Hardness

The Vickers method is based on indenting a polished carbide surface with a diamond pyramid. The hardness is inversely proportional to the size of impression

Hardness is normally determined using the Vickers indentation method according to EN 23 878 (ISO 3878). This method allows a range of loads but HV30 is preferred. The force of a 30 kg weight, 294 N, is used to create a measurable indentation with minimal cracking at the corners. For the hardest grades, the size of the impression and cracking contribute to reduced precision and accuracy.

Sometimes other methods are used such as Rockwell A (ISO 3738). The Rockwell method is similar to the Vickers method but is based on the use of a diamond cone and the depth of the indendation is used as a measure of the hardness. There is no theoretical basis for conversion between the two methods. Instead, actual determination must be used for comparisons.
Hardness increases with decreasing binder content and decreasing grain size.

The hardness range extends roughly from that of tool steels, 700, up to 2200 HV30. Hardness decreases with increasing temperature due to increasing plasticity.