ALLOYS AND THEIR EFFECT UPON STEEL
In view of the fact that alloy steels are coming into a great deal
of prominence, it would be well for the users of these steels to
fully appreciate the effects of the alloys upon the various grades
of steel. We have endeavored to summarize the effect of these alloys
so that the users can appreciate their effect, without having to
study a metallurgical treatise and then, perhaps, not get the crux
of the matter.
NICKEL
Nickel may be considered as the toughest among the non-rare alloys
now used in steel manufacture. Originally nickel was added to give
increased strength and toughness over that obtained with the ordinary
rolled structural steel and little attempt was made to utilize its
great possibilities so far as heat treatment was concerned.
The difficulties experienced have been a tendency towards laminated
structure during manufacture and great liability to seam, both
arising from improper melting practice. When extra care is exercised
in the manufacture, particularly in the melting and rolling, many
of these difficulties can be overcome.
The electric steel furnace, of modern construction, is a very important
step forward in the melting of nickel steel; neither the crucible
process nor basic or acid open-hearth furnaces give such good results.
Great care must be exercised in reheating the billet for rolling
so that the steel is correctly soaked. The rolling must not be
forced; too big reduction per pass should not be indulged in, as
this sets up a tendency towards seams.
Nickel steel has remarkably good mechanical qualities when suitably
heat-treated, and it is preeminently adapted for case-hardening. It
is not difficult to machine low-nickel steel, consequently it is
in great favor where easy machining properties are of importance.
Nickel influences the strength and ductility of steel by being
dissolved directly in the iron or ferrite; in this respect differing
from chromium, tungsten and vanadium. The addition of each 1 per
cent nickel up to 5 per cent will cause an approximate increase of
from 4,000 to 6,000 lb. per square inch in the tensile strength and
elastic limit over the corresponding steel and without any decrease
in ductility. The static strength of nickel steel is affected to
some degree by the percentage of carbon; for instance, steel with
0.25 per cent carbon and 3.5 per cent nickel has a tensile strength,
in its normal state, equal to a straight carbon steel of 0.5 per
cent with a proportionately greater elastic limit and retaining
all the advantages of the ductility of the lower carbon.
To bring out the full qualities of nickel it must be heat-treated,
otherwise there is no object in using nickel as an alloy with carbon
steel as the additional cost is not justified by increased strength.
Nickel has a peculiar effect upon the critical ranges of steel,
the critical range being lowered by the percentage of nickel; in
this respect it is similar to manganese.
Nickel can be alloyed with steel in various percentages, each percentage
having a very definite effect on the microstructure. For instance, a
steel with 0.2 per cent carbon and 2 per cent nickel has a pearlitic
structure but the grain is much finer than if the straight carbon
were used. With the same carbon content and say 5 per cent nickel,
the structure would still be pearlitic, but much finer and denser,
therefore capable of withstanding shock, and having greater dynamic
strength. With about 0.2 per cent carbon and 8 per cent nickel, the
steel is nearing the stage between pearlite and martensite, and
the structure is extremely fine, the ferrite and pearlite having
a very pronounced tendency to mimic a purely martensite structure.
Steel with 0.2 per cent carbon and 15 per cent nickel is entirely
martensite. Higher percentages of nickel change the martensitic
structure to austenite, the steel then being non-magnetic. The
higher percentages, that is 30 to 35 per cent nickel, are used
for valve seats, valve heads, and valve stems, as the alloy is a
poor conductor of heat and is particularly free from any tendency
towards corrosion or pitting from the action of waste gases of
the internal-combustion engine.
Nickel steels having 3-1/2 per cent nickel and 0.15 to 0.20 per
cent carbon are excellent for case-hardening purposes, giving hard
surfaces and tough interiors.
To obtain the full effect of nickel as an alloy, it is essential
that the correct percentage of carbon be used. High nickel and
low carbon will not be more efficient than lower nickel and higher
carbon, but the cost will be much greater. Generally speaking,
heat-treated nickel alloy steels are about two to three times stronger
than the same steel annealed. This point is very important as many
instances have been found where nickel steel is incorrectly used,
being employed when in the annealed or normal state.
CHROMIUM
Chromium when alloyed with steel, has the characteristic function
of opposing the disintegration and reconstruction of cementite.
This is demonstrated by the changes in the critical ranges of this
alloy steel taking place slowly; in other words, it has a tendency
to raise the _Ac_ range (decalescent points) and lower the _Ar_
range (recalescent points). Chromium steels are therefore capable
of great hardness, due to the rapid cooling being able to retard
the decomposition of the austenite.
The great hardness of chromium steels is also due to the formation
of double carbides of chromium and iron. This condition is not
removed when the steel is slightly tempered or drawn. This additional
hardness is also obtained without causing undue brittleness such as
would be obtained by any increase of carbon. The degree of hardness
of the lower-chrome steels is dependent upon the carbon content,
as chromium alone will not harden iron.
The toughness so noticeable in this steel is the result of the
fineness of structure; in this instance, the action is similar
to that of nickel, and the tensile strength and elastic limit is
therefore increased without any loss of ductility. We then have
the desirable condition of tough hardness, making chrome steels
extremely valuable for all purposes requiring great resistance
to wear, and in higher-chrome contents resistance to corrosion.
All chromium-alloy steels offer great resistance to corrosion and
erosion. In view of this, it is surprising that chromium steels
are not more largely used for structural steel work and for all
purposes where the steel has to withstand the corroding action
of air and liquids. Bridges, ships, steel building, etc., would
offer greater resistance to deterioration through rust if the
chromium-alloy steels were employed.
