The origins of residual stresses in ground surfaces were studied to investigate whether a transitional temperature exists between compressive and tensile residual stresses in ground surfaces. It was found that thermal stresses generated in the grinding process were the primary cause of tensile residual stresses. Effects of the differences between triangular and rectangular heat sources are insignificant. Thermally induced stresses are strongly dependent on workpiece material properties. Yield stress, which is dependent on temperature and heat treatment, is one of the most important factors. A method is described to characterise the onset temperature for tensile residual stress. Some critical transitional temperatures are given for different steels.