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Annealing Work
With the exception of several of the higher types of alloy s...

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

Tungsten
Tungsten, as an alloy in steel, has been known and used for a...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

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

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

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

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

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

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

Conclusions
Martien was probably never a serious contender for the honor ...

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

The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

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

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

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...



Preventing Cracks In Hardening






Category: HARDENING CARBON STEEL FOR TOOLS

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

Previous: Hints For Tool Steel Users



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