What are the final finishing operations?
- surface hardening
- Heat treatment
- Deformation processing
In this lecture we will deal salient features of surface hardening. The next lectures deal with other methods.
Surface hardening
Surface hardening methods are used to harden the surface. The different methods are:
1. Thermo chemical surface hardening
2. Thermal surface hardening
3. Coating
In thermo-chemical surface hardening composition of steel surface is altered and then steel is heat treated with or without quenching.
Austenitic type of steels are hardened by carburizing, carbonitriding or cyaniding treatment. In all these methods non-metallic elements C either singly or in combination with nitrogen are diffused into the austenitic phase.
In ferrite type of steels both nitriding and nitro- carburizing treatments are performed. Carbon or Carbon + nitrogen are diffused in the ferrite phase.
In thermal surface hardening, heat alone is used to alter the microstructure without altering the composition. Steel can be heated either by induction of laser or by electron beam or by flame.
Induction heating involves heating the component by induced eddy current to a temperature at which austenite forms rapidly. Metal surface is heated by using special inductors using an alternating current of frequencies between 50 hertz to 1000 hertz. depending on the required depth of hardening. Steel is then quenched for martensite transformation |
