CAO Jianchun
,
LIU Qingyou
,
YONG Qilong
,
SUN Xinjun
钢铁研究学报(英文版)
Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA lowcarbon 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.
关键词:
niobium;transformation;ferrite;austenite
LIU Qingyou
,
DENG Suhuai
,
SUN Xinjun
,
DONG Han
,
WENG Yuqing
钢铁研究学报(英文版)
Hot deformation processing was designed to study the effects of niobium (Nb) on DIFT. A prestrain of 051 at 880 ℃ for different isothermal time was used for adjusting the deformed austenite constitution and Nb existing state, followed by a secondary heavy deformation at 780 ℃ for inducing the ferrite transformation. The volume fraction and grain size of deformation induced ferrite (DIF) obtained at different isothermal time between double hits were investigated. It was found that Nb dissolved in austenite is adverse to DIFT; however, the precipitation of Nb is beneficial to DIFT. As Nb plays the role in the conventional TMCP, Nb retards the recrystallization of deformed austenite and enhances the deformation stored energy in the multipass deformation, and in result, Nb promotes DIFT.
关键词:
niobium;precipitation;recrystallization;deformation induced ferrite transformation
ZHANG Shulan
,
SUN Xinjun
,
DONG Han
钢铁研究学报(英文版)
The mechanism of transformation of austenite to cementite and pearlite during the deformation of ultrahigh carbon steel was discussed. The results indicate that the pearlite and cementite can be induced by deformation between Acm to Arcm. The transformation during deformation is still considered as a diffusioncontrolled process. With the increase of time and reduction, the pearlite fraction increased. At the beginning of the transformation, the pearlite was lamelliform. When the rate of reduction was increased to 70%, some of the induced lamellar pearlite was broken up under deformation.
关键词:
ultrahigh carbon steel;microstructure;deformation;transformation
