be the primary cause of strain hardening.“

Jeffries andircher7 point out the following facts regarding the prOperties
and structure of coldpworked metal. "lhen metals are tested at temperatures
well below that of recrystallization, the passing of the elastic limit represents
the‘beginning’of plastic deformation by transcrystalline slip. At temperatures
near or above the recrystallization temperature, intergranular flow may take place
and mark the elastic limit; the stress required varies greatly with the time of
application. kit the yield.point, movement on slip planes is general throughout
the specimen; the effect is visible on the machined surface of a test bar, which
becomes dull.

'Up to the elastic limit, the metal is not permanently altered by the
application of the test load. Beyond this point, however, the deformation in-
cident to the test alters the structure and.prOperties of the metal. Elongation,
reduction of area, and tensile strength therefore depend.not only on the original
condition of the metal but also upon the effect of the testing Operation itself.
The mechanism and effects of plastic deformation must be considered in interpret-
ing the results of tests in which the metal is plastically deformed.‘

.L summary of the prOperties of cold worked metals, stated by Jeffries and e'
Archers, is:

'1. Hardness and.strength of a metal increase with the amount of reduction
by cold work until internal failure is produced.

'2. Plasticity of a metal decreases as the amount of cold work increases.

#3. with change in temperature of test, the prOperties of a cold-worked metal

follow those of annealed steel, any discontinuities in the prOperties of annealed

metal being reflected in those of cold~worked metal.

M4. Elongation of a cold-worked metal increases with respect to the elong—
ation of annealed metal, as the temperature of test decreases below the working
temperature, reaching a maximum value, after which further decrease in temperature
produces a rapid decrease in elongation.

'5. The hardening effects of sligit or mederate deformations are greater
the smaller the initial grain size of the metal.”

Some types of brittleness found in low carbon steel are enumerated by
Savuer9, who saysi "Since steel containing very little carbon is essentially
made up of ferrite, it occasionally exhibits brittleness which must be due
to a likewise occasional brittleness in ferrite, a constituent by nature soft
and ductile. Stead has indicated two kinds of brittleness from which ferrite
may, and occasionally does, suffer, namely (1) inter-granular brittleness, and
(2) inter-crystalline or cleavage brittleness.

a13y inter-granular brittleness is meant a lack of cohesion between the
ferrite grains leading to ready fracture under showk, the line of fracture
following the boundary lines of the grains. Such brittleness is usually
due to the presence of impurities forming brittle and more or less continuous
membranes surrounding the grains. The presence of much phosphorous, however,
appears to produce inter-granular brittleness without producing surrounding
membranes.

”Inter-crystalline or cleavage brittleness is caused by the ferrite grains
assuming nearly the same crystalline orientation so the plane of fracture follows
the cleavage planes and passes from grain to grain almost in a straight line.”

In an article published by Hayes and Burnsle these authors that in reduction
of area (cold) upon cold-worked steel distorted or elongated the grains to a

noticeable degree when there had been a reduction of 20%: the distortion was very

pronounced with 30% reduction in area.

In commenting upon the structure of cold-worked metal, Jeffries and
Archerlbtate that “the most apparent distinction in crystalline grains is
perhaps between equi—axed and elongated grains. In this connection, it must
be remembered.that the elongated grains of coldpworked.metal are, in reality,

a
aggregates of very small grain fragments.

If there has been an accompanying grain movement in the plastic deformation
of the coldeworked metal in question, the following references will indicate
theories that have been advanced to explain how and when this phenomenon takes
place.

12

The following is a brief outline as presented by Howe , in his 'Recapitul-

ation of Movements”:

Intergranular

Fluid

Movements Hen-crystalline Movement of irregular grain
fragments

Block

Slip
Crystalline

Twinning

In distinguishing'between Fluid.and.Block Movement, Howe13 offers:

“Sharply distinguished from fluid movements are what might be called.block
movements, that is the movements of whole blocks, the parts of each which retain
their relative position during the motion, as the parts of the earth retain theirs
during its rotation. Such motion is like that of a book pulled.out from a full
shelf, a card from a pack, or a brick from an imaginary'wall laid with asphalt.’I

Howelhfurther states: ”Block movements may be in turn crystalline or non-
crystalline. For though the crystalline structure of metals may well lead to
strictly crystalline movements, that is to movements along definite crystall-
ographic planes, yet it is compatible with movement along random surfaces, as the

rupture of a masonry'mass may avoid its Joints.

~29...

"For instance, when a mass of low-carbon steel is deformed plastically,
certain of its grains may slide past each other so that their boundaries form
a pattern on its surface, in which case the movement is intergranular. Or as
when half a pack of cards slips past the other half along the bounding faces
of two adjoining cards, the faces of each individual block which moves past its
neighbors within any one grain may consist of definite parallel crystalline planes,
in which case the motion is by slip. Or the particles which compose certain of
the blocks, while retaining their relative distances from each other, may all
rotate through a definite angle, as when the slats of a Venetian blind are
turned, in which case the movement is by rotation. If’this rotation is through
such an angle that the new position is symmetrical with the old, this rotation
is called twinning. Cases of such rotation in metals are very common, and are
referred to twinning, though strict proof of this symmetry has not yet been given.

"Yet in spite of the crystalline organization which slip and twinning imply,
deformation and rupture might avoid these crystalline planes, and be wholly irrega
ular, or if regular they might have the regularity only of the lines of surf on
a flat beach or of a mackerel sky. They need not be either strictly straight or
strictly parallel, and they need not correspond closely if at all to any definite
crystalline planes. In this case the block movement is noncrystalline.

I'Iant only may these four types of'block movement be superposed, but they may
be accompanied by fluid.movement. That is to say, even if the major part of each
of two slices moving past each other remains a crystalline block, and moves like
the muntins and panes of one sash past another, yet the metal along their sliding
contacts may'become decrystallized and revert to the amorphous state.“

Another correlation of movements is attempted by the same author, who
says, 'Thhse block movements, whether superposed or single, because they occur
in a sense independently in the various crystalline grains, may integrate into

what, if viewed on a large scale, is equivalent to fluid movement, quite as in the

movement of a true fluid.we may conceive that the atoms in a given molecule do not

- 3o -

change their relative position, so that here movement which is of the block

type as regards the atoms within the molecule, that is on the atomic scale,
integrates into movement which is fluid when seen on a molecular scale. Every
molecule moves relatively to all its neighbors, but the atoms move relatively only
to their neighbors in other molecules, retaining their relation to the other atoms
in their own molecule unchanged, or at least unaffected.by motion which the fluid
as a whole undergoes.

