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

Steel Making

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

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

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

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

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

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

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

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

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

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

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

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

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

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

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

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



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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