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Steel Making

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

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

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

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

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

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

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

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

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

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...



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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