热老化对国产SA508-III钢断裂韧性的影响及预测模型研究

The integrity of the pressure equipment’s structure in service is the key to the safe operation and development for nuclear power equipment. The fracture toughness of materials is one of the most important parameters to assess and guarantee the integrity of the structure. However, the main difficulty in this field is that the effect of thermal aging on fracture toughness behavior of Chinese SA508-III steel is still unclear. In this research, both the macroscopic test and the microscopic damage mechanism observation are adopted to study the effect of thermal aging on fracture toughness behavior of Chinese SA508-III steel and a prediction model is established. We systematically study the effect of various thermal aging time on fracture toughness behavior of Chinese SA508-III steel at 450 ℃. The 3D X-ray compute tomography is addressed to depict the initiation, growth and coalescence of ductile voids, the distribution pattern of voids, the evolution law of microscopic damage and a new understanding of the ductile fracture mechanism on Chinese SA508-III steel. Moreover, the macroscopic and microscopic test data are combined to calculate the undetermined parameters of GTN model. The effect of thermal aging is considered in the GTN model to predict fracture toughness. Results from this research will be a great promotion to study the influence of thermal aging on the fracture toughness behavior of metal materials. The accumulated data can be of critical significance to the structural integrity assessment, life-cycle extension and optimization for material selection of pressure equipment.

核电稳健运行和发展的关键是保证承压设备在服役期内的结构完整性，而评价和保证其结构完整性能力最为关键的参数之一是服役材料的断裂韧性。目前该领域研究存在的主要问题是热老化对国产SA508-III钢断裂行为的影响机理还不清楚。本研究拟从宏观试验和细观损伤机理两方面着手，研究热老化对国产SA508-III钢断裂行为的影响规律并建立预测模型。宏观上：系统的研究450℃热老化条件下不同热老化时间对材料断裂韧性的影响规律。细观上：采用先进的能够识别出0.7μm微孔洞的X-μCT透视技术，覆盖孔洞萌生、长大和聚合的整个演化过程，获得热老化时间对材料微孔洞的分布模式、细观损伤的演化规律及其内在的影响机理，再结合宏、微观试验数据，标定出GTN模型中的待定参数，建立考虑热老化影响的断裂韧性预测模型。该问题的研究和解决，将是对热老化影响材料断裂行为研究的一大推进，积累的数据对承压设备的结构完整性评定具有重大意义。

核电稳健运行和发展的关键是保证承压设备在服役期内的结构完整性，而评价和保证其结构完整性能力最为关键的参数之一是服役材料的断裂韧性。针对热老化对国产SA508-III钢断裂行为的影响机理还不清楚的问题，本项目首先基于Arrhenius定律进行了不同热老化时间的等效加速热老化测试；其次将热老化试验后的材料制备成标准圆棒拉伸和1寸CT试样进行了不同条件的拉伸和断裂韧度测试，获得了屈服强度、抗拉强度、断后伸长率和断裂韧度；第三，采用SEM和X-μCT等技术观测了试样断口形貌，阐明了热老化对材料断口形貌的变化规律及断裂机理；最后结合宏、微观试验数据获得了考虑热老化影响的GTN损伤模型参数并预测了材料的断裂韧度。本项目获得的宝贵试验数据对核电装备的结构完整性评定具有重大意义。