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Gears
The material used for all gears on the Liberty engine was sel...

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

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

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

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

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

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

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

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...



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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