Why do materials need to have hardness?

If metal parts come into contact with other hard or adhesive materials, they are expected to have a certain degree of hardness because metal's high hardness makes it more resistant to wear.

However, materials with high hardness are also more brittle than softer materials, so it is not necessarily suitable to fully harden the entire workpiece from the exterior to the interior.

In this case, surface hardening can be used to produce a workpiece that is tougher on the inside (because the softer inner layer can absorb stress without cracking) and harder on the surface, providing considerable corrosion resistance.

Commonly and widely utilized heat treatments include processes such as quenching, tempering, carburizing, induction hardening, tempering, and annealing, which allow metals to produce materials with excellent structural performance.