通过纳米力学探针对铁素体相在热老化过程中的力学性能变化进行了研究.采用仪器化冲击试验机研究了材料的冲击行为, 使用SEM观察冲击断口形貌.结果表明: 长期热老化导致铁素体相的塑性变形能力不断下降,材料的冲击韧性也显著下降. 热老化过程中冲击功的损失主要是由于裂纹扩展能量的降低引起,在400℃热老化1×104 h后裂纹稳定扩展能几乎降为0.热老化材料的冲击断裂过程为: 在冲击载荷下裂纹首先在铁素体内萌生并快速扩展,铁素体相发生解理断裂, 裂纹扩展到奥氏体相, 最后裂纹连接贯穿整个试样
Cast austenite stainless steels (CASS) were used in the primary circuit piping of pressurized water nuclear reactors (PWRs), because of their excellent strength, corrosion resistance and good weldability. However, after long–term service at mid–temperature, CASS would suffer a loss of toughness and Charpy impact energy due to thermal aging. The micro–mechanical properties and impact fracture behavior of Z3CN20–09M stainless steel after long–term thermal aging at intermediate temperature were studied in this paper. A nano–indenter was used to study the changes of mechanical properties in the ferrite phases during the aging process. The impact behavior of the aged material was investigated by an instrumented impact tester, and the impact fractures were observed with SEM. The results indicated that long–term thermal aging caused the declining plastic deformation ability of the ferrite phases and the decrease of the impact toughness. The loss of impact energy in the aging process was mainly due to the reduction of stable crack propagation energy. The impact fracture morphology chnged from ductile dimple in the initial stage into a mixture of cleavage in ferrite alonwith tearing in austenite in the later stage. In the impact fracture process, cracks initiated firstly in the errite phases and fast propagated under impact loading, and then the ferrite phases fractured along the cleavage planes. At last, the cracks extended to the austenite phases and the cracks connected through the specimen.
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