Heat Treatment Of Axles





Parts of this general type should be heat-treated to show the following

minimum physical properties: Elastic limit, 115,000 lb. per square

inch; elongation in 2 in., 16 per cent; reduction of area, 50 per

cent; Brinell hardness, 277 to 321.



The heat treatment used to secure these physical properties consists

in quenching from a temperature of from 1,520 to 1,540 deg.F. in water

and tempering at a temperature of from 975 to 1,025 deg.F. Where the

axle shaft is a forging, and in the case of steering knuckles and

arms, this heat treatment should be preceded by normalizing the

forgings at a temperature of from 1,550 to 1,600 deg.F. It will be

noted that these physical properties correspond to those worked

out for an ideal aviation engine crankshaft. If parts of this type

are designed with proper sections, so that this range of physical

properties can be used, the part in question will give maximum

service.



One of the most important developments during the Liberty engine

program was the fact that it is not necessary to use a high-analysis

alloy steel to secure a finished part which will give proper service.

This fact should save the automotive industry millions of dollars

on future production.



If the proper authority be given the metallurgical engineer to

govern the handling of the steel from the time it is purchased

until it is assembled into finished product, mild-analysis steels

can be used and the quality of the finished product guaranteed.

It was only through the careful adherence to these fundamental

principles that it was possible to produce 20,000 Liberty engines,

which are considered to be the most highly stressed mechanism ever

produced, without the failure of a single engine from defective

material or heat treatment.





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