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| STRESS CORROSION CRACKING BEHAVIOR OF GC-4 ULTRA-HIGH STRENGTH STEEL WITH ELECTROPLATED COATINGS |
| Jin Shi and Li Sihjie (Northwestern Polytechnical University) |
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Abstract 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.
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Received: 25 August 1989
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