10.5 PREHEATING

The simplest means to determine hardenability is to measure the depth to
which a piece of steel hardens during quenching from an elevated
temperature. There are several standardized tests for determining
hardenability. A typical test of hardenability is called a Jominy Bar. In this test,
a round bar is heated to a pre-determined elevated temperature until heated
evenly through the cross section. The specimen then subjected to rapid
quenching by spraying water against the bottom end of the round bar. The
hardness of the test specimen is measured as a function of distance away
from the surface being quenched. Steels that obtain high hardness well
away from the quenched surface are considered to have high hardenability.
Conversely, steels that do not harden well away from the quenched surface
are considered to have low hardenability.