Surface Hardening
Surface hardening hardens only the outer layer or selected areas of a part, giving wear resistance where needed while the core stays tough. Methods include induction hardening, flame hardening, carburising and nitriding.
What it is
Thermal methods such as induction and flame hardening rapidly heat the surface of medium-carbon steel and quench it. Diffusion methods such as carburising and nitriding change the surface chemistry to create a hard case.
The method is chosen by material, part size, hardness depth and whether distortion must be minimal.
Typical applications
- Shaft journals and bearing seats
- Gear teeth and splines
- Rails, guideways and slides
- Cams and rollers
- Large wear surfaces
Suitable materials
- Medium-carbon steels (EN8, EN9, C45) for induction/flame
- Alloy steels (EN19, EN24)
- Case-hardening steels (carburising)
- Nitriding steels (EN41B)
Points to consider
- Choose the method by steel grade and required depth.
- Localised hardening keeps other areas machinable.
- Nitriding gives the least distortion.
- Specify hardness pattern and depth on the drawing.
Frequently asked questions
What is the difference between surface hardening and through hardening?
Surface hardening hardens only the outer layer, keeping a tough core; through hardening hardens the whole section.
Which surface hardening method is best?
Induction for localised, fast hardening of medium-carbon steels; carburising for deep cases on low-carbon steels; nitriding for minimal distortion.
Can only part of a component be hardened?
Yes. Induction and flame hardening can harden selected areas only.