| ZOU Yong-chun,WANG Shu-qi,CHEN Guo-liang,ZHANG Chao-ren,WANG Ya-ming,OUYANG Jia-hu,JIA De-chang,ZHOU Yu.Process, Surface Structure and Properties of 304 Steel by Plasma Electrolytic Polishing[J],52(6):51-60 |
| Process, Surface Structure and Properties of 304 Steel by Plasma Electrolytic Polishing |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.06.005 |
| KeyWord:304 steel plasma electrolytic polishing orthogonal experiment surface roughness corrosion resistance |
| Author | Institution |
| ZOU Yong-chun |
Institute for Advanced Ceramics,Harbin , China ;Center of Analysis Measurement and Computing, Harbin Institute of Technology, Harbin , China |
| WANG Shu-qi |
Institute for Advanced Ceramics,Harbin , China |
| CHEN Guo-liang |
Institute for Advanced Ceramics,Harbin , China |
| ZHANG Chao-ren |
Institute for Advanced Ceramics,Harbin , China |
| WANG Ya-ming |
Institute for Advanced Ceramics,Harbin , China |
| OUYANG Jia-hu |
Institute for Advanced Ceramics,Harbin , China |
| JIA De-chang |
Institute for Advanced Ceramics,Harbin , China |
| ZHOU Yu |
Institute for Advanced Ceramics,Harbin , China |
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| Abstract: |
| 304 steel is widely used in aerospace, medical parts, petrochemical, manufacturing and other fields owing to its excellent corrosion resistance, mechanical properties and simple processing technique. The work aims to propose the Plasma Electrolytic Polishing (PEP) technique to polish the surface of 304 steel, in order to meet the requirements of high-quality surface in engineering applications by reducing the surface roughness of 304 steel. The discharge process of PEP was analyzed by high-speed photography technique. The electrochemical characteristics of passivation film formed on 304 steel in different electrolytes were compared. Then, the effect of PEP parameters on surface quality was explored. Furthermore, the orthogonal experiment was designed to investigate the interaction between different factors and the optimal process of PEP was confirmed. The relationship between surface morphology and wettability, corrosion resistance and hardness before and after polishing was explained. According to the electrochemical characteristics, the passivation film on 304 steel exhibited the lowest corrosion potential in (NH4)2SO4 solution, which was easier to be broken down. Therefore, (NH4)2SO4 was selected as the electrolyte for PEP. The results of the orthogonal test and range analysis showed that the minimum roughness (~0.050 mm) of 304 steel was obtained under the conditions of polishing voltage of 370 V, electrolyte temperature of 80 ℃, electrolyte content of 7 wt.% and polishing time of 6 min. The order of effect of each factor on the surface roughness of 304 steel was as follows:electrolyte temperature > polishing time > polishing voltage > electrolyte concentration. Based on the results of the discharge process, the vapor gaseous envelope (VGE) layer was generated from the bottom of 304 steel, contacting with the electrolyte. Under the pressure of the electrolyte, the VGE layer rose up and disappeared at the top and then the next VGE layer followed immediately. The surface was finished by the continuous discharge and repeated VGE layer. According to the surface performance results, the surface quality of 304 steel was significantly improved after polishing, which exhibited a mirror surface. From atomic force microscope (AFM) results in the area of 40 μm × 40 μm, the surface crest and trough area decreased from 469.8 nm and -408.4 nm to 60.4 nm and -41.5 nm, respectively. The content of austenite (γ-phase) in 304 steel was obviously increased after polishing, owing to the γ-phase with superior anti-corrosion property than α-phase. The content of the O element decreased from 3.85 at% to 0 at%, while the Cr element increased slightly. The contact angle was increased from 35.09° to 78.52°, and the corrosion resistance was improved with the polarization resistance from 1.1×105 Ω.cm2 to 2.9×105 Ω.cm2. The surface hardness decreased slightly from 1 735.9±18.5 N/mm2 to 1 676.6±14.6 N/mm2 after PEP treatment, which was attributed to that the α-phase with high hardness was easier to be removed by the microdischarge. The surface roughness of 304 steel is reduced and the surface quality is improved by plasma electrolytic polishing. The PEP technique has the advantages of high polishing efficiency, simple process, energy saving and environmental protection, which can be widely used in the fields of biomedicine, petrochemical industry, mechanical manufacture, etc. |
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