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

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

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

The Modern Hardening Room
A hardening room of today means a very different place from ...

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

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

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

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

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

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

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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

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

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

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

Air-hardening Steels
These steels are recommended for boring, turning and planing...

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



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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