"Fluid movements are habitually rotary, as in the swirl of water. Inter-
granular movements too might be rotary, in the sense that one grain as a whole
might rotate relatively to one or more of its neighbors. The trans-crystalline
movement by twinning is rotary through a fixed angle.'i

An interesting theory relative to the moving of grains in the process of
deformation is that of I'Intercrystalline Slip”, presented by Jeffries andArcher:15
'If a piece of ductile metal is polished and etched to bring out the grain
boundaries, and is then subjected to a load.which causes a slight permanent deform-
ation, examination under the microscoPe reveals systems of parallel lines running
across the grains. In any one grain the lines are approximately straight and
parallel to one another, but their direction is different in different grains.

In the first stages of deformation only a few of these lines appear, and not

in every grain. As the deformation increases, more lines appear, becoming closer
together and appearing in grains previously free from them. Finally, other sets
of lines are developed, parallel to one another in any one grain and crossing

the first set of lines. Close examination shows that the first sets of lines
have been displaced along the second.sets by'a minute amount, so that they no
longer register exactly.

"The nature of these lines has been very carefully investigated by Howe, and

they are known to represent block movement or slip along crysta110graphic planes.

The lines observed are steps on the polished surface produced.by the elevation or

-31..

depression of blocks or fragnents of the gains.”

Bowgeattempts to define and explain the mechanism of "Slip".

'Here a difficulty in nomenclature arise. The name ”slip bands"

ii finely attached to certain lines which defamation develOps on a previously
polished surface. Here ”slip” naturally implies translation without rotation,
so that the very name ”slip" with reference to 'slip Bands” itself begs the
question as to the nature of the thing named, a question to which we are now
going to seek to answer. If we use the nuns I'slip bands'I and thus acmiesce in
this begging, we thereby embarrass the discussion, especially if we call this
vectorial translation 'slip". Osmond tried to avoid the entanglement by calling
these lines ”lines of translation.“ Translation might include all the six forms
of movement except twinning: slip bands are improper till slip has been proved.

”Blip, when combined with the rotation of a given grain as a whole, may be
likened to the movement of a book pulled out from within a row which is mean-
while tipping over. is it slides forward, the book as a crystalline block slips
within the row of books. But as they all tip simultaneously, its orientation
remains uniform with that of the other books on that shelf, and it leaves cert-
ainly retain a comes orientation, while the book itself tips and while the
rowlroftbeastapse whole is rotating relatively to the books on the other shelves.
In shat follows it is most convenient to proceed as if the plastic deformation
occurred by crystalline slip alone, and later to ask how far twinning and
rotary or fluid movement may replace this slip.“

In ”Similiee to hplain the Hechanism of Slip", Howe17seys: We may con-
deive the cement Joints in a thick brickwork mass replaced by wax guides with
limited shearing strength, so that under strong pressure aw row of bricks can
slip past any other and thereby shear across a series of wax guides normal to

this movement, while it is yet held as by irresistible mastication so that it

-32-

can neither rotate nor deflect. The guide can be sheared across: it can move
with the bricks in any direction as long as it remained parrallel to its initial
direction; but from that direction neither the guide nor the brick which it guides
can turn. .

'Ihe passing of the elastic limit means that the stress reaches such intensity
that certain crystalline slices, forming part of certain crystalline gains, start
to slide along the slip planes over the similar neighboring slices in those same
grains.

"An alternative mechanism of slip after Osmond and Gartaud substitutes what is
in effect incomplete twinning, a rocking or rotating of the units which compose
each of the slices of metal involved in the movement, each unity about its right-
hand side, together with a lifting of-each unit by its own rocking and 17 that of
those at its right.’

Further, Jeffries and Lrohsrmettempts to explain the conditions at slip
planes:

Who properties of cold-worked metals and the phenomena of plastic deform-
ation indicate that important changes may take place on the surfaces of slip
during and after deformation. 1 number of propositions regarding the conditions
at slip planes are herewith presented. For the purposes of this discussion, the
term 'slip plane strength“ will be useful to denote the resistance to motion along
a slip plane after slip has started. ”crystal strength“ means the shearing strength
of the unbroken crystal on planes parallel to the slip plane under consideration;
it is the resistance to motion on the slip plane, 221m slip starts.

'0) W
W In coarse-grained metals, slips are readily observed which have
extended for a distance of several thousand atom diameters. In single crystals
tested in tension, the extent of the motion mi individual slip planes is still

greater. After slip has once started, therefore, the resistance to further motion

-33-

on the same plane must, for a while, be less than the resistance to the starting

of slip on a parallel plane and hence less than he original shearing strength of
the crystal. When iron has been recently overstrained, the application of very
small stresses results in permanent deformation which must take place by motion

on the slip planes formed in the first overstraining process. Resistance to motion
on these planes must, therefore, be quite low as compared with their original stren-
gth. The same is true of brass or other metals whose elastic limit is decreased

by overstraining.

“(2) As slip continues, the slip plge strength increases 59 a valg whip;

m b; gegter 339. the gastal strggggh, It is a striking fact that, when single
ductile crystals are tested in tension, failure does not occur on the first slip

plans. Motion continues for a certain distance, after which further deformation
takes place by slip on other planes. This means that the resistance to motion on
the original slip plans must have increased to a value somewhat greater than the
resistance to motion on parallel planes in the crystal. Bis process of slip may
be termed ”self-stopping."

”(3)

4. ;. .7 . -3 .1. H :1 :1"- -.-d ”rt ' ' th 81158;»: '2! .ii' 11 91“:

 

M. In a single crystal which is ductile it is necessary that motion continue
on the first slip plane until the resistance to motion automatically becomes gsater
than that in the unbroken crystal. In an aggregate composed of many grains, hor-
ever, motion on a slip plane in any one grain is opposed by adjacent grains through
which there are no corresponding planes of weakness. Slip may there be brougit
to a halt by and resistance before sufficient motion has taken place to increase
the resistance on the plane to the self-stopping point.

'04) l l s n at es the r sen in co d-wo
195.250 Since the slip plane strength increases with motion along the plane and

since the extent of the motion on the various slip planes is different according

-314-

to the various conditions of external support, it is evident that the resist-
ance‘to motion on the various slip planes after deformation stops may be any—
thing from the minimum to the maximum obtainable.

”(5)81c s turofh toi bond nthesl

t r ti n has st ed there is artia r stab i cut of cohesio

”(6) When the registgz' of the displaced meta; fragmts permits, cohesion

is rgggtablishg g the fragsnts Jginigg intg larger crystalline units. The slip
plane then disappears as such, being replaced by a potential slip plane whose

strength is equal to the crystal strength.

 

do of re st cur. It has been shown tw Lray analysis that new
orientations are created by plastic deformation. Consequently, there mst be
many, probably a large majority, of crystal framents whose orientations do not

permit them to unite except by the process of grain growth.

