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In situ crystallographic observation of dynamic ferrite transformation evolution during hot deformation of low alloy steels

低合金鋼の熱間加工中における動的フェライト変態挙動についてのその場結晶観察

徐 平光  ; 友田 陽*; Koo, M.*; 米村 雅雄*; 鈴木 徹也*; Paradowska, A.*; Zhang, S. Y.*; 足立 吉隆*

Xu, P. G.; Tomota, Yo*; Koo, M.*; Yonemura, Masao*; Suzuki, Tetsuya*; Paradowska, A.*; Zhang, S. Y.*; Adachi, Yoshitaka*

動的フェライト変態は鋼組織の超微細化を図る上で重要な手法として注目されている。変態前の母相を加工して格子欠陥密度を増加させ、核生成の優先サイトを増大させると、核生成速度が大きくなり、変態生成物が微細化されることは既に知られている。しかし、加工が変態中に行われる場合、不均一変形が顕著となるためフェライト変態に及ぼす影響が複雑化し、未だ微細化のメカニズムについては不明な点が残されている。本研究は、試料中の特定部位における複数の相の量や内部応力変化を同時にしかも連続的に観察が可能な飛行時間法中性子回折により、低合金鋼の熱間加工中における動的フェライト変態挙動を調査、検討した。

Deformation induced ferrite transformation related to microstructure refinement has attracted wide attention. However, the in situ crystallographic evolution studies have not been carried out. In this paper, the deformation induced ferrite transformation at two different strain rates was carried out to compare that during isothermal holding without deformation and the effects of hot deformation and strain rate on the dynamic transformation evolution was investigated. The neutron diffraction experiments confirmed that the deformation induced ferrite transformations could appear not only in the austenite region, but also in the austenite-ferrite dual phase region. It was found that the low temperature deformation was more effective than the high temperature to promote the ferrite transformation until a critical strain, and then the accelerating effect was weakened due to the increment of austenite carbon concentration and the appearance of ferrite dynamic recrystallization.

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