Case hardening depth

The case hardening depth tells you how deep the surface layer of a component has actually become hard after hardening. When welding, you have to be careful: if you weld into the hardened zone, you destroy the hardening through heat. The material becomes soft there, and the hardness is gone. If you want to harden again after welding, you need to know how deep the layer went before, otherwise you won't get uniform hardness. So: check beforehand what kind of steel it is and how deep the hardening reaches, then you can decide whether you need to preheat or post-weld heat treat.