EFFECT OF COILING TEMPERATURE ON MICRO-STRUCTURE AND MECHANICAL PROPERTIES OF Ti-V-Mo COMPLEX MICROALLOYED ULTRA-HIGH STRENGTH STEEL
Ke ZHANG1,2,Qilong YONG2(),Xinjun SUN2,Zhaodong LI2,Peilin ZHAO3
1 School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China 2 Department of Structural Steels, Central Iron and Steel Research Institute, Beijing 100081, China 3 R&D Center, Laiwu Iron and Steel Group Co. Ltd., Laiwu 271104, China
Cite this article:
Ke ZHANG,Qilong YONG,Xinjun SUN,Zhaodong LI,Peilin ZHAO. EFFECT OF COILING TEMPERATURE ON MICRO-STRUCTURE AND MECHANICAL PROPERTIES OF Ti-V-Mo COMPLEX MICROALLOYED ULTRA-HIGH STRENGTH STEEL. Acta Metall Sin, 2016, 52(5): 529-537.
Among various hardening factors of steels, precipitation hardening has the least embrittlement vector value except grain refinement hardening. Giving full play to the precipitation hardening of microalloyed carbonitrides is an important aspect in the development of microalloyed high strength steels. Recently, the research on behaviors of precipitation and development of microalloyed high strength steels is mainly focused on these relatively simple microalloyed steels including single V, single Ti, Ti-V and Ti-Mo microalloyed steels, while paid less attention on complex microalloyed steels such as Ti-V-Mo steels. Therefore, it is expected to provide a theoretical basis and a practical significance for the development of Ti-V-Mo microalloyed high strength steel. Various hardening increments at different coiling temperatures were calculated. Meanwhile, the effect of coiling temperatures on yield strength and the influence of MC particles on uniform elongation were discussed by means of OM, EBSD, TEM, XRD and physical-chemical phase analysis. The results show that Ti-V-Mo steel has the best mechanical properties with ultimate tensile strength of 1134 MPa, yield strength of 1080 MPa, elongation of 13.2% and uniform elongation of 6.8% at coiling temperature of 600 ℃. The precipitation hardening increment was high to about 444~487 MPa due to the mass fraction of about 72.6% of total precipitates with a size of ?10 nm. In addition, precipitation hardening and grain refinement hardening are the main mechanisms to improve the strength of Ti-V-Mo steel, while the variation in precipitation hardening increment causes a significent difference in yield strength. With the coiling temperature increases from 500 ℃ to 600 ℃, the ultimate tensile strength and yield strength increase continuously, but the uniform elongation increases slowly instead of decreasing, which is mainly attributed to an increase of precipitation hardening increment.
Fund: Supported by National Basic Research Program of China (No.2015CB654803), National Natural Science Foundation of China (No.51201036) and National Science and Technology Pillar Program (No.2013BAE07B05)