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Steel Making

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

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

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

Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

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

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

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

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

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

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

Gears
The material used for all gears on the Liberty engine was sel...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

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

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

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Annealing Work
With the exception of several of the higher types of alloy s...



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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