Hardness measures the resistance of metals to plastic deformation by indentation. The table below lists the various hardness test, the indentor type, and the method of measurement. Carbon steels and low Alloy steels show a good correlation between hardness and ultimate tensile strength. Hardness is a good indication
of consistency and when correlated with the composition and heat treatment of cast ferrous and nonferrous Alloys it is a handy measure of the control and acceptability of castings. The low cost and simplicity of hardness tests leads to their use for a number of quality control applications.

Hardness Testing

Test	Indentor	Measurement
Brinell hardness	¼” steel of tungsten carbide ball	Indentation diameter
ASTM E10 Rockwell Hardness	1/16” or 1/8” steel ball or	Penetration depth
Diamond pyramid	conical diamond indentor	Ave. indentation diagonals
Vickers Hardness	diamond pyramid	Ave. indentation diagonals
Knoop Hardness	elongated diamond pyramid	Ave. indentation diagonals

                  

Source: Investment casting Institute Handbook 1997 Edition