异种钢焊接接头复合失效机理及寿命评估

Materials used in large fossil power plants consist of heat-resistant steels and stainless steels with good high temperature performance. Austenitic stainless steels are often used in the boiler heating surface tube because of the higher working temperature, while the less expensive martensite heat-resistant steels are often used in the relatively low temperature regions, thereby generating a large number of dissimilar metal welds in the boiler. Because of the differences in chemical composition, metal structure and thermophysical properties between the two materials, premature fracture failure can occur during the service, resulting in forced plant outages, causing significant economic losses..This program combines macroscopic and microscopic research, material science and mechanics research, field test and laboratory test. The chemical composition, microstructure and mechanical properties of dissimilar metal welds are analyzed after long-term service, the stress distributions of dissimilar metal welds are studied, and the multiple failure mechanism of dissimilar metal welds are discussed. Considering material aging state and actual stress level of dissimilar metal welds, the life evaluation method of dissimilar metal welds is developed. The life estimation method is suitable for engineering practice and will be used for engineering demonstration..

现代大型火电机组构成材料，主要为具有良好高温性能的各类耐热钢与不锈钢。锅炉受热面管子因工作温度较高常采用奥氏体不锈钢，从经济角度考虑，温度相对较低的部位多采用价格相对低廉的马氏体耐热钢，由此在锅炉内产生大量异质对接接头。由于这两种材料的化学成分、金属组织和热物理性能等相差颇大，因此接头在使用过程中常发生早期断裂失效，导致机组非计划停机检修，引起重大经济损失。. 本项目采用宏观与微观研究相结合、材料学与力学研究相结合、现场试验与试验室试验相结合的方法，分析长期服役后异种钢焊接接头化学成分、微观组织及力学性能的变化特征，研究异种钢焊接接头的应力场分布规律，探讨异种钢焊接接头复合损伤失效机理。综合考虑异种钢焊接接头材料老化状态和实际应力水平，探讨异种钢焊接接头寿命评估方法。形成适用于工程实际的异种钢焊接接头寿命评估技术，并用于工程示范。

异种钢焊接接头除传送高温高压蒸汽外，还要承受炉膛火焰和烟气高温的作用，加之深度调峰时负荷的大幅度波动，使用条件十分恶劣，是高效超临界电站锅炉运行中的事故多发部位。本项目重点解决影响超临界、超（超）临界电站锅炉异种钢焊接接头运行安全的瓶颈难题，以材料性能评价为共性基础，以复合失效机理研究作为技术核心，形成电站锅炉异种钢焊接接头寿命评估技术方法，并通过研究成果集成和工程示范，建立适合我国电站锅炉运行情况的安全高效、经济可靠的异种钢焊接接头寿命评估技术体系。.本项目通过理论分析、试验研究、工程验证等方式，围绕着电站锅炉异种钢焊接接头实际运行过程中的早期失效问题，在电站锅炉异种钢焊接接头基础性能、复合失效机理、寿命评估等方面进行了系统研究，超额完成了任务书规定的研究任务，全面达到了考核指标的要求，主要创新点如下：.揭示了实际服役电站锅炉异种钢焊接接头在频繁深度调峰工况下的复合失效机理，分离了不同的因素对破坏的作用。关联宏观损伤参量和寿命，发明了新型的异种钢焊接接头寿命评估方法。在亚临界、超临界电站锅炉上开展了工程示范，构建了异种钢焊接接头寿命预测技术体系。