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화학적 부동태 처리에 따른 듀플렉스 스테인리스 강의 피막 특성에 관한 연구
장휘운(Heui-un Jang),이정훈(Jung-hoon Lee),김용환(Yong-hwan Kim),정원섭(Won-sub Chung) 한국표면공학회 2012 한국표면공학회지 Vol.45 No.6
The aim of the present study was to investigate the corrosion resistance and characteristics of passive layer between naturally passivated and chemically passivated duplex stainless steel, UNS S31803 (EN 1.4462) using CPT, XPS, and EIS. The treatment of HNO3(II) and HNO3(III) in ASTM A 967 was applied. In case of chemically passivated specimen, CPT of HNO3(II) and HNO3(III) were higher than that of naturally passivated specimen. In addition, from XPS results, the protectiveness index (Cr/(Fe+Cr)) of chemically passivated specimens was also higher than that of naturally passivated specimen. The reason for this result is considered due to post-cleaning treatment in chemical passivation process, that is, immersion in Na2Cr3O7 solution. The fact that HNO3(II) passivation treatment showed the highest film resistance and ‘n’, which is exponent related with constant phase element (CPE) of passivation film, was in good agreement with results of CPS and XPS. The chemical passivation treatment was an effective method to improve corrosion resistance of duplex stainless steel.
인코넬 718합금 선재의 냉간 인발시 δ 상 저온 석출 현상 연구
박재만 ( Jae Man Park ),김용환 ( Yong Hwan Kim ),장휘운 ( Heui Un Jang ),정원섭 ( Won Sub Chung ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.7
Low temperature δ-precipitation phenomenon below 2-step aging (718℃, 8 hr + 621℃, 8 hr) temperature of cold drawn Inconel 718 alloy wire was investigated. The investigation was carried out on wires with a cold drawn ratio of 0, 20, 50 and 70% using OM, SEM, XRD, TEM, and DSC. In microstructures of 50 and 70% drawn wire, many precipitates were found along the grain boundaries and the twin boundaries in deformation band. From the results of the XRD and TEM analysis, the precipitates were identified as platelike δ-phase. From the results of the DSC analysis, it was also found that a temperature of δ-precipitation decreases with an increase of the cold drawn ratio. We concluded that cold drawing of inconel 718 wire promotes the δ-precipitation, and under the condition of a high drawing ratio, the δ-phase could be precipitated at a temperature below the aging temperature (718℃).