Changes in microstructure and properties of weld heat-affected zone of high-strength low-alloy steel  

作　　者：Shu-jun Jia Qi-lin Ma Yu Hou Ba Li He-song Zhang Qing-you Liu 

机构地区：[1]Central Iron and Steel Research Institute Co.,Ltd.,Beijing 100081,China [2]Collaborative Innovation Center for Steel Commonality,University of Science and Technology Beijing,Beijing 100083,China [3]Construction Project Management Branch of China National Petroleum Pipeline Network Group Co.,Ltd.,Langfang 065000,Hebei,China

出　　处：《Journal of Iron and Steel Research International》2024年第8期2041-2052,共12页钢铁研究学报（英文版）

基　　金：The authors appreciate the financial support from National Key Research and Development Program of China(2017YFBO304900).

摘　　要：The evolution of the microstructure and toughness of APL5L X80 pipeline steel after thermal welding simulation was investigated by X-ray diffraction,electron backscatter diffraction,and transmission electron microscopy.The results indicated that primary heat-affected zones can be divided into weld,coarse-grained,fine-grained,intercritical,and sub-critical zones.The microstructure of the weld zone is mainly composed of bainitic ferrite and a small amount of granular bainite;however,the original austenite grains are distributed in the columnar grains.The structure of the coarse-grained zone is similar to that of the weld zone,but the original austenite grains are equiaxed.In contrast,the microstructure in the fine-grained zone is dominated by fine granular bainite,and the effective grain size is only 8.15μm,thus providing the highest toughness in the entire heat-affected zone.The intercritical and subcritical zones were brittle valley regions,and the microstructure was dominated by granular bainite.However,the martensite-austenite(M/A)constituents are present in island chains along the grain boundaries,and the coarse size of the M/A constituents seriously reduces the toughness.The results of the crack propagation analyzes revealed that high-angle grain boundaries can significantly slow down crack growth and change the crack direction,thereby increasing the material toughness.The impact toughness of the low-temperature tempering zone was equivalent to that of the columnar grain zone,and the impact toughness was between those of the critical and fine-grained zones.

关 键 词：Welding thermal simulation Impact toughness Crack propagation Martensite-austenite constituent High-strength low-alloy steel weld Heat-affected zone 

分 类 号：TG457.11[金属学及工艺—焊接]