破壊領域観察にもとづく鉄鋼の水素脆化機構に関する研究(第 3 報) : ベイナイト組織と水素脆化破面形態

概要

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The three-point bending strength for HT-80 of bainitic structure obtained by isothermal heat treatment with hydrogen and hydrogen free were investigated in relation to the prior austenite grain size and ferrite lath size. The fracture surface and unit facet size were observed by two stage replica method and Electron Scanning Microscope. The fracture stress of specimen with hydrogen depended on prior austenite grain size and was lower than that of hydrogen free specimen. Those fracture surfaces were observed remarkably secondary cracks along the boundary of ferrite lath and interface between matrix and carbide. The unit fracture facet for hydrogen embrittlement, therefore, was defined the zone between secondary cracks. The unit facet size for hydrogen embrittlement was smaller 1/2∿1/3 than unit facet size for cleavage fracture of hydrogen free specimen at -196℃ tested. The fracture morphologies of hydrogen embrittlement at 25℃ tested were different from hydrogen free specimen at -196℃ tested. The fracture morphologies of specimen with hydrogen were observed the QC_<HE>, not observed the intergranular fracture. The fracture morphology of hydrogen embrittlement was influenced by hydrogen diffusion and accumulation in ferrite lath boundary.
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1975-12-05