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Steel Making

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

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

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

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

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

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

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

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

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

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

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

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

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

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

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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



The Theory Of Tempering






Category: HARDENING CARBON STEEL FOR TOOLS

Steel that has been hardened is generally
harder and more brittle than is necessary, and in order to bring
it to the condition that meets our requirements a treatment called
tempering is used. This increases the toughness of the steel, i.e.,
decrease the brittleness at the expense of a slight decrease in
hardness.

There are several theories to explain this reaction, but generally
it is only necessary to remember that in hardening we quench steel
from the austenite phase, and, due to this rapid cooling, the normal
change from austenite to the eutectoid composition does not have
time to take place, and as a consequence the steel exists in a
partially transformed, unstable and very hard condition at atmospheric
temperatures. But owing to the internal rigidity which exists in
cold metal the steel is unable to change into its more stable phase
until atoms can rearrange themselves by the application of heat.
The higher the heat, the greater the transformation into the softer
phases. As the transformation takes place, a certain amount of heat
of reaction, which under slow cooling would have been released in
the critical range, is now released and helps to cause a further
slight reaction.

If a piece of steel is heated to a certain temperature and held
there, the tempering color, instead of remaining unchanged at this
temperature, will advance in the tempering-color scale as it would
with increasing temperature. This means that the tempering colors
do not absolutely correspond to the temperatures of steels, but the
variations are so slight that we can use them in actual practice.
(See Table 23, page 158.)





Next: Temperatures To Use

Previous: Quenching Tool Steel



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