 

“(8) =-
at --s st be - am;- a a. a due -‘ s .oria;-;.t.i-n s reaa s the arr-
f t t the s e.
I'(9) m r a - a

   
  

   

W. The characteristic properties of typical
amorphous materials are, first, the great influence of time upon deformation, and
second, the rapid change in properties with change in temperature. Cold-worked
metals behave as though the resistance to motion on the slip planes varies in a
similar manner with the time and temperature. The slip plane strength increases
on cooling and decreases on heating at a more rapid rate than does the crystal
strength. for example, the tensile strength of cold-worked iron increases on

cooling much more rapidly than the tensile strength of annealed iron.

I(1°) A "J '..- 5.‘ i-“‘;nt ' ‘ . 1' 0 £43. 1:. C .- - ; 3:10; 1... 31L..- 0
Lag: flag are 3M1; gssgcigtgg with rgggstgllizgtigg, During the spontaneous

-35-

 

 

i. - o
, . . - , i
“w ,s
e
,
s- , — ,, .. ..
I ‘ a
a
x
x
-‘4 , s e - . ., .w . . ‘,
w
.- .. . .n, v —. — .
e
. - _. .—. . .- .
.
- . w ‘ ‘
.
. -c
. . A . '
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v
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aging of overstrain'ed iron at ordinary temperature, or the rapid recovery of
elasticity at a blue heat, the slip plane strength increases so that small stresses
no longer produce permanent deformations.‘ his increase in slip plane strength,

or I'healing", as it may be called, may consist in the growing together of fragnents
of sufficiently similar orientation, or in the establishment of cohesion at add-
itional places on the planes between fragments that do not register. Rosenhain
has observed that, when a piece of iron is polished imediately after overstrain,
lines are found which probably represent the intersection of the polished plane

of the specimen with the surfaces of slip. These line (called Lbands by flows)

are not found in the specimen if permitted to rest or recover before polishing.

Lee has reported that the recovery of iron or mild steel from overstrain is acc-
onpanied by an increase in density. All evidence is to the effect that the healing
process involves an increase in the continuity of the metal. Although the elect-
rical conductivity of metals is decreased by cold working and is, in general,

least when the metal is in its hardest condition, it is to be expected that the
hardening of a cold-worked metal like iron by aging or heating at low temperatures
would be accompanied by an increase in conductivity.“

There has been much conJecture as to the presence of amorphous material
in the grain boundaries. Some noted metallurgists disprove this theory and
offer an alternative theory stating that the grain boundaries must contain
disoranised metal. The arguments are herewith presented.

Jeffries and Archer19 desigiate crystalline materials as follows:

'Crystalline materials are characterised by the orderly arrangement of their
constituent particles, i.e., atoms or molecules in definite geometrical patterns.
laterials whose molecules do not posses any such regularity of arrangement are
amorphous. The term I'amorpilous” is tlms'in the broadest sense, directly opposite
to that of crystalline.“

-36-

Sameureocontemplates the existence of an amorphous cement holding the gains
together: “It is believed by Rossnhain and Ewen that the amorphous films cementing
together the crystalline gains of pure metals act as a vehicle for crystal growth
under suitable temperature conditions. This intercrystalline amorphous cement
migt play the part ascribed to eutectic films in Ewing and Bosenhain's earlier
theory. While according to the former theory the gains of strictly pure metals
could not grow on annealing, even after straining, owing the absence of eutectic
films, the amorphous cement theory permits such gowth, and this is in better
harmony with observed facts,

”Any annealing of cold worked metal should result in the transformation
of some of the strong but hard and brittle cement resulting from cold working,
into crystallized metal, and this should be accompanied by decreased hardness
and increased ductility, thus accounting for the well-known influence of anneal.-

‘ ing on cold worked metal. The effect of annealing cold worked metals may be also
explained on the ground that it converts a mass of extremely small gain frag-
ments, hence possessing greater resistance to slip, into relatively large equi-
axed grains with decreased resistance to slip."

With due regard to the possibilities of “mixed orientation at grain bound-
aries“, Howea states: ”Along the gain boundaries there is a narrow band in which
the orientation is a mixture of that of the two adjoining gains, as if dendrites
here interlocked, and in Emefrey's belief, a region of progessive confusion of
orientation. To decide if this were true would used very precise observations
directed expecially to this point."

Sauveurza firther believes this amorphous metal to be very hard: ”It is now
pointed out that the regularity of atomic arrangement in crystals leads to mech-
anical weaknesses along certain crystallographic planes. The absence of such
planes of weakness in amorphous materials leads to great hardness at low temp-
eratures. The hardness and strength of amorphous materials in gain boundaries
my be the cause of hardness produced by cold deformation. An increase in gain

.. 37 n

boundary surface must, therefore, result in an increase in.hardness. This affords

a ready explanation of the fact that the hardness of metals increases as the grain
size becomes smaller. Carrying this idea to the extreme, Rosenhain proposed.that

the great hardness of hardened steel is due to the “presence of an extremely

minute network of amorphous layers” surrounding the very fine gains of Alpha iron
which result from.the rapid transformation of Gamma iron. He regarded the amor—
phous iron as being expecially hard in this case because of iron carbide in solution.‘

Bav'ser 28.ng the existence of both crystalline and amorphous phases in
m pure metal: ”Assuming the coexistence of two phases, crystalline and amor-
phous, in any pure metal, it is essential to bear in mind that some of their
physical prOperties differ materially.

“According to Jeffries, the cohesion of the amorphous phase is nil at the
melting point, while that of the crystalline phase is considerable. On cooling,
moreover, the cohesion of the amorphous phase increases more rapidly than that of
the crystalline phase, resulting in the equal cohesion of both phases at a certain
temperature called by“him.the “soul-cohesive temperature“. Since the resistance
to deformation mnst be greater the greater the cohesion, it follows that the cryst-
alline phase will cause greater resistance to deformation above the equi-cohesive
temperature than an equal amount of the amorphous phase, while on the contrary,
the amorphous phase will cause greater resistance to deformation below the equi-
cdhesive temperature than the same amount of the crystalline phase. It follows,
in turn, from this consideration that for the same metal, a coarse-grained
structure, since it contains less amorphous material, will offer greater resist- '
ance to deformation above the equi-cohesive temperature than a fine-gained metal,
while on the contrary, below the cohesive temperature the fine-grained metal will
be more resistant to deformation. At the equi-cohesive temperature the resistance

to deformation would be the same both for the coarse-gained and fine-grained

-33-

metals, since the two phases have now the same cohesion..1t is believed that
the recrystallization implying grain growth will not take place until a temp-
erature is reached at which the amorphous phase is less cohesive than the
crystalline, from which it would follow that the equi-cohesive temperature must
correspond to the minimum temperature at which grain gowth can begin.”

