ANNUAL REVIEW ISSUE
Plant o f the Inlund Steel Co. at Indiana Harbor, Ind.
N
either by the success of the manufacturers in producing stainless steels with
I. N. Zavarine
an extremely low carbon content or by
f " ~ ~ ~ ~ c ~ e l ~ h ~ ~ ~ ~stabilizing
~ s s ~thee material
~ ~ ~ byr the
~ ~addition
s i $ ~ ~ o ~
of titanium
in ~small
setts institute of ~
~ ~~~b~~ and
~
t
,or columbium
~
~
Associate Member, A.I.M.E.
amounts. The welding of stainless steel
is now accepted practice and thoroughly
successful in the hands of skilled operators and with suitable metallurgical
control. The second difficulty, that of
pit corrosion. especially when the steel
is in contact with salt water, has not
yet been wholly overcome and is the
object of intensive research both here
and abroad. Addition of molybdenum
in amounts of approximately 3 per cent
has made a marked improvement and
these molybdenum stainless steels are
used successfully under conditions formerly believed impossible. But molybStainless Steels
denum adds to the cost of the steel and
TAINLESS steels, especially of the
for this and other reasons it seems
18 per cent chromium 8 per cent
probable that these special stainless
nickel type. are of increasine i m-~ o r steels will not be used generally but
Robert S. Williams
tance and have been the object of rerather for certain applications in which
search along many lines and in many
their increased resistance to pitting is
laboratories. Two of the major troubles 900 deg. and 1400 deg. F., as for ex- of major importance. Although the
with stainless steels of this general type ample during welding, and second, steel with 18 per cent chromium and 8
have been, first, their susceptibility to failures due to corrosion of the pinhole per cent nickel still remains the most
intergranular attack as a result of heat- or pitting type. The first difficulty has usual example of its type, wide variaing in a temperature range between been overcome to a marked degree tions in the percentages of the two ele-
O new ferrous alloys have been
produced in the last five or six
years that are as outstanding
contributions to civilization as were the
high-speed steels of the early part of
the century or the stainless steels announced at the close of the World War.
There have been, however, many developments of major importance having
to do either with modifications of existing alloys or with new methods of
treatment of older iron or steel alloys.
Only a limited number of these new
developments can be discussed and their
selection does not necessarily imply
that these are the most important but
merely that they are of general interest
rather than perhaps of greater importance in highly specialized fields.
S
JANUARY, 1939
-
By Robert S. Williams and
ANNUAL REVIEW ISSUE
ments are being studied and for certain purposes some have been found
better than the original composition.
The field of corrosion-resistant materials is and will continue to be one of
great importance to industry and new
alloy modifications of the commoner
types are certain to be developed.
Another recent development in the
manufacture of stainless steels about
which little information is available is
the direct production of the iron,
chromium, and nickel alloys from suitable mixtures of their oxides. This
would seem to have real possibilities.
Flame Hardening and Flame
Softening
LAME hardening has been carried
F
out more or less casually and at
times unintentionally in the past but
has recently been developed to such a
degree as the result of research that
it has now reached a position of major
importance in the treatment of steel and
its use will be materially extended.
Much work still needs to be done in the
design and operation of the equipment
and especially with regard to the structure and properties of steel hardened
in this way. Flame hardening consists
simply in applying the heat from an
oxyacetylene flame to any steel that is
capable of hardening by the conventional methods and following this heating by an immediate quench. The essential technique of the process is that a
predetermined area of the part to be
hardened is heated above the critical
range to a depth of 1/16 to 1/4 in. leaving the rest of the metal unaffected.
Quenching is usually done by means of
a water jet or water spray often attached t o the heating torch but in any
case following the last flame at a
distance which may just avoid the flame
or may a t times be as much a s an inch
behind it. The advantages of the
method are several. In the conventional
hardening method the part to be hardened is heated throughout so that deepseated transformations occur in the
whole mass of metal, often accompanied
by serious volume changes and consequent distortion. Since in flame hardening only a small amount of metal is
heated above the critical hardening temperature, the main mass of steel undergoes no volume change with the result
that distortion is materially reduced.
