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

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

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

Standard Analysis
The selection of a standard analysis by the manufacturer is t...

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

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

Annealing
There is no mystery or secret about the proper annealing of d...

Heating
Although it is possible to work steels cold, to an extent de...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

Corrosion
This steel like any other steel when distorted by cold worki...

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

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

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

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

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

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



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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