鋭敏化した 17Cr-12.5Ni-2Mo-0.05Nb-0.2N 鋼の極低温での機械的性質に及ぼすりんとボロンの影響

概要

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This research was undertaken to clarify effect of phosphorus and boron on cryogenic mechanical properties of a sensitized 17Cr-12.5Ni-2Mo-0.05Nb-0.2N steel. The steel was sensitized at 923∿993K for 270∿720ks and was investigated at low temperature, especially at 4K. An addition of either phosphorus or boron affected precipitation at grain boundaries during sensitization. Phosphorous increased the grain boundary precipitates. Boron suppressed the phosphorous effect. Both elements, however, did not show clear effect on tensile properties at 4K of the sensitized steel. In a high phosphorus alloy, Fe_2Mo other than CrNbN, M_<23>C_6, Cr_2N and Nb (CN) precipitated and led to intergranular fracture. Therefore a deterioration of fracture toughness at 4K for sensitized steel became much evident with an increase in phosphorous content. On the otherhand, boron addition prevented intergranular failure and resulted in high fracture toughness for the sensitized one. Segregated phosphorus atoms seem to promote nucleation of precipitation and weaken and interfacial binding of precipitates, especially Fe_2Mo. On this assumption, effect of phosphorus and boron addition on mechanical properties at 4K could be explained.
社団法人日本鉄鋼協会の論文
1989-12-01