二次热循环对S690QL钢热影响区粗晶区组织与韧性的影响

Effect of Twice Thermal Cycles on Microstructure and Impact Toughness of Coarse Grained HAZ for S690QL Steel

采用热模拟方法,对S690QL钢进行了不同热输入热模拟试验,研究了二次热循环对一次模拟热影响区粗晶区组织与韧性的影响。结果表明,二次加热峰值温度低于一次峰值温度,二次热循环对改善粗晶区韧性具有一定效果;模拟热影响区粗晶区组织均为板条马氏体加少量下贝氏体的混合组织,二次加热峰值温度越高组织越粗大,相应冲击韧性越低;模拟热影响区粗晶区经历峰值温度950℃的二次加热后,具有组织遗传倾向,但由于晶内板条马氏体自回火作用加强,低温冲击韧性仍得到明显改善。

The thermal simulation experiments of S690QL steel for twice thermal cycle were carried out under the condition of heat inputs and the influence of the second thermal cycle on the microstructure and toughness in coarse grain zone of the simulated heat-affected zone （HAZ） for first thermal cycle was studied. The results show that, the second thermal cycle has certain effects on the improvement of toughness in coarse grain zone when its peak temperature is lower than the first one. The microstructure in the coarse grain zone of simulated HAZ is the mixture of lath martensite and small amount of low bainite, which is coarser with increasing reheating peak temperature, leading to lower impact toughness. After being reheated at a peak temperature of 950oC, the coarse grain zone has the tendency of structural heridity. But, due to enhancement of self-tempering of intraerystalline lath martensite, its lower temperature impact toughness recovers partially.