• 한국주조공학회지
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• 제27권4호
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• pp.179-183
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• 2007

The TiC layer was formed on Ti and Ti alloys by plasma carburizing method. The main experimental parameters for plasma car boozing were temperature and time. XRD, EDX, hardness test and corrosion test were employed to analyze the evolution and material properties of the layer. The preferred orientation of TiC layers is (220) at treated temperature of $700^{\circ}C\;and\;880^{\circ}C$ However, it is changed to (200) at temperature of $800^{\circ}C$ The thickness of carbide layer increase with increasing carburizing temperature. Highest hardness of hardened layer formed on CP-Ti was obtained at the carburizing condition of processing temperature $880^{\circ}C$ and processing time 1080min. The corrosion potential of carburizing specimen was higher than untreated CP-titanium, and corrosion potential increased as carburizing temperature and time increased. Thus the corrosion resistance of CP-Ti was greatly enhanced after plasma carburizing treatment.

• 한국표면공학회지
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• 제50권4호
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• pp.272-276
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• 2017

The response of AISI 310 type austenitic stainless steel to the novel low temperature plasma carburizing process has been investigated in this work. This grade of stainless steel shows better corrosion resistance and high temperature oxidation resistance due to its high chromium and nickel content. In this experiment, plasma carburizing was performed on AISI 310 stainless steel in a D.C. pulsed plasma ion nitriding system at different temperatures in $H_2-Ar-CH_4$ gas mixtures. The working pressure was 4 Torr (533Pa approx.) and the applied voltage was 600 V during the plasma carburizing treatment. The hardness of the samples was measured by using a Vickers micro hardness tester with the load of 100 g. The phase of carburized layer formed on the surface was confirmed by X-ray diffraction. The resultant carburized layer was found to be precipitation free and resulted in significantly improved hardness and corrosion resistance.

• 한국재료학회지
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• 제12권10호
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• pp.776-783
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• 2002

Austenitic stainless steel (STS304) has been carburized using glow discharge plasma and its microstructure, wear resistance and corrosion property have been investigated. A repeat boost-diffuse carburizing was used as an effective plasma carburizing method. The effective case depth of the plasma carburized specimens was increased with the carbon concentration at the surface area. The specimens prepared by 3 hours plasma carburizing under $600^{\circ}C$ did not have the standard hardness for the effective case depth, but the specimen prepared by 11 hours plasma carburizing at $500^{\circ}C$ had nearly the same hardness with the specimen plasma carburized for 3 hours at $800^{\circ}C$. The wear resistance increased with temperature but the corrosion properties of the specimens prepared over $600^{\circ}C$ decreased rapidly due to the grain boundary sensitization. However, the specimen plasma carburized for 11 hours at $500^{\circ}C$ had nearly the same wear resistance with the specimen plasma carburized for 3 hours at $800^{\circ}C$ without deterioration of corrosion property. This could be resulted from the fact that the microstructure of the specimen plasma carburized for 11 hours at $500^{\circ}C$ was composed of martensite and austenite, because a partial martensite transformation was occurred only in the specimen plasma carburized for 11 hours at 50$0^{\circ}C$.

• 대한금속재료학회지
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• 제46권3호
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• pp.125-130
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• 2008

Conventional plasma carburizing or nitriding for austenitic stainless steels results in a degradation of corrosion resistance. However, a low temperature plasma surface treatment can improve surface hardness without deteriorating the corrosion resistance. The 2-step low temperature plasma processes (the combined carburizing and post nitriding) offers 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. In the present paper, attempts have been made to investigate the influence of the introduction of Ar gas (0~20%) in nitriding atmosphere during low temperature plasma nitriding at $370^{\circ}C$ after low temperature plasma carburizing at $470^{\circ}C$. All treated specimens exhibited the increase of the surface hardness with increasing Ar level in the atmosphere and the surface hardness value reached up to 1050 HV0.1, greater than 750 $HV_{0.1}$ in the carburized state. The expanded austenite phase (${\gamma}_N$) was observed on the most of the treated surfaces. The thickness of the ${\gamma}_N$ layer reached about $7{\mu}m$ for the specimen treated in the nitriding atmosphere containing 20% Ar. In case of 10% Ar containing atmosphere, the corrosion resistance was significantly enhanced than untreated austenitic stainless steels, whilst 20% Ar level in the atmosphere caused to form CrN in the N-enriched layer (${\gamma}_N$), which led to the degradation of corrosion resistance compared with untreated austenitic stainless steels.

• 한국재료학회지
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• 제10권7호
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• pp.505-514
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• 2000

플라즈마 침탄한 저 탄소 Cr-Mo 강(0.176C-1.014Cr-0.387Mo)의 침탄 특성과 피로성질을 고찰하였다. 플라즈만 침탄한 시편의 유효경화깊이는 가스 침탄한 시편에 대해 상대적으로 침타나시간이 짧고 침탄온도가 낮음에도 불구하고 50%정도까지 증가되었다. 플라즈만 침탄시 유효경화깊이의 증가는 표면탄소농도의 증가와 같은 경향을 보였으며, 표면탄소농도의 증가와 같은 경향을 보였으며, 표면탄소농도의 증가율이 침탄시간의 증가에 따라 감소하였다. 플라즈만 침탄간의 피로한도는 가스 침탄강의 경우보다 높았다. 이를 표면근처의 미세구조, 경화깊이 잔류, 오스테나이트와 압축잔류응력으로 조사한 결과 경화깊이와 압축잔류응력의 차이가 거의 없었다. 따라서 플라즈만 침탄의 피로강도 향상은 가스침탄에 비해 표면이 상승층이 저감되어 표면에서의 미소균열의 발생 및 초기 균열 전파과정이 지연 되어진 것으로 판단된다. 파단면 관찰결과 표면에서 균열이 시작되고 플라즈마 침탄의 경우 입내파괴가 현저하였다.

