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ANA
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THE GNFLUEMEE OF SECTQON SIZE
ON PRQPERWES 0F
5%53CKEL—MOL‘3’BDENUM CAST IRGNS

Thais far firm Der-gran of M. S.

Miffikiififlfl STATE COLLEGE

Mahammmfi Ssharéf Elia:
1943

_ 1115818

This is to certifg that the

thesis entitled

THE INFLUENCE OF SECTION SIZE
ON PROPERTIES OF
NICKEL—I'AOLYBDENUM CAST IRONS

 

presented bg

Mohammed Shurif Riaz

I a . t has been accepted towards fulfillment

of the requirements for

__ Ill-é.- _-,degree in_._,M_°_E_;:I__

j Major professor

Prof. L.G. Miller

Date __ ___-_

April 14, 1948

M-795

 

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t» llllll 'IIl'E (trill

ll (ll 'Illll. 'ullll.{z| II {I
Ii ‘1. (l {I

 

lllll'lfll'llll Ill I l l

THE INFLUENCE OF SECTION SIZE ON PROPERTIES OF

NICKEL - MOLYBDENUM CAST IRONS

By

MOI-{AHMED SHARIF' RIAZ

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1948

 

'l“..[.[ [[[l l 'l'. [I'll l I l l

é/Q/tis

ACKNOWLEDGEMENT

The author is grateful to Prof Howard
L. Womochel for his encouragement, technical
advice and guidance in the course of con-
ducting the research reported in this manu-
script.

The author also wishes to take this
opportunity to thank Douglas Harvey,
Raymond Pearson and Don Sable for their
help during pouring and machining of irons

under consideration.

303.17% 3

 

'll'll‘ll‘llllll

I.

II.
III.
IV.

CONTENTS

INTRODUCTION
A. INTRODUCTORY
B. SECTION SENSITIVITY

SURVEY OF PUBLISHED LITERATURE

SCOPE OF INVESTIGATION

MELTING PRACTICE

A.
B.
C.
D.
E.

PREPARATION OF HOLDS

CHARGE

INOCCULATION

TAPPING d: POURING TEMPERATURES
METAL CASTING-S

PAGES

NWHH

\O

10
10
10
11
11
11

V. INVESTIGATION

Aw .
1. Chemical Analysis
2. Transverse Testing
3. Tensile Testing
4. Hardness
5. Microscopic Examination.

B3 DISCUSSION*

1.

VI. SUMMARY

Tensile
Hardness
Microstructure
Toughness
Machinability

VII. BIBLIOGRAPHY

PAGES
12
12
14
14
14
17
17’
17
27
28
29
29
3O
32

LIST OF FIGURES, ETC.
FIGURES- PAGES
1. Photomicrograph of iron R1 in 1.2 inch sections 21

 

2. Photomicrograph of iron R1 in 4 " " 22
3. Photomicrograph of iron R2 in 1.2 " " 23
4. Photomicrograph of iron R2 in 4 " " 24
S. Photomicrograph of iron R3 in 1.2 " " 25
6. Photomicrograph of iron R3 in 4 " " 26
GRA?E§

I Tensile Strength V. Section size, all heats 16
II Hardness V'Diameters; heat R1 16
III Hardness " R2 18
IV Hardness “ R3 18
V Surface Hardness V Section size, all heats 19
VI Center Hardness V ” l9
TABLES

I Chemical Analysis, all heats 13

II Physical Properties in 1.2 inch Sections, all heats 13
III Physical Properties in various sections: 15:
IV’Micro Results 20

 

If [all I 'I all I

I INTRODUCTION

A. INTRODUCTORY'

1.

Since the early twenties there has been a great.
interest among foundrymen in having better properties
in cast iron. Earlier, plain irons of low carbon
contents were used for castings requiring high strength.
Due to poorly controlled melting practices, the
foundryman found himself involved in difficulties such
as poor fluidity and abnormal matrix in the irons.

These irons sometimes showed good properties and at
others very poor properties depending upon the kind
and magnitude of the difficulty. Later some of these
difficulties were overcome by the use of alloying
elements. The use of nickel became common by about
1925 while Molybdenum became better known to the
foundrymen by the end of the twenties.

