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  • Title/Summary/Keyword: hardened layer

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Effects of Alloying Elements on Hardening of 13Cr Stainless Steels Using Plasma Nitriding Process (플라즈마질화처리에 의한 13Cr 스테인리스강의 표면경화특성에 미치는 질화물형성원소첨가의 영향)

  • ;;;;中田一博
    • Journal of Welding and Joining
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    • v.16 no.1
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    • pp.88-97
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    • 1998
  • The surface characteristics of 13Cr stainless steel systems by plasma nitriding were investigated. The plasma nitriding for the 13Cr steels, in which the nitriding forming elements such as Ti, V, W, Nb, Al, Zr and Si were added about 2~3wt.%, respectively, was performed. In all nitrided specimens, .epsilon.-F e23N, UPSILON.'-F e4N and CrN were detected as the nitrides with the a-Fe in the nitrided layer. VN and .betha.- W2N were also detected in 13Cr-3V and 13Cr-3W alloys. The growth of the nitrided layer was controlled by the diffusion process. The thickness of the nitrided layer was similar in the 13Cr-2Nb and 3Zr specimens to that of 13Cr(BM) specimen, while the others exhibited the thinner layer. The activation energy for the growth of the nitrided layer in the temperature range of 773-873K was about 130kJ/mol in 13Cr(BM), 13Cr-2Ti, 3W, 3Al, 3Zr and 3Si alloys. The hardness of the nitrided specimens was significantly increased above Hv1000, comparing to the non-nitrided specimen. The specimens with the nitrided forming elements revealed much higher hardness values and, especially, 13Cr-3Al, 3V and 3Si specimens were significantly hardened up to Hv1300.v1300.0.

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Characterization of Aluminum Coated Layer in Hot Press Forming of Boron Steel (고온 프레스성형시 보론강 알루미늄 코팅층 거동특성)

  • Jang, Jeong-Hwan;Joo, Byeong-Don;Lee, Jae-Ho;Moo, Young-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.21 no.4
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    • pp.183-188
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    • 2008
  • Hot press forming allows geometrically complicated parts to be formed from sheet and the rapid cooling hardens them to extremely high strength. The main purpose of this research is to characterize Al coated layer in Al coated boron steel during hot press forming. For the hot press hardening experiment, test specimens were heated up to 810930C and held for 3, 6 and 9 minutes, respectively. And then, some specimens were press hardened and others were air-cooled without any pressing for the comparison purpose. Al coated layer shows four distinct micro-structural regions of interest; diffusion zone, Al-Fe zone(I) low-Al zone(LAZ) and Al-Fe zone(II). Band-like LAZ is clearly shown at temperature ranges of 810870C and sparsely dispersed at temperature higher than 900oC. The micro-cracking behavior in the Al coated layer during forming were also analyzed by bending and deep drawing tests. The strain concentration in softer LAZ is found to be closely related with micro-cracking and exfoliation in coated layer during forming.

The Effects of Processing Parameters on Surface Hardening Layer Characteristics of Low Temperature Plasma Nitriding of 316L Austenitic Stainless Steel (316L 오스테나이트계 스테인리스강의 저온 플라즈마질화처리시 공정변수가 표면경화층 특성에 미치는 영향)

  • Lee, Insup
    • Journal of Surface Science and Engineering
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    • v.52 no.4
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    • pp.194-202
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    • 2019
  • 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 (370C to $430^{\circ}C$) 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 370C to 430C, 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 430C 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 430C 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% N2 and 5% CH4 content at 430C, where the thickness of S phase layer of about 17μm and a surface hardness of 980HV0.1 were obtained (before treatment 250HV0.1 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.

