On Fish-eye Fracture Of Radical Nitrided Die Steel.
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N. Kawagoishi, K. Morino, K. Fukada, Q. Chen & E. Kondo
On fish-eye fracture of radical nitrided die steel N. Kawagoishi% K. Morino^, K. Fukada^ Q. Chen^ & E. Kondo^ ^ Faculty of Engineering, Kagoshima University, Japan. ATogyo Co., Abstract In order to investigate the effect of radical nitriding on fatigue strength of die steel, rotating bending fatigue tests were carried out at room temperature and 450°C. Fatigue strength was increased by nitriding at both temperatures due to surface hardening and compressive residual stress generated in the surface region. Comparing with the non-nitrided steel in which the fracture origin was at surface slip bands or surface defects, the nitrided steel fractured with the origin at inner inclusions at both temperatures. In the nitrided steel, cracks initiated from inclusions in the non-hardened layer or near the boundary between hardened and non-hardened layers. The difference in fatigue strength between the two temperatures was discussed based on the feature offish-eye. 1 Introd