Jeffries and Archerahdiscourse upon Amorphous metals:

“there must of necessity be some disorganization of the crystalline structure
at the grain boundaries of’metals and on most of the surfaces of slip. The
degree of disorganization probably varies all the way from.perfect crystallinity
to the completely disorganized structure denoted by the term.'vitreous amorphous.”
All such metal of disorganized structure simlates the vitreous amorphous materials
its mechanical properties.

'Fluidity is the important characteristic of amorphous materials. Plastic
deformation takes place by the same‘kind of flow as in ordinary liquids, except
that at a low temperature, the viscosity is great. Whereas the strength of a
crystal depends on temperature and is practically unaffected by the duration of
loading, the resistance to deformation of an.amorphous material not only varies
rapidly with the temperature for a given rate or duration of loading, but if the
temperature is constant depends entirely on the rate and duration of loading.

”In general, the relative amount of amorphous metal increases with pain
refinement and with cold working. The properties which.metals have at high
temperature of yielding slowly'under constant load is presumably due to the
viscous flow of disorganized or amorphous metal at the grain boundaries. Since
the amount of this disorganized or amorphous metal is greater in a fine-gained
metal than in a coarse grained metal, it would be expected that the fine-grained
metal would be softer at high temperatures and harder at low.”

0: “Possible Structure at Grain Boundaries”, Jeffries and Archegsoffer:

”Since amorphous cement cannot be produced alone, the best evidence of

-39-

amorphous metal is probably to be found in the conditions at grain boundaries.

In the original statement of their intercrystalline cement hypothesis, Rosenhains
and Ewen advanced the idea that the crystallization of metals takes place by the
addition of crystal units containing large numbers of atoms. In the region
where two crystals abut against one anothero-that is, at the grain boundaries-—
there would have to be some metal which could not attach itself to either crystal
because of being too small in amount to form crystal unite. Furthermore, since
the crystalline gains have different orientations, the units or blocks of

one would not fit in with the blocks of the other, and interstices of irregular
shape would be left which could not be filled up with other crystals no matter
what their orientation. The metal remaining in these interstices must then
retain the structure of the liquid--i.e., must be amorphous. This conception

is no longer teneable, inasmuch as it now appears quite certain that the crystal
units consist of one atom each. The actual conditions must nevertheless be very
similar, in a qualitative way and on a smaller scale. Certainly, where two
crystals of different orientation meet, it is not geometrically possible for all
of the atoms present to have places in an undisturbed space lattice without
leaving some voids.

"There are three possible conditions: (1) There are voids between the two
crystals: (2) there is a zone in which some of the atoms are held in both crystal
lattices, in which case the lattices would be distorted at the surface of contact;
or (3) there is a sessrsfngisorganised or amorphous metal. There is at present
no known way of determining the actual structure at the grain boundaries of metals.“

That some noted metallurgists are inclined to disagree with the existence
of a so called Zamorphous cement" is indicated in the following:26

“hem the analog of slow flow of amorphous materials like pitch there was
built up, a couple of decades ago, the idea that metals contain an amorphous

constituent. It was obvious that the crystalline gain could not be amorphous;

so it was postulated that a submicroscopic boundary layer of “cement" about the grain
- ho,-

or crystal is amorphous. While the more cautious early advocates of the amor.
phous theory were careful to phrase their comments to the effect that the boundary
material M as thong: it were amorphous, others were less hesitant and fell into
calling it actually amorphous. Several studies have indicated the boundary material
is essentially crystalline. layers of sputtered metal only a few atoms thick have
been prepared which appeared structureless when examined by Lrays but which shifted
over to crystalline form on very sligt heating. Recent work, however, indicates
that the advocates of amorphous metal are in a defensive position.“

Permanent defamation of a metal involves a displacement within the material,
during which the cohesion is overcome between the parts undergoing relative
displacement. The property of plasticity therefore means that the displaced
parts must reestablish cohesion in their new places. Howez7 differentiates between
llastic and Plastic Deformation thus:

”Stress within the elastic limit causes elastic deformation, from which
the metal recovers its size and shape exactly, after the release of the stress.
Stress beyond the elastic limit continues to increase the elastic deformation, and
apparently at the same rate as before, but adds plastic deformation to it. On
the release of the stress the metal recovers m- so much of the existing deform-
ation as is elastic but retains that which is plastic. Thus we recogise the
plastic deformation as permanent set. ”Plastic Deformation" in the cold is
identical with cold work and overstrain. Stress pushed far enough beyond the
elastic limit causes rupture.'

Jeffrieszgand Archer further point out that “When the external shape of
a piece of metal is changed by a deforming load, the shapes of the gains undergo
similar changes. Normally, the gains are so shaped that, on the average, their
diameters are equal in all directions. Such gains are called equi-axed gains.
Now if the metal is deformed, as by drawing out into a wire, the gains are simi-
larly drawn out. The change in the external shape of a gain is made up of a
multitude of minute slips, each so small that the grain retains an apparently

smooth outline. Lines visible within the grains are undoubtedly due to cold

-hl-

deformation. Bosenhain considers these to be the traces of slip planes on
the plane of the micra-section. Howe is less certain of their nature, and
calls them 'L-Bands".

”The changes which occur in the structure of the metal when it is plastically

deformed will be described briefly.29 They are:

"l. Slip takes place on the glide planes, spaced many atoms apart.

'2. With continued cold work, the grain fragnents are oriented in a definite
direction.

#3. As slip progresses shear resistance to further slipping on these planes
increases.

”h. The mechanism of plastic flow appears to be one of block displacement,
by rotation and translation.

”5. The ”blocks" are fragments of grains and become smaller and smaller as the
cold working is continued, but the blocks retain their identity even
after the severest plastic deformation.

”6. The ”blocks” are fragnents of grains, particles of varying dimensions,
some being colloidal. Lray and electron diffraction studies prove
that the lattice dimensions as well as the cubical synnetry is changed
slightly as the particle size within the displaced blocks becomes smller
and sunller.

'7. The density of the metal is decreased due to an increase in spacing be-
tween the displaced blocks (Lray method can detect this).

'8. The particles within the blocks tend to roughen the glide surface, and
resistance to further slipping is increased, with the result that the
metal hardens and its ductility is lowered. (The blocks referred to

in this discussion is as used in block displacement).'

-ha-

The general summary included in this section is derived from the
research work discussed in Section One; that is, from the metallographic
study of the three sections of steel analyzed. The correlation of this
summary'with the theories and facts advanced.by various authorities in
the field of metallurgy and metallography (from Section Two) then make it
possible to draw certain conclusions relative to the coldpworked steel in

question.