Prolonged heating and high temperatures have a very bad effect upon
chromium steels. In this respect they differ from nickel steels,
which are not so affected by prolonged heating, but chromium steels
will stand higher temperatures than nickel steels when the period
is short.
Chromium steels, due to their admirable property of increased hardness,
without the loss of ductility, make very excellent chisels and
impact tools of all types, although for die blocks they do not give
such good results as can be obtained from other alloy combinations.
For ball bearing steels, where intense hardness with great toughness
and ready recovery from temporary deflection is required, chromium
as an alloy offers the best solution.
Two per cent chromium steels; due to their very hard tough surface,
are largely used for armor-piercing projectiles, cold rolls, crushers,
drawing dies, etc.
The normal structure of chromium steels, with a very low carbon
content is roughly pearlitic up to 7 per cent, and martensitic
from 8 to 20 per cent; therefore, the greatest application is in
the pearlitic zone or the lower percentages.
NICKEL-CHROMIUM
A combination of the characteristics of nickel and the characteristics
of chromium, as described, should obviously give a very excellent
steel as the nickel particularly affects the ferrite of the steel
and the chromium the carbon. From this combination, we are able to
get a very strong ferrite matrix and a very hard tough cementite.
The strength of a strictly pearlitic steel over a pure iron is due
to the pearlitic being a layer arrangement of cementite running
parallel to that of a pure iron layer in each individual grain. The
ferrite _i.e._, the iron is increased in strength by the resistance
offered by the cementite which is the simple iron-carbon combination
known to metallurgists as Fe3C. The cementite, although adding
to the tensile strength, is very brittle and the strength of the
pearlite is the combination of the ferrite and cementite. In the
event of the cementite being strengthened, as in the case of strictly
chromium steels, an increased tensile strength is readily obtained
without loss of ductility and if the ferrite is strengthened then
the tensile strength and ductility of the metal is still further
improved.
Nickel-chromium alloy represents one of the best combinations available
at the present time. The nickel intensifies the physical characteristics
of the chromium and the chromium has a similar effect on the nickel.
For case-hardening, nickel-chromium steels seem to give very excellent
results. The carbon is very rapidly taken up in this combination,
and for that reason is rather preferable to the straight nickel steel.
With the mutually intensifying action of chromium and nickel there
is a most suitable ratio for these two alloys, and it has been found
that roughly 2-1/2 parts of nickel to about 1 part of chromium
gives the best results. Therefore, we have the standard types of
3.5 per cent nickel with 1.5 per cent chromium to 1.5 per cent
nickel with 0.6 per cent chromium and the various intermediate
types. This ratio, however, does not give the whole story of
nickel-chromium combinations, and many surprising results have
been obtained with these alloys when other percentage combinations
have been employed.
VANADIUM
Vanadium has a very marked effect upon alloy steels rich in chromium,
carbon, or manganese. Vanadium itself, when combined with steel very
low in carbon, is not so noticeably beneficial as in the same carbon
steel higher in manganese, but if a small quantity of chromium
is added, then the vanadium has a very marked effect in increasing
the impact strength of the alloy. It would seem that vanadium has
the effect of intensifying the action of chromium and manganese, or
that vanadium is intensified by the action of chromium or manganese.
Vanadium has the peculiar property of readily entering into solution
with ferrite. If vanadium contained is considerable it also combines
with the carbon, forming carbides. The ductility of carbon-vanadium
steels is therefore increased, likewise the ductility of chrome-vanadium
steels.
The full effect of vanadium is not felt unless the temperatures to
which the steel is heated for hardening are raised considerably.
It is therefore necessary that a certain amount of "soaking" takes
place, so as to get the necessary equalization. This is true of all
alloys which contain complex carbides, i.e., compounds of carbon,
iron and one or more elements.
Chrome-vanadium steels also are highly favored for case hardening.
When used under alternating stresses it appears to have superior
endurance. It would appear that the intensification of the properties
due to chromium and manganese in the alloy steel accounts for this
peculiar phenomenon.
Vanadium is also a very excellent scavenger for either removing
the harmful gases, or causing them to enter into solution with the
metal in such a way as to largely obviate their harmful effects.
Chrome-vanadium steels have been claimed, by many steel manufacturers
and users, to be preferable to nickel-chrome steels. While not
wishing to pass judgment on this, it should be borne in mind that
the chrome-vanadium steel, which is tested, is generally compared
with a very low nickel-chromium alloy steel (the price factor entering
into the situation), but equally good results can be obtained by
nickel-chromium steels of suitable analysis.
Where price is the leading factor, there are many cases where a
stronger steel can be obtained from the chrome and vanadium than
the nickel-chrome. It will be safe to say that each of these two
systems of alloys have their own particular fields and chrome-vanadium
steel should not be regarded as the sole solution for all problems,
neither should nickel-chromium.
MANGANESE
Manganese adds considerably to the tensile strength of steel, but
this is dependent on the carbon content. High carbon materially adds
to the brittleness, whereas low-carbon, pearlitic-manganese steels
are very tough and ductile and are not at all brittle, providing the
heat-treating is correct. Manganese steel is very susceptible to
high temperatures and prolonged heating.
In low-carbon pearlitic steels, manganese is more effective in
increasing ultimate strength than is nickel; that is to say, a
0.45 carbon steel with 1.25 per cent manganese is as strong as a
0.45 carbon steel with 1.5 per cent nickel. The former steel is
much used for rifle barrels, and in the heat-treated condition will
give 80,000 to 90,000 lb. per square inch elastic limit, 115,000 to
125,000 lb. per square inch tensile strength, 23 per cent elongation,
and 55 per cent reduction in area.