A tensile strength of 40,000 or 45,000 pounds per
square inch in 1.2 inch sections was not considered
enough hence the use of alloy combinations, Ni-Cr, Mo-Cr
or Ni-Cr-Mo, were adopted. The use of Molybdenum in
smaller quantities was usually recommended because of
its higher cost. With these alloy combinations and with
better control of foundry practices it became common to
melt irons of 65,000 or 70,000 psi in 1.2 inch sections.

The use of Chromium as an alloying element, alone:
or in combination with other alloying elements, produced
irons of higher strengths but it offered one serious

difficulty --- its effect of inducing chill. These irons

are usually very hard and are sometimes very<iifficult to ma-
chine particularly in smaller sections where it has a greater“
chilling tendency. Use of cast irons for crankshafts made it
necrssary that the irons should be easily machinable in order
to meet with production requirements. Use of Molybdenum in-
stead of Chromium became more and more general because of less-
er tendency of Molybdenum to induce chill.

work done by Kentsmith & Young}1, Phillips15 , and Crosby7
in early thirties showed all round better properties of Ni-Mo
irons.

8*

In 1937. Flinn a Reese realized that if the strength of
machinable gray cast iron was to be raised above 75,000 psi in
1.2 inch sections, a structure other than pearlite was neces-
sary. It was the time when highest strength in gray irons was
associated with a matrix having 100% pearlite. Work done by
various metallurgists and foundrymen in this field, among whom
Flinn, Timmons a Young with their associates are notable. In
England British Cast Iron Research Association has conducted an
interesting research in this field. It is of interest to note:
that Flinn & Reese8 were able to cast gray iron having tensile
strength equal to 105,000 psi in a 1.2“ section after giving
it a simple heat treatment‘of drawing at 700° F. The iron had
a composition of 2.25% total Carbon, 2.35% Silicon, 3% Nickel
and 0.81% Molybdenum. It had a structure which is now called

”Acicular“. This acicular structure is a characteristic of

high alloy Nickel and Molybdenum irons;

 

* These numbers refer to the articles listed in the Bibliography.

These acicular irons are of great interest to the foundry
industry.

The two limitations that are experienced in getting the
best results from acicular irons are the presence of ferrite
and pearliteein the matrix and the dispersion of massive
cementite:

The complex carbides, due to their higher hardness and a-
brasive properties, generally make the machining of the casts
ings very difficult. In some cases the casting may be so diff-
icult to machine that scrapping of the casting may result.

Ferrite is the softest of the microeconstituents and its
presence in the matrix lowers the properties of irons.

Contacts with the users and producers of gray alloy irons-
for diesel crankshafts have indicated that considerable diffi-
culty is still being experienced in meeting with the specifi-
catienas Iron castings have either been found too hard or too
soft. The difficulty would seem to be in avoiding massive
carbide while keeping the acicular matrix free from ferrite.
and pearlite. The presence of hard cementite would be attrib—
uted to the stablilizing effect of some Chromium in the chem-
ical composition of the iron. This would suggest an attention
to Ni-Mo irons. Molybdenum is a weak chill inducer and will
therefore reduce the chances of formation of hard spots which
could only be avoided altogether by the addition of a balanced
amount of Nickel. Beanies avoiding hard spots; Ni-Mo irons:
could give the best known high strength acicular matrix free.
from both ferrite and pearlite.

3.

A survey of the published literature on Ni-Mo irons has
shownithe difficulty of co-relating the available information;

The metallurgists and the foundrymen who have been working
on acicular irons have worked with irons of different chemical
composition. Some have worked with irons of as low a carbon
content as 2.25%, some with as high as 3.25%, while the rest
with some composition in between. It is very well known to
the foundrymen using pearlite irons that the maximum use of
alloying elements.can be obtained with low carbon in composition.
But there is a limit to the lowest desirable composition be-
cause with still lower carbon content, an iron will show poor
fluidity, greater chilling tendencies and an abnormal matrix.
Melting of low carbonziron also necessitates greater use of
steel scrap. Further, it is rather impossible today for a
cupola foundryman to melt iron of as low a composition as 2.25%.
Such an iron could be melted in an electric or an air furnace.
This limits the number of foundries that can use the results
of a research on such extremely low carbon irons;

In addition to carbon as a variable, the silicon and man-
ganese contents of the irons discussed in the literature also
varies through whde limits. These variations in analysis of
cast irons make it difficult to interpret.as such much of the
available data.

