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소둔 및 용접후열처리가 슈퍼 오스테나이트계 스테인리스강의 부식거동에 미치는 영향
윤덕빈 ( Duck Bin Yun ),박진성 ( Jin Sung Park ),조동민 ( Dong Min Cho ),홍승갑 ( Seung Gab Hong ),김성진 ( Sung Jin Kim ) 한국부식방식학회 2021 Corrosion Science and Technology Vol.20 No.6
The effect of two different annealing temperatures on the level of the second phase precipitated in the microstructure and the corrosion behaviors of super austenitic stainless steel were examined. The sample annealed at a higher temperature had a significantly lower fraction of the sigma phase enriched with Cr and Mo elements, showing more stable passivity behavior during the potentiodynamic polarization measurement. However, after the welding process with Inconel-type welding material, severe corrosion damage along the interface between the base metal and the weld metal was observed regardless of the annealing temperature. This was closely associated with the precipitation of the fine sigma phase with a high Mo concentration in the unmixed zone (UMZ) during the welding process, leading to the local depletion of Mo concentrations around the sigma phase. On the other hand, the fraction of the newly precipitated fine sigma phase in the UMZ was greatly reduced by post-weld heat treatment (PWHT), and the corrosion resistance was greatly improved. Based on the results, it is proposed that the alloy composition of welding materials and PWHT conditions should be further optimized to ensure the superior corrosion resistance of welded super austenitic stainless steel.
초고강도급 자동차용 강재 내 ε-carbide (Fe<sub>2.4</sub>C)가 부식 및 수소확산거동에 미치는 영향
박진성 ( Jin-seong Park ),윤덕빈 ( Duck Bin Yun ),성환구 ( Hwan Goo Seong ),김성진 ( Sung Jin Kim ) 한국부식방식학회 2021 Corrosion Science and Technology Vol.20 No.5
Effects of ε-carbide (Fe<sub>2.4</sub>C) on corrosion and hydrogen diffusion behaviors of ultra-strong steel sheets for automotive application were investigated using a number of experimental and analytical methods. Results of this study showed that the type of iron carbide precipitated during tempering treatments conducted at below A<sub>1</sub> temperatures had a significant influence on corrosion kinetics. Compared to a steel sample with cementite (Fe<sub>3</sub>C), a steel sample with ε-carbide (Fe<sub>2.4</sub>C) showed higher corrosion resistance during a long-term exposure to a neutral aqueous solution. In addition, the diffusion kinetics of hydrogen atoms formed by electrochemical corrosion reactions in the steel matrix with ε-carbide were slower than the steel matrix with cementite because of a comparatively higher binding energy of hydrogen with ε-carbide. These results suggest that designing steels with fine ε-carbide distributed uniformly throughout the matrix can be an effective technical strategy to ensure high resistance to hydrogen embrittlement induced by aqueous corrosion.
Zn-Al-Mg 합금도금강판의 헤어라인 처리가 표면흑색화 및 열확산도에 미치는 영향
박진성(Jin Sung Park),윤덕빈(Duck Bin Yun),김상헌(Sang Heon Kim),김태엽(Tae Yeob Kim),김성진(Sung Jin Kim) 한국표면공학회 2023 한국표면공학회지 Vol.56 No.1
The effects of hairline treatment on surface blackening and thermal diffusion behaviors of Zn-Al-Mg alloy coated steel sheet were evaluated by the three-dimensional surface profiler and laser-flash technique. The metallographic observation of coating damages by hairline treatments showed that several cracks were initiated and propagated along the interface between primary Zn/eutectic phases. As the hairline processing became more severe, the crack occurrence frequency in eutectic phase of coating layer and the surface roughness increased, which had a proportional relationship with the level of blackening on the coating surface. In addition, the higher interfacial areas of the blackened coating surface, caused by the hairline process, led to an increase in thermal diffusivity and conductivity of the coated steel sheet. On the other hand, when the coating damage by hairline treatment was excessive and the steel substrate was exposed, there was little difference between the thermal diffusivity/conductivity of the untreated sample though the blackening degree was higher than that of untreated sample. This work suggests that the increase in the surface areas of the coating layer without exposure to steel substrate through hairline treatment can be one of the effective technical strategies for the development of Zn-Al-Mg alloy coated steel sheets with higher blackening level and thermal diffusivity.