cult it becomes to eliminate them.
The only satisfactory method so far in commercial use for the
elimination of hard spots is to give forgings a very severe quench
from a high temperature followed by a proper tempering heat to
secure good machine ability as outlined above.

The important carbon-steel forgings consisted of the cylinders,
the propeller-hubs, the propeller-hub flange, etc. The material
used for parts of this type was S. A. E. No. 1,045 steel, which
is of the following chemical composition: Carbon, 0.400 to 0.500
per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045
maximum per cent; sulphur, 0.050 maximum per cent.

All forgings made from this material must show, after heat treatment,
the following minimum physical properties: Elastic limit, 70,000;
lb. per square inch, elongation in 2 in., 18 per cent, reduction
of area, 45; per cent, Brinell hardness, 217 to 255.

To obtain these physical properties, the forgings were quenched in
water from a temperature of 1,500 to 1,550 deg.F., followed by tempering
to meet proper Brinell requirements by heating to a temperature
of 1,150 to 1,200 deg.F. and cooled slowly or quenched. No trouble
of any kind was ever experienced with parts of this type.

The principal carbon-steel pressed parts used on the Liberty engine
were the water jackets and the exhaust manifolds. The material
used for parts of this type was S. A. E. No. 1,010 steel, which
is of the following chemical composition: Carbon, 0.05 to 0.15 per
cent; manganese, 0.30 to 0.60 per cent; phosphorus, 0.045 maximum
per cent; sulphur, 0.045 maximum per cent.

No trouble was experienced in the production of any parts from
this material with the exception of the water jacket. Due to the
particular design of the Liberty cylinder assembly, many failures
occurred in the early days, due to the top of the jacket cracking
with a brittle fracture. It was found that these failures were
caused primarily from the use of jackets which showed small scratches
or die marks at this joint and secondarily by improper annealing of
the jackets themselves between the different forming operations.
By a careful inspection for die marks and by giving the jackets
1,400 deg.F. annealing before the last forming operation, it was possible
to completely eliminate the trouble encountered.

HIGHLY STRESSED PARTS

The highly stressed parts on the Liberty engine consisted of the
connecting-rod bolt, the main-bearing bolt, the