Although inoculation is a common practice in the melting of
high strength irons, there is very little definite information
concerning the relative effect of the several inoculants in

common use. This introduces another variable generally not

considered in the available literature and makes it diffi-
cult tc interpret the date presented on the high alloy irons.
The present day need of irons as high in strength as
possible and existence cf’difficulties in co-relating the
available literature gave an impetus to conduct a systemat-
ic research on acicular irons in the Laboratories of Miche
igan State College.
The present work is the first part of the project
which will be further continued.

3 SECTIQN_SENSITIVITY

It is now well known among foundrymen that size of a
casting affects greatly the tensile strength, hardness
and other properties shown by an iron. Published data on
pearlitic gray irons, both plain as well as alloyed, has
shown that as the section size of a casting is increased,
its tensile strength goes down. The loss in the strength
of a heavier section compared to some standard section,
indicates the section sensitivity of the iron.

In increasing the section size the factor that affects
the structure of an iron is the cooling rate. Thus the-
center of a thin section is cooled faster than the center
of a heavier one. Cooling rate depends on many factors;
such as superheating temperature, temperature of iron at
pouring, rate of pouring, volume of metal to be cooled,
area of the surface of metal in contact with mold, conduc-
tivity of heat of the mold, amount of sand surrounding the;
mold position of gates and risers, and the atmospheric con-

ditions in the foundry.

 

The cooling rate affects both the size and distribution
of graphite flakes, and the fbrm of matrix. Slow cooling may
result in coarser graphite flakes and the inclusion of fer-
rite in a pearlitic matrix or as in the present case the in-
clusion of both ferrite and pearlite in the desired acicular
matrix. A casting will have the same strength as that of a
testing bar only if the cooling rates of the two are the same.

Austin4 in 1946 showed that "while 1.2 inches standard ar-
bitration bar does serve to provide properties comparable with
those of a casting of similar dimensions, it cannot furnish
similar data for metal poured into castings having profound di-
mensional differences".

To illustrate this point, it will be worthwhile to consider
a simple casting like a crankshaft. Crankshafts are being cast
from half an inch to twelve inches Journal diameter and i
inches to 4 inches web thickness. In the case of a crankshaft
of 4" web and 12" Journal diameter, evidentially Journal will
be much weaker if the iron used for casting is more sensitive
to section size. The shaft may be even so hard that it could
not be machined at a point where a change in section occurs.

It has therefore been considered that an attempt should be
made to study the section sensitivity of acicular irons in
order to establish basic compositions of a few irons which may

later be more effectively used in the proposed extended work.

II. SURVEY OF PUBLISHED LITERATURE

Kentsmith a Youngll noted in 1932 that "the combination
of Ni-Mo alloys under favorable conditions show a range of
physical properties for C. I. which suggest that the matrix
partakes somewhat of the properties of a high grade alloy
steel". It will be worthwhile to note that they produced
irons from electric furnace which had tortional strength of
the order of 55,000 inch-pound.“

Crosby7 in 1937 stated that acicular matrix is developed
in molybdenum irons containing 1% or more of molybdenum. He
further held the opinion that "certain alloy combinations on-
able one to secure this structure with much lower Molybdenum".
In an iron of 2.9% c, 2152% Si, 1.52% Mo, he noticed marten-
site and retained austinite in the matrix besides acicular
pearlite. He held the opinion that ”acicular pearlite is
most desirable for maximum impact properties."

Rothléin 1939 found that a low temperature draw at 600°FL
700°F shows better physical prgperties of Ni-Mo irons.

In 1941, Timmons & Crosby1 found that "keeping tapping,
temperature above 2600°F” in the case of high strength irons

when the presence of ferrite in the matrix is undesirable.

 

* For example, iron of composition 3.04% C, 2.24% Si, 1.2%.Ni,
1.71% Mo had a tensile strength of 67,000 psi, 293 B.H.N;,
5250# transverse breaking load and a tortional strength of
about 55,000 inch pound. All tests were carried on 1.2“ bar.

8
Interesting work has been done by Flinn & Reese . They

found that although acicular irons do not show much.higher
strength in the as cast condition as compared to the pearlitic
irons, they do show markedly superior physical properties after
a.draw at 500-7000F for ever 5 hours. They obtained strength
consistantly above 90,000 psi in 1.2" section bars, while in
one case the strength was as high as 105,000 psi. They show-
ed that the formation of acicular structure is due to a trans-
formation in the third region of transformation intermediate
between pearlite and martensite. They attributed the forma-
tion of a second nose in the S-Curve to the presence of Moly-
bdenum. The isothermal curves investigated by Flinn, Cohen

& Chipman are noteworthy.

