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Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

Crankshaft
The crankshaft was the most highly stressed part of the entir...

The Modern Hardening Room
A hardening room of today means a very different place from ...

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

Sulphur
SULPHUR is another element (symbol S) which is always found i...

Impact Tests
Impact tests are of considerable importance as an indication ...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Nickel-chromium
A combination of the characteristics of nickel and the charac...

Annealing Work
With the exception of several of the higher types of alloy s...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...



Highly Stressed Parts






Category: APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY

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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