异种钢接头的材料模型建立与力学行为演化集成计算方法开发

Cracks usually occur in the weld interface and the sensitization zone of dissimilar metal welded joints used in nuclear and thermal power plants. The high tensile residual stress due to welding process and the sensitization caused by multiple thermal cycles are the most important two factors resulting in cracking. For controlling the generation of crack in dissimilar metal joints, it is very important to obtain the information on residual stress distribution and sensitization zone in the actual welded structure. In this project, through establishing a high precision material model and developing an integrated computational approach considering multiple physical processes, we will simulate the stress/strain evolution and predict the location of sensitization zone in typical dissimilar metal joints. Moreover, we will focuses on stress state of the interface mixed zone between the parent metal and the weld metal. We will measure the temperature-dependent mechanical properties of the interface mixed zone and tempered zone of heat restraint steel through using a series of experimental methods, and will develop a high-precision material model to simulate welding residual stress. The new material modelling includes the interfacial mixed zone material model and the tempering model. In addition, we will develop a computational approach to determine sensitization zone based on welding thermal cycle and TTS diagram. On this basis, we will further develop an integrated computational method with the consideration of multiple physical processes such as preheating, welding, heat treatment, and service loading to simulate the material mechanical behaviors. This approach will be helpful in assessing structural integrity and predicting service life for welded structures.

核电与火电装备中关键部件的裂纹通常发生在异种钢焊接接头的熔合区和敏化区。焊接过程中产生的高拉伸残余应力和焊接多重热循环导致的材料敏化是诱发裂纹的重要因素。在实际工程结构中，为了有效抑制异种钢接头的裂纹产生，获取焊接接头残余应力和敏化区位置十分重要。本项目以核电和火电典型异种钢接头为对象，通过建立高精度材料模型和开发考虑多物理过程的集成算法来仿真材料的应力/应变演化过程和预测敏化区位置，并重点探究母材与焊缝之间界面混合区的应力状态。通过设计系列实验来测量界面混合区和耐热钢回火部位的高温力学性能参数，建立用于残余应力高精度计算的材料模型。新建材料模型中包含界面混合区材料模型和回火模型。同时，基于焊接热循环和TTS图开发敏化区的计算方法。在此基础上，开发考虑多物理过程（如预热、焊接、热处理和服役等）的计算方法来仿真材料在多工艺链中的力学行为演化过程，为焊接结构的健全性评价和寿命预测提供科学依据。

核电与火电装备中关键部件的裂纹通常发生在异种钢焊接接头的熔合区和敏化区。焊接过程中产生的高拉伸残余应力和焊接多重热循环导致的材料敏化是诱发裂纹的重要因素。在实际工程结构中，为了有效抑制异种钢接头的裂纹产生，获取焊接接头残余应力和敏化区位置十分重要。本项目以核电和火电典型异种钢接头为对象，通过建立高精度材料模型和开发考虑多物理过程的集成算法仿真了材料的应力/应变演化过程；预测了敏化区位置和敏化程度。基于本项目发的高精度材料模型，采用数值模拟与实验相结合的方法研究了P92/SUS304异种钢接头的残余应力和焊接敏化。首先，基于时间-温度-碳化物沉积(TTP)曲线建立了用于预测SUS304不锈钢碳化物析出程度和焊接敏化区的计算模型，基于时间-温度-敏化(TTS)曲线开发了用于预测SUS304不锈钢焊接敏化程度的计算模型。然后，采用FEM软件建立了“热-冶金-力学”耦合的焊接有限元计算方法，对异种钢对接接头的焊接残余应力进行了数值模拟研究；基于FEM软件平台开发了“热-敏化”耦合的有限元计算方法，对异种钢对接接头不锈钢侧的焊接敏化区域和程度进行了数值模拟研究。同时，采用中子衍射法和小孔法分别测量了异种钢对接接头内部和表面的残余应力/应变分布，采用腐蚀实验和双环EPR电化学试验对焊接敏化模拟结果进行了实验验证。P92/SUS304异种钢平板对接接头的残余应力模拟结果与测量结果吻合良好，异种钢对接接头的残余应力分布呈现出极强的不均匀性和很大的应力梯度，P92钢焊接热影响区的纵向和横向残余应力峰值均超过600 MPa。异种钢对接接头不锈钢侧的焊接敏化区域和敏化程度与测量结果吻合良好。在异种钢对接接头不锈钢侧焊根处存在较高纵向拉伸应力、较大累积塑性应变及严重的材料敏化，因此，该区域具有较高的应力腐蚀开裂倾向。以SA508/316异种钢管-板接头为研究对象，开展了多工艺链集成计算，研究了异种钢接头在“堆焊-热处理-机加工-焊接”加工制造过程中的应力演变。本项目取得的研究成果已转化成了工程实用技术。