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Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

The Influence Of Size
The size of the piece influences the physical properties obta...

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

Nickel
Nickel may be considered as the toughest among the non-rare a...

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

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

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Chromium
Chromium when alloyed with steel, has the characteristic func...

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

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

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

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

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

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...



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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