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

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

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

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

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

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

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

The Influence Of Size
The size of the piece influences the physical properties obta...

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

Corrosion
This steel like any other steel when distorted by cold worki...

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

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

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

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

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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