One of the recent contributions to the development of
acicular structure has been the work carried out by the Brit-
ish Cast Iron Research Association. In the Fourth Report on
Special Duty Cast Irons, the reporter, Mr. Pearce13, has pre-
sented a few points which need attention. The investigation
shows.that variation in Silicon content in the composition
has no effect. Fbr optimum properties carbon content should
be between 2.7 to 3.1%, and Phosphorus below 0.15%. Mr.
Pearce does not recommend the use of copper for heavy sec-
tions. He also recommends the use of a balanced composition
of Nickel and Molybdenum and the‘giving of a heat treatment

to the irons for better properties.

III. SCOPE OF INVESTIGATION
In the present investigation electric furnace irons

were cast in 7/8, 1.2, 2, 3 and 4 inches round cylinders
.to determine the influence of alloy contents on section
sensitivity. The base iron selected was of the following
composition:

Carbon: : 2.65-2.80%

Silicon : 1.90-2.10%

Manganese : 0.7-0.9%

Sulphur : 0.05-0.08%

Phosphorus; : 0.07-0.12%
An electric furnace of indirect arc rocking type of 250
lbs capacity was used.

All the sections under consideration were tested for:
tensile strength and hardness and microstructures were
examined in each case. In all heats test bars in 1.2"
sections were tested for transverse breaking load and de-
flection at that load. Chemical analysis for all the

heats were carried out and various results studied.

10

IV. MELTING-PRACTICE
A. PREPARATION OF moms
All the molds were made from Lake core sand. They
were washed with a commercial non-carboneous wash and
were dried again before use.
B. CHARGE
Three heats, each with a charge of 250 lbs, were run.
The charge mainly consisted of low phosphorus, low sili-
con'and high carbon pigs and steel scrap. Electrolytic
Nickel was used for alloying and was charged while the
furnace was cold. Ferro-sulphur and ferro—molybdenum
were added about 10 minutes before tapping, while ferro-
manganese, and silicon as ferro-silicon and calcium sili-
cide were added about 5 minutes before tapping. A part
of the total silicon content was added as an inoculant
in the ladle.
The amounts of various basic charges were:
Pigs : 170 #
Steel Scrap 3 78 #
Ferro-Sulphur (50%) t 5 oz
Ferro-Silicon (90%) : 11 oz
Ferro-manganese (80%) : 5 oz
Calcium Silicide (60%) t 1 #,
Calcium Silicide (60%)”: 15 oz
* Used as inoculant for 3 ladles, each of

70 lbs capacity.

 

 

4 III“ it'll. l l

11

C. INOCULATION

Research on inoculants conducted at the Engineering
Experiment Station of Michigan State College during the
summenrl947, showed that in the case of high strength
irons a heavy inoculation of Calcium Silicide is desir-
able for obtaining the optimum properties from the iron.
This is in agreement with the results reported by
Pearcel3. Pearce recommends the use of as much as 0.5%
silicon of the total amount present in the iron, in the
form of Calcium Silicide addition.

It was therefore designed to add about 10% of the
total silicon content in the composition as Calcium
Silicide into the ladle in the form of an inoculant.

In all cases, inoculant was added about 2 minutes
before pouring to insure a complete solution of the
inoculant in the melt.

D. TAPPING 8t EQURING TEMPERATURES

Each melt was superheated to a temperature between
2800-28500F before tapping. Irons were poured in all
cases between 2600 to 2650°F. All the temperatures
were measured by an optical pyrometer.

E. METAL CASTING

All castings were allowed to completely cool down

to room temperature before they were knocked out of the

flasks. Later, the castings were cleaned by wire brushe

ing before testing.

A.

V. INVESTIGATION

PROCEDURE

1.

CHEMICAL COMPOSITION:

In making the chemical analysis of each sample, the
drillings were obtained as follows. In the case of heat
R l, the castings were quite easy to machine in all sec-
tions while in the case of heats R 2 and R 3 irons were
comparatively harder in 1.2" sections, while 4" sections
were quite easy to machine.) Drillings for heat R l were,
therefore, taken from the basin of 1.2“ test bar, while
in the case of other heats they were taken from the hard-
ness blocks from 4“ diameter cylinders in each case. In
both the last two heats drillings were taken after the
hardness readings were taken. In each case each speci-
man was drilled half way through.

