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采用含Nb及不含Nb两种焊丝对高速列车转向架用S355J2G3钢板进行焊接, 分析了焊态下接头各区域的性能差别, 研究了合金元素Nb和焊后热处理制度对焊缝金属组织和性能的影响. 结果表明: 焊缝金属的韧性是焊接接头性能的薄弱环节. 焊态下Nb的加入提高了焊缝金属的强度, 但对塑性和韧性无明显影响. 经去应力退火后, 不含Nb焊缝金属的强度降低, 延伸率和冲击功升高, 而含Nb焊缝金属的强度升高, 延伸率和冲击功降低, 退火后含Nb焊缝金属中 NbC颗粒析出是影响焊缝金属组织和性能的主要因素. 在焊后正火处理条件下, 随着正火温度的升高, 不含Nb焊缝金属的组织和性能均无明显变化, 而含Nb焊缝金属的强度明显升高, 延伸率和冲击功显著降低. 严格控制正火温度是含Nb焊缝金属获得高强韧性的关键. 含Nb焊缝中魏氏组织的含量随正火温度的升高而明显增多. 电镜观察表明, 经920 ℃正火处理后, 焊缝中的NbC颗粒尺寸大于退火态焊缝金属中的NbC相, 而在1200 ℃正火处理后NbC颗粒溶解消失.

There is a strong demand within the steel industry to develop high strength microalloyed steels and matching welding materials for satisfying the ever increasing industrial needs. Nb microalloyed steel is one of the important structure materials. The weldability determines the industrial application prospect of Nb microalloyed steel. The majority of previous studies concerning Nb bearing steels have been focus on the transformation behavior of Nb bearing steels in thermomechanical process and the effect of Nb element on the process. However, the research on the matching welding materials for Nb bearing steels and the effects of heat treatment process on the microstructure and mechanical properties of Nb bearing weld metal were seldom reported. In this paper, Nb bearing S355J2G3 steel plates for high-speed train bogie were welded using welding wires with and without Nb addition. Differences of properties at the different regions in the as-welded joint, and the effects of the Nb element and the different post weld heat treatments on the microstructure and the mechanical property of the weld metal were analyzed systematically. Experimental results showed that the weld metal toughness is the weakest link of the welding joint properties. Nb addition can improve the strength of the weld metal, but has no obvious effects on the plasticity and impact toughness. After stress relief annealing, the strength of the Nb free weld metal decreased, while the elongation and impact toughness increased. However, for the Nb bearing weld metal, stress relief annealing can improve the strength of the weld metal significantly, but deteriorate the elongation and impact toughness. NbC particles were found in the as-annealing weld metal. With the increase of the normalizing temperature, the microstructure and mechanical property of the Nb free weld metal have no obvious change, while, for the Nb bearing weld metal, the strength increases obviously and the elongation and impact toughness decrease. Therefore, setting the normalizing temperature properly is the key to get higher toughness for the Nb bearing weld metal. It was simultaneously found that the content of widmanstatten ferrite in the Nb bearing weld metal increases obviously with the increase of the normalizing temperature. Furthermore, when the normalizing temperature was set at 920 ℃, the size of the NbC particles in weld metal is larger than that in the as-annealed weld metal. However, when the normalizing temperature was raised to 1200 ℃, the NbC particles will disappear because of its dissolution at\linebreak higher temperature.