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0-169

 

This is to certify that the

thesis entitled .
AN INVESTIGATION'TO DETERMINE TEE
MANNER OF SOLIDIFICATION AND
TRANSFORMATION OF NODULAR
CAST IRON

presented by
Douglas J. Harvey

has been accepted towards fulfillment
of the requirements for

Master of degree in MechanicOl Engineering
Science

{6%

Major professor

Domini 2;; . 1951

 

‘F—f

 

 

 

 

s
I
F_-A____.—.

An Investigation to Determine the Manner
of Solidification and Transformation

of Nodular Cast Iron

BY

Douglas J. Harvey

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
1951

‘fHESIS

 

 

6/97/5/ 11

ACKNOWLEDGEMENTS

The author expresses his deepest gratitude to H. L.
Womochel, under whose able direction this investigation
was conducted, and wishes to thank the many students and
staff members who were instrumental in the progress of this

research.

111

TABLE OF CONTENTS

INTRODUCTION

SURVEY OF WORK ON GRAPHITE FORMATION
PURPOSE AND SCOPE

PROCEDURE

DISCUSSION OF RESULTS

SUMMARY AND CONCLUSIONS

BIBLIOGRAPHY

Page

14
16
31
35
51

-1-

INTRODUCTION

The recent development of nodular iron has been the
most important discovery in the field of cast ferrous metals
since Seth Boyden first produced black heart malleable iron
in 18261. Although nodular iron is still in the development
stage many tons are being produced every day.

Gray cast iron is essentially a ferrous alloy with 2.6-
3.75% carbon and l.25-2.75% silicon. During solidification
most of the carbon leaves solution and appears in the cast
metal as graphite flake inclusions. These inclusions break
up the continuity of gray cast iron and account for its
brittle and nonductile prOperties.

In certain composition ranges castings with thin sections
can be made with all their carbon in the combined form. These
white iron castings can be made into malleable iron by a long
and costly heat treatment. The malleable iron that is pro-

duced in this country has its free carbon in small clumps.
~These clumps of graphite, commonly called temper carbon, do
not break up the continuity of the malleable iron as severely
as the graphite flakes in gray cast iron. Thus we see how a
difference in graphite shape changes the properties from

brittle to ductile and increases the tensile strength two to

 

1. Simpson, Bruce, L., Dev610pment of the Metal Castings
Industry, American Foundrymen‘s Association, Chicago,
Illinois, 1948, p. 196.

three times.

Nodular iron has its graphite in nodules that appear
very similar to the clumps of temper carbon in malleable
iron. The shape of the graphite in nodular iron is respon-
sible for its high strength and good ductility. Nodular iron
can be produced from a base iron in the common ranges for
malleable iron, gray iron, or even pig iron. This new material
is made by additions of magnesium.to the molten base iron.

The magnesium addition is followed by inoculation with ferro-
silicon. Cast iron so treated solidifies as nodular cast iron.
and needs no costly heat treatment.

The first hint that an iron could be cast with its graph-
ite in nodular ferm came in 1950. Von Keil2 published he had
produced cast iron with nodular graphite. The methods he used
were essentially the same as those used today. Additions of
magnesium were made to the molten metal followed by inocula-
tion with silicon. The cast alloy which received this treat-
ment had its graphite in nodular form. For some unknown
reason this early reference to "as cast" nodular graphite
escaped widespread attention.

There is no indication that anything more was done with

3

nodular iron until 1947 when Morrogh and Williams of the

 

2. von Keil, 0., Die Graphitbildung im.Gusseisen., Archiv

fur das Eisenhuttenwesen, Vol. 4, pp. 245-250, (November, 1950)
3. Morrogh, H. and Williams, W. J., "Graphite Formation in
Cast Irons and in Nickel-Carbon and Cobalt-Carbon Alloys,"
Journal of the Iron and Steel Institute, vol. 155, pp. 321-
570, (March, 1947).

British Cast Iron Research Association made public their
work on graphite formation. This important work was carried
on using nickel-carbon alloys which are analogous in their
behavior to alloys of a composition in the cast iron range.
They found that nodular graphite could be produced in these
alloys under certain conditions.

Morrogh and Williams4

in a later work demonstrated they
could consistantly produce nodular cast iron. This new mater-
ial was produced by additions of cerium to an iron that was
hypereutectic.

On May 7, 1948 at the American Foundryman Society
meeting in Philadelphia Thomas H. Wickenden5 of the Inter-
national Nickel Co. announced that his company had produced
nodular iron using additions of magnesium.

The first work on magnesium additions was published in
February, 1949 by C. K. Donoho6 of the American Cast Iron
Pipe Co.

During the period 1949-1951 many articles have been pub-

lished on nodular iron. However very few of these publica-

 

4. Morrogh, H. and Williams, w. J., "The Production of
Nodular Graphite Structures in Cast Iron," Iron and Steel,
vol. 158, pp. 306-314 (1948).
5. Discussion by Thomas H. Wickenden, International Nickel
00., Inc., of the paper entitled "Production of Nodular
Structure in Cast Iron", by H. Morrogh, presented at the May
1948 annual meeting of the American Foundrymen's Society.

