微粒子ピーニングを施したSCM435H鋼の残留応力と疲労特性に及ぼす基材および投射粒子硬さの影響

概要

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In order to determine the fine particle peening (FPP) treatment conditions that generate a high compressive residual stress, the effect of specimen hardness and shot particle hardness on residual stress was investigated. The results showed that the higher the generated specimen hardness, the higher the compressive residual stress at the surface. Additionally, in the case of high hardness specimens, the shot particle hardness affected the residual stress. This was because shot particle was deformed during the FPP treatment process. Furthermore, in order to clarify the effect of FPP treatment on fatigue properties of SCM435H steel with different hardnesses, fatigue tests were performed at room temperature using a rotational bending fatigue testing machine. In the case of higher hardness substrate, the fatigue strength was dominantly increased by FPP treatment ; however, in the case of lower hardness substrate, the increasing level was very small. This was because compressive residual stress generated on the surface of higher hardness specimen was much larger than that generated on lower hardness specimen and the higher compressive residual stress remained on the surface of higher hardness specimen under the application of cyclic loading. These results indicate that the FPP treatment is highly significant to improve the fatigue strength for higher hardness substrate.