F550Z海洋平台用钢SAW焊接接头低温韧性研究

Research of low-temperature toughness for F550Z offshore platform steel SAW welded joints

为研究大热输入条件下埋弧自动焊(submerged arc welding,SAW)对海洋平台用550MPa钢焊接接头组织与低温韧性的影响,采用50 kJ·cm-1的焊接热输入,测定接头各区域冲击吸收功,并观测各区断口形貌及显微组织.结果表明:焊接接头韧性从焊缝到母材,呈现先降低后升高的趋势,最低处在熔合线及熔合线2 mm处.焊缝处组织为针状铁素体加细小弥散的碳化物,断口形貌为韧窝和解理台阶,-60℃冲击吸收功为110 J.熔合线及熔合线2 mm处断口形貌基本相同,只由放射区组成,无纤维区,微观特征为大面积的解理面,没有韧窝;微观组织为粗大粒状贝氏体,冲击吸收功非常低只有25 J.熔合线5 mm处断口纤维区面积较大,微观形貌含有大量的韧窝,微观组织为细小的铁素体、碳化物及粒状贝氏体,该区为焊接接头的正火区,具有优异的低温韧性,-60℃冲击吸收功为202 J.

In this work,low-temperature toughness and microstructure of 550 MPa offshore platform steel SAW welded joint is researched .The heat input is 50 kJ＆#183; cm -1 .Optical and scanning election microscopy has been used to investigate the microstructure and the fracture morphology of different regions of welding joints .Charpy impact tests are evaluated to measure the charpy absorbed energy of different regions in detail .The result shows that the toughness of welded joints from the weld seam to the base metal decreases first and then increases .The microstructures of weld seam are acicular ferrite and fine dispersed carbide .The fracture is characterized by dim-ple and cleavage step, and the charpy absorbed energy in weld seam at -60℃is 110 J.The fracture morphology of fusion line and the zone 2 mm away from fusion line consists of radioactive zone and non -fiber zone , and its microcosmic morphology is characterized by large cleavage plane without dimple;the microstructure of the two re-gions is coarse granular bainite , the charpy absorbed energy in this zone at -60℃is only 25 J.A large area of fi-brous zone with lots of dimples is observed in the fracture 5mm away from the fusion line.The fracture is located in normalized zone whose microstructure consists of fine ferrite , carbide and granular bainite .Normalized zone shows excellent low-temperature toughness and its charpy absorbed energy at -60℃is 202 J.