热老化对核电主管道材料冲击性能影响及老化趋势研究

EVALUATION OF THE THERMAL AGING EFFECT ON CHARPY IMPACT PROPERTIES OF THE PRIMARY PIPE MATERIAL IN NUCLEAR POWER STATION

利用示波冲击试验系统研究核电主管道奥氏体-铁素体两相不锈钢铸件材料在老化温度(400℃)下时效3000h过程中冲击断裂性能随时效时间的变化规律。室温冲击实验结果表明:在长期时效过程中,随着时效时间的延长,屈服载荷增加,延性位移减小,表征裂纹稳定扩展速度的卸载角度在时效100h后快速增加。冲击过程中材料的裂纹形成能量、裂纹扩展能量以及总冲击能量均随时效时间的延长先略上升而后逐渐下降,呈现出明显的脆化迹象;相比之下,热老化将主要导致材料裂纹扩展能量的下降。采用脆化动力学公式,对长期时效下热老化趋势进行预测,结果显示采用脆化动力学预测的材料冲击性能下降规律与试验结果基本吻合,但整体偏于保守。SEM结果表明试样表面的微观特征从较浅的韧窝型断裂逐渐演变到典型的解理性脆性断裂,材料在热老化过程中发生了脆化。

Instrumented impact test was performed on the Nuclear Power Plant primary pipe material, Z3CN20.09M duplex stainless steel aged at 400oC for up to 3000 hours to characterize the thermal aging embrittlement effect on the Charpy impact properties.The impact test results show that,with the increment of the aging time for more than 100 hours,the ductile displacement decreases while the dynamic yielding load and the unloading slope presenting the crack propagation rate increase.The crack initiation energy,crack propagation energy and the total Charpy impact energy increase slightly then decrease sharply with the increment of the aging time for thermal aging embrittlement effect.The results also indicate that the reduction of the crack propagation energy is the predominant reason of the thermal aging effect on the impact property of Z3CN20.09M steel. Comparing the experimental results with the semi-empirical predictions using the embrittlement kinetics theory,itis found that the predictions agree well with the experimental results.The SEM results show that fracture surface patterns change from ductile fracture with shallow dimples to cleavage brittle fracture with the increment of the aging time.