om rapid cooling from the carbonizing
heat is the retaining of the majority of the excess cementite in
solution which produces a less brittle case and by so doing reduces
the liability of grinding checks and chipping of the case in actual
service.

In the case of the camshaft, it is not possible to quench directly
from the carbonizing heat because of distortion and therefore excessive
breakage during straightening operations. All Liberty camshafts
were cooled slowly from carbonizing heat and hardened by a single
reheating to a temperature of from 1,380 to 1,430 deg.F. and quenching
in water.

Considerable trouble has always been experienced in obtaining uniform
hardness on finished camshafts. This is caused by insufficient
water circulation in the quenching tank, which allows the formation
of steam pockets to take place, or by decarbonization of the case
during heating by the use of an overoxidizing flame. Another cause,
which is very often overlooked, is due to the case being ground off
one side of cam more than the other and is caused by the roughing
master cam being slightly different from the finishing master cam.
Great care should be taken to see that this condition does not occur,
especially when the depth of case is between 1/32 and 3/64 in.

CARBON-STEEL FORGINGS

Low-stressed, carbon-steel forgings include such parts as carbureter
control levers, etc. The important criterion for parts of this type
is ease of fabrication and freedom from over-heated and burned
forgings. The material used for such parts was S. A. E. No. 1,030
steel, which is of the following chemical composition: Carbon, 0.250
to 0.350 per cent; manganese, 0.500 to 0.800 per cent; phosphorus,
0.045 maximum per cent; sulphur, 0.050 maximum per cent.

To obtain good machineability, all forgings produced from this
steel were heated to a temperature of from 1,575 to 1,625 deg.F. to
refine the grain of the steel thoroughly and quenched in water
and then tempered to obtain proper machineability by heating to a
temperature of from 1,000 to 1,100 deg.F. and cooled slowly or quenched.

Forgings subjected to this heat treatment are free from hard spots
and will show a Brinell hardness of 177 to 217, which is proper for
all ordinary machining operations. Great care should be taken not
to use steel for parts of this type containing less than 0.25 per
cent carbon, because the lower the carbon the greater the liability
of hard spots, and the more diffi