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Steel Making

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

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

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

Connecting Rods
The material used for all connecting rods on the Liberty engi...

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

Annealing
There is no mystery or secret about the proper annealing of d...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

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

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

The Thermo-couple
With the application of the thermo-couple, the measurement of...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

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

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

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

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

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...



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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