| Different series of stainless steel prices vary widely,more economical materials can not meet the high corrosion resistance requirements,moreover,conventional chemical passivation of stainless steel corrosion resistance is limited.On the other hand,the traditional chromium salt passivation treatment has been gradually eliminated,stainless steel passivation treatment has shifted to the direction of environmentally friendly development.In recent years,stainless steel surface citric acid passivation and silane treatment have become a new direction for people to study.The former has its environmental characteristics because its passivation liquid component is free of chromium salt,and the latter has found that the silane coupling agent is chemically absorbed on the metal surface to form a protective silane film with crosslinked network structure.At present,the research on the combination of citric acid passivation and silane treatment of stainless steel is still relatively few,but the research for the combination of stainless steel and silane is relatively little.Therefore,the different corrosion resistance of martensitic stainless steel 2Cr13 with different treatments,such as chemical passivation,silane treatment and citric acid passivation combined with acidic silane system treatment,were studied,and lastly,the corrosion mechanism of different layers on the surface was also discussed.It could provide a reference for the new direction of stainless steel passivation treatment,and has certain practical significance.In this paper,the corrosion resistance and mechanism of chemical passivation,silane treatment and composite treatment of martensitic stainless steel were studied.The discoloration time of different passivation treatment samples was compared by blue point method.The weight loss rate of different passivation samples was compared by using salt water immersion weight loss test.The neutral salt spray test was used to compare the salt spray resistance of different passivation samples.The difference of pitting corrosion resistance and the blocking ability of corrosive medium were compared by electrochemical test.The thickness of the silane film was characterized by film weight test.And the surface films of different passivation samples were characterized by scanning electron microscopy,energy dispersive spectrometer,X-ray diffractometer,X-ray photoelectron spectroscopy and All-reflection Fourier Transform Infrared Spectrometer.The structure of different films was analyzed.Research indicates:（1）The four corrosion resistance test methods consistently showed the difference in corrosion resistance of different surface treatments:The corrosion resistance of the samples treated with silane alone was better than that of the traditional nitric acid-dichromate passivation.The corrosion resistance of the samples with the composite treatment of silane treatment after passivation of citric acid was further enhanced compared with that of the silane alone.The composite treatment of silane treatment after passivation of citric acid had excellent corrosion resistance and environmental protection characteristics,which was expected to replace the traditional nitric acid-dichromate passivation treatment.（2）According to the results of film weight test,the film weight of the sample with the composite treatment was lower than that with the acidic silane system treatment alone,indicating that the composite film’s excellent corrosion resistance not only relied on the surface of the silane film,but also benefited from its double film structure.（3）Combined with the surface analysis,it was found that passivation film had integrity and compactness,and the nitric acid-dichromate passivation film mainly contained Cr,Fe,O three elements,and its material compositon included Cr OOH,Cr（OH）3,Cr2O3,Fe OOH,Fe3O4,Fe2O3.（4）In conjunction with the surface analysis,silane film and composite film were integrity and compactness,silane film and composite film mainly contained Si,C,O three elements.（5）According to ATR-FTIR analysis,it was found that the chemical adsorption between the silane film and the substrate and between the inner and outer layers of the composite film resulted in the bonding of the chemical bond of Si-O-Fe.（6）According to XPS and ATR-FTIR analysis,it was found that there were groups such as C-O,C-Si,Si-O,C=O and-OH in the silane film and the outer layer of the composite film.Silanol hydroxyl groups set off dehydration condensation reaction,formed cross-linked network structure of the three-dimensional film and eventually constituted dense silane film. |
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