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Steel Making

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

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

Drop Forging Dies
The kind of steel used in the die of course influences the he...

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

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

The Modern Hardening Room
A hardening room of today means a very different place from ...

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

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

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

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

Hardening
Steel is hardened by quenching from above the upper critical....

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

The Influence Of Size
The size of the piece influences the physical properties obta...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...



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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