I n the older method of surface hardening, as for example by carbon or nitrogen, there is often much difficulty in
protecting certain parts of the steel
which it may be necessary to leave in
the unhardened condition. I n flame
hardening it is often possible to heat
and quench within a limited area and
so produce highly localized hardening.
-
Courtesy L a d e A t f Produals Co.
A n 18-tooth bevel gear being flame hardened
to a depth o f '/n to 5/32 m.
Any plain carbon steel containing more
than 0.40 per cent carbon may be hardened by this method though great care
must be taken if the carbon content
exceeds 0.70 per cent to avoid surface
checks or cracks. In addition certain
of the alloy steels that are not easily
casehardened may be successfully
treated. At present the method is being used to a considerable extent with
the low-alloy, high-tensile steels which
give an excellent combination of good
ductility and high surface hardness.
The method of flame hardening has
been used to harden parts as widely different in size as pipe-wrench jaws and
a 90-ton spindle. Obviously it has
many advantages but should not be considered as a universal method of local
hardening. The conventional methods
of complete hardening by quenching,
casehardening, and nitriding will of
necessity be used in many applications
but flame hardening will certainly be
used to an increasing extent particularly
for local or differential hardening in
those parts in which a hard surface
with a ductile core is desired.
Flame softening is as its name suggests the reverse of flame hardening.
Although the use of flame heating for
the relief of strain has been common
for years, only recently has research
been carried on to systematize the operation and to extend its field of usefulness. The method is being used to
an increasing extent to remove the incidental and usually undesired surface
hardness often resulting from such operations as electric welding, flame cutting, or shearing. When medium- and
high-carbon steels are cut by a torch,
the steel adjoining the cut is locally
heated to a temperature considerably
above its critical point and is drastically quenched by the cold steel of
which it forms the surface. This lead3
to extreme hardness and often brittleness a t the flame-cut edges, making subsequent machining difficult o r a t . times
actually causing the development of
cracks. Flame softening may be acM I N I N G AND METALLURGY
ANNUAL REVIEW ISSUE
tizing by silicon, coupled with the excellent mechanical properties of this
steel and especially with its capacity
for hardening. As the material is
originally rolled it is essentially pearlitic though it may or may not show a
small amount of graphite in a fine state
of subdivision. If now the rolled bar
is annealed a t 1750 deg. F. and cooled
in the furnace the combined carbon will
drop from about 1.20 per cent to 0.38
per cent and the graphite will increase
from 0.28 per cent to 1.10 per cent. The
structure is now clearly laminated
pearlite with the characteristic patches
of temper carbon usually associated
with malleable iron. If now the annealed bar is reheated to 1550 deg. F.
G r a p h i t i c Steel
RAY cast iron has long been known and air-cooled (normalized), the strucas a metal highly resistant to ture at low magnification seems to be
wear, with excellent antifrictional prop- unchanged, although the percentage of
erties, ease of machining, and high total carbon has increased to 0.90 per
damping capacity. Steel on the other cent and the amount of graphite has
hand has higher tensile properties, can been reduced to about 0.60 per cent.
be worked more easily, and is readily Black, irregular patches looking exactly
susceptible to heat-treatment. Recent' like graphitic carbon are still evident
research, still actively in progress, has in about the same number and of the
led to the development of metals com- same size as the true graphite patches
bining many of the good characteristics in the fully annealed bar before norof both. Two of these metals known by malizing. Since, however, the amount
the trade names Graph-sil and Graph- of graphite has materially decreased,
mo well illustrate the application of di. this can only mean that the dark areas
rected research to an important indus- which originally contained graphite are
trial problem. It is well known that either partly empty or are complete
silicon is all-important in controlling voids. If now this normalized material,
the precipitation of graphite in gray containing these voids which have been
iron. Charpy and Grenet had shown produced as the result of the partial
that a s the percentage of silicon de- redissolving of the graphite from those
creases below about 1.2 per cent the areas in which it originally existed, is
temperature a t which graphite sepa- water-quenched the expected martensitic
rates rapidly increases, varying from structure results, with a corresponding
1200 deg. F. at a composition of 1.2 increase in hardness. The hardened
per cent silicon and higher up to more metal mav of course be t e m ~ e r e das
than 2000 deg. F. with the silicon re- needed to meet the particular purpose
duced to approximately 0.25 per cent. for which it is to be used.