Manganese when added to steel has the effect of lowering the critical
range; 1 per cent manganese will lower the upper critical point
60°F. The action of manganese is very similar to that of nickel
in this respect, only twice as powerful. As an instance, 1 per
cent nickel would have the effect of lowering the upper critical
range from 25 to 30°F.
Low-carbon pearlitic-manganese steel, heat-treated, will give dynamic
strength which cannot be equaled by low-priced and necessarily
low-content nickel steels. In many instances, it is preferable to use
high-grade manganese steel, rather than low-content nickel steel.
High-manganese steels or austenite manganese steels are used for a
variety of purposes where great resistance to abrasion is required,
the percentage of manganese being from 11 to 14 per cent, and carbon
1 to 1.5 per cent. This steel is practically valueless unless
heat-treated; that is, heated to about yellow red and quenched
in ice water. The structure is then austenite and the air-cooled
structure of this steel is martensite. Therefore this steel has to
be heated and very rapidly cooled to obtain the ductile austenite
structure.
Manganese between 2 and 7 per cent is a very brittle material when
the carbon is about 1 per cent or higher and is, therefore, quite
valueless. Below 2 per cent manganese steel low in carbon is very
ductile and tough steel.
The high-content manganese steels are known as the "Hadfield manganese
steels," having been developed by Sir Robert Hadfield. Small additions
of chrome up to 1 per cent increase the elastic limit of low-carbon
pearlitic-manganese steels without affecting the steel in its resistance
to shock, but materially decrease the percentage of elongation.
Vanadium added to low-carbon pearlitic manganese steel has a very
marked effect, increasing greatly the dynamic strength and changing
slightly the susceptibility of this steel to heat treatments, giving
a greater margin for the hardening temperature. Manganese steel
with added vanadium is most efficient when heat-treated.
TUNGSTEN
Tungsten, as an alloy in steel, has been known and used for a long
time. The celebrated and ancient damascus steel being a form of
tungsten-alloy steel. Tungsten and its effects, however, did not
become generally realized until Robert Mushet experimented and
developed his famous mushet steel and the many improvement made
since that date go to prove how little Mushet himself understood
the peculiar effects of tungsten as an alloy.
Tungsten acts on steel in a similar manner to carbon, that is,
it increases its hardness, but is much less effective than carbon
in this respect. If the percentage of tungsten and manganese is
high, the steel will be hard after cooling in the air. This is
impossible in a carbon steel. It was this combination that Mushet
used in his well-known "air-hardening" steel.
The principal use of tungsten is in high-speed tool steel, but
here a high percentage of manganese is distinctly detrimental,
making the steel liable to fire crack, very brittle and weak in
the body, less easily forged and annealed. Manganese should be
kept low and a high percentage of chromium used instead.
Tools of tungsten-chromium steels, when hardened, retain their
hardness, even when heated to a dark cherry red by the friction of
the cutting or the heat arising from the chips. This characteristic
led to the term "red-hardness," and it is this property that has
made possible the use of very high cutting speeds in tools made
of the tungsten-chromium alloy, that is, "high-speed" steel.
Tungsten steels containing up to 6 per cent do not have the property
of red hardness any more than does carbon tool steel, providing
the manganese or chromium is low.
When chromium is alloyed with tungsten, a very definite red-hardness
is noticed with a great increase of cutting efficiency. The maximum
red-hardness seems to be had with steels containing 18 per cent
tungsten, 5.5 per cent chromium and 0.70 per cent carbon.
Very little is known of the actual function of tungsten, although
a vast amount of experimental work has been done. It is possible
that when the effect of tungsten with iron-carbon alloys is better
known, a greater improvement can be expected from these steels.
Tungsten has been tried and is still used by some steel manufacturers
for making punches, chisels, and other impact tools. It has also
been used for springs, and has given very good results, although
other less expensive alloys give equally good results, and are
in some instances, better.
Tungsten is largely used in permanent magnets. In this, its action
is not well understood. In fact, the reason why steel becomes a
permanent magnet is not at all understood. Theories have been evolved,
but all are open to serious questioning. The principal effect of
tungsten, as conceded by leading authorities, is that it distinctly
retards separation of the iron-carbon solution, removing the lowest
recalescent point down to atmospheric temperature.
A peculiar property of tungsten steels is that if a heating temperature
of 1,750°F. is not exceeded, the cooling curves indicate but one
critical point at about 1,350°F. But when the heating temperature
is raised above 1,850°F., this critical point is nearly if not
quite suppressed, while a lower critical point appears and grows
enormously in intensity at a temperature between 660 and 750°F.
The change in the critical ranges, which is produced by heating
tungsten steels to over 1,850°F., is the real cause of the red-hard
properties of these alloys. Its real nature is not understood,
and there is no direct evidence to show what actually happens at
these high temperatures.
It may readily be understood that an alloy containing four essential
elements, namely: iron, carbon, tungsten and chromium, is one whose
study presents problems of extreme complexity. It is possible that
complex carbides may be formed, as in chromium steels, and that
compounds between iron and tungsten exist. Behavior of these
combinations on heating and cooling must be better known before
we are able to explain many peculiarities of tungsten steels.
MOLYBDENUM
Molybdenum steels have been made commercially for twenty-five years,
but they have not been widely exploited until since the war. Very
large resources of molybdenum have been developed in America, and
the mining companies who are equipped to produce the metal are
very active in advertising the advantages of molybdenum steels.
