Glow Discharge Plasma Nitrocarburizing and Post Oxidation Treatments of SCM 435 Steel

이인섭(Insup Lee) 동의대학교 정보통신연구소 2002 정보통신연구지 Vol.3-1 No.-

Plasma nitrocarburizing and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin 1-2 f.l m ferritic oxide layer on top of a 15-25 f.l m E - Fe2-3(N,C) nitrocarburized layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily split from the compOlmd layer either for oxidation temperatures above 450'C, or for oxidation time more than 2 hours at oxidation temperature of 400 'C. It was confirmed that the relative amount of Fe203, compared with Fe304, increased rapidly with the oxidation temperature. The amounts of r-Fe₄(N,C) and θ-Fe₃C, generated from dissociation of ε-Fe2-3(N,C) phase during O₂ plasma sputtering, were also increased with the oxidation temperature.

AISI 316L stainless steel에 저온 플라즈마 침탄 및 질화처리 시 가스조성이 표면특성에 미치는 영향

이인섭(Insup Lee),안용식(Yong-Sik Ahn) 한국표면공학회 2009 한국표면공학회지 Vol.42 No.3

The 2-step low temperature plasma processes (the combined carburizing and post-nitriding) offer the increase of both surface hardness and thickness of hardened layer and corrosion resistance than the individually processed low temperature nitriding and low temperature carburizing techniques. The 2-step low temperature plasma processes were carried out for improving both the surface hardness and corrosion resistance of AISI 316L stainless steel. The influence of gas compositions on the surface properties during nitriding step were investigated. The expanded austenite (γN) was formed on all of the treated surface. The thickness of γN and concentration of N on the surface increased with increasing both nitrogen gas and Ar gas levels in the atmosphere. The thickness of γN increased up to about 20 ㎛ and the thickness of entire hardened layer was determined to be about 40 μm. The surface hardness was independent of nitrogen and Ar gas contents and reached up to about 1200 HV0.1 which is about 5 times higher than that of untreated sample (250 HV0.1). The corrosion resistance in 2-step low temperature plasma processed austenitic stainless steels was also much enhanced than that in the untreated austenitic stainless steels due to a high concentration of N on the surface.

저온 플라즈마 침질탄화처리된 마르텐사이트계 석출경화형 스테인리스강의 내식성에 미치는 시효 전처리의 영향

이인섭(Insup Lee),이천호(Chun-Ho Lee) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.2

Various aging treatments were conducted on AISI 630 martensitic precipitation hardening stainless steel in order to optimize aging condition. Aging treatment was carried out in the vacuum chamber of Ar gas with changing aging temperature from 380℃ to 430℃ and aging time from 2h to 8h at 400℃. After obtaining the optimized aging condition, several nitrocarburizing treatments were done without and with the aging treatment. Nitrocarburizing was performed on the samples with a gas mixture of H₂, N₂ and CH₄ for 15 h at vacuum pressure of 4.0 Torr and discharge voltage of 400V. The corrosion resistance was improved noticeably by combined process of aging and nitrocarburizing treatment, which is attributed to higher chromium and nitrogen content in the passive layer, as confirmed by XPS analysis. The optimized condition is finalized as, 4h aging at 400℃ and then subsequent nitrocarburizing at 400℃ with 25% nitrogen and 4% methane gas for 15h at vacuum pressure of 4.0 Torr and discharge voltage of 400V, resulting in the surface hardness of around 1300 HV0.05 and α"N layer thickness of around 11 μm respectively.

