Effect of Vanadium on the Microstructure and Properties of Fire-resistant Weathering Steels
Methods such as dilatometer, optical microscope, electrolytically extraction and TEM were used to investigate the effects of vanadium addition on the CCT diagrams, the microstructural evolution and tensile properties at both room temperature and 600°C in three series of hot-rolled high-strength, low-alloy weathering steels containing both V and Mo (the first with 0.60%Mo, the second with 0.3%Mo+0.0020%B and the last with 0.30% Mo content). The results of this study have brought the following conclusions: ① The addition of 0.10%V has a limited effect on the CCT curves of 0.60%Mo weathering steels and 0.30%Mo-B weathering steels whereas the addition of 0.20%V promoted the formation of polygonal ferrite in the 0.60%Mo weathering steel. ② The control of the bainite fraction in the microstructure is essential for weathering fire resistant steels in order to obtain good high-temperature yield strength and high YS ratio even for steels containing 0.60%Mo. ③ Precipitates of vanadium were found in all vanadium-containing experimental steels and they seemed to become finer and denser as the vanadium content increased or accelerated cooling after hot-rolling was used. ④ If a suitable fraction of bainite was introduced in the microstructure, the Mo content could be reduced to about 0.30%Mo while the high-temperature yield strength and YS ratio were still kept at high level. ⑤ The addition of vanadium, especially combined addition of vanadium and nitrogen, would result in additional strengthening at both room temperature and 600°C, at least for the plates that were subject to accelerated cooling after hotrolling. The effect of vanadium might be attributed to the precipitation of vanadium.
vanadium, fire-resistant, weathering steel.
Zheng Zhiwang，Liu Qingchun
Panzhihua Iron & Steel Research Institute
Application Technologies of Vanadium in Flat-rolled Steels –Vanitec Symposium, Suzhou, China, Oct. 2005, pp.79-90