EFFECTS OF Nb ON RECOVERY OF HOT-DEFORMED AUSTENITE
NIE Wenjin1, 2), SHANG Chengjia1), WU Shengjie1), SHI Peijian2), CHENG Junjie2), ZHANG Xiaobing2)
1) School of Material Science and Technology, University of Science and Technology Beijing, Beijing 100083
2) Chief engineer office, Jiangsu Sha Steel Group, Zhangjiagang 215625
Cite this article:
NIE Wenjin SHANG Chengjia WU Shengjie SHI Peijian CHENG Junjie ZHANG Xiaobing. EFFECTS OF Nb ON RECOVERY OF HOT-DEFORMED AUSTENITE. Acta Metall Sin, 2012, 48(7): 775-781.
Abstract Solute and precipitates of Nb can effectively affect stastic recrystallization and recoverry of austnite in steels during hot rolling process. However, more research is concerned about the role of Nb precipitation on the strain accumulation in finish rolling process, the solute drag effect of Nb is neglected comparing with precipitates. In this paper, the stress-relaxation curves of the low C high Mn steels with different Nb content were investigated by thermal simulation test, the evolution of dislocation and its interaction with Nb solute and precipitate during recovery process of deformed autentie in a Fe-40%Ni-0.1%Nb (mass fraction) modle steel was also studied by transmission electron microscopy (TEM). Thereby, a theoretical model about recovery of deformed austenite was developed according to the slip of dislocations and the solute drag. The values calculated by the model are consistent with the experimental results and the metallurgic principles. It is shown that both solute and precipitation of Nb can slow down the recovery and enhance the strain accumulation. The Nb solute drag can increase the activation free energy of the recovery U0 and decrease the activation length. It is believed that for Nb micro-alloyed steels with low C and high Mn, the strain accumulation during finish rolling process would be relied on the Nb solute drag effect in hot-strip mill, and both solute drag and precipitation pin effects in heavy plate mill.
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