Deformed austenite continuous cooling transformation in Nb microalloyed anti-seismic rebar
CAO Jian-chun1, YE Ya-ping1, YIN Shu-biao2, ZHANG Wei-qiang3, CHEN Wei3, ZHANG Yong-qing4
1. School of Materials Science and Engineering, Kunming University of Technology, Kuming 650093, Yunnan, China 2. College of Metallurgy and Energy Engineering, Kunming University of Technology, Kuming 650093, Yunnan, China 3. Kunming Iron and Steel Co.,Ltd., Wugang Group, Anning 650302, Yunnan, China 4. CITIC-CBMM Microalloying Technology Center, CITIC Metals Co., Ltd., Beijing 100004, China
Abstract:In order to study the effect of niobium on the microstructure transformation of high strength anti-seismic rebar,the microstructure and phase transformation of deformed austenite in Nb-free carbon steel bars and niobium microalloyed steel bars (0.03% niobium) at different cooling rates were studied by thermal simulator and dynamic continuous cooling curves,CCT of the tested steel were obtained. The results show that the addition of 0.03% Nb causes a significant change in the continuous cooling transformation of austenite in tested steels. It can be seen from CCT that after the addition of Nb,the cooling rate range of ferrite and pearlite phase transformation decreases,the ferrite and pearlite transformation temperature decreases. Cooling rate interval for the bainite transformation is shifted to the right as a whole. The addition of Nb can refine the microstructure,and the hardness of the niobium containing steel is greater than that of the Nb-free steel. The TEM was used to observe the precipitates in the niobium containing steel at different cooling rates. It was found that Nb(C,N) was dispersed in the steel. With the increase of cooling rate,the precipitation of Nb(C,N) gradually decreased,and the size of the precipitated phase decrease first and then increase. Size of precipitates obtained is finer and the number of precipitates is larger at cooling rate of 2 ℃/s.
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