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

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

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

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

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

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

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

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

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

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

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

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

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

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

Lathe And Planer Tools
TO FORGE.--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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