Quality characteristics for flake graphite cast iron.
Relative hardness is the quotient of actually achieved hardness HB (measured with a 30 mm standard test bar, see Brinell hardness test) and the standard hardness calculated from the tensile strength which is calculated from Eq. 1 as follows:
According to Eq. 2, the relative hardness is directly calculated from the measured Brinell hardness HB and the tensile strength Rm as follows:
In general, cast iron with low relative hardness and a high degree of normality (q. v.) should be pursued.
Tensile strength/Hardness quotient