Mechanical properties of ion-nitrided steel are studied for SCM4 and SCM22. Flat narrow plates ion-nitrided on one side are used as specimens and they were treated under various nitriding conditions by changing nitriding temperature and time.
The deflection of the specimens is measured in various elevated temperature and the coefficient of thermal expansion is calculated from curvature-temperature relation. Young's modulus of nitrided layer are obtained from the deflection test of a cantilever ser-up. For the data analysis, the specimens are assumed to be composed of two homogeneous layers.
It is found that Young's modulus of the diffusion layer of nitrided steel shows an increase of 20 to 50 % over that of non-nitrided steel. The coefficient of thermal expansion of diffusion layer has been increased by 1.5 to 2.5 %.
Using the results, residual stresses are computed. In room temperature, the peak compressive residual stress, which occurs in the diffusion layer, is found to be about 44 kg/㎟.
