This study investigates the corrosion characteristics of Q235 steel and 16Mn steel in the sulfur-containing alkaline solution. The composition and the morphology of the corrosion products were analyzed by XPS and SEM respectively. The electrochemical behavior of Q235 steel and 16Mn steel was evaluated by potentiodynamic polarization curve and EIS. The results indicated that the corrosion rate of Q235 steel is greater than 16Mn steel in the early corrosion. Pitting and selective corrosion appeared on the surface of the two steels, and the surface product layer was granular and defective. XPS and EDS indicate that the structurally stable iron oxide is formed on the surface of the two steels. Electrochemical results show the corrosion kinetics of Q235 steel and 16Mn steel are simultaneously controlled by the charge transfer and ion diffusion, and the formation mechanism of corrosion products was clarified.

As one of the most promising 3rd generation advanced high strength steels (AHSS), medium Mn steels attract much attention because of their exceptional mechanical property and reasonable cost. However, their application in the modern automotive industry is limited by poor weldability. In this study, 7Mn steel was welded by resistance spot welding (RSW), which was followed by high-temperature annealing to increase the cross-tension property. With this effort, enhanced cross-tension strength (CTS) with a partial interfacial fracture (PIF) mode was realized. During the annealing after RSW that produced martensite, austenitization was realized and then evolved into martensite by the following air cooling. This process produced structure homogeneity across the joint. With respect to the RSW joint, martensite remained the dominant structure after annealing while the diffusion of C and Mn solutes was triggered. With the increase of annealing temperature, the diffusion was enhanced, and the grain boundary embrittlement was reduced, leading to higher CTS.