Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.
Hardness is dependent on ductility, elasticity, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.
Metals undergo different processes before being converted into a final product. Each process can have an effect on the mechanical and chemical attributes of metal. For example, the strength of steel is determined by its chemical composition and micro structural transformations. Macroscopic variables are used to control the final product quality. Hardness is one characteristic of metal that can be easily monitored.