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In this study, the effect of nickel content in two kinds of supermartensitic stainless steels, the new composition SMSS + Ni and already known SMSS–Ni, is compared concerning their mechanical properties as a function of tempering temperatures. The SMSS + Ni showed a microstructure composed of well-distributed thin martensite within austenite. In contrast, in the SMSS–Ni, there was much less austenite, and martensite was thicker, thus exposing it more to the environment. Therefore, one observed that the thinner the martensite, the higher the hardness and tensile stresses, and the lower the ductility. Overall, tempered samples at 620 °C presented better toughness. Therefore, the weldability of the steel SMSS + Ni was also analyzed in this tempering temperature condition, presenting excellent welding performance. However, after welding, there was an increase in austenite and thickening of martensite laths in the heat-affected zone (HAZ), leading to its poor distribution within austenite. Corrosion properties were studied comparing both kinds of steels tempered at 620 °C, which was also performed in the steel SMSS + Ni in the welded condition. It was observed that the better the distribution of martensite, the better the corrosion properties. The pitting potential for the SMSS + Ni was the lowest; its polarization curve was positioned in a nobler region, with lower corrosion potential and corrosion current density than these for the SMSS–Ni and in its welded condition.

In this study, the effect of high and low phosphorus contents on the mechanical and corrosion properties of two supermartensitic stainless was evaluated as a function of tempering temperature (570, 620, 670 and 690 °C). The best heat treatment condition (tempered at 620 °C) was determined by conducting potentiodynamic polarization tests in natural seawater. At all temperatures, the two tempered steels presented nearly the same values of hardness, yield strength (0.2%), ultimate tensile strength and elongation. A high phosphorus content promoted the formation of nanoprecipitates of CrP4 between the retained austenite (3%) and martensitic grain boundaries. This structure significantly improved the impact toughness. The steels also presented similar pit potentials (0.290 V). Nevertheless, chromium phosphide (CrP4) shifted the anodic corrosion curve toward a nobler region and produced a passive region that was more stable against corrosion.