A Numerical Analysis of Eddy-Current Electromagnetic Field for the In-Process Measurement of Case Depth in Laser Surface Hardening Processes (레이저 표면경화공정에서 경화층깊이의 실시간 측정을 위한 와전류 전자기장의 이론적 해석)

  • 박영준;조형석;한유희
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.529-539
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    • 1994
  • In laser heat treatment process of steels, the thin layer of substrate is rapidly heated to the austenitizing temperature and subsequently cooled at a very fast rate due to the self-quenching effect. Consequently, it is transformed to martensitic structure which has low magnetic permeability. This observation facilitates the use of a sensor measuring the change of electromagnetic field induced by the hardening layer. In this paper, the eddy-current electromagnetic field is analyzed by a finite element method. The purpose of this analysis is to investigate how the electrical impedance of the sensor's sensing coil varies with the change in permeability. To achieve this, a numerical model is formulated, taking into consideration the hardening depth, distance of the sensor from the hardened surface and the frequency driving the sensor. The results obtained by numerical simulation show that the eddy-current measurement method can feasibly be used to measure the changing hardening depth within the frequency range from 10 kHz to 50 kHz.

A Study on the Toughness of Die Steel Coated with VC (vanadium carbide) by Immersing in Molten Borax Bath (용융염 침적법에 의한 VC Coating 금형강의 인성에 관한 연구)

  • Lee, B.K.;Nam, T.W.
    • Journal of the Korean Society for Heat Treatment
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    • v.6 no.2
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    • pp.59-69
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    • 1993
  • Bending fracture strength test and impact strength test were made for VC coated die steels treated by immersing in molten borax bath and for hardened steels which were quenched and tempered, in order to clarify the effect of VC coating at 1000C. The material used in this investigation was representative cold and hot work die steels STD11, STD61. The results obtained are as follows. 1) The bending fracture strength of VC coated die steel (STD11, STD61) was lessened with increasing the thickness of the VC coated layer. 2) With increasing the immersing time (imcreasing the thickness of the VC coated layer) the maximum hardness was obtained at 480 minutes holding, after that holding time hardness was decreased. 3) The impact strength of the VC coated die steel was not decreased. In the casse of STD11, it was higher than that of the quenched condition especially at low tempering temperature, and vice versa at high tempering temperature. However in the case of STD61 shows the result to the contrary.

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A Study on Dusting of Formed Concrete Surface (목제(木製)거푸집 사용으로 콘크리트표면(表面)에 발생(發生)하는 경화불량현상(硬化不良現象)에 대한 연구(研究))

  • Moon, Han Young;Choi, Jae Jin
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.3 no.2
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    • pp.73-85
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    • 1983
  • We occasionally find a thin layer of imperfectly hardened concrete surface when the wood form is stripped off. It has been generally believed that the principal causes were the effects of reactive form oil, adhesive agent or formalin which has been used in the course of plywood manufacturing. However, in this experiment, it became clear that the concrete surface could be influenced more harmfully by a certain species of wood form and the storage conditions of wood form rather than any other causes. Especially, the main cause of the severely dusty layer is the use of wood form exposed to sun for a long period. Countermeasures, therefore, for preventing concrete surface from dusting are also discussed in this paper.

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The Effects of Gas Compositions During Post Nitriding on the AISI 316L Stainless Steel after Plasma Carburizing

  • Lee, Insup
    • Journal of Surface Science and Engineering
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    • v.48 no.6
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    • pp.269-274
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    • 2015
  • In this experiment, post-nitriding treatment was performed at 400C on AISI 316 stainless steel which was plasma carburized previously at 430C for 15 hours. Plasma nitriding was implemented on AISI 316 stainless steel at various gas compositions (25% N2, 50% N2 and 75% N2) for 4 hours. Additionally, during post nitriding Ar gas was used with H2 and N2 to observe the improvement of surface properties. After treatment, the behavior of the hybrid layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. Meanwhile, it was found that the surface hardness increased with increasing the nitrogen gas content. Also small percentage of Ar gas was introduced in the post nitriding process which improved the hardness of the hardened layer but reduced the corrosion resistance compared with the carburized sample. The experiment revealed that AISI 316L stainless steel showed better hardness and excellent corrosion resistance compared with the carburized sample, when 75% N2 gas was used during the post nitriding treatment. Also addition of Ar gas during post nitriding treatment degraded the corrosion resistance of the sample compared with the carburized sample.

