利用Gleeble--1500热模拟机对弛豫--析出--控制相变(RPC)得到的低合金钢进行不同焊接工艺下的热模拟实验, 研究了激光焊接条件下热影响区粗晶区(CGHAZ)组织、韧性及其变化规律。结果表明, CGHAZ 组织为粒状贝氏体；CGHAZ韧性随800—500℃冷却时间t8/5的增大先增大然后减小, 当t8/5为3—8 s时, －40℃CGHAZ冲击吸收功远高于母材的冲击吸收功, 表明在合适的激光焊接条件下, 激光焊接CGHAZ可获得很好低温韧性。考虑马氏体--奥氏体(M--A)组元平均宽度、总量、分布、形态对粒状贝氏体韧性的综合影响, 提出了M--A组元韧性参数的概念, 并利用M--A组元韧性参数阐述了CGHAZ韧性随t8/5的变化规律。
The microstructure and toughness of the coarse--grained heat--affected zone (CGHAZ) in laser welding of RPC (relaxation--precipitation controlling transformation) steel were investigated by thermal simulation with a Gleeble-1500 thermal simulator. The influence of the time cooled from 800-500℃, t8/5(0.3-30 s), on the microstructure of CGHAZ and the low temperature toughness were discussed. The experimental results indicate that the granular bainite is the dominate microstructure of the CGHAZ in laser welding of RPC steel, and the impact energy of the CGHAZ is much higher than that of base metal when t8/5 is between 3 s and 8 s. Considering the effect of the size, volume, number and shape of the M-A constituent on the toughness, a toughness factor of the M-A constituent is defined. As the toughness factor increases, the toughness of the granular bainite increases. The varied trend of the impact toughness with t8/5 is mainly determined by the toughness factor of the M-A constituent.
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