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

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

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

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

Effect Of Different Carburizing Material
[Illustrations: FIGS. 33 to 37.] Each of these different p...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

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

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

Heating
Although it is possible to work steels cold, to an extent de...

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

Critical Points
One of the most important means of investigating the properti...

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

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

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

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

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



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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