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Steel Making

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

Annealing
ANNEALING can be done by heating to temperatures ranging from...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

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

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

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

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

Hardening
Steel is hardened by quenching from above the upper critical....

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

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...



Application Of Liberty Engine Materials To The Automotive Industry






Category: APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY

The success of the Liberty engine program was an engineering achievement
in which the science of metallurgy played an important part. The
reasons for the use of certain materials and certain treatments
for each part are given with recommendations for their application
to the problems of automotive industry.

The most important items to be taken into consideration in the
selection of material for parts of this type are uniformity and
machineability. It has been demonstrated many times that the ordinary
grades of bessemer screw stock are unsatisfactory for aviation
purposes, due to the presence of excessive amounts of unevenly
distributed phosphorus and sulphide segregations. For this reason,
material finished by the basic open hearth process was selected,
in accordance with the following specifications: Carbon, 0.150 to
0.250 per cent; manganese, 0.500 to 0.800 per cent; phosphorus,
0.045 maximum per cent; sulphur, 0.060 to 0.090 per cent.

This material in the cold-drawn condition will show: Elastic limit,
50,000 lb. per square inch, elongation in 2 in., 10 per cent, reduction
of area, 35 per cent.

This material gave as uniform physical properties as S. A. E. No.
1020 steel and at the same time was sufficiently free cutting to
produce a smooth thread and enable the screw-machine manufacturers
to produce, to the same thread limits, approximately 75 per cent
as many parts as from bessemer screw stock.

There are but seven carbon-steel carbonized parts on the Liberty
engine. The most important are the camshaft, the camshaft rocker
lever roller and the tappet. The material used for parts of this
type was S. A. E. No. 1,020 steel, which is of the following chemical
analysis: Carbon 0.150 to 0.250 per cent; manganese, 0.300 to 0.600
per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.050 maximum
per cent.

The heat treatment consisted in carbonizing at a temperature of
from 1,650 to 1,700 deg.F. for a sufficient length of time to secure
the proper depth of case, cool slowly or quench; then reheat to a
temperature of 1,380 to 1,430 deg.F. to refine the grain of the case,
and quench in water. The only thing that should limit the rate of
cooling from the carbonizing heat is distortion. Camshaft rocker
lever rollers and tappets, as well as gear pins, were quenched
directly from the carbonizing heat in water and then case-refined
and rehardened by quenching in water from a temperature of from
1,380 to 1,430 deg.F.

The advantage of direct quenching from the carbonizing heat is
doubtless one of economy, and in many cases will save the cost
of a reheating. Specifications for case hardening, issued by the
Society of Automotive Engineers, have lately been revised; whereas
they formerly called for a slow cooling, they now permit a quenching
from the pot. Doubtless this is a step in advance. Warpage caused
by quenching can be reduced to a minimum by thoroughly annealing
the stock before any machine work is done on it.

Another advantage obtained from 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.





Next: Carbon-steel Forgings

Previous: Pickling The Forgings



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