Distortion and residual stress measurements of induction hardened AISI 4340 discs

10 Induction hardened discs with two initial hardness levels were used for exploring the influences of the variation of initial hardness as well as induction hardening (IH) recipes on the heat treatment distortions and hardening depth. The results show that for the same initial hardness, the larger the energy input, the higher the distortion size as well as the hardening depth. For a given induction hardening recipe, the increase in initial hardness leads to a deeper hardening depth but a smaller distortion. One disc was selected for the residual stress investigation in three orthogonal directions by neutron diffraction (ND). The corresponding stress-free lattice spacing d₀ was measured from the same material using both ND and X-ray diffraction (XRD) methods. The ND results show that the variation of d₀ in the hardened layer is significant and should be taken into account for stress calculation. However, regarding the core region, the d₀ value measured by XRD is more reliable. Accordingly, a combination of the ND-measured d₀ profiles in the hardened layer and the XRD-measured d₀ value in the core was adopted for the determination of residual stress distributions. - Highlights: • Residual stress profiles of induction hardened 4340 steel were obtained using neutron diffraction. • Effects of induction hardening parameters on hardening depth and distortions were examined. • Effects of initial hardness on hardening depth and distortions were examined. • d₀ Depth distribution was investigated by neutron diffraction technique. • The variation in d₀ can significantly affect the residual stress results