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Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

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

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

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...

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

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

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

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

Preventing Cracks In Hardening


The blacksmith in the small shop, where equipment is usually very
limited, often consisting of a forge, a small open hard-coal furnace,
a barrel of water and a can of oil must have skill and experience.
With this equipment the smith is expected to, and usually can,
produce good results if proper care is taken.

In hardening carbon tool steel in water, too much cannot be said in
favor of slow, careful heating, nor against overheating if cracks
are to be avoided.

It is not wise to take the work from the hardening bath and leave
it exposed to the air if there is any heat left in it, because
it is more liable to crack than if left in the bath until cold.
In heating, plenty of time is taken for the work to heat evenly
clear through, thus avoiding strains caused by quick and improper
heating, In quenching in water, contraction is much more rapid
than was the expansion while heating, and strains begin the moment
the work touches the water. If the piece has any considerable size
and is taken from the bath before it is cold and allowed to come to
the air, expansion starts again from the inside so rapidly that the
chilled hardened surface cracks before the strains can be relieved.

Many are most successful with the hardening bath about blood warm.
When the work that is being hardened is nearly cold, it is taken
from the water and instantly put into a can of oil, where it is
allowed to finish cooling. The heat in the body of the tool will
come to the surface more slowly, thus relieving the strain and
overcoming much of the danger of cracking.

Some contend that the temper should be drawn as soon as possible
after hardening: but that if this cannot be done for some hours, the
work should be left in the oil until the tempering can be done. It
is claimed that forming dies and punch-press dies that are difficult
to harden will seldom crack if treated in this way.

Small tools or pieces that are very troublesome because of peculiar
shape should be made of steel which has been thoroughly annealed.
It is often well to mill or turn off the outer skin of the bar,
to remove metal which has been cold-worked. Then heat slowly just
through the critical range and cool in the furnace, in order to
produce a very fine grain. Tools machined from such stock, and
hardened with the utmost care, will have the best chance to survive
without warping, growth or cracking.

Next: Shrinking And Enlarging Work

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