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Inconel 718의 국부 부식 저항성에 미치는 용체화 열처리의 영향
이윤화,이준섭,권순일,신정호,이재현,Yoonhwa Lee,Jun-Seob Lee,Soon Il Kwon,Jungho Shin,Je-hyun Lee 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.5
The localized corrosion resistance of the Ni-based Inconel 718 alloy after solution heat treatment was evaluated using electrochemical techniques in a solution of 25 wt% NaCl and 0.5 wt% acetic acid. Solution heat treatment at 1050 ℃ for 2.5 hours resulted in an increased average grain diameter. Both Ti carbides (10 ㎛ diameter) and Nb-Mo carbides (1 - 9 ㎛ diameter) were distributed throughout the material. Despite heat treatment, the shape and composition of these carbides remained consistent. An increase in solution temperature led to a decrease in pitting potential value. However, the pitting potential value of solution heat-treated Inconel 718 was consistently higher than that of as-received Inconel 718 at all tested temperatures. Localized corrosion initiation occurred at 0.4 V<sub>SSE</sub> in a temperature environment of 80 ℃ for both as-received and solution heat-treated Inconel 718 alloys. X-ray photoelectron spectroscopic analysis indicated that the composition of the passive film formed on specimen surfaces remained largely unchanged after solution heat treatment, with O1s, Cr2p<sub>3/2</sub>, Fe2p<sub>3/2</sub>, and Ni2p<sub>3/2</sub> present. The difference in localized corrosion resistance between as-received and solution heat-treated Inconel 718 alloys was attributable to microstructural changes induced by the heat treatment process.
고농도 침탄강의 탄화물 형성과 피팅 피로강도에 미치는 탄소 포텐셜의 영향
소상진 ( Sangjin So ),신정호 ( Jungho Shin ),임재원 ( Jae-won Lim ),이석재 ( Seok-jae Lee ) 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.3
In the present work, we investigated the effects of the carbon potential on the formation of carbide at the carburized surface and anti-pitting fatigue strength in the supercarburized steels. Two low carbon steels with different Cr concentrations were adopted and the repeated supercarburizing treatment carried out with the different carbon potential conditions. The microstructure and carbides at the supercarburized surface were observed by using optical microscope and scanning electron microscope. The microhardness test was performed and the hardness distribution and the effective case depth at the supercarburized surface were discussed. The roller pitting fatigue test was carried out and the fatigue strength was evaluated with different the carbon potential conditions. The microstructure of the fatigue specimen surface was observed by means of scanning electron microscope and scanning transmission electron microscope. Depending on the chemical composition of the steels and the carbon potential condition, the resistance of temper softening and pitting failure was influenced due to the carbide distribution and the formation of coarse network carbide. Thus, it was confirmed that the control of the carbide formation is a key factor to improve the anti-pitting fatigue strength in the supercarburized steels.
이준섭 ( Jun-seob Lee ),이예진 ( Yejin Lee ),권순일 ( Soon Il Kwon ),신정호 ( Jungho Shin ),이재현 ( Je-hyun Lee ) 한국부식방식학회 2021 Corrosion Science and Technology Vol.20 No.6
Localized corrosion behavior of Ni-based Inconel 718 alloy was investigated by electrochemical anodic polarization techniques in NACE TM 0177 A solution of 5 wt% NaCl + 0.5 wt% acetic acid at room temperature. After the solution heat treated at 1080 ℃ for 2.5 h, Inconel 718 was age-hardened at 780 ℃ for 8 h. The microstructure of the alloy surface was investigated by optical microscopic or scanning electron microscopic technique. The austenitic phase with the presence of metal carbides was observed on the surface of Inconel 718. Metal-carbides such as Nb-Mo and Ti-carbide with diameters of approximately 10 and 3 μm, respectively, were formed in Inconel 718. Anodic polarization results revealed that localized corrosion was observed at the interface between austenitic phase of a substrate and metal carbides. Difference in electrochemical property between a metal carbide and an austenitic substrate could provide an initiation site for localized corrosion of Inconel 718 surface.