The metal resulting from a suitable
With these facts in mind the investigators carried out an intensive study of sequence of operations is characterized
the effects of variations in silicon con- by free machining properties, high
tent and heating temperature on high- hardenability, long life, and definite
carbon steels of the water-hardening lubrication characteristics due either to
a controlled amount of free graphite
tool or die-steel type.
The behavior of a steel with about 1.5 or to the capacity of the surface to reper cent total carbon and 1 per cent sili- tain oil by absorption in the voids. Sewcon, with manganese, sulphur, and phos- ice records show that in a certain apphorus in the usual ranges, may be plication of this new material a sizing
taken as an example. By variations in die made of the conventional hardened
the heating temperature and cooling steel was roughened to such an extent
rate the combined carbon may be varied as to be most unsatisfactory after the
from 0.26 per cent to 0.86 per cent, the sizing of 10,000 pieces whereas a simiultimate tensile strength from 81,000 lb. lar die made of properly heat-treated
per sq. in. to 202,000 lb. per sq. in., the Graph-sil was still in good condition
elongation from 8.5 per cent to 23.5 after its use in the sizing of 310,000
per cent in 2 in., and the hardness identical Darts.
from 163 to 388 Brinell. This wide
I n some instances an oil-hardening
variation in obtainable properties is an steel which will retain the free machinindication of the number of possible ap- ing and lubricating properties of the
plica,tions of the material but the out- water-hardening type is needed. For
standing advantages are associated with this purpose another alloy known as
the structure attributable to the graphi- Graph-mo has been developed. The
complished by attaching banks of
flames to the cutting tool. These heating flames may either move ahead of
the cutting flame, causing a preheating
of the metal to be cut with a corresponding reduction of the cooling rate,
or the heating flames may follow the
cutting torch and so soften the quenched
metal. Other methods of flame softening are being investigated and it seems
quite certain that a much more carefully controlled application of an old
principle will become standard practice in many operations in which hardening is unintentionally but unavoidably produced.
G
JANUARY, 1939
carbon content is substantially as before but the silicon is reduced to about
0.75 per cent and 0.25 per cent of
molybdenum is added. As with the
plain carbon alloy, marked increase in
the operating life of certain tools has
been clearly shown by service tests. Although the two ferrous alloys described
have shown many unique properties,
there is evidently a great opportunity
for the study of other compositions and
the structural and mechanical effects of
other heat-treating cycles. Research in
this field is in active progress in several
laboratories and new properties and
new uses are certain to develop.
Castings S u b s t i t u t e d for Forgings
RAPID
strides have been made in
recent years in the substitution of
castings for machine elements formerly
forged. The outstanding examples of
this development are the use of cast
crankshafts and camshafts. There are
several valid reasons for this change,
partly economic and partly of a definite
engineering nature. Automobile crankshafts and to a lesser degree camshafts
present certain difficult problems in
forging so that the degree of precision
obtainable in the unmachined forging is
much less than that in a casting to be
used for the same purpose. This makes
possible a considerable saving in machining costs, since the castings are
much nearer their final dimensions than
are the forgings. A definite saving in
metal also results as much smaller allowances for machining are possible in
the casting. The saving is still further
increased by the practice of casting
journals and webs hollow, in this way
reducing weight with virtually no loss
in the essential mechanical characteristics. An added economy results from
the fact that although the forged shafts
are commonly annealed before machining and are subsequently casehardened
and heat-treated to ensure the necessary
wear resistance, it is quite possible to
adjust the foundry practice so as to
produce castings immediately machinable and at the same time to increase
hardness, if desired, by the use of chills
in the sand mold. Finally, there are
the additional advantages of the cheaper
production of a casting compared to a
forging due to the lower melting cost
and the greater ease of casting in inexpensive molds. The modern development of crankshafts has been determined by the necessity of providing
for great resistance to dynamic torsional
stresses. To meet this need the weight
of the forged shaft was being continually increased and a t the same time
the diameter of the journal was also
increasing in order to decrease wear.
This combination of tendencies reduced
ANNUAL REVIEW ISSUE
the working stresses to such a degree
that cast metal could be considered.
