Effects of Cr and Ni on the Microstructure and Corrosion Resistance of Low Carbon Alloy Steel

Abstract

For exploring the superposition-promotion effects of Cr and Ni contents on the structure and properties of low carbon alloy steel, the effects of Cr and Ni on the microstructure and corrosion resistance of low carbon alloy steel in the simulated seawater (3.5% NaCl solution) were investigated by SEM, XRD, hardness tests, electrochemical tests, immersion tests and XPS analysis. Results showed that simultaneously increasing the content of Cr and Ni could significantly promote the formation of more fine sized carbides Cr3C2 in steel, which further promoted the decrease of the grain size, the refinement of the martensite and the increase of the hardness. Simultaneously increasing the content of Cr and Ni in steel improved the thermodynamic stability, kinetic stability, and resistance to corrosion damage in the simulated seawater environment more than increasing the Cr or Ni content alone. Moreover, the increase of Cr in the steel could increase the proportion of NiFe2O4 and FeO in the corrosion products, the increase of Ni could increase the proportion of FeCr2O4 and FeO in corrosion products, simultaneously increasing the Cr and Ni content in steel has a higher promotion effect on increasing the percentage of NiFe2O4, FeCr2O4 and FeO, etc. than increasing the Cr or Ni content alone. Besides, the more NiFe2O4, FeCr2O4 and FeO, the higher the densification of corrosion products, the better the protection for the substrate, and the higher the corrosion resistance of the steel. Therefore, simultaneously increasing the content of Cr and Ni had superposition-promotion effects on the microstructure and corrosion resistance of low carbon alloy steel.

Keywords

• cr|ni|low carbon alloy steel|microstructure|corrosion resistance|superposition-promotion effects