921A钢激光-MAG复合焊接头组织及性能

针对6 mm厚的921A钢板，采用激光-MAG复合焊接工艺进行对接焊试验，并对焊接接头的显微组织、硬度、拉伸性能、耐腐蚀性能等进行了分析。结果表明，采用激光-MAG复合焊工艺可获得成形连续美观的焊接接头，无未熔合、裂纹、气孔等缺陷；焊缝组织为针状铁素体、少量沿晶界析出的先共析铁素体及长条状贝氏体，热影响区组织为马氏体；焊接接头的拉伸性能和冲击性能均符合国家标准要求，焊缝强度高于母材,但塑韧性低于母材。峰值硬度在热影响区，为315 HV，焊缝硬度约为280 HV，符合最高硬度不得超过410 HV的规定。焊缝耐电化学腐蚀性能最强，母材次之，热影响区最低；激光和MAG电弧2种热源共同作用区域的组织分布更加均匀，硬度及耐腐蚀性能较激光单独作用区域有了明显改善。创新点： 采用激光-MAG复合焊实现了6 mm厚度921A钢板无缺陷对接焊的一次焊接成形。焊缝晶粒更加细化，分布更加均匀；焊缝抗拉强度、硬度、电化学腐蚀性能均高于母材，冲击吸收能量满足船级社要求。

Microstructure and mechanical properties of 921A steel welded joint by laser-MAG hybrid welding

For 921A steel plates with thickness of 6 mm, butt welding test was carried out by laser-MAG hybrid welding process, and microstructure, hardness, tensile properties and corrosion resistance of welded joints were analyzed. The results showed that continuous and beautiful welded joints without defects such as incomplete fusion, crack and porosity, could be obtained by laser-MAG hybrid welding process. Microstructure of weld was acicular ferrite, a small amount of pre-eutectoid ferrite precipitated along grain boundaries and long strip bainite. Microstructure of heat affected zone was martensite. Tensile and impact properties of welded joints were in line with national standards. Strength of the weld was higher than that of base metal, while plastic and toughness of weld were lower than those of base metal. The peak hardness 315 HV was in heat affected zone, and hardness of weld was about 280 HV, which met requirements of the maximum hardness value that should not exceed 410 HV. Electrochemical corrosion resistance of weld was the strongest, followed by base metal, and heat affected zone was the lowest. Microstructure distribution in the interaction zone of laser and MAG arc was more uniform, and hardness and corrosion resistance were obviously improved in comparison with zone of laser action alone.Highlights: Butt welding of 6 mm thick 921A high strength steel plate was achieved without defects by laser-MAG hybrid welding. Grains of weld were finer and more evenly distributed. Tensile strength, hardness and electrochemical corrosion properties of weld were higher than those of base metal, and impact absorption energy met requirements of Classification Society.