The Influence of Pickling Treatment Parameters on the Surface State and Pre-Passivation Behavior of Super 13Cr Martensitic Stainless Steel

Abstract

As a pre-treatment process in the pre-passivation of stainless steel, pickling treatment has a significant effect on the formation of the pre-passivation film. Thus, the surface composition and defects of Super 13Cr martensitic stainless steel (Super 13Cr) were evaluated under different pickling parameters to further improve the corrosion resistance of the pre-passivation film. The samples were prepared using the acid immersion method and by changing the immersion duration and the acid concentration. The inclusion and chemical composition on the Super 13Cr surface were characterized via a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The pickling treatment contributes little to the morphology, dimension, and other characteristic parameters of the inclusions. With the increasing duration and acidification concentration, the Cr content on the surface of Super 13Cr increases initially and then decreases. By contrast, the Fe content decreases initially and then increases. The pickling parameters corresponding to the lowest Fe content and the highest Cr content are identical, i.e., the exposure duration is 50 s and the acid concentration is 48 g/L. The pickling treatment in this case could be divided into two stages: outer film dissolution and inner film dissolution. The pickling parameters basically contribute little to the defects of martensitic stainless steel but can significantly affect the surface Cr and Fe content. Retaining the Cr-enriched inner layer could improve the content of Cr in the pre-passivation film and then improve the corrosion resistance of the film. Thus, compared with the original sample with native film, the corrosion resistance of the sample with a Cr-enriched inner layer improved by a factor of about 40.