高強度鋼の遅れ破壊における脆性破壊条件について

抄録

The fracture process of cathodically charged, quenched and tempered SNCM439 steel specimens was studied from the viewpoint of fractographic analysis with a special emphasis on the characteristics of the morphology of crack propagation and the mechanistic condition of delayed fracture. The fracture initiated at an inclusion in the specimen, and the fracture appearance was initially radial quasi-cleavage, followed by quasi-cleavage, intergranular and microvoid coalescence. The brittle fracture condition of the delayed fracture could be formulated on the basis of Griffith's fracture criterion in the following. σ·d^0.44=2440 (σ: stress [MPa], d: depth of the crack origin [μm]) The life of the delayed fracture corresponded to hydrogen diffusion in order to attain the critical condition for crack initiation around the possible origin of inclusion.