Dynamic ferrite transformation behavior during hot deformation of low alloy steels studied by neutron diffraction

中性子回折による低合金鋼熱間加工中の動的フェライト変態挙動

徐 平光   ; 友田 陽*; Paradowska, A.*; Vogel, S. C.*

Xu, P. G.; Tomota, Yo*; Paradowska, A.*; Vogel, S. C.*

近年、変形誘発フェライト変態は組織微細化の重要なルートとして重視されてきたが、高加工速度その場実験が困難のため、熱間加工中微細組織の結晶学変化はまだ直接観察されなかった。本研究は飛行時間法中性子回折技術を用いた無加工の静態等温フェライト変態挙動と二つ熱間圧縮速度で熱間加工中の等温変形誘発フェライト変態挙動を比較した。オーステナイト単相域とオーステナイト・フェライト両相域で変形誘発フェライト変態を確認した。

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. It confirmed that the deformation induced ferrite transformations could appear not only in the austenite single phase region, but also in the austenite-ferrite dual phase region. It was found that the high strain rates were helpful to accelerate the ferrite transformation at different temperatures. Moreover, 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 of low temperature deformation on ferrite transformation was weakened because of the evident increment of carbon concentration in austenite and the appearance of dynamic recrystallization of ferrite.