GENERAL SUMMARY or THE THREE SECTIONS

The following facts are now enumerated to summarize briefly’the
research work for the three sections of steel:

1. Though each section is a different piece of metal, a reduction in
area was noted from one end of each section to the other, the reduction
in Section 'E' being approximately twice the value for each of the other
sections.

2.1 Section "A" and section ”E" gave indications of‘both "ghost lines"
or ferrite strips and "killed steel“, while this quality was not noticed in
Section "B".

3. Cementite or what appeared to be cementite occurred in all three
sections, appearing in the grain boundaries. It was more noticeable in
Sections "3' and ”E”, than in Section 11". This occurrence was in the form
of strips near pearlite, in sections devoid of pearlite, and in the shape of
”divorced” cementite.

M. The hardness values as determined by the Rockwell Hardness Tester
agreed.within 10 points Rockwell B (on the average) from end to end of the
three sections. The hardest points occurred.at the points of bending.

There was therefore in these sections (1) no increase in hardnessdue to

decrease in area, and (2) no increase in hardness resulting from elongation
of grains.

- M3 -

5. ‘She reduction in grain size was about the same for Sections "A”
and as", in the neighborhood of 30%. Section "3", as analyzed, exhibited
a maximum reduction of about 8%. These values were found.by counting the
number of grains across the diameters of each specimen.

6. Grain fragmentation or what is believed to be conclusive evidence
of the phenomenon, was found in each section.

7. The reduction in grain size did not appear to increase or decrease
regularly with the reduction in area encountered.

8. Distortion to a marked degree was found in Figures No. 55 and 56,
where the greatest reduction in area was noted. The most distortion found

was at the point of'bending in Specimen E}.

CONCLUSIONS

1. With reduction in area from coldpworking, there was no increase in
hardness, a fact contrary to theories advanced.

2. With reduction in area from coldpworking, there was a decrease in
grain size. Since decreased grain size is supposed to increase grain
boundaries and consequently, the amount of amorphous cementing material in
the grain boundaries ( if such a constituent does exist), there should.be a
an accompanying increase in hardness._ Such was not the case, at least as
shown‘by'the Rockwell Tester.

3. The points of greatest hardness were at the places where bends in
the strips were in evidence. Since there was not always an indication of
elongation of grains at these points, what then must this hardness be due
to?

h. The hardness from end to end of each of the three sections analyzed
agreed very closely. Thus cold working has not increased hardness or

brittleness in this instance.

- uh.—

5. Low-carbon steel is supposed to be very ductile, a factor important
in the coldpworking phenomena. Since there appeared (up to a reduction in
area of about 20%) no regular indications of grain elongation, and since there
did appear to be many indications of grain fragmentation, it would seem, within
these limits, that the elastic limit of the grains had not been exceeded, even
though the entire section had itself been plastically deformed. Thus the
tremendous pressure of the dies used in cold-working had served to crack the
grains. Or is this fragmentation possibly due to what is known as character-
istic Ferrite Brittleness?

6. There must have been a movement of grains in the metal, for how else
could there have been a reduction of area in each section? Is it possible
that rolling characteristics of the hot-working preliminary to coldrworking
effected this? '

7. There were definite indications of the presence of cementite in the
grain boundaries at points devoid of Pearlite. Where did this cementite come
from? Indications here would seem to show that the presence of this constit-
uent in the grain boundaries did not serve to make the metal harder.

8. Since cementite has been found in the grain boundaries, this sub-
stantiates the belief that grain boundaries consist of at least some crystalline
material; whether amorphous material is also present is beyond comprehension.

9. The grains begin to be noticeablely distorted at the point where
a reduction in area of 30% occurs. This is in agreement with the recent work
of Hayes and Burns.10

10.{ The size of the grains was reduced considerably. This would enchanee
the formation of more and new grain boundaries. Where does this grain boundary
metal come from? Did.the grain fragmentation produce this material, or is
there a void.between grains? Or is it possible that a difference in orientation

‘7
has produced this phenomenon. To go on, with increased grain boundaries, there

-15..

should.be more disorganized metal or perhaps amorphous materials. This should
increase the resistance to slip. With increased resistance to slip there
should be increased hardness. This was not the case in this investigation.
11. That the hardness has not increased with (1) reduction in area, (2)
decrease in grain size, and (3) increase in so-called amorphous cement in
grain boundaries, would seem to disprove, in this instance, that there is any
amorphous constituent in the grain boundaries, a fact contrary to theories
advanced. Even at the points where distortion was evident, there ttill did

not seem to be an increase in hardness.

That the conclusions stated above are not in harmony with previously
stated facts and theories advanced by noted metallurgists and metallographers,
is quite evident. Not only that, but the experimental evidence itsthf seems
to formulate conclusions which are in some cases contradictory to each other.
ror instance, the strip of steel exhibited a reduction in area from one end
to the other. Yet the hardness and elongation of grain structure that is
supposed to accompany this reduction was not in evidence. The grains them-
selves were fragmented in many instances and decreased in size with reduction
in area. Yet this reduction in grain size was not gradual or regular to any
appreciable degree. The strips of metal were plastically deformed, yet the
grains, which are supposed to be the fundamental units in the steel, were not
elongated. Shouldn't they have'been stretched.with this narrowingbout of
the metal and consequently a movement of grains? Even where elongation was
in evidence, in Section "E", the hardness did not increase with respect to
the hardness exhibited.at other points. Lowbcarbon steel is supposed to be
ductile and with the accompanying reduction in area to support this fact,

the fragmentation of the grains in the metal then avpeared to contradict it.

- N6 -

These statements lead us to the always pertinent question: Are we really
viewing the true grain structure of metal under a microscOpe? Does the etching
solution reveal the true structure or are we merely scratching the surface?

In the cold-worked steel herein discussed, there has been a reduction in area
and hence a stretching or pulling out of the strip metal. Was this stretching
accomplished by each one of'the multitude of grains being separately stressed,
elongation or fragmentation taking place? Or did the long strip stretch out
as a ihole piece of’metal would if of fibrous structure freehand to end?

A possible answer to these questions might be obtained in this manner:
Carefully cut and polish a small thin section of lowzcarbon (ductile) and
etch.it in the customary manner. Next clamp it in a small machine designed
to stress the metal, being accomplished by means of heavy gears so constructed
that the specimen.will be slowly and steadily stretched or elongated; that is,
pulling on the two ends of the metal much as one would stretch a.rubber’band.
'hile this stress is occurring, view the specimen thru a.mdcroscope and if
possible, take motion pictures of the phenomena. If the etched grain structure
retains its characteristic position and moves as individual blocks that are
being elongated, it is definite proof that we are viewing'true grain structure,
and not a surface phenomena. If, on the other hand, the ferrite and pearlite
seem to smear over each other and pull out to destroy the grain structure,
thus leaving an irregular, Jumbled mass, then the metal is evidently being
stretched as one large complete unit. Then our conceptions of grain structure

and supposed grain movements would receive a tremendous setback.

