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Steel Making

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

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

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

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

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

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

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

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

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

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

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

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

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

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

Annealing
ANNEALING can be done by heating to temperatures ranging from...

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

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



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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