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

Conclusions
Martien was probably never a serious contender for the honor ...

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

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

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

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

Nickel-chromium
A combination of the characteristics of nickel and the charac...

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

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

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

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

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

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

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

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

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

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

Tungsten
Tungsten, as an alloy in steel, has been known and used for a...



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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