-ln-

BIBLIOGRAPHY

1.

2.

3.
It.

5.

7.

8.

9.

10.

11.

12.

13.

1h,

15.

16.

17.

18.

Metals Handbook, The American Society for Metals, 1937.
Metals Handbook, The American Society for Metals, 1937.
Metals Handbook, The American Society for Metals, 1937.

"Cold Worked Steel", The Metallography and Heat Treatment of Iron and
Steel, Dr. A. Sauveur, pp 191-193.

“Deformation", The Science of Metals, Zay Jeffries and Robert Archer,
p 162s

"Increased Hardness Resulting from Cold Working”, The Metallography and
Heat Treatment of Iron and Steel, Dr. A. Sauveur, pp 203-20M.

"Preperties and Structure of Cold Worked Steel”, The Science of Metals,
Zay Jeffries and Robert Archer, pp152-l53.

"Summary of Properties", The Science of Metals, Zay Jeffries and Robert
Archer, pp20l—PO2.

”Brittleness in Low Carbon Steel“, The Metallography and Heat Treatment
of Iron and Steel, Dr. A. Sauveur, pp 28-30.

”Cold Rolling of Mild Steel Sheets and Strips”, Transactions of Amer-
ican Society for Metals, Anson Hayes and R. S. Burns, Vbl. XXV, No. 1,
PP 129-157e

'Cold.Work or Plastic Deformation", The Science of Metals, Zay Jeffries
and Robert.Archer, pp “8-h9.

"Capitulation of Movements”, The Metallography of Steel and Cast Iron,
Henry M. Howe, p295.

“Fluid and.Rlook Movement”, The MetallOgraphy of Steel and Cast Iron,
Henry M. Howe, p293.

”Crystalline and Noncrystalline Movements", The Metallography of Steel and
Cast Iron, Henry M. Howe, p29”.

”Intercrystalline Slip", The Science of Metals, Zay Jeffries and Robert
Archer, ppHI-uS.

“Slip", The Metallography of Steel and Cast Iron, Henry M. Howe, p295.

'Similies to Explain the Mechanism of Slip", The Metallography of Steel
and Cast Iron, Henry M. Howe, p336.

"Conditions at Slip Planes”, The Science of Metals, Zay Jeffries and Robert
Archer, pp 202-206.

19.

20.

21.

22.

23.

2h.

25.

26.

27.

28.

"Definition of Amorphous", The Science of Metals, Zay Jeffries and
Robert Archer, p63.

"Amorphous Cement Theory vs. Heat Treatment of Pure Metals", The Metal-
lography and Heat Treatment of Iron and Steel, Dr. A. Sauveur, pp30-3l.

"Mixed Orientation at Grain Boundaries", The Metallography of Steel and
Cast Iron, Henry M. Howe, p321.

"Amorphous Metal at Grain Boundaries", The Metallography and Heat Treat-
ment of Iron and Steel, Dr. A. Sauveur, p292.

"Equi-cohesive Temperature", The Metallography and Heat Treatment of Iron
and Steel, Dr. A. Sauveur, pp l9h-l96.

"Amorphous Metals", The Science of Metals, Zay Jeffries and Robert Archer,
p166e

”Possible Structure at Grain Boundaries", The Science of Metals, Zay
Jeffries and Rebert Archer, pp 72-73.

”Plastic Deformation and So-Called Amorphous Metal”, Alloys of Iron and
Carbon, Vol. II, Preperties, F. T. Sisco, pp h97-h98.

”Elastic and Plastic Deformation", The Metallography of Steel and Cast
Iron, Henry M. Howe, p293.

"Cold Work or Plastic Deformation", The Science of Metals, Zay Jeffries
and Robert Archer, pp M8-N9.

”Recrystallization Structures”, Transactions of American Society for
Metals, Vol. XXIV, December 1936, p 981.

SECTION II.

is INVESTIGATION or
man IAILUBE Ill
moo lb. some

INTRODUCTION

The following report is an investigation of a tube failure in the
water walls of a 11400 pound pressure boiler installed at the Firestone Tire
and Rubber Co., Akron Ohio. I

A letter from W. X. Adkins, Power Engineer of the Firestone Tire and
Rubber Co. is herein included. This letter states the specific conditions
under which the tube failure occurred.

A second letter states that the results obtained agreed with work done
by others upon the same failure.

It is thought that this investigation well illustrates the application

of metallographic theory to a practical and in industry.

mon, OMOe
rebruary, 18, 1937.

“re Ce Le Grandall,

Department of Chemical Engineering,
Michigan State College,

East Lansing, Michigan.

Dear Mr. Crandall:

This will acknowledge receipt of your letter dated
February 15 relative to your recent interview and to the tube failure
in our ll+OO lb. boiler.

We are sending you, under separate cover a small sec-
tion, at the point of failure, from the side wall tube which failed in
our high pressure boiler the early part of this year. We are also
sending a cross section of the sam tube at a point located two feet
above the failure. Following are answers to the questions in the last
paragraph of your letter.

1) The boiler had been operating at full load for five
days. It was started up Sunday evening, and failure occured Friday 1.1!.
he boiler is normally out of service over week ends and is bottled 1m
for periods of from floaty-four to thirty-six hours during which time
the pressure drape to, from 300 to 500 lbs.

2) Failure occured in the left side wall, when facing
the front of the boiler, in the twenty-seventh tube from the rear wall,
and at a point sixteen feet above the lower side wall header.

3) Tubes are straight carbon steel '0” ago, and are
hot seamless drawn, furni shed by the Globe Steel Tube Company throufi
Combustion Engineering Corporation.

1*) Water is all condensate. We carry pH from 11 to 11.2
Total maximum dissolved solids 150 ppm of which seventy parts is sodium
hydroxide, sixty parts sodium sulphate, and twwty parts sodium chloride.
There is also a small amount of suspended solid which is about 50% copper
and 50% ferrous ledroxide.

5) Slag accumulates on side wall tubes to a maximum
thickness of from 3/8" to 1/2' which has the following analysis:

810 39.60% 11 16.9% MgO 0.32%

Yours very truly,
THE l'IRESTONE TIRE AND RUBBER CO.

'e I. ma.
Power hgneer

Akron, Ohio
March 31, 1937

he 0. Le Grendel].

Department of Chemical Engineering
Michigan State College

last Lansing, Michigan

Dear Mr. Grand all:

$951 TUBE FAILURE

Wish to acknowledge receipt of your report
in connection with tube failure in our lhOOi' boiler.

