异种钢水下湿法焊接接头非均匀特征及接头性能优化机制研究

Heterogeneous characteristics and properties optimization mechanism of underwater wet welded dissimilar steel joints between low alloy steel and austenitic stainless steel are investigated. Using Ni-based self-shielded flux-cored wire, the heterogeneity of dimensions, element distribution and microstructural characteristics of underwater wet welded dissimilar steel joints will be studied with adjustments of welding wire flux-cored alloying system and welding process specifications. Hydrogen-induced cracking susceptibility of dissimilar steel joints will be clarified by studying diffusion hydrogen content and residual stress distribution in underwater wet welded dissimilar steel joints. Fracture mechanism of underwater wet welded dissimilar steel joints will be revealed by analyzing mechanical properties and fracture morphology of dissimilar steel joints. Corrosion behavior of dissimilar steel welded joints in 3.5% NaCl solution is analyzed by electrochemical method. The internal relationship between composition, structure and properties of underwater wet welded dissimilar steel joints can be established, the heterogeneous characteristics “composition-microstructure-stress-properties” of underwater wet welded dissimilar steel joints will be revealed, and the optimization mechanism of structure and properties of underwater wet welded dissimilar steel joints will be clarified. The research achievement of this project can lay a foundation for underwater wet welding repair of dissimilar steel joints of low alloy steel/austenitic stainless steel, which has important theoretical significance and engineering application value.

针对低合金钢/奥氏体不锈钢异种钢水下湿法焊接接头非均匀特征及接头性能优化机制进行研究。采用自制的镍基自保护药芯焊丝，并调整焊丝药芯合金化体系及焊接工艺规范，分析异种钢水下湿法焊接接头尺寸、元素分布及微观组织的非均匀特征；研究异种钢水下焊接接头扩散氢含量及残余应力分布，探讨异种钢水下湿法焊接接头氢致裂纹倾向；通过分析异种钢水下湿法焊接接头的力学性能及断口形貌，揭示异种钢水下湿法焊接接头断裂机制；采用电化学方法，研究异种钢水下湿法焊接接头局部特征区域在3.5%NaCl溶液中的腐蚀行为；建立异种钢水下湿法焊接接头成分、组织及性能之间的内在联系，阐明异种钢水下湿法焊接接头“成分-组织-应力-性能”的非均匀特征，揭示异种钢水下湿法焊接接头组织性能优化机制。本课题的研究成果，可以为低合金钢/奥氏体不锈钢异种钢水下湿法焊接修复奠定基础，具有重要的理论意义及工程应用价值。

低合金钢/奥氏体不锈钢异种钢结构在海洋平台、油气管线等领域具有广泛的应用，亟需开展异种钢结构的水下焊接修复技术研究。本项目针对异种钢水下焊接过程中存在的成形质量差、接头性能低等问题，通过设计镍基自保护药芯焊丝和工艺优化，系统研究了不同工艺条件下的异种钢水下焊接接头化学成分、显微组织、性能及应力分布的非均匀特征，揭示了异种钢水下湿法焊接接头化学成分、微观组织及接头性能之间的内在关系，实现了具有较高质量的16Mn/304L异种钢结构件的水下湿法焊接。. 针对所研发的镍基自保护药芯焊丝，获得最佳的异种钢水下湿法焊接工艺参数为：电弧电压28V，焊接电流185A，焊接速度132mm/min，坡口角度60°，间隙2mm。异种钢接头16Mn侧熔合线存在微观组织及元素分布的不均匀过渡区，16Mn侧焊缝金属存在不连续的II型晶界，异种钢水下焊接接头的抗拉强度约为510MPa，16Mn钢侧热影响区的冲击性能较低，仅为39J/cm2。相比陆上环境的异种钢接头，水环境下异种钢接头的微观组织及元素非均匀分布特征更显著，ER308焊丝异种钢水下焊接接头16Mn侧过渡区易形成冷裂纹，相比奥氏体不锈钢焊缝，镍基焊缝金属更耐稀释，在水下环境中可以保持较好的力学性能。在拉伸载荷及夏比冲击载荷作用下，异种钢接头的薄弱位置分别为焊缝金属和16Mn钢热影响区。为了缓解异种钢水下焊接接头低合金钢侧热影响区的淬硬倾向，并进一步提升异种钢接头的综合性能，利用钨极氩弧焊填丝的方法在16Mn低合金钢侧预置不同厚度的ERNiCrMo-3隔离层，分析隔离层厚度对异种钢水下焊接接头不同区域的元素分布、微观组织特征及接头的力学性能的影响。发现随着隔离层厚度的增加，16Mn钢侧热影响区马氏体数量逐渐减少，异种钢水下湿法焊接接头在保持较高抗拉强度的同时，低合金钢侧热影响区的冲击韧性明显提高50%，达到89J/cm2。. 本项目的研究成果可以丰富和完善异种钢结构件水下焊接修复技术，推动异种钢结构件在核电、船舶及海洋等领域的应用。