In materials engineering and metallurgy, hot hardness or red hardness (when a metal glows a dull red from the heat) corresponds to

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

of a

material A material is a matter, substance or mixture of substances that constitutes an Physical object, object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical property, physical ...

at high temperatures. As the temperature of the 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 An alloy is a mixture of chemical elements of which in most cases at least one is a metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have properties ...

References

Hardness tests Solid mechanics {{classicalmechanics-stub