It was early found that 1 part molybdenum was the equivalent of from
2 to 2-1/2 parts of tungsten in tool steels, and magnet steels. It
fell into disrepute as an alloy for high-speed tool steel, however,
because it was found that the molybdenum was driven out of the
surface of the tool during forging and heat treating.
Within the last few years it has been found that the presence of
less than 1 per cent of molybdenum greatly enhances certain properties
of heat-treated carbon and alloy steels used for automobiles and
high-grade machinery.
In general, molybdenum when added to an alloy steel, increases the
figure for reduction of area, which is considered a good measure
of "toughness." Molybdenum steels are also relatively insensible
to variations in heat treatment; that is to say, a
chromium-nickel-molybdenum steel after quenching in oil from 1,450°F.
may be drawn at any temperature between 900 and 1,100°F. with
substantially the same result (static tensile properties and hardness).
SILICON
Silicon prevents, to a large extent, defects such as gas bubbles
or blow holes forming while steel is solidifying. In fact, steel
after it has been melted and before it has been refined, is "wild"
and "gassy." That is to say, if it would be cast into molds it
would froth up, and boil all over the floor. A judicious amount
of silicon added to the metal just before pouring, prevents this
action--in the words of the steel maker, silicon "kills" the steel.
If about 1.75 per cent metallic silicon remains in a 0.65 carbon
steel, it makes excellent springs.
PHOSPHORUS
Phosphorus is one of the impurities in steel, and it has been the
object of steel makers for years to eliminate it. On cheap grades
of steel, not subject to any abnormal strain or stress, 0.1 per
cent phosphorus is not objectionable. High phosphorus makes steel
"cold short," i.e., brittle when cold or moderately warm.
SULPHUR
Sulphur is another impurity and high sulphur is even a greater
detriment to steel than phosphorus. High sulphur up to 0.09 per
cent helps machining properties, but has a tendency to make the
steel "hot short," i.e., subject to opening up cracks and seams
at forging or rolling heats. Sulphur should never exceed 0.06 per
cent nor phosphorus 0.08 per cent.
Steel used for tool purposes should have as low phosphorus and sulphur
contents as possible, not over 0.02 per cent.
We can sum up the various factors something as follows for ready
reference.
The ingredient Its effect
Iron The basis of steel
Carbon The determinative
Sulphur A strength sapper
Phosphorus The weak link
Oxygen A strength destroyer
Manganese For strength
Nickel For strength and toughness
Tungsten Hardener and heat resister
Chromium For resisting shocks
Vanadium Purifier and fatigue resister
Silicon Impurity and hardener
Titanium Removes nitrogen and oxygen
Molybdenum Hardener and heat resister
Aluminum Kills or deoxidizes steel
PROPERTIES OF ALLOY STEELS
The following table shows the percentages of carbon, manganese,
nickel, chromium and vanadium in typical steel alloys for engineering
purposes. It also gives the elastic limit, tensile strength, elongation
and reduction of area of the various alloys, all being given the same
heat treatment with a drawing temperature of 1,100°F. (600°C.). The
specimens were one inch rounds machined after heat treatment.
Tungsten is not shown in the table because it is seldom used in
engineering construction steels and then usually in combination
with chromium. Tungsten is used principally for the magnets of
magnetos, to some extent in the manufacture of hacksaws, and for
special tool steels.
TABLE I.--PROPERTIES OF ALLOY STEELS
------------------------------------------------------------------------------
\Manganese,/ \Chromium,/ |Elastic|Tensile |Elongation|Reduction
Carbon,\ per /Nickel,\ per /Vanadium,|limit, |Strength,|in 2 in., | of area,
per | cent | per | cent |per cent |lb. per|lb. per |per cent | per cent
cent | | cent | | |sq. in.|sq. in. | |
-------|------|-------|------|---------|-------|---------|----------|---------
0.27 | 0.55 | | | | 49,000| 80,000 | 30 | 65
0.27 | 0.47 | | | 0.26 | 66,000| 98,000 | 25 | 52
0.36 | 0.42 | | | | 58,000| 90,000 | 27 | 60
0.34 | 0.87 | | | 0.13 | 82,500| 103,000 | 22 | 57
0.45 | 0.50 | | | | 65,000| 96,000 | 22 | 52
0.43 | 0.60 | | | 0.32 | 96,000| 122,000 | 21 | 52
0.47 | 0.90 | | | 0.15 |102,000| 127,500 | 23 | 58
0.30 | 0.60 | 3.40 | | | 75,000| 105,000 | 25 | 67
0.33 | 0.63 | 3.60 | | 0.25 |118,000| 142,000 | 17 | 57
0.30 | 0.49 | 3.60 | 1.70 | |119,000| 149,500 | 21 | 60
0.25 | 0.47 | 3.47 | 1.60 | 0.15 |139,000| 170,000 | 18 | 53
0.25 | 0.50 | 2.00 | 1.00 | |102,000| 124,000 | 25 | 70
0.38 | 0.30 | 2.08 | 1.16 | |120,000| 134,000 | 20 | 57
0.42 | 0.22 | 2.14 | 1.27 | 0.26 |145,000| 161,500 | 16 | 53
0.36 | 0.61 | 1.46 | 0.64 | |117,600| 132,500 | 16 | 58
0.36 | 0.50 | 1.30 | 0.75 | 0.16 |140,000| 157,500 | 17 | 54
0.30 | 0.50 | | 0.80 | | 90,000| 105,000 | 20 | 50
0.23 | 0.58 | | 0.82 | 0.17 |106,000| 124,000 | 21 | 66
0.26 | 0.48 | | 0.92 | 0.20 |112,000| 137,000 | 20 | 61
0.35 | 0.64 | | 1.03 | 0.22 |132,500| 149,500 | 16 | 54
0.50 | 0.92 | | 1.02 | 0.20 |170,000| 186,000 | 15 | 45
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NON-SHRINKING, OIL-HARDENING STEELS
Certain steels have a very low rate of expansion and contraction
in hardening and are very desirable for test plugs, gages, punches
and dies, for milling cutters, taps, reamers, hard steel bushings
and similar work.
