Case hardening and Surface hardening:
In actual service a metal part is never subjected to uniform stresses through out the section. It the surface which have the nicks scratches, tool marks etc. rotating shafts have maximum at the surface. Wear seizure and galling also occur at the surface and produce stress raisers. Hence load-bearing components require better properties at the surface than the interior (core). Core should be relatively soft to provide resistance to brittle failure of the component and it should be tough enough to resist impact loads while surface is hard and wear resistant.
Case hardening may be defined as the process of hardening a steel in such a manner that the surface layer know as the case is harder than the remaining material known as core. This can be achieved by two methods.
1. By changing the chemical combination of the surface of steel which is called as case hardening
 |
| Image from http://image.slidesharecdn.com/surfacetreatments-150304101614-conversion-gate01/95/surface-treatments-6-638.jpg?cb=1425485905 |
2. With out changing the chemical combination at the surface which is called as surface hardening
1.Case hardening:
In this method the surface of the steel to be hardened is induced with carbon and nitrogen by various methods. The chemical composition of steel at the surface is changed by the diffusion of induced carbon or nitrogen or other elements. Different types of case hardening methods are
a) Carburizing
b) Cyaniding and
c) Nitriding.
2.Surface hardening:-
In this process no chemical changes takes place. Large sized objects are subjected to heating followed by rapid cooling. The process is classified according to various methods of heating the steel. They are
a) Flame hardening
b) Induction hardening
c) Electron beam hardening &
d) Laser hardening
COMMENTS