Residual Stresses Induced by Surface Working and Their Improvement by Emery Paper Polishing

In many of machine parts and structural components, materials surface would be worked. In this study, residual stresses on the surfaces were measured by X-ray diffraction method, and effects of surface working on the residual stresses were examined. In case of lathe machining of type 304 stainless steel bar, the residual stresses in circumferential directions are tensile, and those in axial directions are almost compressive. Highly tensile residual stresses in the circumferential directions were improved by emery paper polishing. 10 to 20 times of polishing changes high tensile residual stresses to compressive residual stresses. In the case of shot peening on a type 304 stainless steel plate, the compressive residual stress inside is several hundred MPa lower than that on the surface. By applying the emery paper polishing to the shot peened surface 10 or 20 times, the residual stress on the surface is improved to &minus
700 MPa. While fatigue strength at 288 &deg
C in the air of the shot peened material is 30 MPa higher than solution heat treated and electro-polished material, the fatigue strength of the shot peened and followed by emery paper polished material is 60 MPa higher. Thus, the emery paper polishing is simple and a very effective process for improvement of the residual stresses.