-50℃用低合金细晶钢焊接热影响区组织与性能研究

Study on Microstructure and Properties of Welding HAZ of Low Alloy Fine Grain Steel for -50℃

利用Gleeble3800热模拟机测定不同t_(8/5)下-50℃用低合金细晶钢的膨胀-温度曲线。采用光学显微镜和显微硬度仪对热模拟试样进行显微组织观察及硬度测试,通过分析-50℃用低合金细晶钢连续冷却转变(CCT)特性,得出-50℃用低合金细晶钢热影响区(HAZ)的SH-CCT曲线。结果表明,-50℃用低合金细晶钢的SH-CCT曲线分为3个相变区:马氏体相变区、贝氏体相变区、铁素体+珠光体相变区。当t_(8/5)较小时,冷却过程中过冷奥氏体转变为贝氏体和马氏体组织;随着t_(8/5)时间的延长,贝氏体组织形态从针状向条片状转变,贝氏体所占比例逐渐增加,甚至出现粒状贝氏体组织;当t_(8/5)≥100 s时会出现块状多边形铁素体和黑色团状的珠光体组织。随t_(8/5)的增加,热模拟HAZ试样的硬度减小,而冲击吸收能先增大后减小。

The expansion-temperature curves of a low alloy fine grain steel for -50℃ were measured by Gleeble 3800 thermal simulator at different t_(8/5). The microstructure observation and hardness test of thermal simulated samples were carried out by optical microscope and microhardness tester. SH-CCT curves of the low alloy fine grain steel for -50℃ was obtained by analyzing the continuous cooling transformation(CCT) characteristics of base metal. The results show that the SH-CCT curves of HAZ of the low alloy fine grain steel for-50℃ can be divided into three transformation zones: martensitic transformation zone, bainite transformation zone and ferrite+pearlite transformation zone. When t_(8/5)is small, undercooled austenite is turned into bainite and martensite. With the increase of t_(8/5), the morphology of bainite transforms from needle to lath, and the ratio of bainite increases gradually, even granular bainite appears. When t_(8/5)is bigger than 100 s, massive polygonal ferrite and black pellet pearlite appear. The hardness of thermal simulated HAZ sample decreases with the increase of t_(8/5), while the impact absorbed energy increases first and then decreases.