Effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel

Abstract

The effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel (HSLAs) were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electrochemical tests, X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the grain size and microstructure of the steel were optimized due to the increase of crystallinity and Cr3C2 relative content by adding Cr and Ni. The tensile strength was enhanced because of the refined crystalline strengthening, phase transformation strengthening and solution strengthening. Electrochemical tests displayed that the self-corrosion current density of steel and the total anode current density as well as the number of total anodes of the WBE decreased significantly by adding Cr and Ni during immersion in 3.5 wt% NaCl solutions for 24 h. During the corrosion process, the composition and phase structure of the rust layers changed for the existence of Cr and Ni in the Cr–Ni steel, and the formation of NiFe2O4 and FeCr2O4 promoted the increase of the Fe2+/Fe3+ ratio and the relative content of α-FeOOH in the rust layers enhancing the compactness and protectiveness of the corrosion products. Besides, the microstructure of the steel containing Cr and Ni had significant effects on the mechanical strength and corrosion resistance.