It is recommended that for forging these steels it be heated slowly
and uniformly to a bright red, but not in a direct flame or blast.
Harden at a dull red heat, about 1,300°F. A clean coal or coke
fire, or a good muffle-gas furnace will give best results. Fish
oil is good for quenching although in some cases warm water will
give excellent results. The steel should be kept moving in the bath
until perfectly cold. Heated and cooled in this way the steel is
very tough, takes a good cutting edge and has very little expansion
or contraction which makes it desirable for long taps where the
accuracy of lead is important.
The composition of these steels is as follows:
Per cent
Manganese 1.40 to 1.60
Carbon 0.80 to 0.90
Vanadium 0.20 to 0.25
[Illustration: FIG. 13.--Effect of copper in steel.]
EFFECT OF A SMALL AMOUNT OF COPPER IN MEDIUM-CARBON STEEL
This shows the result of tests by C. R. Hayward and A. B. Johnston
on two types of steel: one containing 0.30 per cent carbon, 0.012
per cent phosphorus, and 0.860 per cent copper, and the other 0.365
per cent carbon, 0.053 per cent phosphorus, and 0.030 per cent
copper. The accompanying chart in Fig. 13 shows that high-copper
steel has decided superiority in tensile strength, yield point and
ultimate strength, while the ductility is practically the same.
Hardness tests by both methods show high-copper steel to be harder
than low-copper, and the Charpy shock tests show high-copper steel
also superior to low-copper. The tests confirm those made by Stead,
showing that the behavior of copper steel resembles that of nickel
steel. The high-copper steels show finer grain than the low-copper.
The quenched and drawn specimens of high-copper steel were found
to be slightly more martensitic.
HIGH-CHROMIUM OR RUST-PROOF STEEL
High-chromium, or what is called stainless steel containing from
11 to 14 per cent chromium, was originally developed for cutlery
purposes, but has in the past few years been used to a considerable
extent for exhaust valves in airplane engines because of its resistance
to scaling at high temperatures.
Percentage
Carbon 0.20 to 0.40
Manganese, not to exceed 0.50
Phosphorus, not to exceed 0.035
Sulphur, not to exceed 0.035
Chromium 11.50 to 14.00
Silicon, not to exceed 0.30
The steel should be heated slowly and forged at a temperature above
1,750°F. preferably between 1,800 and 2,200°F. If forged at temperatures
between 1,650 and 1,750°F. there is considerable danger of rupturing
the steel because of its hardness at red heat. Owing to the
air-hardening property of the steel, the drop-forgings should be
trimmed while hot. Thin forgings should be reheated to redness
before trimming, as otherwise they are liable to crack.
The forgings will be hard if they are allowed to cool in air. This
hardness varies over a range of from 250 to 500 Brinell, depending
on the original forging temperature.
ANNEALING can be done by heating to temperatures ranging from 1,290
to 1,380°F. and cooling in air or quenching in water or oil. After
this treatment the forgings will have a hardness of about 200 Brinell
and a tensile strength of 100,000 to 112,000 lb. per square inch.
If softer forgings are desired they can be heated to a temperature
of from 1,560 to 1,650°F. and cooled very slowly. Although softer
the forgings will not machine as smoothly as when annealed at the
lower temperature.
HARDENING.--The forgings can be hardened by cooling in still air
or quenching in oil or water from a temperature between 1,650 and
1,750°F.
The physical properties do not vary greatly when the carbon is
within the range of composition given, or when the steel is hardened
and tempered in air, oil, or water.
When used for valves the following specification of physical properties
have been used:
Yield point, pounds per square inch 70,000
Tensile strength, pounds per square inch 90,000
Elongation in 2 in., per cent 18
Reduction of area, per cent 50
The usual heat treatment is to quench in oil from 1,650°F. and
temper or draw at 1,100 to 1,200°F. One valve manufacturer stated
that valves of this steel are hardened by heating the previously
annealed valves to 1,650°F. and cooling in still air. This treatment
gives a scleroscope hardness of about 50.
In addition to use in valves this steel should prove very satisfactory
for shafting for water-pumps and other automobile parts subject to
objectionable corrosion.
