As the temperature of material increases, hardness decreases and at some point a drastic change in hardness occurs. The hardness at this point is termed the hot or red hardness of that material. Such changes can be seen in materials such as heat treated alloys.

Does temperature affect hardness?

The hardness of steel is lower after tempered at high temperature, which reduces the resistance to plastic deformation, such as cutting, and chipping.

Does heat increase hardness?

Hardening. The most common heat treatment process of all, hardening is used to increase the hardness of a metal. In some cases, only the surface may be hardened. A work piece is hardened by heating it to the specified temperature, then cooling it rapidly by submerging it into a cooling medium.