新型耐热钢焊接接头早期蠕变损伤机制研究

The problems of early creep damage mechanisum and predicting method of new type heat resistance steel are needed solved by developing new gerneration power plant equipment. The creep test shamples with simulated microstructure at different zone of welding joint will be prepared by thermo-mechanical gleeble machine. The creep model and creep caracking strain are determined by the round bar creep test and prestrain creep cracking test.Microstructure characterization will carried out with creep test specimen, and the relationship of creep damage and microstructure, especially the grain boundary character will be clarified. Combined with microstructure mapping and Finite Element simulation, the influences of the welding residual stresses, graine size, grain boundary charater, precipitated phase mophology and size at early creep damage are studied, and the creep parameters are evaluated for related factors. Therefore, with the creep test of welding simulation ring specimen and mesurement of creep cracking strain, the paramenters of creep damage model for welding joint will be modified.The creep cracking ring specimen test considering welding residual stresses of welding joint will be proposed..Based on experiments, a comprehensive understanding on the mechanisum of early creep behavior of welding joint is achieved, that provide theoretical and technical support to design of welding joint and structure, and development of new generation heat resistance steel.The research result has theoretical significane and technical application.

新型耐热钢接头早期蠕变损伤机制及预测方法是发展新一代电站设备亟需解决的问题。采用热-力模拟试验机制备焊接接头不同区域组织的蠕变试样，通过园棒蠕变试验和预应变蠕变断裂试验，确定相关蠕变模型和蠕变开裂应变。对蠕变试样微观组织进行表征，揭示蠕变损伤与微观组织，特别是晶界特征的关系。结合微观组织映射和有限元模拟，探讨焊接残余应力、晶粒尺寸、晶界特征、析出相大小、形态等对焊接接头蠕变损伤的影响，评定对蠕变参数的影响。在此基础上，结合焊接模拟件蠕变试验和开裂应变测量，对焊接接头蠕变损伤模型参数进行改进。 提出了考虑接头残余应力的蠕变开裂环状试样的试验方法。.项目以实验为基础，对焊接接头早期蠕变损伤的机理形成全面认识，结合试验评定和数值计算为新型耐热钢焊接接头与结构设计和新一代耐热钢开发提供理论和技术支撑。研究成果具有重要理论意义和应用价值。

新型耐热钢接头早期蠕变损伤机制及预测方法是发展新一代电站设备亟需解决的问题，项目研究了焊接接头局部微观组织、残余应力场和工作载荷叠加作用下的蠕变损伤和蠕变裂纹行为。提出了适用于连续冷却过程计算的改进的Johnson-Mehl-Avrami-Kolmogorov（J-M-A-K）方程，结合基于模式搜索法的全局优化方法，确定改进的J-M-A-K方程的动态参数。研究发现，耐热钢焊接接头在热影响区最大焊接残余应力的位置可以通过焊材的选择来控制，高强匹配的填充金属将拉伸残余应力峰值外推至母材区域，避开强度较低的热影响区。提出了改进的预压缩-紧凑拉伸蠕变试样，通过压缩-释放，在半圆形缺口附近预制了残余应力场，能够在实验室环境下有效地研究三轴残余应力场对蠕变裂纹萌生和扩展性能的影响，阐明了焊接残余拉应力是引起早期蠕变失效的关键因素。设计了一种通过局部重熔引入焊接残余应力与焊缝显微结构的蠕变试样，分析残余应力作用下，不同微观组织的蠕变裂纹开裂行为和蠕变断裂模式。引入基于微观蠕变孔洞长大的多轴延性耗竭蠕变损伤分析，实现管道环焊缝接头在实际工作载荷和温度环境下的蠕变寿命预测。

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