Drillings from each sample were thoroughly mixed
before the analysis were carried out.

While all the irons were analysed for carbon, sili-
con, nickel and molybdenum, sulphur was analysed for R 1
only and manganese for heat R 2 only. Since the basic
charge was the same for all the heats, the value of sul-
phur.and manganese for the rest of the heats.were OOH?
sidered to be approximately the same. The analysis for
phosphorus, as shown in the table I is the desired com-
position aimed at while basic charge was calculated.

Table I shows the results of chemical analysis for

each heat.

113

TABLE I

CHEMICAL ANALYSIS (F HEATS

 

% CHEMICAL conicalrltn

 

 

 

 

hair .

C Si an E* 3 Ni Mo
a1 2.7a 1 00 0 75 . 0 09 0.055 1 05 . 0 52Q
32 2.69 1.98 . 0.75 . 0.09 . 0.055 . 0.995 . 1.12
A5 . 2.65 . 1.9h . 0.75 . 0.08 . 0.055 . 2.04 . 1.15

 

' The composition indicated is the desired analysis.

PHYSICAL

TASLE II

PRCPERTIES OF IRCKS IL 1.2 IRCE SECTION

 

Trans: Deflec= Tensile d. h. N. Nod: of
hEAT . ' . . . . .

Load, # inches Strengt? Surface Center Rupture,psi.
RI . 5740 0.59h5 . 70.750 . 2R5 . 2°5 . 90.200 .

 

32 . A500 .

0.585A . 76,720 . 521 . 521 . 119,h00 .

 

s5 . 4255 .

0.5955 . 7h,950 . 5A1 . 5A1 . 112,550 .

I

 

2.

3.

4.

TRANSVERSE STRENGTH:

Four transverse test bars, of 1.2" diameter and 21“
long, from each heat were broken according to A.S.T.M.d
specifications. Breaking load and maximum deflection at
that load were recorded for’each bar. The observed
results were corrected by suitable correction factors in
each case.

Table II shows the average results of transverse.
testing.

From the results obtained in transverse testing, the
value of modulus of rupture was calculated according to
theyformula:

Modulus of Rupture : Load in # x 26.53

TENSILE STRENGTH:

Tensile test specimens were cut from the top of the
lower half of cylinders in each section. In each case
specimens were machined from the center portion of each bar.

Each specimen was pulled in a tensile testing machine.
The results are recorded in table III. The influence of
tensile strength on section size is shown in graph I.

HARDNESS:

Hardness specimens of about one inch thickness were cut.
from the bottom of the top half cylinders left after cutting
the tensile specimens. All specimens were well polished
before any hardness reading was taken.

Hardness tests were taken at intervals of i inch along"

14

TABLE III

PHYSICAL PRLEERTIES LF IRONS IN

VA RI (.- US

‘15

8 EC TI CNS

 

1.2 inches Test Bar

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

° Section Tensile Hardness
heats Size Strength Surface . Center Trans: Deflection
Load
3/4 _ 541 3‘11 _ _
1.2 70,750 285 . 285 5740 0.5945
R1 2.0 64,140 241 . 241 ._ _
5.0 55,500 209 . 209 _ ._ .
t.0 46,900 201 . 197 ._ _
5/4 _, 541 . 541 __ __
1.2 76,720 521 . 521 4500 0.5854
a2 2.0 69,200 295 . 285 ._ _
5.0 67.675 285 269 _ _
4.0 52,550 265 . 241 _, ,_
5/4 _ .444 444 _ _ .
1.2 74,850 541 . 541 4255 0.5956 .
a5 2.0 74.575 235 . 277 _ _
5.0 68,000 269 . 255 __ _
4 .0 62.975 265 . 241 _ _ .

 

TENSILE STRENGTH -- p81

BRINELL HARDNESS

GRAPH I

85,000

75,000

05,000

55 ,000

45,000

 

35’0” 1.2 2 3

SECTION SIZE --- inches

450

400

350

300

250

200

 

150

2 1 ‘ 0 1 2

DIAMETER --- inches
HEAT Rl

two diameters of each test piece. Two surface hardness
readings were also taken for each case. In each case two
diameters of each indentation were measured and the average
of each of these two readings were recorded.

