26 Hardness

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

In metallurgy, hardness is the characteristic of a solid material expressing its resistance to permanent deformation. Hard materials are tool steels and diamonds.

In general, different materials differ in their hardness; for example, hard metals such as titanium and beryllium are harder than soft metals such as sodium and metallic tin, or wood and common plastics. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, hardness can be measured in different ways, such as scratch hardness, indentation hardness, and rebound hardness.  One very common test for hardness used in machine and metalworking shops is the Rockwell C scale testing instrument.

Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter.

The next section is all about the testing for hardness of metals.

Derived from Hardness – Wikipedia retrieved 18 January 2024; and The Virtual Machine Shop:

• http://www.jjjtrain.com/vms/eng_metallurgy/eng_metallurgy_05.html
• http://www.jjjtrain.com/vms/eng_heat_treat/eng_heat_treat_07.html,

retrieved from the Wayback Machine internet archive 17 January 2024.