. Donoho, C. K., Producing Nodular Graphite with Magnesium",
American Foundryman, vol. 15, pp. 50-35 (February, 1949).

tions have any information on the mechanism.of nodular graph-
ite formation. Why,after certain additions, does the graphite
form.nodules instead of the familiar flakes?. How are these
nodules formed? When during the process of solidification

do the nodules of graphite make their appearance? No complete

answer to any of these important questions has been published.

SURVEY OF WORK ON GRAPHITE FORMATION

Howe7

with a knowledge of the stable and metastable
iron iron-carbide equilibrium diagrams described the solidi-
fication of cast iron. His view was that primary dendrites
of austenite are formed first in hypoeutectic alloys while
in hypereutectic alloys the primary dendrites are iron-carbide.
The freezing of the primary structure is followed by the
solidification of the eutectic liquid. Howe's concept of
solidification was in perfect agreement with the observed
structure of white iron. The difference in white iron and
gray iron were explained by Howe in terms of the stable and
metastable equilibria. He gave no hint as to the manner or
mode of the formation of graphite in gray cast iron.

The mechanism.and manner of graphite formation in gray
iron has been and still is a controversial issue. Hurst8
writing in 1926 gave arguments for two possible answers to
the graphite problems solidification of the primary followed
by the formation of a graphite austenite eutectic; or solidi-
fication of the primary dendrites followed by the formation

of an austenite cementite eutectic and then an ensuing

reaction in which graphite is formed. Hurst maintained at

 

7. Howe, H. E., The Metallography of Steel and Cast Iron,
chraw-Hill Book Co., New York, N.Y., 1926.

8. Hurst, J. E., Metallurgy of Cast Iron, Isaac Pitman &
Sons, London, 1926.

the time the information on the subject was unsatisfactory
and there was a great need for more work on graphite forma-
tion in cast iron.

In 1936 work was carried on at Battelle Memorial Insti-
tute to determine the mechanism of graphite flake formation
in gray cast iron. This work was carried on under the direc-
tion of Alfred Boyles. A full report of this work is con-
tained in Boyles' book, The Structure of Cast Iron.9 In
this important study, samples of cast iron were allowed to
cool slowly than quenched in water while in various stages of
solidification. During slow cooling solidification proceeds
according to the stable equilibria, but when the specimen is
quenched solidification is so speeded up that the metastable
system is more applicable. Therefore the specimen has a
dual structure: the structure that forms during slow cooling
and the structure that is formed during rapid cooling when
the specimen is quenched. By studying the slow cooled struc-
ture in several specimens which were quenched at various
stages during solidification the sequence of events during
solidification could be determined.

From his very excellent work Boyles draws the following

conclusions. "Freezing begins with the formation of skeleton

 

9. Boyles, Alfred, The Structure of Cast Iron, American
Society for Metals, Cleveland, Ohio, 1947.

crystals or dendrites of primary austenite, followed by crys-
tallization of eutectic liquid from independent centers with-
in the interstices of the dendrites. This mode of solidifi-
cation is common to many alloy systems in which a primary
constituent and a eutectic occur. In the case of the iron-
carbon-silicon alloy the graphite flakes come into existence
during the freezing of the eutectic. They do not appear
until the eutectic starts to freeze and once the eutectic is
completely frozen the flake structure is established and does
not change as the alloy cools down to room temperature.”10
Boyles goes further to say, "The flakes grow more or less rad-
ially from.the crystallization centers of the eutectic, form-
ing colonies composed of graphite flakes and austenite such
as those shown in Figure (1.)."11

Very little has been published on nodular graphite forma-
tion theory. There is little or no experimental evidence to
support the material that has been published.

In their work with cerium treated nodular iron Morrogh
and Williamslz plotted cooling curves of a nodular iron with

the following composition:

 

10. Boyles, Alfred, The Structure of Cast Iron; American
Society for Metals, Cleveland, Ohio, 19i77 p. 53.

11. Ibid.

12. Morrogh, H. and Williams, w. J., "The Production of
Nodular Graphite Structuresgin Cast Iron," Journal of the
Iron and Steel Institute, vol. 158, pp. 316-317 (March, 1948).

-8-

 

FIGURE 1. Graphite flake Colony

:9-

total C. Si. Mn. 3. P. Ce.

3.91% 2.71% .51% .006% .024% .049%
The cooling curves they obtained were very similar to the
ones shown in this work. The first arrest came at 2110°F.
and the second came at 2090°F. A sample was quenched from
a temperature of 1990°F. This sample was found to be com-
pletely graphitized and to have the same graphite structure
as the slowly cooled specimen. A sample was also quenched
Just after complete solidification (Just after the termina-
tion of the final arrest). This second sample was substanti-
ally white with some small and some large graphite spherulites.
Morrogh and Williams said, "The large nodules were usually
duplex in structure and were surrounded in every case by a
zone free from.carbide. This suggests that the hypereutectic
spherulites form very early in solidification and, in their
vicinity, graphitization proceeds very rapidly by deposition
on the hypereutectic nuclei. Ingots quenched from.temperatures
between the two arrest points and also from above the first
arrest point had structures (of) fine spherulites in a back-
ground of acicular white-iron eutectic."l:5

It must be kept in mind that Morrogh and Williams worked

with an iron which was hypereutectic. It may be true that

 

13. Morrogh, H. and Williams, W. J., "The Production of
Nodular Graphite Structures in Cast Iron", Jouggal of thg
Iron and Steel Institute, vol. 158, pp. 316-317 (March, 1948)

-10-

they found nodules of graphite forming before and during
solidification in their irons that were hypereutectic. But
it does not follow that hypoeutectic nodular irons are formed
in a similar way.