Hardness along one diameter for various sections in
theivarious heats have been plotted in graphs II, III and
IV, while surface and center hardnesses for each section
have been recorded in table III. Graph V shows the effect
of surface hardness on section size, while graph VI shows
the influence of center hardness on the same.

5. MICROSCOPIC EXAMINATION:

Samples of about 3/8 x 3/8 x i inches were out both at
the surface and from the center. 'All the samples were
polished in steps and final polishing was done on a silken
wheel. All samples were examined both unetched and etched
with 3% Nital.

The results of micro examination have been recorded in
table IV.

Photo-micrographs of 1.2" and 4" sections were taken and
are shown in figures 1 to 6. All the photo—micrographs
were taken near the surface of the specimens concerned.

B. DISCUSSION
1 TENSILE STRENGTH:

Tensile strength in the case of heat Rl decreases quite
raprdly up to 4' section. The presence of ferrite and the
change in matrix seems to be the main cause of rapid

decrease of tensile strength as compared to other heats.

17

BRIN ELL HARDNESS

BRIN ELL HARDNESS

18

GRAPH III

400

350

300

250

200

 

150
2 l 0 1 2

DIAMETER --- inches
HEAT R2

450 GRAPH IV

400

350

300

250

200

 

150

2 1 0 1 2

DIAMETER --- inches
HEAT R3

19

GRAPH V

4.

 

0
0
2 z

.Zfld i mmfizg HUafiflDm

150

SECTION SIZE --— inches

GRAPH VI

450

0 0 0 0 0
0 5 0 5 0
4 3 3 2 2
z.m.m i Mala: “NEED

 

150

SECTION SIZE --- inches

21)

TABLE IV

SUNRARY 0F RICROSCCrIC EXAMINATICN RESULTS

‘ssor

SIZE

3/4

1.2

2.0

4.0

 

1 hair A1 A hEAT a2 ; hair 85
i . ‘ l
. _.,II-NH ,2 - , .. ,nq.laN_MU.,,lhxl,..-m_umi-w-il ”livid
Structure similar ; Structure similar to 1 Structure similar %
.to fig 5 with §fig 5. to fig 5 with a .
isomewhat finer flakes greater pronortion E
E i of martensite. {
E i -.
‘ Dendrites of very A Structure entirely i Aciculsr structure
fine pearlite. areas hcicular, some with areas of martené
bf acicular structuremartensite & fine site. '
some martensite. & dispertion of massive ' Fig 5.
fine graphite. Carbides.
‘ See fig 1. ; See fig 5.
( Structure similar 2 Structure sinilar to ' Structure similar .
to with much less fig 5 with some fine :to fig 5. A
ferrite. pearlite. 8
Structure similar to A lacge amount of : Structure similar
to fig 2 with less fine pearlite, some ito fig 5 with some
ferrite. eciculsr structure, with.fine dispersion of
1 a small amount of tmsssive cementite.
martensite & massive '
carbides. Graphite flakes
somewhat coarser than '
2 inch section size.
5 Large amount of xi ‘Matrix largely fine - Acicular matrix
pearlite & ferrite pearlitic with some with some martensite'
with coarser flakes. fferrite along flakes Shows massive carbide
' bee fig 2. f& some inclusions of & coarser flakes.
massibe carbides. . bee fig 6. 3

g : See fig 4.

x
I
.'

A

N.B.= 1. fiatrix in all cases was found to be unifom from surface
to center.

2. Graphite distribution in all cases was found normal.

'V

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- , '2.

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7.“ "‘v. .-
. . ‘ g'w " _
\\,‘.‘.§ 7* . ‘ 9R? 1%;
“3%???“ ' ‘1

n 3’

 

IRON R1, SECTION 1.2 INCHES
ETGHED um 37% MILL, 250x

Fig 1'

 

IRON. a1, ssonon 4 moans

norms ram 5% mm. 250}:

Fig 2

 

IRON R2, SECTION 1.2 INCHES

13me WITH 3% NITAL, 2501:.

Fig 5.

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w -' .bhflfi‘ ' ’ >z‘
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n. .. ' ‘ .

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IRON 32, SECTION II INCHES
EICHED II'IH 5% NITAL, 2501:.

Fig ll

:r
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Cc“ .¥§\..
. 4%? q.

a. r.

