超超临界火电机组异种钢焊接接头高温断裂机理综述

我国现役超超临界（Ultra-supercritical，USC）火电机组锅炉受热面管系中有大量由铁素体耐热钢与镍基合金/奥氏体耐热钢构成的异种钢焊接接头（Dissimilar metal welded joints，DMWJs）。生产实践表明，大量的DMWJs在服役7万～10万h后发生早期失效，使用寿命远低于设计寿命30年或20万h。DMWJs早期开裂事故的频发，不仅对机组的安全运行造成极大危害，而且给发电企业带来了巨大的经济损失和负面的社会影响，同时也反映了当前对异种钢焊接，尤其是DMWJs高温服役性能的认识仍存在不足。为深入解析DMWJs的早期失效原因，回顾并总结了国内外近20年对9-12% Cr钢/镍基合金、9-12% Cr钢/奥氏体耐热钢DMWJs在高温蠕变、高温疲劳等高温力学性能方面的研究结果；分别从环境温度、加载应力、DMWJs的热力学特性、焊接残余应力、微观组织演变等方面，总结了不同因素对DMWJs高温断裂模式和断裂特征的影响，详细阐述了DMWJs在高温蠕变和疲劳条件下的断裂机理，归纳了当前较流行的高温断裂损伤物理模型及其发展应用。最后，本文建议了两种较为有效的可改善接头高温力学性能的方法，并对未来的研究方向进行了建议和展望。

A Review on High Temperature Rupture Mechanisms of Dissimilar Metal Welded Joints for the USC Thermal Power Units

There are numerous dissimilar metal welded joints (DMWJs) composed of ferrite heat-resistant steel and austenitic heat-resistant steel/nickel-based alloy in the boiler heating surface pipe system of ultra-supercritical (USC) thermal power units in China. The productive practices demonstrate that most of the DMWJs have early failure after service for 70 000-100 000 hours, and their service life is far less than the design life of 30 years or 200 000 hours. The frequent occurrence of early cracking accidents of DMWJs not only causes great harm to the safe operation of the unit, but also suffers great economic losses and negative social effects to the power generation enterprises. Meanwhile, it also reflects that the current understanding about weldability of dissimilar metals, especially the high temperature service performance of DMWJs, is still insufficient. In order to further reveal the early failure reasons of DMWJs, this work reviewed and summarized the research results of high temperature mechanical properties of 9-12%Cr/Nickel superalloy and 9-12% Cr/Austenitic dissimilar welded joints under high temperature creep and high temperature fatigue around China and other countries in the past two decades. The effects of various factors on the high temperature failure modes and failure characteristics of DMWJs were summarized through the ambient temperature, loading stress, thermodynamic characteristics, welding residual stress, microstructural evolution, et al. The fracture mechanisms of DMWJs under high temperature creep and fatigue conditions were expounded in detail, and it was also introduced a considerable of currently popular physical models about high temperature fracture damage and their development and application. Finally, it was proposed that two effective methods to improve the high temperature mechanical properties of DMWJs, and prospected for the relative researching trend in future.