模拟研究了Q550D低碳贝氏体钢焊接接头热影响区粗晶区冲击韧性受t8／5（从800℃冷却至500℃的时间）影响的变化规律，并选取t8／5为20S时的热模拟条件研究焊后热处理工艺对粗晶区冲击韧性的影响，从而确定该钢的焊后热处理工艺。结果表明：Q550D钢粗晶区的冲击功随t8／5的增加有下降趋势，在t8／5≤30S时粗晶区冲击韧性保持较高水平；在250～600℃进行焊后热处理时母材的拉伸、冲击性能变化不大，粗晶区在350℃和550℃附近存在回火脆性，在500℃附近保持较高的冲击韧性；Q550D钢较佳的焊后热处%The ruler about coarse grain zone impact ductility of low carbon bainite steel welded joint heat affected zone changing with the t8/5 （the cooling time of temperature decrease from 800 ℃ to 500 ℃ ） was studied, and the effect of heat treatment process after welding on impact ductility of coarse grain zone were researched under the thermal simulation condition when t8/5 was 20 s, then the heat treatment process after welding of the steel was confirmed. The results show that the impacting energy of coarse grain zone in Q550D steel decreased with the increase of t8/5, and the impact ductility of coarse grain zone kept in higher level when t8/5 was no more than 30 s. The tensile and impact properties of base metal changed little when heat treatment after welding was done between 250 ℃and 600 ℃, coarse grain zone had temper brittleness nearby 350 ℃ and 550 ℃ and kept higher impact ductility nearby 500 ℃. The better heat treatment process of Q550D steel was tempering at 520 ℃ for 1.5 h.
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