 

IRON a},

HES

0

SECTION 1.2 IN

2501‘

amass mm 5% NITAL,

Fig 5

u, A
‘ he. 3.

I‘. ' Mict‘m‘gh
. ‘>~ '3‘

I . a: fl 1.3“. l'.’
“_ l 7“

3' _ o

 

IRON 115, SECTION A INCHES
ETOHED VITH 5% mm. 2501:

Fig 6

2.

It is very interesting to note that the tensile
strength in sections up to 3” do not differ much in heats
R2 and R3, while in heat R3, matrix does not change by
far up to the section sizes considered, in heat R2, the
matrix of 4" section is largely pearlitic as compared to
3" section which has only areas of fine pearlite. The
presence of pearlite and some ferrite near graphite flakes
in 4" section in heat R2 decreased the tensile strength
rapidly.

HARDNESS:

In the case of heat R1, hardness throughout all the
sections was fairly uniform. However, in the heaviest
section, a drop of 4 Brinell only was recorded for the:
center'hardness as compared to the rest of the section
which was quite uniform throughout.

An increase of molybdenum to 1% produces an iron
somewhat less uniform in hardness from center to surface.
(Compare graphs I & II).

A further increase of nickel by 1% in iron R2, seems
to have made the iron closer and denser in heavier sections
and has resulted in a somewhat greater uniformity of
hardness along diameters in each section.

It will be interesting to note that hardness in
sections up to 2" is uniform throughout the section.

Surface hardness and center hardness graphs reveal

interesting results. In both the graphs curves for

heatsMRl and R3 follow more or less similar slopes.

27

It may be noted here that heat R3 had double the amount
of alloying elements than heat R1.

In the case of heats R2 and R3, there does not seem
to be much.difference between surface hardnesses and the
center hardnesses for sections 1.5 to 4 inches.

3. MICRO-STRUCTURE:

Micro examination of all heats revealed a normal
distribution of graphite all through the matrix in all
sections.

The structure of matrix was found fairly uniform
throughout the section in all sections except in 3 &.4
inch sections in heats R2 & R3, in which case a coarser
matrix was noted near the center as compared to the
structure near the surface. It is due to this coarser
structure that the hardness near the centers of these
sections is less than at other points of the section.

While no'pearlite appears in various sections of
heat R3, it is found to appear first in 1.2" in heat R1
and in 2" section in heat R2. It may further be noted
that in heat Rl, ferrite appears in all sections above
1.2" and that some ferrite shows up along graphite
flakes in 4” section in heat R2. There was no massive
ferrite found in R3 in any section under consideration.

The effect of variation in matrix of different
sections in each heat on the various prOperties of each

iron has been discussed under those properties.

4.

5.

TOUGHNESS:

It will be seen that deflection in 1.2 inch section
in all these irons varies more or less in the same way
as does the transverse breaking load. This shows that
the toughness of all the irons considered also varies
directly with the variations in the breaking load.
Accordingly iron R2 shows greater toughness than iron R3.

MACHINABILITI:

There is no standard test for machinability. It was,
therefore, decided that a comparison of machinability of
irons in various sections may be made from the ease with
which each tensile test specimen is machined. It was
found that except for 1.2" section in iron R3, it was not
difficult to cut tensile specimens from the rest. The
difficulty in machining 1.2” section of heat R3 could be

attributed to the presence of martensite in the matrix.

29

VI. SUMMARY

An investigation has been carried out to determine the com-
position of a Ni-Mo iron suitable for castings of section up to
4 inches.' A composition can be regarded suitable for a given
section when it has an acicular matrix free from massive ferrite
and pearlite or large amounts of massive carbides.

This investigation reveals that an iron of the following
approximate composition 6 2.75%. Si 2%, In 0.75%,Ni 2% and
Mo 1% is suitable for the range of sections 1.2 inch to 4
inchesnround.

The iron is acicular in this range of sections and contains
a small amount of very finely dispersed massive cementite.

This iron is readily machinable in all sections down to 1.2“
round. Due to the presence of martensite in the section, 1.2"
section can be machined although with some difficulty. It is?
believed that the machinability and the physical properties of
this iron can be further improved by drawing at some suitable
temperature.

