30CrMo/Q420qE桥梁钢焊接接头显微组织及断裂韧性研究

Study on Microstructure and Fracture Toughness of Welded Joint of 30CrMo/Q420qE High Performance Bridge Steel

针对大厚度30CrMo/Q420qE高性能桥梁钢焊接接头,利用金相显微镜、扫描电镜和能谱仪对焊接接头母材、热影响区和焊缝的微观结构进行了系统的表征,采用维氏硬度和裂纹尖端张开位移测试技术对接头不同厚度区域的力学性能进行评价,旨在阐明板厚、显微组织与断裂韧性之间的关联机制。结果表明:焊接接头成型良好,无明显缺陷;30CrMo/Q420qE桥梁钢焊接接头30CrMo侧HAZ过热区由粒状贝氏体(GB)+针状铁素体(AF)+少量珠光体(P)组成,正火区由铁素体(F)+珠光体组成,Q420qE侧正火区与过热区均为细小的铁素体+珠光体组成,焊缝组织由铁素体和珠光体组成,并存在柱状晶区和等轴晶区,这是通过焊接工艺所实现的;焊接接头两侧热影响区的维氏硬度高于焊缝和母材。焊接接头不同位置CTOD平均值从大到小排序为:焊缝>Q420qE侧热影响区>30CrMo侧热影响区,最大值为0.756 3 mm,最小值为0.278 0 mm;试验的所有试样CTOD值均大于相关标准所规定的最小值。

The microstructure of base material,heat affected zone,and weld seam of the welded joint of 30CrMo/Q420qE high-performance bridge steel with large thickness was systematically characterized by metallographic microscope,scanning electron microscope and energy dispersive spectrometer.The mechanical properties of welded joints in different regions were evaluated by Vickers hardness and crack tip opening displacement testing techniques to clarify the correlation mechanism between the microstructure and fracture toughness of welded joints.The test results show that the welded joint is well-formed and has no obvious defects.The HAZ superheating zone of the 30CrMo/Q420qE bridge steel welded joint on the 30CrMo side is composed of granular bainite(GB)+acicular ferrite(AF)+a small amount of pearlite(P),and the normalizing zone is composed of ferrite(F)+pearlite.Both the normalizing zone and superheating zone on the Q420qE side are composed of fine ferrite+pearlite.The welded structure is composed of ferrite and pearlite,and there are columnar crystal regions and epitaxial crystal regions,which are realized by the welding process.The Vickers hardness of heat affected zone on both sides of the welded joint is higher than that of the weld and base material.The average value of CTOD at different positions of welded joints was in order from large to small:weld>Q420qE side heat affected zone>30CrMo side heat affected zone,the maximum value was 0.7563 mm,and the minimum value was 0.2780mm.The CTOD values of all samples tested were greater than the minimum values specified in the relevant standards.