The Rockwell Superficial hardness test method consists of indenting the
test material with a diamond cone (N scale) or hardened steel ball
indenter. The indenter is forced into the test material under a
preliminary minor load F0 (Fig. 1A) usually 3 kgf. When
equilibrium has been reached, an indicating device that follows the
movements of the indenter and so responds to changes in depth of
penetration of the indenter is set to a datum position. While the
preliminary minor load is still applied an additional major load, is
applied with resulting increase in penetration (Fig. 1B). When
equilibrium has again been reach, the additional major load is removed
but the preliminary minor load is still maintained. Removal of the
additional major load allows a partial recovery, so reducing the depth
of penetration (Fig. 1C). The permanent increase in depth of
penetration, e, resulting from the application and removal of
the additional major load is used to calculate the Rockwell Superficial
hardness number.
HR = E - e
F0 = preliminary minor load in kgf F1 = additional major load in kgf F = total load in kgf e = permanent increase in depth of penetration due to major load
F1, measured in units of 0.001 mm E = a constant of 100 units for diamond and ball indenters
HR = Rockwell hardness number D = diameter of steel ball
