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Steel Making

Hardening
Steel is hardened by quenching from above the upper critical....

High Speed Steel
For centuries the secret art of making tool steel was handed ...

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

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

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

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

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

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Corrosion
This steel like any other steel when distorted by cold worki...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

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...

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

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

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...



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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