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   Home - Steel Making - Categories - Manufacturing and the Economy of Machinery

Steel Making

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Annealing
There is no mystery or secret about the proper annealing of d...

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

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Bessemer Process
The bessemer process consists of charging molten pig iron int...

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Chromium
Chromium when alloyed with steel, has the characteristic func...

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

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

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

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

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

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

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

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

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

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

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

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...



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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