The effects of Nb and C addition on the corrosion performance of metal-injection-molded 440C martensitic stainless steel were investigated. In addition to 440C and Nb440C samples, samples with different carbon contents were prepared from the Nb440C pre-alloyed powder mixed with graphite powders. The results show that Nb is uniformly distributed in the matrix in the form of carbides. This can reduce the activity of C in the matrix and inhibit grain growth. The corrosion resistance of all the samples was characterized by anodic polarization, electrochemical impedance spectroscopy, and double-loop electrochemical potentiokinetic reactivation analyses. The added Nb consumes C atoms in the matrix, allowing more Cr atoms to diffuse to the surface to form a passive film. As a result, resistance to pitting corrosion and intergranular corrosion is improved. However, increased carbon content negatively affects corrosion resistance.
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Yu et al. (2019) studied this question.
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