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Effects of Nb on Bainite Transformation Behavior and Mechanical Properties of Low‐Carbon Bainitic Steels
Author(s) -
Chen Zhenye,
Li Jianxin,
Qi Jianjun,
Chen Liqing,
Sun Li,
Wang Guodong
Publication year - 2019
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.201900050
Subject(s) - bainite , isothermal transformation diagram , materials science , austempering , isothermal process , metallurgy , niobium , continuous cooling transformation , austenite , nucleation , ferrite (magnet) , ultimate tensile strength , carbon fibers , microstructure , composite material , thermodynamics , physics , composite number
The bainite transformation behavior and the mechanical properties of low‐carbon bainitic steels with and without niobium (Nb) are investigated by two different heat‐treatment methods − isothermal transformation process (ITP) and continuous cooling process (CCP). The results indicate that for ITP, the kinetics of bainitic transformation for the Nb‐added sample is accelerated at the beginning of the isothermal holding process due to more nucleation sites followed by its further deceleration as a consequence of the formation of ferrite prior to austempering. For all ITPs, Nb addition resulted in a decrease in the final amount of transformed bainites. In addition, different from the generally accepted result, the tensile strength of the steel is degraded by Nb addition during both ITP and CCPs, and the addition of Nb did not improve the final comprehensive properties of the steels. Moreover, Nb addition caused an increase in the critical temperature of high‐temperature transformation (Ar 3 ); however, it yielded no significant effects on critical temperatures of Ac 1 and Ac 3 .