Dr. Warren Larson1

4 has made x-ray diffraction studies
of graphite taken from various alloys. From his work with
nodular graphite he has drawn the following conclusion.
Nodules appear above and during the eutectic arrest. Dr.
Larson also said that this early formation of nodular graph-
ite during solidification explains the higher shrinkage which
has been observed in nodular iron.

Rehder15 from his work with nodular iron tentatively
concludes: "1. Nodular graphite is the result of growth on
specific nuclei. 2. There are radial and non-radial graphite
types. 3. A nucleus exists in every nodule. 4. The nucleus
is hard, relatively chemically inert. 5. The nucleus is
hexagonal in crystal habit. 6. Size and size distribution
of nodules is influenced by the nodulizing inoculant used.

7. Nodules contain silicon, iron, and titanium, with the
existence of T102 and Fe203 (this was) confirmed by x-ray

diffraction. 8. The nucleus may be a carbide or a nitride."16

 

l4. Scobie, Herbert, F., "Nodular Iron Symposium Shows We
Still Have a Long Way to Go", The American Foundryman, vol.
18, pp. 46-48 (October, 1950).
15. Ibid. ppe 47-48.

160 Ibide ppe 47‘48-

-11-

According to De Sy,l7 "Graphite nodules are born in
supersaturated primary austenite." He states that his cool-
ing curve studies correlate well with this conclusion. From
highly hypereutectic nodular irons the nodules seem to form
in the liquid. To back up this statement De Sy has photo-
micrographs from quenched specimens which show nodular graphite
surrounded by martensite. In conclusion De Sy said, "Nodules
are formed in the fully liquid or the fully solid, but never
at a liquid-solid interface as in flake graphite."18

De Sy19 also reports on two cast irons melted in the same
manner in an induction furnace. The same raw material, the
same magnesium treatment, and the same inoculation with fero-
silicon was used in both heats. The only difference was in
the carbon contents which were 2.02 and 3.56 per cent. Accord-
ing to De Sy in the low carbon heat, "The graphite appears in
interdendritic strings of the mixed spherulitic and vermicular
variety. This graphite issued from the liquid eutectic phase,
or close to the eutectic composition, after the primary solidi-
fication of the dendrites of austenite."20 The high carbon

heat showed, "A structure of nodular cast iron which is as

 

17. Scobie, Herbert F., "Nodular Iron Symposium Shows We Still
Have a Long Way to Go", The American Foundryman, vol. 18, pp.
47. (October, 1950).

18. Ibid. p. 48.

19. De Sy, Albert, "Further Results of Belgian Nodular Cast
Iron Research", The American Foundryman, vol. 17, pp. 75-83
(May, 1950)

20. Ibid. p. 77.

-12-

perfect as can be obtained. The composition of this cast
iron comes close to the eutectic. Such a structure should
be considered as having developed in the reverse(of the low
carbon iron); the graphite is issued from a phase, probably
a complex carbide, of primary precipitation. Such a structure
is likely to be obtained only if we succeed in forcing the
primary precipitation of almost all the carbon in excess of
that soluble in the austenite." De Sy goes on to say, "To
visualize formation of this structure we can start with a
convenient composition and speculate on the concentration
gradient of the silicon which is supposed to exist after the
secondary inoculation with silicon."21 '
Summing up the findings on nodular graphite formation

to date it has been found that:

1. Graphite nodules form.in the liquid.

2. Graphite nodules form.in the solid.

3. Graphite nodules form during solidification.

4. Graphite nodules form around small non-metallic
inclusions.

5. Graphite nodules form around small metallic inclusions.

6. Graphite nodules form around graphite nuclei.

7. Graphite nodules have no nucleus.

 

21. De Sy, Albert, "Further Results of Belgian Nodular Cast
Iron Research", The American Foundryman, vol. 17, pp. 78.

-13-

8. There is a high degree of segregation of the nodules.

9. There is no segregation of the graphite nodules.

It is highly improbable that all of the above statements
are true; in fact some are very contradictory.

Nodular iron is still definitely in the develOpment stage.
As more is learned about some of the underlying principals
of graphitization in this new material the closer it will be

to becoming an important engineering alloy.

-14-

PURPOSE AND SCOPE

1. To develop equipment for studying the graphitization
of nodular iron.

2. To plot cooling curves of solidifying nodular iron.

3. To study the mode of graphite formation in a hypo-
eutectic nodular iron.

In Boyles' work a small sample of cast iron of the
desired chemical composition was melted in a crucible sus-
pended in a vertical tube furnace.22 After the sample had
melted and reached the proper temperature the furnace power
was turned off. When the furnace and sample cooled down to
the required temperature the specimen and crucible were
dropped from the furnace into a tank of water. This system
works very good when gray cast iron is being investigated,
but the making of nodular iron involves the addition of mag-
nesium followed by an inoculation with ferrosilicon. Magnes-
ium is a very active element and burns explosively in air.
The boiling point of magnesium is lower than the super heat

23 Addition of magnesium to

temperature of molten cast iron.
molten iron in a tube furnace would be difficult and possibly

dangerous.

