Rockwell Hardness - ASTM D785
Rockwell hardness is a measure of the indentation resistance of a material. Testing is performed by first forcing a steel ball indentor into the surface of a material using a specified minor load. The load is then increased to a specified major load and then decreased back to the original minor load. Rockwell hardness is a measure of the net increase in depth of the indentor. Each Rockwell scale division represents a 0.002 mm (0.00008 in) penetration of the indentor.
|Scale||Minor Load (kg)||Major Load (kg)||Indentor Diameter (in)||Indentor Diameter (mm)|
Rockwell hardness is calculated by subtracting the penetration divided by the scale division from 130. For example, if the indentor has a net depth increase of 0.12mm, the Rockwell hardness is
Hardness = 130 - (penetration / scale division)
Hardness = 130 - (0.12mm / 0.002mm) = 70
Shown below is a hardness comparison chart. Hardness is a complex material property influenced by a variety of factors. Any conversions using this chart will be a rough estimate and should not
be considered an exact conversion.