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Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

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

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

Manganese
Manganese adds considerably to the tensile strength of steel,...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

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

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

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

The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

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

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

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



Quenching Tool Steel






Category: HARDENING CARBON STEEL FOR TOOLS

To secure proper hardness, the cooling of quenching of steel is
as important as its heating. Quenching baths vary in nature, there
being a large number of ways to cool a piece of steel in contrast
to the comparatively few ways of heating it.

Plain water, brine and oil are the three most common quenching
materials. Of these three the brine will give the most hardness,
and plain water and oil come next. The colder that any of these
baths is when the piece is put into it the harder will be the steel;
but this does not mean that it is a good plan to dip the heated
steel into a tank of ice water, for the shock would be so great
that the bar would probably fly to pieces. In fact, the quenching
bath must be sometimes heated a bit to take off the edge of the
shock.

Brine solutions will work uniformly, or give the same degree of
hardness, until they reach a temperature of 150 deg.F. above which
their grip relaxes and the metals quenched in them become softer.
Plain water holds its grip up to a temperature of approximately
100 deg.F.; but oil baths, which are used to secure a slower rate of
cooling, may be used up to 500 deg. or more. A compromise is sometimes
effected by using a bath consisting of an inch or two of oil floating
on the surface of water. As the hot steel passes through the oil,
the shock is not as severe as if it were to be thrust directly
into the water; and in addition, oil adheres to the tool and keeps
the water from direct contact with the metal.

The old idea that mercury will harden steel more than any other
quenching material has been exploded. A bath consisting of melted
cyanide of potassium is useful for heating fine engraved dies and
other articles that are required to come out free from scale. One
must always be careful to provide a hood or exhaust system to get
rid of the deadly fumes coming from the cyanide pot.

The one main thing to remember in hardening tool steel is to quench
on a rising heat. This does not mean a rapid heating as a slow
increase in temperature is much better in every way.





Next: The Theory Of Tempering

Previous: Double Annealing



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