 

22. Boyles, Alfred, The Structure of Cast Iron, American
Society for Metals, CIeveland, Ohio, 1947.

23. Boiling point of magnesium 252OOF. cast iron melts at
2110°F., but is superheated to 2815°F. before magnesium is
added.

-15-

The effect of magnesium wears off in a short time if
the iron is held in the molten state.24 The cooling rate of
the tube furnace and sample would be much too slow. For
these reasons a method different than the one used by Boyles
had to be developed.

It was decided early in this investigation that cooling
curves of nodular iron must be plotted to determine the tem-
peratures at which solidification begins and ends.

Because most of the nodular iron made using magnesium
are hypoeutectic in composition it was decided to investi-

gate an alloy that was hypoeutectic.

 

24. Donoho, C. K., "Producing Nodular Graphite with Magnesium”,
The American Foundryman, vol. 15 p. 32 (February, 1949).

-16..

PROCEDURE

The first equipment used is shown in Figure 2. This
equipment consisted of a baked sand mold with six cavities
connected by a common pouring basin. This mold was placed
on an iron plate over a tank of water. Holes were drilled
in the plate directly under each mold cavity. These holes
allowed the specimens to be ejected into the water at any
desired time. To keep the iron in the pouring basin from
solidifying around the specimens, a drOp out chamber was
provided. As soon as the mold cavities and pouring basin
were full the thin section of sand over the drop chamber
was broken and the excess metal drained into it. This left
six separate specimens ready to be quenched at the proper
time.

Before the mold was poured a cromel vs. alumel thermo-
couple in a quartz protection tube was placed in one of the
mold cavities. This thermocouple was connected to an indi-
cating and recording potentiometer. This instrument produced
a cooling curve of the solidifying specimen. It was assumed
all of the specimens would cool at approximately the same
rate. The object was to quench specimens at temperatures
ranging from.molten down to 12000F. By studying a microstruc-
ture from each of these six specimens, the sequence of events

during graphitization might be determined.

-17..

 

 

    

POURING
CORE

 

 

 

 

 

 

 

 

SAND
MOLD

I'" I 7 I

.. e ' ' l ' :

:. I I I I

:' . ---I I I

...:., .t h”: . .‘.. ‘.e-...:: L-J L.-l

V/// A ' I7//////°/ I T: J j

 

 

 

WATER TANK

 

 

 

Scale: %"=1"

FIGURE 2. Quenching Equipment

-18-

In heat N0. N2 a steel and graphite charge was used. The
iron was hypoeutectic having a carbon content of 3.5% and sili-
con at 1.95%.

Due to very rapid cooling of the specimens in the sand
mold, temperature control was difficult. The samples were
difficult to remove at the proper moment. Samples that were
partly molten stuck on the end of the ejector rod. In spite
of these difficulties some valuable information was obtained
using this equipment.

Figure 3 is a photomicrograph taken of a sample that
was quenched when partially molten. The primary dendrites
of austenite are plainly visible. Centers of crystallization
each solidifying around a nodule of graphite can be seen in
the eutectic liquid. This microstructure shows that the
nodules of graphite are formed very early during solidification.

Figure 4 is a microstructure of the sample quenched at
near 1000°F. The size, shape, and distribution of the graphite
nodules is very similar to those in Figure 3.

At this point some tentative conclusions can be drawn.

1. Freezing begins by solidification of the primary
dendrites of austenite.

2. Graphite nodules appear in the eutectic liquid after
the primary dendrites have formed.

3. The eutectic liquid freezes around the graphite

nodules.

w
-
i-

1.3

 

N2

FIGURE 5. Heat No.

when partially

Treatment : Quenched

”Iteno

Hagnification: 50 X

n..

Y. ,
.1 “(on .y.
t a,

 

FIGURE 4. Host No. N2

Treatment: Quenched from 1000 OF.

Magnification: 50 X-

-21-

4. Very little graphite is formed after solidification
is complete.

Before abandoning the dry sand mold equipment (Figure 2.)
several unsuccessful attempts were made at reproducing the
results obtained from heat N0. N2.

The next attempt was made using a wedged shape casting.
The plan was to quench the wedge when it had partly solidified.
It was thought that the rapidly cooled casting would give a
quenched structure of all phases of solidification. Some of
the difficulties were that the tip of the wedge solidified so
rapidly it was chilled white and it was difficult to tell how
far solidification had progressed along the wedge. This made
it difficult to know when to break the mold and quench the
specimen. The two following difficulties made it next to
impossible to gain information by this method: the light
section of the casting that could be cooled rapidly by the
quench solidified abnormally; the heavy section of the wedge
that solidified normally was too large and transformation
could not be arrested by action of the quench.

At this point it was clear just what the equipment needed
should be able to do. A small sample of iron should be used
so it could be quenched effectively. This small sample should
be cooled slowly enough so that solidification would progress
in a normal manner. The temperature of the sample should be
accurately known at all times so the proper time to quench

could be determined.

