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Steel Making

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

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

Hardness Testing
The word hardness is used to express various properties of me...

Bessemer Process
The bessemer process consists of charging molten pig iron int...

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

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

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

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

Nickel-chromium
A combination of the characteristics of nickel and the charac...

Hardening
The forgings can be hardened by cooling in still air or quen...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

Compensating Leads
By the use of compensating leads, formed of the same materia...

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...



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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