TABLE 2.--COMPARISON OF PHYSICAL PROPERTIES FOR HIGH-CHROMIUM
STEELS OF DIFFERENT CARBON CONTENT --------------------------------------------------------------------------
| C 0.20 | C 0.27 | C 0.50
| Mn 0.45 | Mn 0.50 |
| Cr 12.56 | Cr 12.24 | Cr 14.84
-----------------------------------------|----------|----------|----------
Quenched in oil from degrees Fahrenheit | 1,600 | 1,600 | 1,650
Tempered at degrees Fahrenheit | 1,160 | 1,080 | 1,100
Yield point, pounds per square inch | 78,300 | 75,000 | 91,616
Tensile strength, pounds per square inch | 104,600 | 104,250 | 123,648
Elongation in 2 in., per cent | 25.0 | 23.5 | 14.5
Reduction of area, per cent | 52.5 | 51.4 | 33.5
--------------------------------------------------------------------------
TABLE 3.--COMPARISON OF PHYSICAL PROPERTIES BETWEEN AIR, OIL AND
WATER-HARDENED STEEL HAVING CHEMICAL ANALYSIS IN
PERCENTAGE OF
-------------------------------------------------------------------------
Carbon 0.24
Manganese 0.30
Phosphorus 0.035
Sulphur 0.035
Chromium 12.85
Silicon 0.20
-------------------------------------------------------------------------
| Hardened | | Elastic | Tensile | |
Hardening| from, | Tempered | limit, |strength,|Elongation|Reduction
medium | degrees |at, degrees| per lb. |lb. Per | in 2 in. |of area,
|Fahrenheit|Fahrenheit | sq. in. | sq. in. | per cent |per cent
---------|----------|-----------|---------|---------|----------|---------
| | 930 | 158,815 | 192,415 | 13.0 | 40.5
| | 1,100 | 99,680 | 120,065 | 21.0 | 59.2
Air | 1,650 | 1,300 | 70,785 | 101,250 | 26.0 | 64.6
| | 1,380 | 66,080 | 98,335 | 28.0 | 63.6
| | 1,470 | 70,785 | 96,990 | 27.0 | 64.7
---------|----------|-----------|---------|---------|----------|---------
| | 930 | 163,070 | 202,720 | 8.0 | 18.2
Oil | 1,650 | 1,100 | 88,255 | 116,480 | 20.0 | 56.9
| | 1,300 | 77,950 | 105,505 | 25.5 | 63.8
| | 1,380 | 88,255 | 98,785 | 27.0 | 66.3
---------|----------|-----------|---------|---------|----------|---------
| | 930 | 158,815 | 202,050 | 12.0 | 34.2
Water | 1,650 | 1,100 | 90,270 | 120,735 | 22.0 | 59.8
| | 1,300 | 66,080 | 102,590 | 25.8 | 64.8
| | 1,380 | 67,200 | 97,890 | 27.0 | 65.2
-------------------------------------------------------------------------
This steel can be drawn into wire, rolled into sheets and strips
and drawn into seamless tubes.
CORROSION.--This steel like any other steel when distorted by cold
working is more sensitive to corrosion and will rust. Rough cut
surfaces will rust. Surfaces finished with a fine cut are less
liable to rust. Ground and polished surfaces are practically immune
to rust.
When chromium content is increased to 16 to 18 per cent and silicon
is added, from 2 to 4 per cent, this steel becomes rust proof in
its raw state, as soon as the outside surface is removed. It does
not need to be heat-treated in any way. These compositions are
both patented.
S. A. E. STANDARD STEELS
The following steel specifications are considered standard by the
Society of Automotive Engineers and represents automobile practice in
this country. These tables give the S. A. E. number, the composition
of the steel and the heat treatment. These are referred to by
letter--the heat treatments being given in detail on pages 134
to 137 in Chap. 8. It should be noted that the percentage of the
different ingredients desired is the mean, or halfway between the
minimum and maximum.
TABLE 4.--CARBON STEELS
------------------------------------------------------------------------------
S. A. E. | Carbon | Manganese | | |
Specification|(minimum and |(minimum and |Phosphorus| Sulphur | Heat
no. | maximum) | maximum) |(maximum) |(maximum)| treatment
-------------|-------------|-------------|----------|---------|---------------
1,010 | 0.05 to 0.15| 0.30 to 0.60| 0.045 | 0.05 |Quench at 1,500
1,020 | 0.15 to 0.25| 0.30 to 0.60| 0.045 | 0.05 | A or B
1,025 | 0.20 to 0.30| 0.50 to 0.80| 0.045 | 0.05 | H
| | | | |
1,035 | 0.30 to 0.40| 0.50 to 0.80| 0.045 | 0.05 | H, D or E
1,045 | 0.40 to 0.50| 0.50 to 0.80| 0.045 | 0.05 | H, D or E
1,095 | 0.90 to 1.05| 0.25 to 0.50| 0.040 | 0.05 | F
------------------------------------------------------------------------------
TABLE 5.--SCREW STOCK
---------------------------------------------------------------------------
S. A. E. | Carbon | Manganese | Phosphorus | Sulphur
Specification no.| | | (maximum) |
-----------------|--------------|--------------|------------|--------------
1,114 | 0.08 to 0.20 | 0.30 to 0.80 | 0.12 | 0.06 to 0.12
---------------------------------------------------------------------------
TABLE 6.--NICKEL STEELS
-----------------------------------------------------------------------------
S. A. E. | | | Phosphorus| | |
Specification | | | (maximum) | | |
no. ---- | \ / | |
| Carbon | Manganese | | Sulphur | Nickel | Heat
|(minimum and|(minimum and| |(maximum)|(minimum and|treatment
| maximum) | maximum) | | | maximum) |
---------|------------|------------|-------|---------|------------|----------
2,315 |0.10 to 0.20|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75|G, H or K
2,320 |0.15 to 0.25|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75|G, H or K
2,330 |0.25 to 0.35|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75| H or K
| | | | | |