The equipment which was used successfully is pictured
in Figure 5. It consists of a glow bar type tube furnace
suspended vertically from a mono rail hoist. The position
of the tube furnace could be changed by rolling the hoist
along the rail. A 10 m1. alundum crucible supported by a
cromel wire hanger was suspended in the tube furnace. The
crucible hanger and a casting are shown in Figure 6. The
cromel wire hanger was long enough to extend approximately
two feet from the upper end of the tube. This allowed the
crucible to be lowered into the induction furnace or quench-
ing tank. A cromel vs. alumel thermocouple protected by a
quartz tube was placed in the crucible. The thermocouple
extention wires and their insulators were fastened to the
crucible hanger wire.

The rapid recorder was assembled in the college shOp and
is very similar to the one used by Boyles in his work on
inoculation25. The measuring part of the recorder consists
of a Leads and Northrup portable potentiometer. A large pulley
was substituted for the hand adjustment knob. The recording
part consists of a chart driven by a synchronous motor drive.
The pen of the recorder is connected to the pulley on the
potentiometer by a wire. The position of the pen is very

accurately controlled by the position of the pulley adjust-

 

28. Boyles, Alfred, "The Structure of Cast Iron", American
Society for Metals, CIeveland, Ohio,*1947} p. 70.

-25-

 

 

FIGURE 5. Equipment used in heats N15-N21.
From.1eft to right: fixture for adding magnesium,
induction furnace power supply, tube furnace in
position over induction furnace, quench.tank, and

control unit.

 

\Is ’IMIIIII'
. ./.-\A\r\.ll

.. 1:-r\ new All
’Ifiun.‘

 

-24-

“ put)”.

‘23.” v s ‘4
U l.P‘Te°"'

 

FIGURE 6. Casting and Crucible

ones-

ment knob on the potentiometer. Lines on the chart can be
easily calibrated to millivolts or directly into degrees F.
Figure 7 is a picture of the indicating and recording potentio-
meter.

After trying this equipment with heat No. N15 it was
decided that heat No. N16 would be used to determine the
temperature at the beginning and end of solidification. By
allowing the sample to solidify completely in the tube furnace,
it could also be determined if a sample cooled slowly in the
crucible would have a normal structure compared to iron from
the same heat cast in a sand mold. A thirty pound heat of
the following composition was melted using a 20 K.W. Ajax
induction furnace:

Carbon Silicon Mn. S.
5.24% 2.76% .44. .023

When the temperature reached 2815°F., as measured with a
Leads and Northrup optical pyrometer, 0.2% magnesium was
added as a 80% nickel 20% magnesium alloy. After the violent
reaction of the burning stopped a 0.6% silicon (as 90% ferro-
silicon) inoculation was made. The tube furnace was then
moved over the induction furnace crucible. The small alundun
crucible was lowered down and a sample was taken up into the
tube furnace. The temperature of the tube furnace was held
constant at 17500F. The cooling curve of this sample is shown

in Figurelil After the sample was taken the tube furnace was

-26-

2'1"" IIIIIII V

 

FIGURE 6. Rapid Temperature Recorder

-27-

moved away to allow pouring the remainder of the heat. From
the cooling curve it was determined that solidification began
at 2150°F. and ended at 2080°F. The time required for solidi-
fication was four minutes. At the end of nine minutes the
sample was lowered from the tube furnace. This was necessary
because the temperature of the sample was approaching the
temperature of the tube furnace. The point of removal can

be seen on the curve.

From heat N0. N2 it had been learned that the nodules
made their appearance very early during solidification. It
was learned from heat No. N16 that solidification of the
sample in the tube furnace required four minutes. Using this
information it was decided to quench samples at the beginning
of solidification, at one minute, at two minutes, at three
minutes, and one near the end of solidification.

The sample from heat N15 had already been quenched at the
beginning of solidification; N17 was quenched at one minute,
N18 after two minutes, N20 after three minutes, and N21 was
quenched near the end of solidification.

Cooling curves were plotted for all heats from N15 to N21
and reproductions of these curves are shown in Figures 9 to 14.

Charges for heats N15 to N21 were made up as near alike
as possible. Malleable pig iron was used. Composition of the
furnace charge was controlled by adding ingot iron and ferro

alloys to the charge. The composition of these alloys are

-28-

shown in Table 1. The amounts used are shown in Table 3.
The pig iron was sawed into sections around one inch thick.
This was necessary to get the pig into a size which could be
charged into the induction furnace. So that the composition
could be closely controlled enough pigs were sawed up for
seven heats. Pig iron for any one heat came from several
different pigs.

The make-up of heats N15 to N21 are shown in Table No. 2.

Table No. 3 is the log of heat N15. In heats N16 to N21
everything was performed exactly the same up to the treatment
of the small sample in the tube furnace. .

The results of the chemical analysis is shown in Table
No. 4. Total carbon was determined by direct combustion in
oxygen followed by absorption of the carbon dioxide in soda-
asbestos (ascarite). Silicon content was determined by
evaporation with perchloric acid. Sulphur was determined by
the combustion method. .The manganese was determined by the
ammonium persulfate oxidation method. Phosphorus could be
very closely estimated at .10% from a knowledge of the phos-

phorus content of the components of the charge.

