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Steel Making

High Speed Steel
For centuries the secret art of making tool steel was handed ...

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

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

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

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

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

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

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

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

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

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

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

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

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

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



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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