| Stainless steel is an important industrial material.Because of its low price,high strength,corrosion resistance and wear resistance,stainless steel is widely used in many fields,such as chemical industry,construction and medical treatment,but the corrosion problem has always been a key technical problem that is difficult to solve.In order to solve this problem,stainless steel surface rust removal and passivation treatment technology had been studied by many scholars,but the research results have many defects.Most of the traditional processes use inorganic strong acids,such as hydrochloric acid,nitric acid,hydrofluoric acid and so on.Although the process effect is good,a large number of acid fog and hydrogen embrittlement side effects will be produced in the operation process,and waste liquid often causes environmental pollution.In this study,304 austenitic stainless steel was used as the base material.The surface oxide layer was removed by chemical pickling and the protective film was prepared by passivation.The influence of components of rust remover and passivator and process conditions on corrosion resistance of passive film was studied.The passive film quality was evaluated by blue point method,electrochemical test and neutral salt spray test.The main research conclusions are as follows:?1?The optimal formula of the rust remover was obtained as follows:17.00 g/L citric acid,6.50 g/L sulfamic acid,4.50 g/L HEDP,7.00 ml/L phytic acid,5.00 g/L EDTA-2Na.The optimal conditions of the chemical picking process were obtained as follows:t=60 min,T=70?,pH?6.40.?2?The optimal formula of passivator was determined as follows:zirconium nitrate0.20 g/L,lanthanum nitrate 2.00 g/L,polyvinyl alcohol 10.00 g/L,polyacrylic acid 2.00ml/L,sodium molybdate 20.00 g/L,sodium tungstate 12.00 g/L,phytic acid 6.00 ml/L,tartaric acid.00g/L.The optimal conditions of the chemical passivation process were obtained as follows:t=40 min,T=70?,pH?6.80.?3?The oxidation layer of the stainless steel was tested in 3.5%NaCl medium after rust removal.The results showed that the current density of self-corrosion was5.3204×10-5A/cm2,which was almost 9 times as high as that before rust removal.The corrosion voltage was also negatively shifted to-551 mV.The polarization impedance also decreased from 243.04?·cm-2to 181.52?·cm-2.Therefore,the effect of environmental protection type rust remover is better.?4?The oxidation layer of the stainless steel was tested in 3.5%NaCl medium after environmental protection passivation.The results showed that the current density of self-corrosion was 1.6218×10-8A/cm2,which was nearly 20 times smaller than that of natural passivation.The corrosion voltages was positively shifted from-143mV to176mV.Therefore,the environmental protection passivation greatly improves its surface corrosion resistance.?5?The surface of stainless steel was treated through removing the passivation,natural passivation,traditional passivation and environmental passivation,and was characterized by SEM,EDS,XRD and XPS.The results showed that the surface of non-passivation film was rough with deep scratches.The surface of the natural passivation obviously has a layer of film,and the main component is Fe2O3,containing a small amount of Cr2O3,easy to corrosion.The traditional passive film has the best quality,and the main components are Cr2O3 and Fe2O3,which has strong corrosion resistance.The environmental protection passive film has oxides such as MoO3,MoO2,WO3,etc.,studied in this paper,which is flat and dense,complete and uniform,and has good gloss,enhancing its anti-corrosion ability and stronger corrosion resistance than the natural passive film.It is also intended to solve the problem of environmental pollution. |
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