 

 

 

Table l. Furnace Charge Compositions (Per Cent)
Malleable Pig Ferrosilicon Ingot Iron
C 4.2 C 0.44 Fe 99.9
Si 1.52 Si 27.4
3 0.025 8 0.018
P 0.099 P 0.033
Mn 0.36 Mn 0.84
Table 2. Furnace Charge Heat N15 to N21 (pounds)
Charged
Hanna pig 23.3
Ferro-manganese(80%) .084
Ferrosilicon(27.4%) .263
Ingot iron 5.06
Inoculant
80% nickel 20% magnesium alloy .3
Ferrosilicon (90%) .2
Table 3. Log of Heat No. N15
9:45 A.M. Ingot iron charged on bottom of crucible
FeSi and FeMn charged on top of ingot iron
Pig iron on top
10:00 Power on 15 K.W.
10:15 Power up to 20 K.W.
11:10 Last of pig added
11:30 Melt down complete
11:45 Temp. 2760°F.
11:50 Temp. 2825°F.
11:51 Pour chill
11:52 Add Magnesium alloy
11:53_ Skim.and add FeSi inoc.
11:53 Sample taken into tube furnace
11:56 Sample quenched

-30-

Table 4. Results of Chemical Analysis

Heat No. Carbon % Silicon % Manganese % Sulphur %

 

 

 

 

 

 

 

N2 3.5 1.96 --- ---

N15 3.25 2.76 .44 .023
N16 3.24 2.76 .46 .023
N17 3.25 2.76 .46 .022
N18 3.30 2.75 .46 .023
N19 3.29 2.04 --- .025
N20 3.25 2.75 .47 .023
N21 3.29 2.74 .46 .023

 

Calculated phosphorus Heats N15-N21

0.10%

DISCUSSION OF RESUDTS

Samples from heat N2 were quenched at temperatures
ranging from molten down to 1000°F. For this heat the equip-
ment shown in Figure 2 was used. Figure 3 is a photomicro-
graph of a specimen quenched when partially molten. The
primary dendrites of austenite are plainly visible. These
dendrites have partially transformed into martensite. The
intervening spaces between the dendrites show areas of solidi-
fication each centered by a graphite nodule. There is strong
evidence that the light etching background was molten at the
time the specimen was quenched. Figure 4 shows a photomicro-
graph taken from the sample that was quenched near 1000°F.
This sample shows a considerable amount of massive cementite.
This cementite was caused by casting the iron in a small
section. The size, shape, and distribution of the graphite
is very nearly the same as shown in the partially molten
sample. The graphite in Figure 3 and Figure 4 is definitely
nodular.

Figure 17 is a photomicrograph taken from specimen N15.
The cooling curve for specimen N15 is shown in Figure 9. This
specimen was quenched at the very start of solidification. The
primary dendrites of austenite (transformed to martensite) are
easily seen. The matrix is a fine dispersion of austendte

and cementite presumed molten at the time of quenching.

Figure 16 is a photomicrograph of a fine shot forced from

the partially molten specimen when it was quenched. Graphite
was found to be present in these small shot. Positive iden-
tification of these small inclusions as graphite was made

at high magnification with the use of polarized light. These
shot are believed to be of eutectic composition as no primary
dendrites were found in theme

Figure 18 is a photomicrograph of specimen N17. The
cooling curve for specimen N17 is shown in Figure 11. Speci-
men Nl7 was quenched one minute after solidification began.
The primary dendrites in this specimen are larger than the
ones in N15. This is reasonable as they had more time to
form. Specimen N17 shows no graphite in any form.

Figure 19 is a photomicrograph of specimen N18. The
cooling curve for N18 is shown in Figure 12. This specimen
shows the usual primary dendrites of austenite (now trans-
formed into martensite), Graphite nodules are also visible
in the interstices of the dendrites. The austenite cementite
background was apparently liquid when the specimen was quenched.
The structure of this specimen is very similar to the specimen
from N2 shown in Figure 3. It should be noticed in Figure 19
that the structure solidifying around the nodules is different
in appearance than the structure of the primary dendrites.

Figure 20 is a photomicrograph of specimen N20. The

cooling curve for specimen N20 is shewn in Figure 13. This

-55-

specimen was quenched after three minutes of solidification.
Several etching techniques were tried, but the primary den-
drites could not be made visible. As can be seen by the
photomicrOgraph very little of the specimen was liquid when
the specimen was quenched. The graphite nodule shape and
distribution is very similar to sample N18.

Figure 21 is a photomicrograph of specimen N21. The
cooling curve for specimen N21 is shown in Figure 14. Speci-
men N2l was quenched at 3 minutes 45 seconds after solidifi-
cation began. As can be seen from the photomicrograph very
little of the specimen was molten at the time of quenching.

In the photomicrograph of specimen N21 the primary dendrites
are not visible. There is very little difference in the size,
shape, or distribution of the graphite nodules between speci-
mens N18 and N21.

Figure 22 is a photomicrOgraph of specimenN17K. This
photomicrograph was taken of a sample from.a keel block cast-
ing poured from heat N17. This casting solidified in a core
sand mold in a normal manner. The graphite shape and distri-
bution is very similar to specimen N18, Figure 19. Each
nodule is surrounded by a ring of ferrite. These ferrite rings
were formed after solidification by a secondary precipitation
of graphite on the existing nodule. Figure 23 is a photomicro-
graph from.specimen N18K. Sample N18K was taken from a keel

block cast from heat N18. This structure is very similar to

N17K.

