V, Nb 添加 9% Cr フェライト系耐熱鋼のクリープ破断強度と靱性におよぼす Mo 量の影響

概要

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The effect of molybdenum content on creep-rupture properties and room-temperature toughness of high chromium ferritic heat resisting steels was investigated. Molybdenum content was varied from 1 to 2 wt%. In order to obtain 9Cr-Mo-V-Nb ferritic steels with both high creep-rupture strength and superior toughness, the amount of delta ferrite was controlled below 25%, and the optimum tempering condition and mechanical properties after simulated welding have been investigated. The influence of molybdenum content on creep-rupture strength and Charpy absorbed energy was investigated with respect to the ratio of delta ferrite to tempered martensite, the precipitates, and the microstructures. Charpy absorbed energy of the 0.05C-9Cr-1Mo-0.15V-0.05Nb steel tempered at 800℃ and then heated at 600∿650℃ for 10^4 h was as high as 20∿30 kgf-m. By contrast, Charpy absorbed energy of 0.05C-9Cr-2Mo-0.15V-0.05Nb steel was reduced to about 4 kgf-m after heating at 600∿650℃ for 10^4 h. It is considered that the steel of 1Mo shows superior toughness because of its low carbon content and a single phase of martensite. It was concluded that combination of superior creep-rupture strength and toughness can be obtained by optimum heat treatment for the 9Cr-1Mo-V-Nb steel containing 0.05 wt%C.
社団法人日本鉄鋼協会の論文
1988-10-01