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Steel Making

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

Nickel
Nickel may be considered as the toughest among the non-rare a...

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

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

The Forging Of Steel
So much depends upon the forging of steel that this operation...

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

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

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

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

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

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

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

Crankshaft
The crankshaft was the most highly stressed part of the entir...

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

Double Annealing
Water annealing consists in heating the piece, allowing it to...

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

Heating
Although it is possible to work steels cold, to an extent de...



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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