| Pickling passivation is an essential process in the processing of stainless steel,but sometimes there are some unexpected product quality problems,such as the appearance of inconsistent,local corrosion resistance changes,etc.Among them,the appearance of uneven white spots on the surface of stainless steel after pickling is a common kind of problem.In order to optimize the pickling passivation process of 316L stainless steel and realize the purpose of optimizing and improving the performance and reliability of the product,the influence of non-uniform white spots on the corrosion resistance of 316L stainless steel during pickling passivation process was studied,and the surface differences between white spots and non-white spots on the surface of 316L stainless steel were analyzed.According to the above experimental results,the influence of pickling passivation time on the corrosion resistance,surface morphology,surface passivation film thickness and optical constant of 316L stainless steel was further studied,and the correlation between them was comprehensively analyzed,and the formation reason of white spot was discussed.The main research progress is listed as follows:(1)It was found that the white spots appeared on 316L stainless steel after pickling passivation will not have a negative impact on the corrosion resistance of 316L stainless steel using the electrochemical method.According to the analyses of surface morphology,and roughness white spot and non-white spot area,it is found that the white spot area is coarser than the non-white spot area,and the reason is analyzed.Finally,the results of electrochemical test,surface morphology observation,surface roughness and surface composition analysis showed that the white spots did not reduce the stability of 316L stainless steel surface.(2)The effect of pickling passivation time on corrosion resistance of 316L stainless steel was further studied by preparing 316L stainless steel samples with different pickling passivation time.The corrosion resistance of 316L stainless steel increases after pickling in a short time,but when pickling time is further increased,pitting corrosion phenomenon will appear.It was found that the occurrence of pitting corrosion is attributed to the appearance of micropores on the surface of 316L stainless steel,which provides nucleation site for the pitting corrosion.(3)The composition,thickness and optical constant of the passivation film on 316L stainless steel with different passivation time were further analyzed by XPS and ellipsometry.It was found that Cr2O3 enrichment passivation film was formed on the surface of 316L stainless steel after pickling,and the passivation film became thicker with the increase of pickling passivation time,which was responsible for the improvement of corrosion resistance of 316L stainless steel after pickling passivation.Finally,the causes of white spots were discussed by analyzing the relationship between the passivation time,the thickness of the passivation film and the optical constant of the passivation film.These researches provide theoretical support for reducing the appearance of white spot on 316L stainless steel surface,optimizing the pickling and passivation process,and improving the usability and reliability of the final product. |
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