316L 오스테나이트계 스테인리스강의 저온 플라즈마질화처리시 공정변수가 표면경화층 특성에 미치는 영향

이인섭(Insup Lee) 한국표면공학회 2019 한국표면공학회지 Vol.52 No.4

A systematic investigation was made on the influence of processing parameters such as gas composition and treatment temperature on the surface characteristics of hardened layers of low temperature plasma nitrided 316L Austenitic Stainless Steel. Various nitriding processes were conducted by changing temperature (370℃ to 430℃) and changing N2 percentage (10% to 25%) for 15 hours in the glow discharge environment of a gas mixture of N2 and H2 in a plasma nitriding system. In this process a constant pressure of 4 Torr was maintained. Increasing nitriding temperature from 370℃ to 430℃, increases the thickness of S phase layer and the surface hardness, and also makes an improvement in corrosion resistance, irrespective of nitrogen percent. On the other hand, increasing nitrogen percent from 10% to 25% at 430℃ decreases corrosion resistance although it increases the surface hardness and the thickness of S phase layer. Therefore, optimized condition was selected as nitriding temperature of 430℃ with 10% nitrogen, as at this condition, the treated sample showed better corrosion resistance. Moreover to further increase the thickness of S phase layer and surface hardness without compromising the corrosion behavior, further research was conducted by fixing the N₂ content at 10% with introducing various amount of CH₄ content from 0% to 5% in the nitriding atmosphere. The best treatment condition was determined as 10% N₄ and 5% CH₄ content at 430℃, where the thickness of S phase layer of about 17 μm and a surface hardness of 980 HV0.1 were obtained (before treatment 250 HV0.1 hardness). This specimen also showed much higher pitting potential, i.e. better corrosion resistance, than specimens treated at different process conditions and the untreated one.

AISI316L 강에 저온 플라즈마침탄 및 DLC 복합 코팅처리 시 처리온도에 따른 표면특성평가

이인섭(Insup Lee) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.6

A low temperature plasma carburizing process was performed on AISI 316L austenitic stainless steel to achieve an enhancement of the surface hardness without degradation of its corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface hardened layer during low temperature plasma carburizing in order to obtain thre optimum processing conditions. The expanded austenite (?c) phase, which contains a high saturation of carbon (S phase), was formed on all of the treated surfaces. Precipitates of chroamium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at 55o ℃. The hardened layer thickness of ?c increased up to about 65 ㎛ with increasing treatment temperature. The surface hardness reached about 900 HK0.05, which is about 4 times higher than that of the untreated sample (250 HK0.05). A minor loss in corrosion resistance was observed for the specimens treated at temperatures of 300 ℃-450 ℃ compared with untreated austenitic stainless steel. In particular, the precipitation of chromium carbides at 550 ℃ led to a significant decrease in the corrosion resistance. A diamond-like carbon (DLC) film coating was applied to improve the wear and friction properties of the S phase layer. The DLC film showed a law and stable friction coefficient value of about 0.1 compared with that of the carburized surface (about 0.45). The hardness and corrosion resistance of the S phase layer were further improved by the application of such a DLC film

SDSS (Super Duplex Stainless Steel) 강관의 미세조직 및 부식특성에 미치는 열처리 온도의 영향

이인섭(Insup Lee),천창석(Chang-seok Cheon),임태홍(Tai-Hong Yim),한윤호(Yoon-Ho Han),이면학(Myon-Hag Lee) 한국표면공학회 2015 한국표면공학회지 Vol.48 No.6

The aim of this paper is to determine the proper heat treatment temperature for SDSS tube production without σ-phase precipitation. When Mother steel tube was heat treated at 800℃ temperature, relatively a large amount of σ-phase precipitated and grain refinement of ferrite phase occurred simultaneously. However, in Pilgered and Drawn steel tubes, grain refinement of the ferrite phase did not occur and a small amount of σ-phase precipitated. For all three types of steel tubes, the pitting potential was reduced to 2/5 or less compared with the untreated one and corrosion also occurred in the salt spray test due to the precipitation of σ-phase. When heat treatment temperature was 900℃, grain refinement of the ferrite phase occurred and very little σ-phase precipitated in Pilgered and Drawn steel tubes. But when heat treatment was done at 1,000℃ temperature, all three types of steel tubes had a similar corrosion properties of that of untreated one and also corrosion did not occur in the salt spray test, as σ-phase did not precipitate. Therefore, the optimum heat treatment temperature range is determined to be more than 1000℃ for the SDSS at which corrosion does not occur.

