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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Compensating Leads
By the use of compensating leads, formed of the same materia...

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

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

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

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

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Hardness Testing
The word hardness is used to express various properties of me...

Impact Tests
Impact tests are of considerable importance as an indication ...

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

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Effect Of Different Carburizing Material
[Illustrations: FIGS. 33 to 37.] Each of these different p...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

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

Manganese
Manganese adds considerably to the tensile strength of steel,...

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

Crankshaft
The crankshaft was the most highly stressed part of the entir...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...



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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