Formation and Thermal Stability of Large Precipitates and Oxides in Titanium and Niobium Microalloyed Steel

作     者：ZHUO Xiao-jun WOO Dae-hee WANG Xin-hua LEE Hae-geon 

作者机构：Metallurgical and Ecological Engineering School University of Science and Technology Beijing Belling 100083 China Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohan4g 790 784 South Korea 

出 版 物：《Journal of Iron and Steel Research International》 (JOURNAL OF IRON AND STEEL RESEARCH,INTERNATIONAL)

年 卷 期：2008年第15卷第3期

页      面：70-77页

核心收录：

学科分类：0806[工学-冶金工程] 08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 0703[理学-化学] 0702[理学-物理学] 0801[工学-力学（可授工学、理学学位）] 

主　　题：carbonitride microsegregation dendritic region unidirectional solidification heat treatment thermal stability 

摘      要：As-cast CC slabs of microalloyed steels are prone to surface and sub-surface cracking. Precipitation phenomena initiated during solidification reduce ductility at high temperature. The unidirectional solidification unit is employed to simulate the solidification process during continuous casting. Precipitation behavior and thermal stability are systematically investigated. Samples of adding titanium and niobium to steels have been examined using field emission scanning electron microscope （FE-SEM）, electron probe X-ray microanalyzer （EPMA）, and transmission electron microscope （TEM）. It has been found that the addition of titanium and niobium to high-strength low-alloyed （HSLA） steel resulted in undesirable large precipitation in the steels, i. e. , precipitation of large precipitates with various morphologies. The composition of the large precipitates has been determined, The effect of cooling rate on （Ti, Nb）（C, N） precipitate formation is investigated. With increasing the cooling rate, titanium-rich （Ti,Nb）（C,N） precipitates are transformed to niobium-rich （Ti,Nb）（C,N） precipitates. The thermal stability of these large precipitates and oxides have been assessed by carrying out various heat treatments such as holding and quenching from temperature at 800 and 1 200℃. It has been found that titanium-rich （Ti,Nb）（C,N） precipitate is stable at about 1 200 ℃ and niobium-rich （Ti,Nb）（C,N） precipitate is stable at about 800 ℃. After reheating at 1 200℃ for 1 h, （Ca,Mn）S and TiN are precipitated from Ca-Al oxide. However, during reheating at 800 ℃ for l h, Ca-Al-Ti oxide in specimens was stable. The thermodynamic calculation of simulating the thermal process is employed. The calculation results are in good agreement with the experimental results.