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

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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

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

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

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

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

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

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Critical Points
One of the most important means of investigating the properti...

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

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

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

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

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



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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