Quenching Tool Steel

: The Working Of Steel

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


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.