-34-

Figure 10 is the cooling curve for specimen N16. In
this heat it was established that solidification in this parti-
cular set up required four minutes. This heat was also used
to demonstrate that a sample of nodular iron cooling slowly
in the crucible would solidify in a normal manner. The
microstructures of specimen N16 (crucible) and specimen N16K
(keel block) were very similar to the photomicrograph of NlBK
shown in Figure 23.

Early in this work cooling curves were plotted for heavy
sections of nodular iron. Comparing these curves to curves
of the small sample in the tube furnace it could be seen that

the sample in the tube furnace would not cool abnormally slow.

L_ Vlvw ' l‘l

 

 

 

 

-35..

SUMMARY AND CONCLUSION

Figure 3 is a photomicrograph of a specimen that was
quenched when partly molten. Primary dendrites are visible
and nodules of graphite can be seen in the intervening spaces
between the dendrites. In no case can a nodule be seen in or
as part of a dendrite. Figure 18 is of a specimen quenched
just as the primary dendrites are fully formed. It shows no
graphite. Figure 19 is a photomicrograph of a specimen after
solidification was half complete. This structure correlates
very well with the structure shown in Figure 3.

From information obtained in this work the following
conclusions can be drawn.

Solidification in a hypo-eutectic nodular iron begins
with formation of primary dendrites of austenite. The graph-
ite nodules then form and nucleolate solidification of the
eutectic liquid. The eutectic liquid freezes around these
nodules of graphite and primary dendrites. After solidifica-
tion is complete no new nodules of graphite are formed. How-
ever, additional graphite is precipitated on the already exist-
ing nodules. This graphite leaving solution causes the familiar

ferrite rings surrounding each graphite nodule.

—56-

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-4

 

FIGURE 16 o Haat NO 0N15 o

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No. N15. Magnification: 75 x

-43..

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FIGURE 17. Heat No. N15

 

From.specimen quenched at the

beginning of solidification.

Magnification 75X

-44-

 

FIGURE 18. Heat No. N17
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after beginning of solidification.
Magnification 75 X

-45—

 

FIGURE 19. Heat No. N18
From specimen quenched two minutes
after beginning of solidification.
Magnification: '75 X

 

FIGURE 20. Heat No. N20.

From specimen quenched three minutes
after beginning of solidification.
Magnification: '75 I

-47...

 

N21.

Heat NO 0

FIGURE 21.

 

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of solidification.

‘X

Magnification 75

-48-

 

FIGURE 22. Keel Block

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Magnification: '75 X

-49-

 

FIGURE 23. Keel Block

From.heat No. N17, specimen N17K.
Magnification: 75 X

-60..

BIBLIOGRAPHY

Books

Boyles, Alfred, "The Structure of Cast Iron", American Society
for Metals, Cleveland, Ohio, 1947.

Greinor, E. S., Marsh, J. S. and Stoughton, B., The Alloys of
Iron and Silicon, McGraw-Hill Book Company, Inc. New
York and London, 1933.

Howe, H. M., The Metallggraph of Steel and Cast Iron, McGraw-
Hill Book Co., New York, N. T., 1926.

Hurst, J. E., Metallurgy of Cast Iron, Isaac Pitman & Sons,
London, 1926.

Simpson, Bruce L., DevelOpment of the Metal Castings Industry,
American Foundrymen's Association, Chicago, Illinois,
1948.

Magazine Articles

What's in a Name?, American Foundryman, October, 1949 pp. 54-37.
November, 1949 pp. 44-46.

Burgess, C. 0., "Progress Report on Nodular Iron", The Foundry
Vol. 77, pp. 112-115,(July, 1949).

Deas, R. E. and Conradi, L. T., "Determination of Total Carbon
in Pig Iron, High Carbon Iron and Nodular Cast Iron",
The Foundry, Vol. 77, pp. 68-69,(July, 1949).

De Sy, Albert, "Belgian Research Advances Nodular Graphite Theory",
American Foundryman, Vol. 15, p. 55 (January, 1949).

De Sy, Albert, "Magnesium Effects Nucleation", Metal Progress,
V01. 57, pp. 774-775 (June, 1950).

De Sy, Albert, "Further Results of Belgian Nodular Cast Iron
Research", American Foundryman, Vol. 17, pp. 75-83.
(May, 1950) 0

De Sy, Albert, "Letters to the Editor", American Foundryman,
Vol. 15, p. 60 (February, 1949).

-51-

De Sy, Albert, "Producing As Cast-Ferritic Nodular Iron in
Heavy Sections", Metal Progress, VdL 57, p. 79 (January,
1950

Donoho, C. K., "Producing Nodular Graphite with Magnesium”,
American Foundryman, Vol. 15, p. 50, (February, 1949).

Donoho, C. K., "Producing Spheriodal Structures with Magnesium" ,
Iron and Steel, Vol. 22, pp. 77-82 (December, 1949).

Donoho, C. K., "Letters to the Editor", American Foundryman,
Vol. 19, p. 62 (March, 1951).

