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Standard Analysis
The selection of a standard analysis by the manufacturer is t...

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

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

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

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

Impact Tests
Impact tests are of considerable importance as an indication ...

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

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

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

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

Heating
Although it is possible to work steels cold, to an extent de...

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

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

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

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

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

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...



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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