Papers by Author: Katsuhiro Seki

Abstract: The fine-grained rolling steels NFG600 and the conventional usual rolling steels SM490 were processed by sand paper polishing and mechanical grinding to compare the residual stress generated after processing. The average grain size of NFG600 and SM490 is 3 μm and 15μm respectively. Therefore improvement of mechanical properties for such fine-grained steels is expected, it is important to understand the residual stress state of new fine-grained materials with processing. In this study, multi axial stresses of two kinds of specimens after polishing and grinding were measured by three kinds of analysis methods including cos-ψ method. As a result, as for σ33, the stress of NFG was compression, though that of SM490 was tension.

Abstract: Recently, the study of fine grain steels aimed at achieving into high strength has become active. Welding is one of the most effective methods for connecting the structural components. For those cases, the negative influence of any residual tensile stress induced during the welding process must be considered. It has been proved that shot-peening can effectively solve this problem. However, the influence of the Shot-Peening process on fine grain steels after welding has only been briefly reported up to now. In this study, fine grain steels were used, and specimens were obtained after heat treatment. Residual stress distributions near the surface of the fine grain steel after shot-peening were measured by X-ray diffraction technology. Moreover, the effect of hardness on distributions near the shot-peened surface was also estimated.