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Steel Making

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...

Furnace Data
In order to give definite information concerning furnaces, fu...

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

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

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

Quenching
It is considered good practice to quench alloy steels from th...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

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

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

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

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

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

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

The Electric Process
The fourth method of manufacturing steel is by the electric f...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...



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.)





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Previous: Quenching Tool Steel



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