Category: APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY
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 difficult 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.
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