材料期刊网

应用慢拉伸及断裂力学方法研齐了带镀层的GC-4钢(40CrMnSiMoVA)在3.5％NaCl中的应力腐蚀特性,并与裸钢作了对比。结合扫描电镜及宏观断口分析,探讨了失效机理。研究表明,阴、阳极镀层均使钢的KIscc降低,da/dt(Ⅱ)显著增加,其影响依无氰Cd、Cd-Ti、Cr的次序增加。慢拉伸试验结果说明,阴、阳极极化均使GC-4裸钢延性降低。根据BL-WOL试样裂纹扩展在表面处较内部为快以及阴、阳极镀层、平面应变状态对断口形貌的影响,可以认为带镀层与不带镀层GC-4钢的腐蚀断裂机理为裂尖阳极溶解与氢脆共同作用,并且裂尖溶解将直接参与导致裂纹扩展.从而对高强度钢腐蚀断裂的纯氢脆机理作出修正。

Stress corrosion cracking (SCC) behavior and failure mechanism of GC-4 steel (40CrMnSiMoVA) with electroplated coatings in 3.5% NaCl solution were investigated and compared with those of bare steel using slow-strain rate tension and fracture mechanics methods. Both micro and macro-fractographic analyses were conducted using SEM and optical microscope. It was found that both anodic and cathodic electroplated coatings decreased K_(ISCC) and increased the crack propagation rate da/dt (Ⅱ ). The extent of influence on the cracking behavior by different electroplated coatings increased in the sequence of noncyanide Cd,Cd-Ti, and Cr. The slow tensile tests showed that both anodic and cathodic polarization reduced the ductility of steel. According to the fact that the crack propagated faster on the side surface than in subsurface layer and even than in the central part of BL-WOL specimens, and according to the influences of different platings as well as the plane strain conditions on the macro-fractographic morphology of crack growth, it was suggested that the SCC mechanism of GC-4 steel with and without plating in aqueous solutions involves combined action of local anodic dissolution at the crack tip and hydrogen assisted cracking rather than hydrogen embrittlement alone. In addition, the crack tip dissolution contributed to the crack propagation directly.