ステンレス鋼溶接金属の熱・負荷履歴によるミクロ組織変化(<特集>高温強度)

概要

論文の詳細を見る
As a fundamental study of developing a long term creep-fatigue evaluation method of weldment of stainless steel that incorporates the degradation of weld metal, the authors investigated the mechanism of micro damage in the structure of 308 and 316 type weld metals that had been subjected to thermal and mechanical histories using transmission electron micrography. The results obtained are as followes. (1) M_<23>C_6 and Laves phase that precipitated in δ-ferrite phase were transformed into σ phase that is more stable under high temperatures after long time heating. (2) While δ-ferrite phase remained in the microstructure at 550℃ even after supplying alloying elements to precipitates and changing to Fe-rich composition, at above 600℃ it disappeared after transforming completely to σ phase or austenite phase. (3) The rate of dissolution of δ-ferrite phase under cyclic stresses for fatigue or creep-fatigue failure was higher than that under constant stress for creep failure, and was accelerated by 10 to 100 times compared with that under no load. (4) The dissolution of δ-ferrite phase led to initiation and propagation of cracks at the interfaces of σ phase and remaining δ-ferrite phase or austenite phase by making a difference of mechanical properties between the phases.
1997-01-15