表面硬化処理したSCM420H鋼の水素添加による遅れ破壊寿命特性評価

抄録

The delayed fracture properties were evaluated by conducting constant load test using notched round bar specimens with different stress concentration factor (K_t) of gas carburized JIS SCM420H. The amount of hydrogen added to specimens after gas carburizing were almost same regardless of K_t value. The testing method employed was a weight-lever method with constant load application, and the displacement of the specimen during the test was measured with a laser displacement meter. Both the deformation rate and the fracture time did not depend on K_t, but the delayed fracture limit decreased as K_t increased. Based on the morphology of fracture surface analysis and the distribution of hydrostatic stress (σ_m), this study was conducted in two cases for the carburizing region near the notch where hydrogen accumulated and for the internal non-carburizing region obtaining the averaged σ_m in each area, σ_mC and σ_mNC. The presented stresses could evaluate the delayed fracture limit and the fracture time.