 

Eagan, T. E. and James, J. D., "A Practical Evaluation of
Ductile Cast Iron", Iron Age, Vol. 164, pp. 77- 82
(December 15, 1949).

Gillett, H. W., "Some Notes on the History of Nodular Irons" ,
Iron Age, P. 30, (June, 1949).

Holdeman, G. E. and Sterns, J. H., "Variables in Producing
Nodular Cast Iron" , American Foundryman, Vol. 16,
pp. 56- 41 (August, 1949).

Kuniansky, Max, "Problems in Producing Ductile Iron", The
Foundry, Vol. 78, pp. 62-64, (January, 1950).

LaRochelle, A. E. and Fournier, J. A., “Magnesium in Iron
Determined By Mercury Cathode Method American Foundry-
man, Vol. 17, pp. 65- 66 (January, 1949).

 

Morral, F. R., "Nodular Iron", The Foundry, Vol. 78, P. 155
(March, 1950).

 

Morrogh, H., "Nodular Graphite Structures Produced in Gray
Cast Irons", American Foundryman, pp. 91- -106, (April,
1948) and A. F. S. Transactions, V01. 56, pp. 72-90
(1948).

 

Morrogh, H., "Polishing Graphite for Microexamination", Journal
Iron and Steel Institute, Vol. 145, PP. 195-205. (I9415.

Morrogh, H., "Some Notes on the History of Nodular Irons”,
Iron Age, p. 100 (May, 1949).

MorrOgh, H. and Grant, J. nW.,"Nodu1ar Cast Irons, Their Produc-
tion and PrOperties" , Foundry Trade Jounnal, Vol. 85,
pp. 199-200 (August 26, 1948).

Morrogh, H. and Grant, J. w., "Nodular Cast Irons, Their Pro-
duction and Properties", Foundry Trade Journal, Vol. 85,
pp. 27-34 (July 8, 1948).

,pMprrogh, H. and Williams, w. J., "Graphite Formation in Cast
Irons and in Nickel Carbon-Cobalt Carbon Alloys", Iron
and Steel Institute, Vol. 158, pp. 521-571 (March, I947).

MorrOgh, H. and Williams, w. J., “Graphite", Iron and Steel,
Vol. 20, pp. 241-57 (May 25, 1947).

Morrogh, H. and Williams, W. J., "The Production of Nodular
Graphite Structures in Cast Iron", Iron and Steel,
Vol. 158 (1948).

Reese, D. J., "Symposium on Nodular Cast Iron", American
Foundryman, Vol. 16. pp. 52-41 (July, 1949 .

Reese, D. J., INCO "Factors Affecting Deve10pment of Ductile
Iron", The Foundry, Vol. 78, p. 58 (January, 1950).

Rehder, J. E., "Magnesium.Additions and Desulphurization of
Cast Irons", American Foundryman, Vol. 16, pp. 55-57.
(September, 1949).

Rehder, J. E., "Letters to the Editor", American Foundryman,
Vol. 19, p. 89 (March, 1951).

Schaeffler, A. L., "Rapid Hand Polishin of Micro Samples”,
Metal Progress, Vol. 46, p. 285, %l944).

Scobie, Herbert F., "Nodular Iron Symposium Shows We Still
Have a Long Way to Go", “American Foundryman, Vol. 18,
pp. 46-48, (October, 19507.

Smelley, Oliver, ”Letter", The Iron Agg, Vol. 171, p. 18
(December 50, 1948).

Smith, E. K., "Experiments in Nodular Iron”, American Foundry-
man, Vol. 16, pp. 45-47 (December, 1949).

State, E. M., and Stott, B. L., "Producing Ductile Iron",
The Foundry, Vol. 78, p. 80 (July, 1950).

Yarne, J. L. and Sobers, w. B. "Magnesium.Determinations in
Nodular Cast Iron-Sampling and Analysis Methods",
American Foundryman, Vol. 17, pp. 55-55 (June, 1950).

-53-

Pamphlets

 

Bolton, J. W. "Graphitization and Inclusions in Gray Iron”
Transactions of the American Foundryman's Association,
Vol. 24, p. 467 (1957).

Boyles, A.,"The Freezing of Cast Iron", American Institute of
Mechanical Engineers Transactions, Vol. 125, (1957).

Boyles, Alfred, "The Formation of Graphite in Gray Irog"
American Foundryman's Association, Preprint No. 58-15.

Boyles, A., "The Pearlite Interval in Gray Cast Iron",
Transactions of the American Foundryman‘s Association,
Vol. 48, p. 551 (March, 1941).

Flinn, R. A. and Kraft, R. w., "Improved Test Bars for Standard
and Ductile Grades of Cast Iron", American FoundrymenTs
Association Preprint, No. 50-1.

Morrogh, H. and Williams, W. J., Paper No. 875., 44th Annual
Meeting, 1947, Institute of British Foundrymen.

Rehder, J. E. "An Introduction to the Annealing of Nodular
Iron", American Foundrymen's Society Preprint No. 50-17.

"Symposium.on Nodular Graphite Cast Iron", Transaction, American
Foundrymen's Society, Vol. 57, p. 576 (1949).

Von Keil, 0., Die Graphitbildung im.Gusseisen, Arch IV Fur
das Eisenhuttenwesen, Vol. 4, (November; 19507.

. [.201"
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