The report is very well done and the conclusions
reached agree with these advanced by others.

Wish to take this opportunity to express

our appreciation of the interest that you have shown in
the subject.

Yours very truly,
HHS'PONE TIE! a. RUBBER COMP”!

1'. K. Adkins,
Power higineer

SUMMARY OF NVESTIGATION

The investigation of the boiler tube failure was carried out along
mstallographic lines. Photomicrographs were taken of the section two
feet from the failure and of that portion where failure occurred. Con-
clusions were reached that the failure was not due to embrittlement,
decarburization, or to some primary defect in the metal.

The failure is believed to be the effect of localized overheating.
The exterior surface of the tube was subjected to a temperature of near
2200° Iahr. in the combustion chamber of the furnace. The tubes are
normally water cooled and thus protected from this heat which is in
excess of the critical temperature of the steel. However, if a gas
bubble should get entrapped next to the inside surface of the metal,
or a piece of scale become adhered to it, then the boiler tube would
no longer be cooled by the water at that point. In two to three minutes,
the temperature of the metal would pass on into the critical range,
1500" Fahr. or higher, and the weakened steel, at red heat, would lose
tensile strength due to the enormous internal pressure, and burst out
suddenly to exhibit the ”ballooning-out” as experienced by the tube failure.
The great drop in pressure of the water bursting out of the tube into
the combustion chamber would serve to cool or quench the hot metal.
This statement is substantiated by photomicrographe of Specimen T2 and
T}, where the structures exhibited show definitely that the steel was
carried through the critical range and subjected to a quick quench.
Thus the effect at this one point in the boiler tube might be compared
to putting a piece of metal in a furnace, heating it above its critical

range, and then quenching it in brine.

 

 

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Figure To. 1 - Showing
Location of Specimens in
Each Section of the Boiler
Tube. Thickness of Tube

3/8“.

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gggrr DISCUSSION 9! METHODS OF ANADYSIS

The purpose of this discussion is to enable the reader to get a
brief description of metallographic methods of analysis. Small sections
or specimens were cut from two pieces of boiler tubing and were desig-
nated as in Figure no. 1. Each specimen was separately mounted in bakeu
olite, polished, and then etched with Nital (Nitric Acid in Mbthyl Alcohol):
the etching reagent acts upon certain constituents of the metal to reveal
the granular structure of the specimen. The entire specimen is then viewed
under a microscope and pictures taken at various magnifications to reveal
the typiga1,structure possessed by the metal. From these pictures, knowing
the kind of steel and the heat treatment it has undergone, the properties
of the metal may be studied. The use of hardness tests also serves as an
aid in the analysis, the Rockwell Hardness Tester being used in this in-
vestigatlon.

If the metal undergoing inspection does not appear to have uniform
properties, that is, it is not in its “normal” state, due to cold or hot
working, quenching, carburizing, straining, etc., then it is necessary
to normalize the specimen before its properties can be determined. 'I‘isman‘I
describes normalizing as follows: “A form of annealing”known as normal-
ieing'consists in reheating to a temperature above the critical range,‘hold-
ing at that temperature a certain length of time, slowly cooling finally
being employed. It is comercially used to secure uniform conditions a:
materials treated in various'ways or where, as in the case of billets,
the finishing temperature and amount of working have resulted in a very

coarse grain.”

‘ - The metallography and Heat Treatment of Iron and Steel, Saveur, McCraw and
Hill Book Co., 1935, p 211.

 

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Specimen.No.T -Cut

” from Section .1 - Showing
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Figure No. 3. ‘
Same as Figure No. 2
except at 25OX - Grains
undistorted and poly»
hedral e

Figure No. 5
Specimen No. T - Out
from Section N3. 2.
Showing quenched struct-
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PROCEDURE AND DISCUSSION IN DETAIL

By combining the procedure and discussion, it is though that a more
comprehensive picture can be obtained of this type of analysis. Each
specimen will be discussed separately.
hecimen N9, “T3"

Figure No. 2 is a photomicrograph of Specimen T1 taken at a magnifi-
cation of 100 diameters (1001), showing a typical structure of the metal.
This picture revealed that the metal was a typical low carbon steel
(.101 to .1553 Carbon). The larger grains of grayish cast are Ferrite (alpha
iron and carbon), while the darker spots are Pearlite. Pearlite is defined
as Ferrite plus Cementite 0.30). Figure No. 3 is a photomicrograph of
Specimen T1 at 2501, this picture showing that the grains of metal were
polyhedral and that the pearlite was in a normal state. Figure No. it was
taken at 1000! to show the condition of the Pearlite in Specimen T1.
It was found to be in what is termed "Normal" or laminated pearlite, in
which alternate dark and light bands or lanallae of ferrite and cementite
appear. Summarizing, these three pictures showed the metal to be a low carbon
steel in a normal state, of .lO-.l5% carbon, with no evidence of distort-

i on, occlusions, etc.

begin; 119, “T3“

Having a knowledge of the structure of the steel in the normal state
before failure, it was next necessary to investigate the metal at the point
of failure. Specimen T2 was photographed in much the same manner as
Specimen T1, photomicrographs being taken at 1001 and 1000}! only. Figure
‘lo. 5 revealed anr‘entirely different structure, and with the aid of rigure

No. 6 at higher magnification (1000 diameters) it was found to be a needle-

 

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Figure No. 6
Same as Figure No. 5
except at lOOOX.

Figure NOe 8
Same as Figure No. 7
except at 2501.

 

Figure NO. 7e
Specimen No. T - Cut
from Section 2} Showing
quenched structure. 1001.

Figure No. 9
Same as figure No. 7
except at 1000K.

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like structure which is typical of a steel which.has been heated above

its critical range, 1500° thr. or higher, and then quenched. as critical
range is meant thermal transformation points where the steel in question
changes certain of its physical and.chemica1 properties. This is in the
region where the metal reaches a ”red” heat. A structure of this type

in steel, under the conditions named, is therefore very conclusive evidence
that the metal must have been under localised heating’phenomena that carried
it up into the "red“ heat range and that when the metal wall burst out,

it must have been quenched by the enormous drop in pressure.

me N ” '

Photomicrographs were next taken of Specimen T3 to determine if the
steel showed the same properties as the adjacent T2 (see Figure No. l).
Photomicrographs at 1001, 2501, and 1000! showed that the steel was still
in a state where it had been carried up through.the critical or ”red" heat
range, but had been cooled (or quenched) at a slower rate. Thus T3, due

to its location and increase in diameter was slower cooled than Tb.

