Table Of ContentThe Pennsylvania State College
The Graduate School
Department of Mineral Technology
Division of Metallurgy
Density and Hydrogen Occlusion of Some Ferrous Metals
A Thesis
by
James Howard Keeler
Submitted in partial fulfillm ent
of the requirements
for the degree of
Doctor of Philosophy
June 1951
Approved*
2.. 1 /
Division of Metallurgy
CMtef, Division of Metallurgy
TABLE OF CONTENTS
Page
INTRODUCTION ' 1
EXPERIMENT 16
Materials 16
Density 18
Hydrogen Occlusion 25
RESULTS AND DISCUSSION 36
Density 36
Occlusive Capacity 59
SUMMARY AND CONCLUSIONS 68
REFERENCES 70
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ABSTRACT
Whether a metal exhibits a decrease in density with cold re
duction was found to depend upon impurities in the metal. A high-
purity iron did not exhibit any decrease in density after cold re
duction. In cold-reduced ingot-iron, only a 43 per cent recovery
of density was found during annealing up to 1200 C, whereas SAE
1020 exhibited almost complete density recovery during recrystalli
zation at 600 C. High-purity iron and ingot iron in the hot-rolled,
the cold-reduced, or the annealed condition exhibited no appreciable
differences in hydrogen occlusion between 250 and 550 C. Hot-rolled
and annealed SAE 1020 displayed an occlusive capacity similar to that
of the high-purity iron and ingot iron, whereas the cold-reduced SAE
1020 exhibited a remarkably large hydrogen ooolusion, especially at
250 C and 300 C. A theory based upon two varieties of voids in the
metal formed during cold-reduction is offered to relate the various
observations.
ACKNOWLEDGEMENT
It is a pleasure to acknowledge the aid and encouragement of
my many friends in this research.
To Dr. H. M. Davis, for his unlimited patience, and for his
guidance as a friend and counselor, the author •wishes to express his
deepest gratitude.
The helpful suggestions, critical advice, and sympathetic
assistance of Dr. R. W. Lindsay and Dr. J. W. Fredrickson cannot be
overlooked.
The author is indebted to the United States Steel Company for
the commercial sheet materials of this investigation and for all
analyses. Stimulating discussions with research personnel of the
Company and with Dr. L. S. Darken of the Research Laboratoiy of the
United States Steel Corporation lent impetus to much of this inves
tigation.
Special thanks are due to Mr. Maynard L. Hill for his many
acts of assistance, both technical and personal, and to Professor
W. J. Reagan and Professor L. F. Haller who helped obtain materials
used in the thesis research.
There are, of course, the unrecoided courtesies and suggestions
of other members of the Division of Metallurgy, and of fellow students
who have aided in the accomplishment of this work.
4,
rapid until 65 per cent reduction was reached, after which the rate
of decrease diminished, and the total density decrease approached
a lim it of about 0*27 per cent* The m aterial, containing more of
carbon and other elements, showed a rapid in itial decrease in density
with cold working* Iftien 50 per cent cold reduction was reached, the
lim iting change of density, about 0*26 per cent, had been obtained*
It was thus observed that, for small reductions, D]_ showed the greater
density loss, but both Ai and D]_ had approximately the same maximum
ohange, about 0*26-0*27 per cent*
The effects of cold reduction and subsequent annealing upon
the recovery of density were studied for two cold-drawn specimens,
(60.7 per cent reduction) and (62*5 per cent reduction)*
"They (the specimens) were heated in vacuo to successive temperatures,
held for 1/2 h r., and subsequently cooled*" (It is assumed by this
statement that the same specimen was used in annealing at various
temperatures, each succeeding temperature being higher than the pre
vious temperature* It was also noted that Di had been normalized
prior to cold-drawing whereas A^ had been annealed prior to cold re
duction* )
Specimen Di, reduced 60*7 per cent, did not show any recovery
of density below 400 C* However, between 400 C and 700 C, the den
sity returned almost to that of the undrawn specimen* The 62*5 per
cent cold-reduoed A^ also showed no recovery when annealed below
400 C. Unlike Di, there was only a slow recovery of density by Ai
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5.
as the temperature -was raised above 500 C. Even after 1/2 hour at
1000 C, the absolute recovery was only 0,09 per cent, which was about
40 per cent of the original change.
Although the lack of a complete recovery of density during
annealing in vacuo at 1000 C, well above the recrystallization temp
erature of the Ax m aterial, was perhaps surprising, similar results
have been reported by Ishigaki^^O for cold-hammered Armco iron.
Ishigaki showed graphically that the Armco iron decreased 0.09 per
cent in density, and recovered only about 70 per cent of the density
change with annealing at 1000 C (time of annealing and whether in
atmosphere or in vacuo were not given).
Andrew made several experiments with another ingot iron
(A3: 0.07 C, 0.01 Si, 0.04 Mn, 0.009 P, and 0.054 S) in order to
determine if the decrease in density with cold work was, in some way,
dependent upon the inclusions present in the iron. As stated by
Andrew, "If cracks or flaws, submicroscopic or visible, were produoed
in the inclusions on cold drawing, they might contribute to a lower
ing of the bulk density of the specimen. On this assumption the den
sity of a cold-worked specimen cannot be fully recovered until the
cracks or flaws in the inclusions are completely healed or eliminated."
