双相不锈钢水下湿法激光焊接接头组织及其失效行为

Microstructure and Failure Behaviors of Duplex Stainless Steel Welds by Underwater Wet Laser Welding

摘要:

针对水下湿法激光焊接有效水深小、焊缝质量不高问题,使用了一种自主设计制备的助焊剂,利用激光焊接系统在6毫米模拟海水中采用湿法焊接方式成功连接了5毫米厚的0Cr25Ni6Mo3N双相不锈钢。焊接后利用金相显微镜观察了焊接接头顶部、中部、底部焊缝(FZ)和热影响区(HAZ)的微观组织,分析组织演变机理。计算焊接接头各区域奥氏体相比例,发现大部分区域奥氏体明显减少,偏离母材平衡数值,结合各区域组织形貌特征分析了这一问题的原因,给出了促进奥氏体生长、保持两相比例平衡的积极建议。实验后对焊缝拉伸断裂类型和摩擦磨损失效行为进行了分析,测得试样平均拉伸强度为810.7MPa,达到母材(BM)拉伸强度的95.3%,平均伸长率为34.4%,断口微观组织显示有明显解理台阶和部分韧窝,失效机制为混合断裂；焊缝平均稳定摩擦系数约为0.557,减摩性优于母材,磨损失效机制为三体磨粒磨损。

Abstract:

In order to improve the quality of underwater wet laser welding, a self-designed flux were successfully applied to the work of underwater wet welding 5mm thick 0Cr25Ni6Mo3N duplex stainless steel which existed at the 6mm depth in simulated seawater by laser beam. After welding, the microstructure of the top, middle, bottom weld and heat-affected zone of the welded joint was observed by metallographic microscope, and the mechanism of microstructure evolution was deduced. The austenite phase ratio in each area of ??the welded joint was calculated, and we have found that the austenite in most areas is significantly reduced, which deviates from the balance value of the base metal. The reason for this problem is analyzed in combination with the microstructure and morphology characteristics of each area. Positive suggestions are given to promote the growth of austenite and maintain the balance of phases. After the experiment, the failure analysis of the tensile fracture type and friction and wear behavior of the weld was carried out. The average tensile strength of the sample is 810.7MPa, which is 95.3% of the tensile strength of base metal and the average elongation of these samples is 34.4%. The microstructure of the fracture shows obvious cleavage step and some dimples, which belongs to the mixed fracture type. The friction coefficient of the weld is about 0.557, and the friction reduction is better than that of the base metal. The wear failure mechanism is three-body abrasive wear.