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Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Compensating Leads
By the use of compensating leads, formed of the same materia...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

Molybdenum steels have been made commercially for twenty-five...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

Highly Stressed Parts


The highly stressed parts on the Liberty engine consisted of the
connecting-rod bolt, the main-bearing bolt, the propeller-hub key,
etc. The material used for parts of this type was selected at the
option of the manufacturer from standard S. A. E. steels, the
composition of which are given in Table 11.

TABLE 11.--COMPOSITION OF S. A. E. STEELS Nos. 2,330, 3,135 AND 6,130

Steel No 2,330 3,135 6,130
Carbon, minimum 0.250 0.300 0.250
Carbon, maximum 0.350 0.400 0.450
Manganese, minimum 0.500 0.500 0.500
Manganese, maximum 0.800 0.800 0.800
Phosphorus, maximum 0.045 0.040 0.040
Sulphur, maximum 0.045 0.045 0.045
Nickel, minimum 3.250 1.000
Nickel, maximum 3.750 1.500
Chromium, minimum 0.450 0.800
Chromium, maximum 0.750 1.100
Vanadium, minimum 0.150

All highly stressed parts on the Liberty engine must show, after
heat treatment, the following minimum physical properties: Elastic
limit, 100,000 lb. per square inch; elongation in 2 in., 16 per
cent; reduction of area, 45 per cent; scleroscope hardness, 40
to 50.

The heat treatment employed to obtain these physical properties
consisted in quenching from a temperature of 1,525 to 1,575 deg.F., in
oil, followed by tempering at a temperature of from 925 to 975 deg.F.

Due to the extremely fine limits used on all threaded parts for
the Liberty engine, a large percentage of rejection was due to
warpage and scaling of parts. To eliminate this objection, many
of the Liberty engine builders adopted the use of heat-treated
and cold-drawn alloy steel for their highly stressed parts. On
all sizes up to and including 3/8 in. in diameter, the physical
properties were secured by merely normalizing the hot-rolled bars
by heating to a temperature of from 1,525 to 1,575 deg.F., and cooling
in air, followed by the usual cold-drawing reductions. For parts
requiring stock over 3/8 in. in diameter, the physical properties
desired were obtained by quenching and tempering the hot-rolled bars
before cold-drawing. It is the opinion that the use of heat-treated
and cold-drawn bars is very good practice, provided proper inspection
is made to guarantee the uniformity of heat treatment and, therefore,
the uniformity of the physical properties of the finished parts.

The question has been asked many times by different manufacturers, as
to which alloy steel offers the best machineability when heat-treated
to a given Brinell hardness. The general consensus of opinion among
the screw-machine manufacturers is that S. A. E. No. 6,130 steel
gives the best machineability and that S. A. E. No. 2,330 steel
would receive second choice of the three specified.

In the finishing of highly stressed parts for aviation engines,
extreme care must be taken to see that all tool marks are eliminated,
unless they are parallel to the axis of strain, and that proper
radii are maintained at all changes of section. This is of the
utmost importance to give proper fatigue resistance to the part
in question.

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