Cr-Mo-V 鍛鋼のクリープキャビティの生成・成長挙動と破断延性に影響する冶金的因子

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In order to clarify metallurgical factors affecting creep rupture ductility of Cr-Mo-V steel, creep tests for the specimens with actual rotor materials differing in quenching temperature and also in impurity content were carried out at 550℃-210MPa and 575℃-160MPa. Creep properties were compared and also nucleation-growth behavior of creep cavities during creep and rupture ductility were investigated. The obtained results are as follows : (1) The high-purity materials have the best rupture ductility among as-heat-treated materials quenched at 940-970℃ and show rupture elongation higher than 10%. Other low-purity materials show rupture elongation lower than 10%. The decrease in ductility corresponds to the increase in impurity content. (2) The rupture ductility of the re-heat-treated rotor materilas quenched at 1025℃ decreases greatly to less than half the value of as-heat-treated materials in (1). The decrease in ductility corresponds to grain growth of prior-austenite grains. (3) The metallurgical factors that affect rupture ductility remarkably are (a) the pre-austenite grain size corresponding to rotor quenching temperature, and (b) the amounts of impurity, and the smaller (a) is and the lower (b) is, the higher is the rupture ductility. (4) Consequently a parameter is proposed so that rupture ductility of Cr-Mo-V steel can be obtained, combining both the above-mentioned (a) and (b) factors. This creep ductility parameter, defined as the Y-factor, is expressed as : Y=0.34[P]+3.8[S]+8.4[Sn]+12.0[As]+5.6[Sb]+2.6G.S. where [P], [S], [Sn], [As], and [Sb] are the contents of respective elements (wt.%), and G.S. is grain size (mm). Rotor materials of Y&g;t0.5 show notch-sensitive behavior, and so the Y-factor is effective in judging the notch-sensitive/notch-insensitive property.
社団法人日本鉄鋼協会の論文
1992-10-01

Cr-Mo-V 鍛鋼のクリープキャビティの生成・成長挙動と破断延性に影響する冶金的因子

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