Use of cast metal crankshafts is not
new but was common practice about the
middle of the last century. The undesirable characteristics of cast iron available at that time led to the substitution
of the stronger and more reliable steel
forgings as the power output of engines
increased. A return to the ideas almost a century old has come about because of the great improvement in the
manufacture of cast irons and ilotably
because of the introduction of alloy cast
irons with excellent mechanical properties. Although this question of tht:
use of .cast metals has been and is being studied l~otll in this country and
in Europe. the major credit is due to
careful and systematic research carried
out by the Ford Motor Co. Starting out
with attempts to make a cast crankshaft
of the same composition as that used for
the forged shaft it soon became evident
that for many reasons this was not practical. The story of the study of changes
in composition, casting technique, and
heat-treatment is too long to be told
here but carefully controlled experilnents finally culminated in the production of a cast metal so satisfactory that
its use is now standard practice and it
lias been used in several million cars.
practice it is possible to produce highly years just ahead. Atmospheres may be
satisfactory shafts consistently and with controlled for any one of several reano heat-treatment after casting. This sons or for more than one reason.
accomplishment in the Ford research Among these purposes are: (1) the
laboratory was again the result of sys- reduction of scaling or its complete
tematic and carefully controlled experi- elimination, (2) the prevention of dements carried out over a considerable carburization, (3) the production of a
period. The material desired was one particular surface, bright or colored,
that could be cast with minimum
foundry losses and that approached the TABLE11. COMPOSITION
OF CAMSHAFT
structure of mottled iron. A white iron
ALLOY
composition was first selected with the
Per Cent
thought that the high carbon would in- Carbon . . . . . . . . . . . . . . . . . . . . 3.30 to 3.60
stire fluidity and also the necessary car- Manganese . . . . . . . . . . . . . . . . 0.15 to 0.35
bides. 'The silicon was kept low to pre- Silicon . . . . . . . . . . . . . . . . . . 0.45 to 0.55
vent the graphitizing of these carbides. Chromium . . . . . . . . . . . . . . . 0.00 to 0.25
Phosphorus . . .
.
.
Less than 0.05
This composition sometimes gave com- Copper . . . . . . . . . . . . . . . . . 2.50 to 3.00
pletely ~atisfactory material with a
chilled tip and a soft core but great
(4) to introduce carbon as a prelimidifficulty was found in controlling the nary step in casehardening, (5) to inrasting conditions to assure a uniform troduce nitrogen in suitable form for
product. Slight and difficultly con- nitrogen hardening (nitriding) . Some
trollable changes would at times pro- of these purposes are contradictory,
duce metal wholly white and too hard others require a special atmosphere for
for the core, or wholly gray and too a definite purpose and usually the efsoft for the tip. Small percentages of 'fect of the atmosphere depends in great
chromium were added to prevent undue measure on the chemical and physical
softening of the tip but this increased characteristics of the metal being
the tendency toward too great harden- treated. This means that there is no
ing of the core. It was finally dis- universal solution to the problem but
covered that copper was an excellent that both furnaces and atmospheres
stabilizing element in that it acted as must be varied to meet the particular
a graphitizer to prevent excessive car- needs. The problem becomes increas.
hide formation in the core but a t the ingly complex as it requires a co-operasame time permitted adequate chilling tive understanding between the metalTABLE1. wEIGHTS
OF cAST
AND
in the thin section of the cam tip.
lurgist, the chemist, and the combustion
FORCED
CRANKSHAFTS
Reduction
The camshaft alloy is much more engineer.
Rough
Finished
by
nearly a true cast iron than is the
Many of the problems may be quite
Weight, Weight* Machining, crankshaft metal, though the usual simply stated but by no means easily
Lb.
Lb.
Lb.
characteristics of conventional iron are
solved. Scaling, as an example, is the
69
60
Cast
greatly
modified
hy
the
copper
additioh.
result of the oxidation of the metal bf
Forged
83
66
l7
The nominal composition of the alloy one or more of the gases with which it
comes in contact. The number of
The composition is approximately as iron used is shown in Tab1e I1.
follows: carbon 1.5 per cent, man.
