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Corrosion
This steel like any other steel when distorted by cold worki...

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

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

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

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Annealing Method
Forgings which are too hard to machine are put in pots with ...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Furnace Data
In order to give definite information concerning furnaces, fu...

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

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...



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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