Hardness penetration capacity

Hardness penetration capacity is characterized by the hardnesspenetration depth achieved in hardening and the thus obtained hardness profile along the cross section.

The hardness penetration capacity of a material is increased by alloying elements, which extend the transformation duration and thus lower the critical cooling rates. Important alloying elements that are chiefly used in heat-treated steel that requires appropriate through hardening are chromium, molybdenum, and nickel. The greater the wall thickness of a workpiece and the lower the cooling rate in the core area, the higher the quantity of alloying elements required.

Additional references:

Case hardening
Electron beam hardening
Torch hardening
Induction hardening
Jominy test
Laser hardening