中文摘要：

超高强合金因其优越的力学性能广泛应用于承力构件如起落架等，40CrNi2Si2MoVA超高强度合金是继30CrMnSiNi2A之后研究出的新超高强度合金，其强度高于30CrMnSiNi2A，但是其在实际服役环境中的服役性能特别是应力腐蚀性能是否优于30CrMnSiNi2A，是决定其成功取代30CrMnSiNi2A应用的关键。采用双悬臂应力腐蚀实验研究了30CrMnSiNi2A及40CrNi2Si2MoVA两种超高强度合金在质量分数为3．5％的NaCI溶液中的应力腐蚀开裂行为（SCC）。通过光学显微镜和扫描电镜（SEM）对两种超高强度合金的形貌以及断口显微组织进行了分析。实验结果表明，30CrMnSiNi2A比40crNi2si2MOVA更早失效，其耐应力腐蚀性能较差。两种材料在NaCI溶液中容易出现裂纹并迅速扩展，裂纹横向扩展，并出现明显的分叉行为，不同取向试样对材料应力腐蚀开裂行为的影响较小。断口分析结果表明两种超高强度合金在应力和腐蚀介质的共同作用下发生失效，裂纹扩展前期主要为解理穿晶断口，裂纹扩展中后期为沿晶形貌。

英文摘要：

Ultra-high strength alloys were widely used in structural parts such as landing gears due to their excellent mechanical prop- erties. 40CrNi2Si2MoVA was a kind of ultra-high strength alloy with higher yield strength after developed the ultra-high strength alloy 30CrMnSiNi2A. However, whether the actual service performance, especially its stress corrosion property, superior to 30CrMnSiNi2A would be a crucial reason that 40CrNi2Si2MoVA alloy could displace 30CrMnSiNi2A in application. The behavior of stress corrosion cracking （SCC） of two kinds of ultra-high strength alloy, 30CrMnSiNi2A and 40CrNi2Si2MoVA, in 3.5% NaC1 solution was investiga- ted by double cantilever beam methods. The microstructure and fracture surface of the two ultra-high strength alloys were characterized by optical microscopy （OM） and scanning electron microscopy （SEM）. The results showed that cracks of 30CrMnSiNi2A propagated to failure more quickly than that of 40CrNi2Si2MoVA, which illustrated that 30CrMnSiNi2A was more sensitive to SCC than 40CrNi2Si2MoVA. The cracks extended towards landscape orientation fast and branched off. The orientations had little influence on the SCC behavior of the specimens. The fracture morphology of two ultrahigh strength alloys showed that the failure mode had the character- istic of trans-granular, cleavage fracture initially and inter-granular fracture at middle-final process by effects of stress and corrosive so- lution.