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
CHEN Xiaoping
,
WANG Xiangdong
,
LIU Qingyou
,
MI Fengyi
,
CHEN Ying
,
LI Yusu
钢铁研究学报(英文版)
The formation of protective rust layer of atmospheric corrosion resistance was discussed for weathering steel. The Rust layers of experimental steels were made by using an accelerating industrial atmospheric corrosion test of dry-wet cyclic immersion. Furthermore XRD were used to measure and analyze the rust layers. The initial corrosion processes below thin water film were observed and the changes of micro-area PH value were measured. The results are as follows: The corrosion processes are obviously different between P-RE weathering steel and carbon steel. The surface of P-RE weathering steel rapidly forms α-FeOOH and the micro-area PH value is above 5.4 during the initial corrosion period. While the component of the rust layer for the carbon steel is mainly Fe3O4 and the micro-area PH value is below 3.8.
关键词:
weathering steel;pH value;micro area;rust phase
YANG Jinghong
,
LIU Qingyou
,
SUN Dongbai
,
LI Xiangyang
钢铁研究学报(英文版)
Using methods of singlehit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxation, the microstructure and the recrystallization behavior of NbVTi high strength microalloyed low carbon pipeline steel were studied, and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated. It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning. The deformation conditions such as deformation temperature, strain, and strain rate influenced the recrystallization kinetics and the microstructure respectively. Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.
关键词:
dynamic recrystallization;static recrystallization;microalloyed steel;austenite