Another less obvious advantage of oxidizing gases normally occurring is
ganese 0.7 per cent, silicon 1.5 to 2.0 these cast metals either in the crank- rather limited, usually including oxygen
shaft or in the camshaft form over steel itself, air, water vapor, and carbon
per cent, copper 0.5 per cent, chromium
0.1 per cent, and phosphorus not above forgings is in their much higher damp- dioxide. It would seem a simple mat0.1 per cent. By suitable heat-treat- ing capacity. m e n steel with its low ter then to eliminate scaling by the remerit the structure shows granular
damping capacity is made to vibrate as moval from the atmosphere of air, wacementite
with temper carbon and a it does in service it is possible that the ter, or carbon dioxide. Actually it is
thin
network
the grain oscillation period may reach that of by no means as easy as it sounds and
boundaries. Such a structure develops
in which case the much research is now in progress to
good rnachinability and high strength. Stresses may become exceedingly high find methods of removing the gaees both
effectively and economically. I t is relaapproximate
of the at times with a corresponding danger of
rough and finished weights of the cast failure by fatigue. The high damping tively easy to remove them on a laboraand the forged shaft (Table I ) in&- capacity of the cast metal materially tory scale but on a commercial scale
cates the advantages of the casting in reduces the possibility of these high the laboratory methods often prove not
periodic stresses with a corresponding only complicated but prohibitively exthis respect.
reduction
of the danger of fatigue fail- pensive. Water may be removed by
camshafts are often made of steel
cooling the gas either by cold water or
forgings though there is an increasing ure from this cause.
by means of a refrigerant causing its
tendency to substitute one of the newer
condensation. It may also be absorbed
alloy cast irons for the forging. Both Controlled Furnace A t m o s p h e r e s
SE of controlled atmospheres in by silica gel or activated alumina. All
with the forged steel and the convenfurnaces is by no means new but of these methods are in commercial use
tional alloy iron subsequent heat-treatthe
number
of papers dealing with the and other methods will be developed.
ment is necessary to obtain satisfactory
properties. The Ford camshaft is ap- subject that have appeared in the last Several pieces of equipment have been
parently unique in that by the use of a few years indicates the great activity in developed quite recently that will abspecial composition of iron and care- this field and gives promise of exceed- sorb carbon dioxide at a reasonable
fully controlled melting and foundry inplg important developments in the roqt. Removal of oxygen from the air
u
M I N I N G A N D METALLURGY
ANNUAL REVIEW ISSUE
niay be a combustion problem or it may
implv the use of an oxygen-free gas.
Although the removal or replacement
of these oxidizing gases may be accomplished, the manufacturer often
finds himself on the other horn of the
dilemma because the nonoxidizing gases
may be found definitely decarburizing
in character. Here again many decarburizing gases are well known. In
the list will be found moist hydrogen,
and nitrogen which in the presence of
moisture is actively decarburizing. It
is commonly necessary then to control
in the furnace atmosphere not merely
the oxidizing gases but the decarburizing gases a t the same time. The implication of this statement is that a
composite gas atmosphere must be produced and maintained in which the undesired action of one gas will be balanced bp the behavior of another. The
question is still further complicated by
the fact that many gases inactive and
harmless a t ordinary temperatures become strongIy active a t higher temperatures and their activity is still further
increased a t times by the catalytic action af the metal being treated or by the
metal parts of the furnace. The balanee between these various reactions is
often so delicate that it is by no means
unusual to have a bright, soft surface
and a scaled, hard surface a t different
places on the same piece of steel.
Much has been accomplished by partial combustion of the furnace gases
and a corresponding elimination of air,
but the tendency seems to be in the
direction of auxiliary equipment in
which the desired gas mixture may be
manufactured and purified before it
reaches the furnace. In some of the
larger installations requiring controlled
atmospheres the auxiliary equipment is
often a complicated and costly chemical plant having nothing to do with
actual treatment of the steel.
