Microstructure and properties in dissimilar/similar weld joints between DP780 and DP980 steels processed by fiber laser welding  

作　　者：Hongshuang Di Qian Sun Xiaonan Wang Jianping Li 

机构地区：[1]State Key Laboratory of Rolling and Automation,Northeastern University,Shenyang 110819,China [2]Shagang School of Iron and Steel,Soochow University,Suzhou 215021,China

出　　处：《Journal of Materials Science & Technology》2017年第12期1561-1571,共11页材料科学技术（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Grant Nos.51274063 and 51305285);the National Program on Key Basic Research Project(Grant No.2011CB606306-2);the Open Research Fund from the State Key Laboratory of Rolling and Automation,Northeastern University(Grant No.2016005);the Project Funded by China Postdoctoral Science Foundation(Grant No.2016M601877)

摘　　要：The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martensite（LM）, and alloying elements in the FZ were uniformly distributed. The hardness in the FZ of dissimilar weld joint was similar to the average value（375 HV） of the two similar weld joints. The microstructural evolution in heat affected zone（HAZ） of dissimilar/similar weld joints was as follows：LM（coarse-grained HAZ） →finer LM（fine-grained HAZ） →M-A constituent and ferrite（intercritically HAZ） →tempered martensite（TM） and ferrite（sub-critical HAZ）. Lower hardness in intercritically HAZ and sub-critical HAZ（softening zones） was observed compared to base metal（BM） in dissimilar/similar weld joints. The size of softening zone was 0.2-0.3 mm and reduction in hardness was ~7.6%-12.7% of BM in all the weld joints, which did not influence the tensile properties of weld joints such that fracture location was in BM. Formability of dissimilar weld joints was inferior compared to similar weld joints because of the softening zone, non-uniform microstructure and hardness on the two sides of FZ. The effect of microstructure on fatigue life was not influenced due to the presence of welding concavity.The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martensite（LM）, and alloying elements in the FZ were uniformly distributed. The hardness in the FZ of dissimilar weld joint was similar to the average value（375 HV） of the two similar weld joints. The microstructural evolution in heat affected zone（HAZ） of dissimilar/similar weld joints was as follows：LM（coarse-grained HAZ） →finer LM（fine-grained HAZ） →M-A constituent and ferrite（intercritically HAZ） →tempered martensite（TM） and ferrite（sub-critical HAZ）. Lower hardness in intercritically HAZ and sub-critical HAZ（softening zones） was observed compared to base metal（BM） in dissimilar/similar weld joints. The size of softening zone was 0.2-0.3 mm and reduction in hardness was ~7.6%-12.7% of BM in all the weld joints, which did not influence the tensile properties of weld joints such that fracture location was in BM. Formability of dissimilar weld joints was inferior compared to similar weld joints because of the softening zone, non-uniform microstructure and hardness on the two sides of FZ. The effect of microstructure on fatigue life was not influenced due to the presence of welding concavity.

关 键 词：Dual phase steel Laser welding Dissimilar weld joints Microstructure Mechanical properties Formability 

分 类 号：TG456.7[金属学及工艺—焊接]