Analysis of Bending Behavior of Ultra-thin SS304 Stainless Steel Sheets Considering the Surface Effect (표면 효과를 고려한 극박 SS304 스테인리스 강판의 굽힘 거동 분석)

  • Jung, J.;Chae, J.Y.;Chung, Y.;Kim, J.H.
    • Transactions of Materials Processing
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    • v.29 no.6
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    • pp.323-330
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    • 2020
  • The surface region of a sheet metal may have different characteristics from the inner region because the surface region is less restricted than the interior. In addition, the grains on the free surface are less hardened because of surface adsorption of the dislocations, rather than piling up. In the case of bulk or thick sheet metals, this effect is negligible because the fraction of the surface region is much smaller than that of the inner region. However, this surface effect is important in the case of ultra-thin sheet metals. In order to evaluate the surface effect, tensile and bending tests were performed for the SS304 stainless steel with a thickness of 0.39 mm. The bending force predicted using the tensile behavior is higher than the measurement because of the surface effect. To account for the surface effect, the surface layer model was developed by dividing the sheet section into surface and inner layers. The mechanical behaviors of the two regions were calibrated using the tensile and bending properties. The surface layer model reproduced the bending behavior of the ultra-thin sheet metal.

Frictional behaviour of Oxide Films Produced on S45C Steel by Plasma Nitrocarburizing and Post Plasma Oxidation Treatment (플라즈마 질탄화 & 후산화처리로 S45C강에 형성된 산화막의 마찰거동)

  • Jeong, Kwang-Ho;Lee, In-Sup
    • Korean Journal of Materials Research
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    • v.16 no.12
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    • pp.766-770
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    • 2006
  • The frictional behavior of oxide films on top of the plasma nitrocarburized compound layers was investigated in terms of post-oxidation treatment temperatures. The post-oxidation treatment at both temperatures(400C,500C) produced magnetite(Fe3O4) films which led to a significant enhancement in corrosion resistance. However, this process did not result in any improvement in frictional behavior of the nitrocarburized surface. The wear mechanisms were governed predominantly by the abrasive action of the slider on the surface irrespective of the counterface material(SiC and Bearing steel). When the specimen was sliding against a SiC counterface, the oxide films were destroyed during the early stage of the sliding process and the wear debris of the oxide film at the sliding track had a great influence on the friction coefficient. On the other hand, when sliding against a bearing steel counterface, the slider was mainly worn out due to the much higher hardness of the surface hardened layer. The fluctuation of the friction coefficient of 400C-oxidized/ nitrocarburized specimen is much severer than that of 500C specimen, due to the less amount of wear debris.

The effects of post nitriding on the AISI 316 stainless steel after Plasma carburizing at various gas compositions (저온 플라즈마침탄처리된 316L 스테인레스 스틸의 플라즈마 후질화 처리시 표면특성에 미치는 가스조성의 영향)

  • Lee, In-Seop;Debnath, Sanket
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2012.05a
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    • pp.177-178
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    • 2012
  • In this experiment, post-nitriding treatment has been performed at 400C on AISI 316 stainless steel which is plasma carburized previously at 430C for 15 hours. Plasma nitriding was implemented on AISI 316 stainless steel at various gas compositions (25% N2, 50% N2 and 75% N2) for 4 hours. Additionally, during post nitriding Ar gas was used with H2 and N2 to observe the improvement of treatment. After treatment, the behavior of the hybrid layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. Meanwhile, it was found that the surface hardness increased with increasing the nitrogen gas content. Also small percentage of Ar gas was introduced in the post nitriding process which improved the hardness of the hardened layer but reduces the corrosion resistance compared with the carburized sample. The experiment revealed that AISI 316L stainless steel showed better hardness and excellent corrosion resistance compared with the carburized sample, when 75% N2 gas was used during the post nitriding treatment. Also addition of Ar gas during post nitriding treatment were degraded the corrosion resistance of the sample compared with the carburized sample.

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