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

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

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

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Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

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

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

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

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

Furnace Data
In order to give definite information concerning furnaces, fu...

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

Sulphur
SULPHUR is another element (symbol S) which is always found i...

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

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

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...



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

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