Figures Nos. 7, 8, and 9 show the above condition to be true.

e N 'T '

Figures no. 10 and No. 11, taken at 100x and 2501 respectively, show
that Specimen Th, taken from the same section of'the tube that failed,
(see Figure No. l) but on the opposite side of the tube, is approximately
of the same structure as Specimen T1. This would indicate that the steel
at the point of failure was not deficient providing Specimens lo. TE and

lb. T3 had not in some manner or other become decerburised. This decan-

burieing effect is discussed in the next paragraph.

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‘r‘fz'xfrigure No. 10

V’gpeclmen No. Tu - Cut

‘ rom Sgction No. 2.

p,ShowingԤteel to be
analogofis’wdth Specimen
NOe T1. "1901;

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iFigure No. 12.
Specimen No. T in
a normalized sta e - heat
: treat at 18000 F. for
.‘1 hr. with furnace cooled.
lOOX.

Figure NOs 11 .
Same as Figure No. 10
except at 2501..

Figure No. 13.
Same as Figure No. 12.
except at 2501.

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lgrmali zing of T and T}

It is impossible to determine by metallographic methods the

carbon content of steel in the quenched state, as pictured in photo-
micrographs No. 5 to No. 9, inclusive. To investigate the two speci-
mens T2 and T3(at the point of failure) it was necessary to normalize
them to ascertain if decarburisation had taken place. The normalizing
was accomplished by placing the specimens in a cold furnace, the temp-
erature then being raised to 1800" Fahr., held at that temperature for
one hour, and then furnace cooled. In this manner, the steel was changed
from the quenched or hardened state to the normlised condition which
consists of Pearlite and Ferrite. Figures No. 12 and No. 13 indicate

a structure analagous to T1 and '11,, showing that the failure was not due
to decarburization; the carbon was present as expected in the form of
Pearlite. Photomicrographs of T3 in the normalised state are the same

as Figures No. 12 and No. 13, and are therefore not shown.

rd s e t
The Rockwell Hardness Tester was next employed in the study of the
boiler tube. Steel in the normal state as evidenced in T1 and i“, and

also in the normalised structures of T2 and T should be softer than

3
the quenched steel in T2 and 1'} (before normalizing). Table lo. 1, under
the section ”Data" indicates that this statement is true, thus further
proving that for this type of steel, there had been a heating through
the critical rungs and an accompanying quench. Also, since T2 was
evidently quicker cooled than T3, it should exhth a higier Rockwell
reading, a statement also true. The hardnesses are in Rockwell 'B",

and the larger the umber, the harder the steel. For instance, Rockwell

893 is harder than Rockwell 603, but softer than Rockwell 953.

If the hardness of T2 or T3 had been very low, say Rockwell 3GB,

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it would have been partial evidence that the steel had become decarburized,
as hardness of steel of this type varies in preportion to the amount of

carbon contained.

Failure Not Dug To Ebgittlemegt
In the opening paragraph, a statement was made that it was thought

that the failure was not due to embrittlememt. Mbrittlement causes have
been the subject of much conjecture in the past; some say that caustic

is responsible for this type of failure, others claiming it is silica in
the presence of caustic. However, in this tube failure, if embrittlement
had been the cause, it is thought that a Jagged, irregular, cracking open
of the metal would be in evidence. The embrittlement would gradually pit
out the metal surface, but the cooling water would always be inside the
tube, thus causing the metal to finally crack open in an irregular fashion.
Photomicrographic‘ examination of this type of failure should show the
metal to be in a normal state as the steel in this case would not be sub-
Jected to localised overheating into the "red heat” range. As has been
stated previously, this ballooning-out effect of the boiler tube, as might
be experienced by a piece of rubber under pressure, could only be accom-
lished with steel if it had been heated up into or above its critical range.
In this range of “red heat”, a decided loss in tensile strength would cause
the now plastic metal to burst out as in the tube failure covered in this

rcpor t e

mm
The emphasis of the fact that deficient metal could not have caused

this failure is again herein included. Also, consideration has been given a

i ..

to the fact that slag collects on the outside of the tubes to thicknesses

of 3/8" to 1/2". This scale would serve as an insulator between the metal

-6-

and the intense heat. Should a piece of this scale drop off the tube,

it is not believed that the increased heat upon the outside surface of

the metal would be sufficient to cause localised overheating, since the
water would still be inside the tube at that point.

The phenomena of localized overheating was said to have been caused
by an entrapped gas bubble or scale of the adherent type, thus insulating
the metal from the cooling water inside of the tube. Where or how this gas
bubble or scale could have occurred at this point and not at other points
in the boiler is not conceivable. If scale had been the cause, it is ob—
vious that the tremendous pressure at the time of the burst out of the
tube would have carried away the scale, thus making it impossible for
a positive statement that this was the factor involved. The gas bubble
effect is thought less possible than the scale adherence, but such entrap-
ment of gas in the water walls would not be absolutely impossible. I t is
thought that aw further cause of the tube failure from this viewpoint

could only be carried on in the power plant.

2335

Table No. 1 gives the hardness reading at various points on each
specimen, as well as average hardnesses.

Table No. 2 is an Index of Photomicrographs taken for this paper,
the pictures being taken with a Bosch and Lamb Metalloscope No. 276, shown

in Figure No. 114.

 

Specimen No. Hardness Readings‘ Average

 

A 4 C D Edness
’1 69 65 50 60 61
re 99 103 100 101 101
T3 85 89 87 89 87
1‘. 1+9 s7 53 61 56
$2" In 56 56 59 5”
I3" 56 62 63 63 61

 

" - All hardness readings in Rockwell “B”.
” - Normalised structures.-

TABLI NO. 1
HARNESS DETERMINATIONS.

 

Figure Specimen he Object. Bellows Hagnifi- Exposur;

 

lo. lo. Piece ive Length cation Time
(cm) (I)
2 r1 7.5 16 m 27.0 1001: 1H0 sec.
3 ml 7.5 3 mm 31:5 2501 5 min.
b ml 7.5 1.3 mm 31.5 10001: 15 min.
5 r2 7.5 16 n 27.0 1001: no see.
6 are 7.5 1.8 m 3h.5 10001: 15 min.
7 r3 7.5 16 III 27.0 1001 no sec.
3 T3 7.5 s m 31:45 2501 5 min.
9 1'} 7.5 1.3 mm 31w; 10001 15 min.
10 Th 7.5 16 m 27.0 1001 1’40 sec.
11 r“ 7.5 8 mm 3M5 2501 5 min.
12 22'- 7.5 16 a. 27.0 1001 rho sec.
13 was 7.5 8 use fins 250x 5 min.

 

" - normalised structure.

TABII l0. 2
INDEX TO PHOTOHIOBOMHS

VJ;

.x‘x.

w:

 

 

 

 

 

 

MICHIGAN STATE UNIVERSITY LIBRARIES

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