Hardening depth in surface hardening is determined by heating depth as hardness increases only in austenitized regions.

For surface hardening, induction or flame hardening is used to quickly austenitize the surface layer at the desired depth and then cool down.

In case of surface hardening, core properties or thermal treatment is not changed.

After surface austenitization and cooling, low temperature tempering is made, which does not affect core tempering as it was done in higher temperature.