Precipitates and their strengthening in Ti-V-Mo microalloyed 22MnB5 steel
HAN Rong1,2, LIU Hong-xi1, YU Wen-chao2, WANG Mao-qiu2, SHI Jie2
1. Faculty of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China; 2. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China
Abstract:Using warm forming instead of hot forming can avoid the problems of surface oxidation in the process of hot forming,but 22MnB5 steel is commonly used in hot forming,and obvious softening occurs after high temperature tempering. By adding microalloyed elements such as Ti,V and Mo to the steel,fine precipitates and fine grains can be formed in the steel to improve the strength,so this problem can be solved. Therefore,by adding Ti,V and Mo microalloyed elements to 22MnB5 steel,the characteristics and strengthening effect of precipitates in the experimental steel were studied by OM(optical microscope),FE-SEM(field emission scanning electron microscope),EBSD(electron backscattering diffraction),TEM(transmission electron microscope),XRD(X-ray diffraction analysis),EDS(energy dispersive spectrometer) and physicochemical phase analysis. The experimental results show that the microstructure of 22MnB5 steel and Ti-V-Mo microalloyed steel after quenching is typical lath martensite. In addition to carburizing,TiC and a small amount of (V,Mo)C are also precipitated in Ti-V-Mo microalloyed experimental steel. The experimental measurement shows that the tensile strength is more than 90 MPa higher than that of 22MnB5 steel. After tempering at 600 ℃ for 1 h,a large number of nano MC(M=Ti+V+Mo) precipitates with a size of less than 20 nm precipitated in Ti-V-Mo microalloy experimental steel,which refined the effective grain size of martensitic steel to about 1.3 μm. Through theoretical analysis,it is found that the precipitation strengthening effect can reach more than 500 MPa. At the same time,the fine grain strengthening effect caused by grain refinement due to the pinning of (Ti,V,Mo)C precipitates at the grain boundary is more than 70 MPa. Under the combined action of precipitation strengthening and fine grain strengthening,the strength of Ti-V-Mo microalloy experimental steel is more than 600 MPa higher than that of 22MnB5 steel. Therefore,according to the results of this study,Ti-V-Mo microalloy experimental steel improves the softening phenomenon of steel plate during medium temperature forming to a certain extent.
韩荣, 刘洪喜, 尉文超, 王毛球, 时捷. Ti-V-Mo微合金化22MnB5钢中析出相及其强化作用[J]. 钢铁, 2022, 57(2): 127-138.
HAN Rong, LIU Hong-xi, YU Wen-chao, WANG Mao-qiu, SHI Jie. Precipitates and their strengthening in Ti-V-Mo microalloyed 22MnB5 steel[J]. Iron and Steel, 2022, 57(2): 127-138.
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