IN
many instances slight decarburization is of no consequence and bright
annetding becomes a comparatively
simple process. The suggestion has
been made that if a decarburizad surface is not permissible the descaling
operation could be followed by a short
oxidizing cycle producing a thin oxide
scale easily removable by subsequent
treatment. This composite treatment
has been used successfully in a number
of instances. With specific reference
to the question of "bright annealing" it
is certain that great care must be exercised to avoid free oxygen. The atmosphere may be coke-oven gas, natural
gas, or dissociated ammonia, special
precautions being taken to ensure the
remcrval of water particularly when dissociated ammonia is used. It is evident
JANUARY. 1939
that the problem of atmosphere control
is an unusually complex one and that
it must have and is getting the attention
not only of the metallurgist familiar
with the metal problem but also of the
combustion engineer and of the chemist
who will understand the behavior of
various gases and gas mixtures under
the conditions of use in the treatment
of steel.
D
ELIBERATE addition of carbon
to the surface of steel in casehardening is almost as old as steelmaking itself and solid carburizers have
been and are being extensively used
for this purpose. The renewed and at
present active interest in the use of
controlled atmospheres for other purposes has stimulated a new attack on
an old ~ r o b l e m and many parts formerly pack hardened are now being gas
carburized, using gases that until a few
years ago had never been considered
in connection with steel treating. Some
of these gases are being used effectively
and economically and it is quite certain that still other gases will be studied in the hope of finding still more
active carburizing atmospheres.
This review has considered only a
limited number of developments in the
steel industry in the last few years, selected on the basis of rather general
interest to those not metallurgical specialists. It would be quite incomplete,
however, without a t least a reference to
certain other activities in the ferrous
field.
The technique and methods of hardening and tempering have been profoundly changed in many details as the
result of the classic papers by Bain and'
his associates leading to rhe development of the "S curve." These papers
indicated so clearly the possibilities of
a modified heat-treatment that active
work has been and is being carried out
today leading to marked improvements
in the quality of the steels and in the
development of properties that were
desirable but which had not been obtained until the fundamental changes
were outlined.
Anothrr phase of development now
receiving wide attention is that of inductive heating. This has already made
marked improvements in heat-treating
methods and shows great promise for
future progress. Heating in this way
may be accomplished in the absence of
harmful gas reactions and makes possible unusually precise temperature
control.
Production of high-strength, lowalloy steels has been one of the important forward steps in the steel industry
in recent years. For certain structural
and engineering uses plain carbon
steels are not quite good enough and
the highly alloyed steels, though of
course satisfactory, are too expensive.
Many steels have been developed with
percentages of one or more alloying
elements sufficiently high to give markedly improved properties to the steel
and at the same time low enough to
keep the price at a much more modest
level than that of the true alloy steels.
Perhaps too many of these low-alloy
steels have been develo~edso that the
question of proper selection is becoming increasingly difficult. It is probable
that future work will consist largely in
consolidating the gains already made
and reducing the number of steels
rather than developing new combinations.
In conclusion grateful acknowledgement must be made to many authors
from whose published papers most of
the factual material has been taken, in
some instances almost directly.
Plans of the Blast Furnace & Raw
Materials Committee
S
IX different countries are now represented on the Blast Furnace and
Raw Materials Committee - United
States, England, France, India, South
Africa, and the Netherlands. The latest
addition is F. W. E. Spies, superintendent of blast furnaces, coke ovens,
and power station of the RoyaI Dutch
Blast Furnaces and Steel Plants (Koninklijke Nederlandsche Hoogovens en
Staalfabrieken N.V.) a t IJmuiden, Holland. Mr. Spies is president of the
. Netherland Foundrymen's Association,
and a memher of the Verein Deutscher
Eisenhuttenleute of Germany.
Our member from South Africa, J. A.
L. Ortlepp, is preparing a paper on
blast-furnace practice in South Africa
which will describe raw materials acd
practice generally, with a heat Ealance representing this practice, and
some forecasts of the direction along
which further economies in Mast-furnace practice may be expected in the
future. Mr. Ortlepp, who is in charge
of the technical control of the mining
and metallurgical activities of the
African Metals Corp., Johannesburg,
hopes to have his paper ready for the
Cleveland meeting, April 26 and 27,
1939.
Two other papers for the Cleveland
meeting are promised from the South
Works organization of the CarnegieIllinois Steel Corp., one dealing with
the effect of solution loss reactions upon
furnace economy, and the other covering low slag volumes and the resulting effect on cost and iron quality.Rnlph H . Sztieetser, Chairman.