2,335 |0.30 to 0.40|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75| H or K
2,340 |0.35 to 0.45|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75| H or K
2,345 |0.40 to 0.50|0.50 to 0.80| 0.04 | 0.045 |3.25 to 3.75| H or K
-----------------------------------------------------------------------------
TABLE 7.--NICKEL-CHROMIUM STEELS
-------------------------------------------------------------------------------
S. A. E. | | | Phosphorus| Sulphur | | |
Specification| | | (maximum)|(maximum) | | | Heat
no. ------ | ------ | ---- | |treatment
| Carbon | Manganese | | | Nickel | Chromium \
|(minimum and|(minimum and| | |(minimum and|(minimum and |
| maximum) | maximum) | | | maximum) | maximum) |
------|------------|------------|----|-----|------------|-------------|--------
3,120|0.15 to 0.25|0.50 to 0.80|0.04|0.045|1.00 to 1.50|0.45 to 0.75*|G,H or D
3,125|0.20 to 0.30|0.50 to 0.80|0.04|0.045|1.00 to 1.50|0.45 to 0.75*|H,D or E
3,130|0.25 to 0.35|0.50 to 0.80|0.04|0.045|1.00 to 1.50|0.45 to 0.75*|H,D or E
| | | | | | |
3,135|0.30 to 0.40|0.50 to 0 80|0.04|0.045|1.00 to 1.50|0.45 to 0 75*|H,D or E
3,140|0.35 to 0.45|0.50 to 0.80|0.04|0.045|1.00 to 1.50|0.45 to 0.75*|H,D or E
3,220|0.15 to 0.25|0.30 to 0.60|0.04|0.040|1.50 to 2.00|0.90 to 1.25 |G,H or D
| | | | | | |
3,230|0.25 to 0.35|0.30 to 0.60|0.04|0.040|1.50 to 2.00|0.90 to 1.25 | H or D
3,240|0.35 to 0.45|0.30 to 0.60|0.04|0.040|1.50 to 2.00|0.90 to 1.25 | H or D
3,250|0.45 to 0.55|0.30 to 0.60|0.04|0.040|1.50 to 2.00|0.90 to 1.25 | M or Q
| | | | | | |
X3,315|0.10 to 0.20|0.45 to 0.75|0.04|0.040|2.75 to 3.25|0.60 to 0.95 | G
X3,335|0.30 to 0.40|0.45 to 0.75|0.04|0.040|2.75 to 3.25|0.60 to 0.95 | P or R
X3,350|0.45 to 0.55|0.45 to 0.75|0.04|0.040|2.75 to 3.25|0.60 to 0.95 | P or R
| | | | | | |
3,320|0.15 to 0.25|0.30 to 0.60|0.04|0.040|3.25 to 3.75|1.25 to 1.75 | L
3,330|0.25 to 0.35|0.30 to 0.60|0.04|0.040|3.25 to 3.75|1.25 to 1.75 | P or R
3,340|0.35 to 0.45|0.30 to 0.60|0.04|0.040|3.25 to 3.75|1.25 to 1.75 | P or R
-------------------------------------------------------------------------------
* Another grade of this type of steel is available with chromium content
of 0.15 per cent to 45 per cent. It has somewhat lower physical properties.
TABLE 8.--CHROMIUM STEELS
-------------------------------------------------------------------------------
S. A. E. | | | | | |
Specification| | | | | |
no. --- Carbon | Manganese | | | Chromium |
|(minimum and|(minimum and|Phosphorus|Sulphur |(minimum and| Heat
| maximum) | maximum) |(maximum) |(maximum)| maximum) |treatment
---------|------------|------------|----------|---------|------------|---------
5,120 |0.15 to 0.25| * | 0.04 | 0.045 |0.65 to 0.85| B
5,140 |0.35 to 0.45| * | 0.04 | 0.045 |0.65 to 0.85| H or D
5,165 |0.60 to 0.70| * | 0.04 | 0.045 |0.65 to 0.85| H or D
| | | | | |
5,195 |0.90 to 1.05|0.20 to 0.45| 0.03 | 0.03 |0.90 to 1.10|M, P or R
51,120 |1.10 to 1.30|0.20 to 0.45| 0.03 | 0.03 |0.90 to 1.10|M, P or R
5,295 |0.90 to 1.05|0.20 to 0.45| 0.03 | 0.03 |1.10 to 1.30|M, P or R
52,120 |1.10 to 1.30|0.20 to 0.45| 0.03 | 0.03 |1.10 to 1.30|M, P or R
-------------------------------------------------------------------------------
--Two types of steel are available in this class, one with manganese 0.25
to 0.50 per cent (0.35 per cent desired), and silicon not over 0.20 per
cent; the other with manganese 0.60 to 0.80 per cent (0.70 per cent
desired), and silicon 0.15 to 0.50 per cent.
TABLE 9.--CHROMIUM-VANADIUM STEELS
-------------------------------------------------------------------------------
S. A. E. | | |Phosphorus| Sulphur | |Vanadium |
Specification| | | (maximum)|(maximum)| |(minimum)|
no. ------ | -- | / - |
| Carbon | Manganese | | | Chromium | | Heat
|(minimum and|(minimum and| | |(minimum and| |treatment
| maximum) | maximum) | | | maximum) | |
------|------------|------------|-------|-------|------------|-------|---------
6,120 |0.15 to 0.25|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | S
6,125 |0.20 to 0.30|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | S or T
6,130 |0.25 to 0.35|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | T or U
6,135 |0.30 to 0.40|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | T or U
6,140 |0.35 to 0.45|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | T or U
6,145 |0.40 to 0.50|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | U
6,150 |0.45 to 0.55|0.50 to 0.80| 0.04 | 0.04 |0.80 to 1.10| 0.15 | U
6,195 |0.90 to 1.05|0.20 to 0.45| 0.03 | 0.03 |0.80 to 1.10| 0.15 U
-------------------------------------------------------------------------------
TABLE 10.--SILICO-MANGANESE STEELS
-----------------------------------------------------------------------------
S. A. E. | | | | | |
Specification| | | | | |
no. ----- Carbon| Manganese | | | Silicon |
|(minimum and|(minimum and|Phosphorus|Sulphur |(minimum and| Heat
| maximum) | maximum) |(maximum) |(maximum)| maximum) |treatment
-------|------------|------------|----------|---------|------------|---------
9,250 |0.45 to 0.55|0.60 to 0.80| 0.045* | 0.045 |1.80 to 2.10| V
9,260 |0.55 to 0.65|0.50 to 0.70| 0.045* | 0.045 |1.50 to 1.80| V
-----------------------------------------------------------------------------
* Steel made by the acid process may contain maximum 0.05 phosphorus.
