350℃下长期时效对17-4PH不锈钢动态断裂韧性的影响

利用示波冲击试验系统研究反应堆用17-4PH马氏体不锈钢在使用温度（350℃）下长期(约11000h)时效过程冲击性能和动态断裂韧度的变化规律，并用扫描电镜观察分析不同时效时间的CharpyⅤ型缺口试样（CVN）的断口形貌。结果表明：该马氏体不锈钢在350℃长期时效的过程中，随着时效时间的延长,其塑性变形能E_PL和撕裂能E_TE以及冲击功E_t均随时效时间的延长而逐渐下降。根据示波冲击曲线获得了该钢的动态断裂韧度K_Id，其动态断裂韧度也随时效时间的延长而逐渐下降，并在试验的初始阶段下降很快，在试验的中后期下降较为缓慢。另外，该不锈钢的CVN冲击试样断口形貌随着时效时间的延长由韧性断裂机制的韧窝断裂为主向脆性断裂机制的准解理断裂和穿晶断裂为主变化。这些均说明，随着时效时间的延长，该材料的韧性降低，发生了脆化，且脆化主要发生在试验的初始阶段。

Effect of Long-Term Aging at 350 ℃ on Dynamic Fracture Toughness of 17-4PH Stainless Steel

The variation of impact performance with the extension of aging time on the type of 17-4PH stainless steel at 350 ℃ was studied in the paper, and the variation of dynamic fracture toughness and fractographys of the type stainless steel for various holding time at this temperature were also researched by instrumental impact test and scanning electron microscope. All results indicate that the plastic deformation energy (E_PL), tearing energy (E_TE), absorbed in fracture energy (E_t) and dynamic fracture toughness (K_Id ) of this type alloy are decreased with the continuation of time at 350 ℃. The KK_Id falls fast at the forepart of aging test and then slowly. It shows that the toughness of the alloy is degraded and the degradation is mainly taken place at the forepart of aging test. The fractography of this alloy is changed from dimple fracture into cleavage fracture and inter granular rapture with the extension of aging time. Those show that the fracture toughness of this alloy has degraded with the extension of aging time at 350 ℃..