Stress corrosion cracking and its mechanism of 16Mn steel and heat-affected zone in alkaline sulfide solutions

Stress corrosion cracking (SCC) of 16Mn steel and its heat-affected zone (HAZ) in alkaline solution with sulfide and Cl^- was investigated by electrochemical technology, slow strain rate tensile (SSRT) test and U-bent specimen immersing test. Results show that the original microstructure, the coarse grain structure acquired by air cooling treatment and the hardening microstructure obtained from quenching performed a passivation behavior in alkaline sulfide solution. Correspondingly, the passivation current density of them decreased gradually with the cooling rate increased. The corrosion potential of the quenching microstructure, air-cooling microstructure and original microstructure decreases sequentially, indicating that HAZ is the cathodic area and the fusion line as well as bulk steel anodic area. Based on the results, the corrosion is feasible to happen nearby the fusion line would increase, and thus the residual tensile stress area would be exposed to the electrolyte after long-term service, which results in SCC. The susceptibility of SCC was lowered down gradually among hardening microstructure, coarse grain microstructure and original microstructure. SCC mechanism of 16Mn steel in the alkaline solution containing sulfide was anodic dissolution (AD) in terms of intergranular fracture.