再熱割れにおよぼす炭化物の影響について : Cr-Mo 鋼の再熱割れに関する研究第 3 報

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This study devoted to the influences of chromium and molybdenum on the reheat cracking sensitivity of Cr-Mo steels from view points of their carbide phases. X-ray analyses, electron microscopic observations and hardness measurements were carried out on the synthetic 12 Cr-Mo steels in order to clarify the carbide reactions and the change of hardness accompanied by carbide precipitation during tempering at 500 to 700℃ for 1 to 100 hours. The results are summarized as follows. 1) Molybdenum carbide M_2C precipitates in such the Cr-Mo steels of relatively lower chromium content and of higher carcking sensitivity. Precipitation of M_2C causes the secondary hardening and the delay of softening both at 550℃ which were revealed by the measurement at room temperature and at high temperature, respectively. Such temperature corresponds to that of crack initiation. Therefore, M_2C prevents the softening of grain interior and promotes to cause cracking along the grain boundary (prior-austenite grain boundary). 2) Chromium carbide M_7C_3 precipitates in such the Cr-Mo steels of higher chromium content and of lower cracking sensitivity. Precipitation of M_7C_3 also causes the secondary hardening, but the hardening temperature is about 500℃ and is lower than that of crack initiation. 3) It has been informed that carbide would precipitate along the grain boundary and cause the brittleness. But such the precipitation along the grain boundary was recognized in this study not only in the steels of higher cracking sensitivity but also in those of lower cracking sensitivity. Therefore it is concluded that grain boundary precipitation of carbide does not cause the grain boundary brittleness.
社団法人溶接学会の論文
1983-02-05

再熱割れにおよぼす炭化物の影響について : Cr-Mo 鋼の再熱割れに関する研究第 3 報

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