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

The Influence Of Size
The size of the piece influences the physical properties obta...

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

The forgings can be hardened by cooling in still air or quen...

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

Reheating for machine ability was done at 100 deg. less than ...

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

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

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

Phosphorus is one of the impurities in steel, and it has been...

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

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

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

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

The Electric Process
The fourth method of manufacturing steel is by the electric f...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

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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