The iron produced a tensile strength ranging from 7#,OOO
psi in 1.2“ sections to 62,000 psi in 4" section, with a range
of surface Brinell hardness from 341 to 265 in the respective
sections. '

Iron R1 of composition 0 2.75%. Si 2%,‘Mn 0.75%. Ni 1% ,
and Me 0.5% showed aipearlitic structure in 1.2" section while
iron R2 of composition C 2.7%, 81 2%, M11 0.75%, Ni 1% and
..Mo 1% is entirely acicular up to 2"”round sections and shows

areas of fine pearlite in 2 inch and heavier sections.

It is planned to continue this investigation to deter-
mine the effect of drawing and of drawing and quenching on
the properties of iron R3.

31

VII. BIBLIOGRAPHY

Although there is not much published literature concern-
ing Nickel-Molybdenum Alloy Cast Iron, yet an attempt has
been made to list herein related material which was consider-
ed useful in carrying on the research. A list of the Publi-
cations indexed has also been added.

In the bibliography, beetles the usual abbreviations
for the months of the year, the following common abbrevia-
tions - v, n, p, H.T. and G. I. for volume, number, page, Heat.

Treatment and Cast Irons, respectively - have also been used.

33

A. PUBLICATIONS INDEED! The following is the list or the
publications indexed in the bibliography.

AFA - American Foundrymen's Association
Transactions (Chicago)
American Foundrymen - (Chicago)

ASM - American Society for Metals
(Cleveland, USA) Transactions--

ASTM - American Society of Testing
Materials, Proceedings

Auto Engr.-Automobile mgineer, Monthly Journal
of the Institution of Automobile
Engineers (London)

Foundry - The Foundry, Monthly,(Cleve1and,USA).

IBF . - Institute of British Fbundrymen
Proceedings, (Manchester, England).

Iron Age - Weekly (Philadelphia, USA).

34

B. Bibliography:

1
1
2.
3.

4.

5.

99.
10.
11.

12.

13.

Acicular Irons.
1946- Auto Engr, v36, n474, Apr, p171.

American.Fbundrymen' 3 Association.
1944 ”Alloy Cast Irons Handbook".

American Society for Metals.
1939 “Metals Handbook”

Austin, C. R.
1946 Test Bar Data Versus Casting Properties.
Iron Age, v158, n13, Sept 26, p70.

Bo egehold , A. L.
1937 Influence of Composition and Section Size
on the Strength-Hardness Ratio in 0.1.

ARA. v45. p599.

"Molybdenum in C. I.”
New York: 500 Fifth Avenue.

Crosby, V. A.
1937 Microstructure and Physical Properties of
Alloy C. I.
AFA, v45, p626.

Flinn, R. A. and Reese, D. J.
1941 The Development and Control of Engineering
Gray Irons.
AFA! V49 e P559 e

Flinn, R. A. and others.
1942 Acicular Structure in Ni-Mo C. I.
ASM, v30, p1255.

Gough, H. J. and Pollard, H. V.
1937 Properties of Materials for Cast Crankshafts,
Auto Engr, v11, p96-166.

Kentsmith, J. and Young, E. R.
1932 Molybdenum in Gray C. I.
Foundry, v60, n8, June, p20.

MacKenzie, J. T.
1931 Tests on Cast Iron Specimens of various
Diameters.
ASTM - Proc, v27, pt. I, p160.

Pearce, J. G. - Reporter.
1948 Acicular Cast Irons.
American Foundrymen, v13, n2, Feb, p41

14.

15.

16.

17.

18.

19.

20.

21.

35

1928 Influence of Size of Section on the
Strength of Gray C. I.
1BE,'v22.

Phillips , G.‘ P.
1935 Impact Resistance and Other Physical
Properties of Alloy Gray C. I.
AFA, v43, p125.

Roth, E. I.
1939 Sixty Thousand Pounds per Square Inch
Cupola Iron.
AFA, v47, p873.

Rather, W, H. and Mazurie, V.
1926 The Strength of C. I. in Relation to
It‘s Thickness.

AFA, v34, p746.

Timmons, G. A. and Crosby, V. A.
1941 Alloy Additions to Gray C. I.
Fbundry, Oct, p64. ‘

Timmons, G. A. and others.
1939 Some Factors Involved in Hardening
and Tampering Gray C. I.

AFA, V47. p397.

1938 Produces High Strength Iron.
Fbundry, v66—67, n12—1, p28-30.

Young, E. R. and others.
1938“ Physical Properties of C. I. in Heavy
Sections.
AFA, n46, p891.

ml " 203176

 

 

 

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