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

Correction For Cold-junction Errors
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Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

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

Annealing Method
Forgings which are too hard to machine are put in pots with ...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

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

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

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

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

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

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

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

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

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...



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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