On the basis of a lower original (annealed) density, and, apparently,
a metallographic examination, the second ingot iron was considered
to have more inclusions than did Ax* It was found that this iron had
a greater density decrease with cdd reduction and showed a recovery
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6
of density with subsequent annealing comparable to that obtained with
the first ingot iron (Ai), On the basis of these tests Andrew thought
that, with ingot-iron specimens, the decrease in density accompanying
cold reduction varies with the composition of the iron and probably
with the inclusion content*
These deductions by Andrew, although in agreement with the
concept that inclusions may vary the density loss on cold working,
are perhaps controversial* The original (annealed) density may not
have been the maximum density for the materials involved* Although
the prior history of these materials was not given, it should be
pointed out that the density of a commercially hot-rolled m aterial,
particularly a low-carbon, low-alloy iron, is variable and may not
be the maximum for the particular composition. Thus Andrew's observed
mflTri mum change in density may have been less than the possible change
of density by cold work. A second qualifying circumstance which
might modify Andrew's deduction was the difference between the in
clusion contents of the test materials* Of the ingot-iron specimens
A^ and A3, the latter was reported as having the greater inclusion
content* The chemical analyses might well support this observation*
However, in such low-carbon irons, the oxygen content is usually con
siderable, and the lack of oxygen analyses leaves some doubt about
the inclusion contents* Metallographic estimations of inclusion con
tent are aooeptable for wide variations in im purities, but are subject
to recognized lim itations of particle size and distribution, both on
i
a macroscopic scale and on a microscopic scale. It would also seem
questionable to attribute great significance to the difference in in
clusion content between the two ingot irons whereas the same differ
ence in density loss is obtained between A3 and the medium-carbon
steel Di* Greater details of composition for the Di steel would
have been welcome. It is not the contention of the writer that the
deductions made by Andrew are incorrect. Rather, i t is to be recog
nized that seme reservations are in order.
In agreement with the work of Andrew on the influence of in
clusion content in ingot iron is the study of density of extremely
high-purity copper by Smart, Smith, and Phillips^3*0, Here it was
found that the high-purity copper disclosed only a very slight de
crease in density with cold drawing. However, the same high-purity
copper with 0,037 per cent oxygen added showed considerable density
decrease with cold drawing. This change was greater than the effect
due to formation of oxide, and the authors commented, possibly
by giving rise to the formation of minute internal voids," Zener^3)#
on the other hand, has shown quantitative calculations indicating that
grain distortion by itse lf can produce expansion of the order of mag
nitude of the experimental observations, Maier^*^ showed that both
the density of iron and that of copper passed through a minimum with
increasing cold reduction. After this minimum (88 per cent reduction
for iron) has been reached, the density begins to increase with fur
ther cold reduction. No other investigator has mentioned this be-
8.
havior.
Finally, the different decreases in density reported by
Andrew^*), Ishigaki^^^, and Maier^^^ should be noted* The maxi
mum loss in density, 1 per cent, was obtained in torsion by Uaier*
/ QJ \
(J* W* Landon'' showed a 2 per cent decrease in density of wrought
iron with torsion*) Andrew's specimens were drawn and show a density
decrease of as much as 0*27 per cent, while Ishigaki measured the
density of cold-hammered iron and obtained a density decrease of 0*09
per cent* It thus appears that the mode of cold reduction, which
determines the characteristic type of plastic flow occurring, can
govern the magnitude of the density loss*
A large amount of infoxmation is available on the subject of
hydrogen in metals* D. P* SndLth^'^ lists a bibliography of 1467
references which takes into account the literature to about the end
of 1946* Zapffe and Sim s^^ published a bibliography on "Hydrogen
in Steel" of over 500 references*
It has been known, as a result of the classical work of
Sieverts(^), that atomic and not molecular gases are dissolved in
metals* Like other metals that take up hydrogen endothermically
(e.g., Ni, Co, Cu, Pt), iron dissolves but a small amount of hydrogen,
and the alloys of iron and hydrogen display but one phase*
i
9.
One of the first considerations in a discussion of hydrogen
in iron and steel is that of the quantity of hydrogen generally
found* Usually it is less than 0*001 per cent by weight and is
usually considered almost insignificant* However, it should be re
membered that this figure is on a weight basis, whereas on an atomic
basis there is fifty-six times as much, or in comparison with the
0*001 weight per cent given above, 0*056 atomic per cent* This fig
ure again assumes greater significance when it is realized that this
amount in the steel, 0.001 per cent by weight, depending upon its
distribution, may produce pressures at ordinary temperature to exceed
the strength of steel* (Examples of this are the flakes and shatter-
cracks in steel ingots*)
In ,tendothermic,, iron there is considerable change in the re
ported solubility of hydrogen with temperature, the change being
exaggerated by phase changes and by the melting of iron* For example,
if relative volumes (the volume that the hydrogen extracted from a
given piece of metal would occupy at standard conditions compared to
the volume of the metal from which it was extracted) are used for com
parative purposes, the amount of hydrogen in iron at various temper
atures can easily be shown^^^. F irst, in liquid iron there is gen
erally found about 2*2 relative volumes of hydrogen* With solidi
fication there is a loss of 1*2 relative volumes leaving 1*0 rela
tive volume of hydrogen s till in the iron* This amount decreases to
0*4 just above the austenite-to-ferrite transformation temperature
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