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Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel
Author(s) -
Wang Xiaonan,
Du Linxiu,
Xie Hui,
Di Hongshuang,
GU Dehao
Publication year - 2011
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201100134
Subject(s) - materials science , metallurgy , bainite , continuous cooling transformation , recrystallization (geology) , ferrite (magnet) , deformation (meteorology) , microstructure , composite material , austenite , paleontology , biology
Abstract For the purpose of achieving the reasonable rolling technology of 780 MPa hot‐rolled Nb‐Ti combined ultra‐high strength steel, the effect of deformation and microalloy elements Nb and Ti on phase transformation behaviors was investigated by thermal simulation experiment. The results indicated: the deformation promoted ferritic transformation; due to the carbon content of the experimental steel was lower (<0.12% wt), the deformation indirectly impacted perlitic transformation through promoting ferritic transformation; the effect of the deformation on bainitic transformation was subject to condition whether proeutectoid ferrite precipitated before bainitic transformation. At low cooling rate of 0.5 °C/s, Nb and Ti promote transformation process γ → α, but that not good for refining the ferrite grain; at high cooling rate of 25 °C/s, Nb and Ti to a certain extent promote bainitic transformation. The recrystallization stop temperature of experimental steel was greater than 1000 °C, and phase transformation point A r3 was 764 °C. In order to obtain the fully bainite microstructure in the practical rolling process, the cooling rate should be controlled above 15 °C/s, the start finish rolling temperature between 950–980 °C, the finishing temperature between 830–850 °C, the coiling temperature between 450–550 °C.