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Steel Making

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

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

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

Machineability
Reheating for machine ability was done at 100 deg. less than ...

Hardening
The forgings can be hardened by cooling in still air or quen...

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

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

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

Vanadium
Vanadium has a very marked effect upon alloy steels rich in c...

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...

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

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

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

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



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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