• 한국표면공학회지
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• 제42권3호
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• pp.116-121
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• 2009

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 (${\gamma}_N$) was formed on all of the treated surface. The thickness of ${\gamma}_N$ and concentration of N on the surface increased with increasing both nitrogen gas and Ar gas levels in the atmosphere. The thickness of ${\gamma}_N$ increased up to about $20{\mu}m$ and the thickness of entire hardened layer was determined to be about $40{\mu}m$. The surface hardness was independent of nitrogen and Ar gas contents and reached up to about 1200 $HV_{0.1}$ which is about 5 times higher than that of untreated sample (250 $HV_{0.1}$). 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.

• 대한금속재료학회지
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• 제46권6호
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• pp.357-362
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• 2008

The 2-step low temperature plasma processes (the combined carburizing and post-nitriding) were carried out for improving both the surface hardness and corrosion resistance of AISI 316L stainless steel. The effects of processing time and temperature on the surface properties during nitriding step were investigated. The expanded austenite (${\gamma}_N$) was formed on all of the treated surface. The thickness of ${\gamma}_N$ was increased up to about $20{\mu}m$ and the thickness of entire hardened layer was determined to be about $40{\mu}m$. The surface hardness reached up to $1,200HV_{0.1}$ which is about 5 times higher than that of untreated sample ($250HV_{0.1}$). The thickness of ${\gamma}_N$ and concentration of N on the surface were increased with increasing processing time and temperature. The corrosion resistance in 2-step low temperature plasma processed austenitic stainless steels was enhanced more than that in the untreated austenitic stainless steels due to a high concentration of N on the surface.

• 열처리공학회지
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• 제16권4호
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• pp.191-196
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• 2003

For improvement of the wear performance of Ti alloy, vacuum-carburizing technique was tried for the first time using propane atmosphere. During the low pressure carburizing carbide was formed at the surface and carbon transfer was occurred from the carbide to the matrix. It was found that: (i) surface hardness increased with the reduction of operating pressure and time; (ii) optimum hardness distribution could be obtained with the proper choice of temperature and carbon flux control; and, (iii) case depth was largely influenced not by time but by temperature. The two steps process was recommended for obtaining thick case depth and high surface hardness of Ti alloy. For the low oxygen partial pressure, it was necessary to introduce additional CO gas to the atmosphere.Grain boundary oxidation and non-uniformity could be prevented.

• 한국재료학회지
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• 제8권8호
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• pp.707-713
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• 1998

현재 자동차용 소재 및 기계부품에 폭넓게 이용되는 SCM415강의 플라즈마 침탄 특성을 연구하기 위해 가스조성, 압력, 전류밀도, 온도 및 시간을 변수로 사용하였다. 가스조성의 경우 저합금강에서는 수소 가스 효과보다 메탄가스에 의해 주로 침탄특성이 좌우되며 메탄가스 100%일 때 시편 내의 모든 방향에서 경화층 분포가 일정하고, 최대의 유효경화깊이를 얻을 수 있었다. 가스압력이나 플라즈마 전압이 상승할 때 전류밀도가 상승하게 되는데, 이에 따라 최표면의 탄소농도가 증가되어 강의 유효경화깊이는 증대되었다. 침탄 온도일 경우 적어도 85$0^{\circ}C$이상되어야 유효경화깊이를 얻을 수 있었고, 온도가 상승할수록 유효경화깊이의 증가를 나타내어 침탄 효과가 우수하였다. 탄소의 확산 깊이는 침탄 시간의 제곱근에 비례하는 것으로 나타났다. 플라즈마 치탄한 강의 피로강도를 평가한 결과 열처리하지 않은 시편이나 재가열처리한 시편에 비해 높은 피로강도를 나타내었다.

• 한국해양공학회지
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• 제25권1호
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• pp.56-60
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• 2011

A low temperature plasma carburizing process was performed 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 low temperature plasma carburizng in order to obtain the optimum processing conditions. The expanded austenite (${\gamma}C$) 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 $500^{\circ}C$. The hardened layer thickness of ${\gamma}C$ increased up to about $35\;{\mu}m$, with increasing treatment temperature. The surface hardness reached about 1000 $HK_{0.05}$, which is about 4 times higher than that of the untreated sample (250 $HK_{0.05}$). Minor loss in corrosion resistance was observed for the specimens treated at temperatures of $310^{\circ}C-450^{\circ}C$ compared with untreated austenitic stainless steel. Particularly, the precipitation of chromium carbides at $500^{\circ}C$ led to a significant decrease in the corrosion resistance.