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Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

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

High Speed Steel
For centuries the secret art of making tool steel was handed ...

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

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

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

The Forging Of Steel
So much depends upon the forging of steel that this operation...

Annealing Work
With the exception of several of the higher types of alloy s...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

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

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



Care In Annealing






Category: HEAT TREATMENT OF STEEL

Not only will benefits in machining be found
by careful annealing of forgings but the subsequent troubles in
the hardening plant will be greatly reduced. The advantages in
the hardening start with the carburizing operation, as a steel of
uniform and fine grain size will carburize more uniformly, producing
a more even hardness and less chances for soft spots. The holes in
the gears will also close in more uniformly, not causing some
gears to require excessive grinding and others with just enough
stock. Also all strains will have been removed from the forging,
eliminating to a great extent distortion and the noisy gears which
are the result.

With the steels used, for the heat-treated gears, always of a higher
carbon content, treatment after forging is necessary for machining, as
it would be impossible to get the required production from untreated
forgings, especially in the alloy steels. The treatment is more
delicate, due to the higher percentage of carbon and the natural
increase in cementite together with complex carbides which are
present in some of the higher types of alloys.

Where poor machining conditions in heat-treated steels are present
they are generally due to incomplete solution of cementite rather
than bands of free ferrite, as in the case of case-hardening steels.
This segregation of carbon, as it is sometimes referred to, causes
hard spots which, in the forming of the tooth, cause the cutter
to ride over the hard metal, producing high spots on the face of
the tooth, which are as detrimental to satisfactory gear cutting
as the drops or low spots produced on the face of the teeth when
the pearlite is coarse-grained or in a banded condition.

In the simpler carburized steels it is not necessary to test the
forgings for hardness after annealing, but with the high percentages
of alloys in the carburizing steels and the heat-treated steels
a hardness test is essential.

To obtain the best results in machining, the microstructure of the
metal should be determined and a hardness range set that covers
the variations in structure that produce good machining results.
By careful control of the heat-treating operation and with the aid
of the Brinell hardness tester and the microscope it is possible
to continually give forgings that will machine uniformly and be
soft enough to give desired production. The following gives a few
of the hardness numerals on steel used in gear manufacture that
produce good machining qualities:

0.20 per cent carbon, 3 per cent nickel, 1-1/4; per cent
chromium--Brinell 156 to 170.

0.50 per cent carbon, 3 per cent nickel, 1 per cent chromium--Brinell
179 to 187.

0.50 per cent carbon chrome-vanadium--Brinell 170 to 179.





Next: The Influence Of Size

Previous: Temperature For Annealing



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