STS 204Cu 스테인리스강의 저온 플라즈마 침질탄화 처리 시 CH₄ 가스 함량에 따른 경화층 (S-Phase) 거동

이인섭(Insup Lee),김호준(Hojun Kim) 한국표면공학회 2018 한국표면공학회지 Vol.51 No.1

Plasma Nitriding treatment was performed on STS 204Cu stainless steel samples at a temperature of 400℃ for 15 hours with varying N2 content as 10%, 15% and 25%. Regardless of the content of N₂, S-Phase which is a hardened layer of Nitrogen (N) supersaturated phase, was formed in the surface of plasma treated samples. When N₂ content was 25%, the thickness of the hardened layer reached up to about 7 μm and the surface hardness reached a value of 560 Hv0.05, which is about 2.5 times higher than that of untreated sample (as received 220 Hv0.05). From potentiodynamic polarization test, it was observed that compared to as received sample, the corrosion potential and the corrosion current density of the plasma treated samples were decreased regardless of the N₂ content, but the corrosion resistance was not increased much due to the precipitation of Cr₂N. On the other hand, pitting potential of the samples treated with 10% and 15% N₂ was higher than that of as received sample, however, the samples treated with 25% exhibited a lower pitting potential. Therefore, 10% N₂ content was selected as optimum plasma nitriding condition and to further increase both the thickness and surface hardness and the corrosion resistance of the hardened layer, different CH₄ content such as 1%, 3% and 5% was introduced into the plasma nitriding atmosphere. With 1% CH₄, the thickness of the hardened layer reached up to about 11 μm and the surface hardness was measured as about 620 Hv0.05, which is about 2.8 times that of as received sample. And the corrosion resistance of the plasma treated sample by using 1% CH4 was improved significantly due to much higher pitting potential, and lower corrosion current density. When the CH₄ content was more than 1%, the thickness and surface hardness of the hardened layer decreased slightly and the corrosion resistance also decreased.

AISI304L 강에 저온 플라즈마침탄 처리 시 처리조건에 따른 표면특성평가

이인섭(Insup Lee) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.1

A low temperature plasma carburizing process was peformed to AISI 304L austenitic stainless steel to achieve the enhancement of surface hardness without a compromise in their corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface-hardened layer during law temperature plasma carburizng in order to obtain the optimum processing conditions. The expanded austenite (yc) was formed on all the treated surfaces. Precipitates of chromium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at 500℃. The hardened layer thickness of yc increased up to about 35 ㎛, with increasing treatment temperature. The surface hardness reached about 1000 HK0.05, which is about 4 times higher than that of the untreated sample (250 HK0.05). Minor loss in corrosion resistance was observed for the specimens treated at temperatures of 310℃-450℃ compared with untreated austenitic stainless steel. Particularly, the precipitation of chromium carbides at 500℃ led to a significant decrease in the corrosion resistance.

전착된 Fe-52%Ni 합금의 결정립 성장과 경도 특성 연구

이민수(Minsu Lee),한윤호(Yoonho Han),엄호경(Hokyung Um),박종수(Jonsoo Park),이인섭(Insup lee),안진호(Jinho Ahn),임태홍(Tai Hong Yim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5

Nanocrystalline Fe-52wt%Ni alloy for a metal substrate of flexible solar cell was fabricated by electroforming. For metal substrate of flexible solar cell, it is required the behavior of thermal expansion which is closed to that of semiconductor layer and outstanding mechanical characteristic. Heat treatment temperature was varied to study the influence of grain size on hardness. From this, we intended to optimize the mechanical properties. Nanocrystalline Fe-Ni alloy was analyzed through XRD and grain size was calculated by Scherrer equation. The grain size of alloys after heat treatment at 400℃, 600℃ and 800℃ was measured by SEM and optical microscope. The grain size of electrodeposited Fe-52wt% Ni alloy was increased from 10㎚ to 5㎛ according to hear treatment. The hardness and grain size relationship in heated microcrystalline Fe-52wt%Ni alloy corresponds to Hall-petch equation.

플라즈마 산질화처리된 SCM435강의 표면경화층의 미세조직과 특성

전은갑,박익민,이인섭,Jeon Eun-Kab,Park Ik-Min,Lee Insup 한국재료학회 2004 한국재료학회지 Vol.14 No.4

Plasma nitrocarburising and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin ferritic oxide layer 1-2 $\mu\textrm{m}$ thick on top of a 15~25 $\mu\textrm{m}$ $\varepsilon$-F $e_{2-3}$(N,C) nitrocarburized compound layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily spalled from the compound layer either for both oxidation temperatures above $450^{\circ}C$, or for oxidation time more than 2 hrs at oxidation temperature $400^{\circ}C$. It was confirmed that the relative amount of $Fe_2$$O_3$, compared with $e_3$$O_4$, increased rapidly with the oxidation temperature. The amounts of ${\gamma}$'-$Fe_4$(N,C) and $\theta$-$Fe_3$C, generated from dissociation from $\varepsilon$-$Fe_{2-3}$ /(N,C) phase during $O_2$ plasma sputtering, were also increased with the oxidation temperature.e.