Residual stress and fatigue strength after transformation hardening and various strain hardening

Abstract

Induction surface hardening of surfaces creates very desirable compressive residual stresses. A major difficulty in induction surface hardening is, however, to ensure a very slight/slow variation in hardness and the existence of compressive residual stresses in transition areas to the hardness of the core material. Additional grinding of induction surface hardened surface deteriorates the stress state in the surface layer, since grinding has always induced tensile residual stresses. Among the strain hardening processes only to heavy shot peening and heavy shot peening followed by light peening processing can be recommended since they provide reproductible results of the residual-stress variation, i.e., fatigue strength. Surface hardening by cold deformation thus turned out very suitable since it provides the desired hardness and residual-stress profiles of the thin surface layer.