Effect of nano-grain carbide formation on electrochemical behavior of 316L stainless steel

The effect of low oxygen-partial pressured carburizing on relaxation process for 316L stainless steel is reported. Phase, morphology, and amount of compound formation during initial stage of carburizing are investigated using X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The results show formation and development of surface multilayer with nano-grain-carbide (Cr(7)C(3), Fe(7)C(3), and/or Cr(3)C(2)) generation in the layer located below outermost protective layer. The relaxation process has been investigated using electrochemical impedance spectroscopy (EIS). Formation of nano-grain carbide(s) during carburizing causes deterioration effect on the electrochemical behavior of steel. However, the steel with large amount of carbide generation (carburized for 30 min) tends to have higher corrosion resistance (indicated by higher values of R(cl) and R(ct)) than the smaller ones (10 and 20 min) due to the effect of phase, grain size, morphology, and amount of compound formation.