The onset of tensile residual stresses in grinding of hardened steels

Residual stress distributions produced by grinding with various conditions have been measured for four steels BS En9, BS En31, AISI M2 and CPM 10V (a trade name for AISI A11), using neutron and X-ray diffraction techniques. The residual stress profiles were found to have the maximum stress magnitude on the surface, which could be compressive or tensile depending on the grinding conditions used. By using experimentally-determined data for the maximum grinding surface temperature, it was found that tensile residual stresses are generated after the grinding temperature reaches a critical level, which was 200 °C for both En9 and En31; 500 °C for M2; and 600 °C for CPM 10V. For all these steels, tensile stresses can result under grinding conditions at which damage such as overtempering or rehardening does not occur. The softening behaviour during overtempering was characterized by means of the Hollomon-Jaffe time-temperature parameter. It was concluded that among the three primary origins of residual grinding stresses-mechanical deformation (Hertzian load), thermally-induced plastic deformation, and phase transformations -it is the mechanical deformation and thermally-induced plastic deformation effects that cause the onset of tensile residual stresses when grinding these quenched and tempered steels.