Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low��Carbon Steel
CAO Jian��chun1,2,LIU Qing��you2,YONG Qi��long2,SUN Xin��jun2
1. Department of Materials and Metallurgy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China;2. Institute of Structural Materials, Central Iron and Steel Research Institute, Beijing 100081, China
Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low��Carbon Steel
CAO Jian��chun1,2,LIU Qing��you2,YONG Qi��long2,SUN Xin��jun2
1. Department of Materials and Metallurgy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China;2. Institute of Structural Materials, Central Iron and Steel Research Institute, Beijing 100081, China
ժҪ Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA low��carbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage, the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.
Abstract��Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA low��carbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage, the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.
CAO Jian��chun;LIU Qing��you;YONG Qi��long;SUN Xin��jun. Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low��Carbon Steel[J]. �й������ڿ���, 2007, 14(3): 51-0.
CAO Jian��chun;LIU Qing��you;YONG Qi��long;SUN Xin��jun. Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low��Carbon Steel. Chinese Journal of Iron and Steel, 2007, 14(3): 51-0.
2007, Vol. 14 
