The Correlation Between the Distribution/Size of Carbides and Electrochemical Behavior of 17Cr-1Ni Ferritic-Martensitic Stainless Steel

The correlation between the distribution/size of carbides and corrosion resistance of 17Cr-1Ni ferritic-martensitic stainless steel after different heat treatment temperatures was investigated by transmission electron microscope, electrochemical tests, and corrosion morphology observations. The results showed that the size of the precipitated phase decreased and corrosion resistance increased with an increase in the annealing temperature. When the tempering temperature was low (290 °C), carbides precipitated mainly at the phase boundaries due to a low degree of atomic matching and higher grain boundary energy. In this case, the polarization curve had a passivation interval and the pits were mainly initiated at the phase boundary. When the tempering temperature was higher than 400 °C, the carbides gradually precipitated in the martensite laths because the accelerated diffusion of Cr healed the Cr depletion zone at phase boundary. This outcome resulted in a polarization curve that had no passivation range and uniform corrosion occurred in martensitic region.