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Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

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

Drop Forging Dies
The kind of steel used in the die of course influences the he...

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

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

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

Quenching
It is considered good practice to quench alloy steels from th...

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

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

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

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

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

The Electric Process
The fourth method of manufacturing steel is by the electric f...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...



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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