高Cr铁素体耐热钢扩散连接界面结合机制及其接头强韧化研究

The development of 700℃ grade advanced ultra-super-critical power plants technology requires the higher manufacturing technology for large-scale heat-resistant steel structures. The advanced joining technology for steel components as diffusion bonding could narrow the differences of microstructures and mechanical properties between joint and base metal resulting from fusion welding, and may improve creep rupture life by avoiding type IV cracking. The bonding quality of interface and microstructure of joint would influence the mechanical properties as impact toughness and shear strength, thereby affecting service reliability of the structures. Hence, this project will focus on interfacial strengthening during diffusion bonding of high Cr ferritic heat-resistant steels used in power plants. Firstly, the micro-mechanism of interface jointing during diffusion bonding will be investigated by microstructure analysis and atomic diffusion kinetics research. Secondly, the physics model will be established to describe the quantitative relations between microstructure characteristic parameters and mechanical properties, and the effect of the bonding process and joint microstructure on mechanical properties of joint will be clarified. On the basis above, the approaches of joint strengthening and toughening will be developed by adjustment of bonding parameters, optimization of interlayer compositions, and introduction of surface nanocrystallization, and finally the guiding principle of bonding process optimization will be developed. The successful implementation of this project would improve the manufacturing technology for high Cr ferritic heat-resistant steels components, and thus facilitate the R&D process of 700℃ grade advanced power plants technology.

700℃等级先进超超临界发电技术的开发对耐热钢整体构件制造技术提出了更高的要求。先进的扩散连接方法可避免熔焊导致的接头与母材间组织及性能的较大差异，并有望避免第IV类断裂的发生，从而提高接头蠕变寿命。连接界面结合质量及接头组织形貌会影响接头的冲击韧性及剪切强度等力学性能，从而影响构件服役可靠性。据此，本项目拟针对火电用高Cr铁素体耐热钢的扩散连接界面强化开展以下研究：结合显微组织分析及原子扩散动力学研究，探究扩散连接界面结合微观机制；并通过建立组织特征参数与性能间的定量模型，澄清界面结合过程及接头组织对力学性能的影响机理；在上述研究基础上，通过工艺参数的调整、中间层合金成分的优化、表面纳米化技术的引入等，探索有效的接头强韧化途径，并形成连接工艺优化指导方案。本项目的顺利开展将有助于高Cr铁素体耐热钢构件制造水平的提升，从而推进700℃先进发电技术的研发进程。

先进超超临界发电技术的发展对机组关键部件制造提出了更高要求。机组构件采用传统熔焊连接时，接头处组织及性能成为薄弱环节，特别是第IV类断裂严重影响构件服役寿命。固相扩散连接技术可实现接头与母材间组织及性能的良好匹配，并有望避免第IV类裂纹的萌生。本项目针对高Cr铁素体耐热钢的直接扩散连接、电沉积Ni作为中间层的扩散连接、Fe-Si-B共晶合金箔作为中间层的瞬时液相扩散连接展开了研究，探明了扩散连接过程中的界面结合微观机制，澄清了界面结合过程及接头组织对力学性能的影响，探索了有效的接头强韧化方法，形成了连接工艺优化指导方案。申请国家发明专利6项，发表标注论文14篇，其中SCI收录13篇。本项目的顺利实施有助于加深对扩散连接过程中界面结合及组织形成微观机制的理论认知，从显微组织的角度澄清连接接头的强韧化机制，并提升高Cr铁素体钢耐热构件的制造水平。