Influence of process parameters for induction hardening on residual stresses

Fatigue behaviour of induction hardened parts is largely dependent on the correct combination of hardening depth and the magnitude and distribution of residual compressive stresses in the surface layer. The objective of this work was to study experimentally the residual stresses at the surface layer of induction hardened cylindrical specimens. Two microstructures, quenched-tempered and normalised were investigated. The process parameters of induction hardening were varied to give a constant hardness penetration depth. The residual stresses were measured using the X-ray diffraction method. The investigated induction hardened samples showed a constant biaxial residual stress-state at the surface. The directions of the principal stresses deviated slightly from the defined circumferential and longitudinal directions. However, the shear stresses at the surface were of a small magnitude. This experimental investigation showed that the process parameters of induction hardening influence the residual stress-state of hardened parts to a great extent.