LIBERTY MOTOR CONNECTING RODS
The requirements for materials for the Liberty motor connecting rods
are so severe that the methods of securing the desired qualities
will be of value in other lines. The original specifications called
for chrome-nickel but the losses due to the difficulty of handling
caused the Lincoln Motor Company to suggest the substitution of
chrome-vanadium steel, and this was accepted by the Signal Corps. The
rods were accordingly made from chromium-vanadium steel, containing
carbon, 0.30 to 0.40 per cent; manganese, 0.50 to 0.80 per cent;
phosphorus, not over 0.04 per cent; sulphur, not over 0.04 per
cent; chromium, 0.80 to 1.10 per cent; vanadium, not less than 0.15
per cent. This steel is ordinarily known in the trade as 0.35 carbon
steel, S. A. E., specification 6,135, which provides a first-rate
quality steel for structural parts that are to be heat-treated.
The fatigue resisting or endurance qualities of this material are
excellent. It has a tensile strength of 150,000 lb. minimum per
square inch; elastic limit, 115,000 lb. minimum per square inch;
elongation, 5 per cent minimum in 2 in.; and minimum reduction
in area, 25 per cent.
The original production system as outlined for the manufacturers
had called for a heat treatment in the rough-forged state for the
connecting rods, and then semi-machining the rod forgings before
giving them the final treatment. The Lincoln Motor Company insisted
from the first that the proper method would be a complete heat
treatment of the forging in the rough state, and machining the
rod after the heat treatment. After a number of trial lots, the
Signal Corps acceded to the request and production was immediately
increased and quality benefited by the change. This method was
later included in a revised specification issued to all producers.
The original system was one that required a great deal of labor
per unit output. The Lincoln organization developed a method of
handling connecting rods whereby five workmen accomplished the
same result that would have required about 30 or 32 by the original
method. Even after revising the specification so as to allow complete
heat treatments in the rough-forged state, the ordinary methods
employed in heat-treating would have required 12 to 15 men. With
the fixtures employed, five men could handle 1,300 connecting rods,
half of which are plain and half, forked, in a working period of
little over 7 hr.
[Illustration: Fig. 14.--Rack for holding rods.]
[Illustration: Fig. 15.--Sliding rods into tank.]
The increase in production was gained by devising fixtures which
enabled fewer men to handle a greater quantity of parts with less
effort and in less time.
In heat-treating the forgings were laid on a rack or loop _A_,
Fig. 14, made of 1-1/4-in. double extra-heavy pipe, bent up with
parallel sides about 9 in. apart, one end being bent straight across
and the other end being bent upward so as to afford an easy grasp
for the hook. Fifteen rods were laid on each loop, there being
four loops of rods charged into a furnace with a hearth area of 36
by 66 in. The rods were charged at a temperature of approximately
900°F. They were heated for refining over a period of 3 hr. to
1,625°F., soaked 15 min, at this degree of heat and quenched in
soluble quenching oil.
In pulling the heat to quench the rods, the furnace door was raised
and the operator pulls one of the loops _A_, Fig. 15 forward to
the shelf of the furnace, supporting the straight end of the loop
by means of the porter bar _B_. They swung the loop of rods around
from the furnace shelf and set the straight end of the loop on
the edge of the quenching tank, then raise the curved end _C_,
by means of their hook _D_ so that all the rods on the loop slide
into the oil bath.
Before the rods cooled entirely, the baskets in the quenching tank
were raised and the oil allowed to partly drain off the forgings,
and they were stacked on curved-end loops or racks and charged into
the furnace for the second or hardening heat. The temperature of
the furnace was raised in 1-1/2 hr. to 1,550°F., the rods soaked
for 15 min. at this degree of heat and quenched in the same manner
as above.
They were again drained while yet warm, placed on loops and charged
into the furnace for the third or tempering heat. The temperature of
the furnace was brought to 1,100°F. in 1 hr., and the rods soaked at
this degree of heat for 1 hr. They were then removed from the furnace
the same as for quenching, but were dumped onto steel platforms
instead of into the quenching oil, and allowed to cool on these
steel platforms down to the room temperature.
PICKLING THE FORGINGS
The forgings were then pickled in a hot solution of either niter
cake or sulphuric acid and water at a temperature of 170°F., and
using a solution of about 25 per cent. The solution was maintained
at a constant point by taking hydrometer readings two or three
times a day, maintaining a reading of about 1.175. Sixty forked or
one hundred single rods were placed in wooden racks and immersed
in a lead-lined vat 30 by 30 by 5 ft. long. The rack was lowered
or lifted by means of an air hoist and the rods were allowed to
stay in solution from 1/2 to 1 hr., depending on the amount of
scale. The rods were then swung and lowered in the rack into running
hot water until all trace of the acid was removed.
The rod was finally subjected to Brinell test. This shows whether
or not the rod has been heat-treated to the proper hardness. If
the rods did not read between 241 and 277, they were re-treated
until the proper hardness is obtained.