LUN 155のクリープ・ラプチャー伸びに及ぼす炭化物析出の影響 : 高温強度特集号
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概要
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It has been established that there is a certain relation between the notch sensitivity and the elongation or ductility in the creep rupture test on austenitic steel, and that the notch sensitivity increases, in general, as ductilities decreases. This relation, however, is not simple, for the carbide precipitation phenomenon does not simply affect the notch sensitivity. Kanamori and Oda showed that the creep rupture elongation of the solution-treated or insufficiently aged austenitic steel decreased under a certain rage of stress, and that marked intergranular corrosion occurred by etching in such a specimen ruptured with low elongation. The elongation, however, does not always decreases even if marked intergranular corrosion occurs. In this investigation we intend to throw light on the mechanism in which a decrease in elongation is inevitably attended with marked intergranular carrosion. The main points of this paper are as follows: (1) Marked intergranular corrosion was due to the existence of the chromium depleted zone which was caused by the diffusion of chromium to the grain boundary during creep. The concentration distribution in the depleted zone was determined by measuring the distribution of anodic equilibrium potential, and it was found the minimum concentration was less than 1 pct. approximately. (2) The Kirkendall effect that could be expected from the diffusion of chromium atoms was verified by the calculation based upon the measured distribution of chromium concentration. (3) the excess vacancy concentration ratio was calculated and the value of more than 10^2 was obtained for LCN 155 aged for 5 h at 700℃, and it was shown that the value of about 10^2 was to be sustained for a longer period of time.(4) the above excess vacancies may promote the formation and growth of voids in the vicinity of grain boundary under a certain stress or above. These voids will, then, lead to cracks and finally to rupture. Therefore, one may expect this mechanism causes the decrease in elongation of solution-treated or insufficiently aged austenitic steels. This paper will show that various creep rupture phenomena on the austentic steel can be accounted for by this theory.
- 社団法人日本材料学会の論文
- 1962-03-15