• 열처리공학회지
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• 제35권3호
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• pp.139-149
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• 2022

In the automobile and shipbuilding industries, various materials and components require superior surface strength, excellent wear resistance and good resistance to repeated loads. To improve the surface properties of the materials, various surface heat treatment methods are used, which include carburizing, nitriding, and so on. Among them, carburizing treatment is widely used for structural steels containing carbon. The effective carburizing thickness required for materials depends on the service environment and the size of the components. In general, however, there is a limit in evaluation of the surface properties with a standardized mechanical test method because the thickness or cross-sectional area of the carburized layer is limited. In this regard, the nanoindentation technique has lots of advantages, which can measure the mechanical properties of the material surface at the nano and micro scale. It is possible to understand the relationship between the microstructural change in the hardened layer by carburizing treatment and the mechanical properties. To be spread to practical applications at the industrial level, in this paper, the principle of the nanoindentation method is described with a representative application for analyzing the mechanical properties of the carburized material.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 추계학술발표회 초록집
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• pp.69-69
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• 2001

We report a study of the nitriding of the martensitic grade of stainless steel AKSK 420 in a low-pressure rl discharge using pure nitrogen. Much studied samples of the austenitic grade AISI 304 were treated at the same time to provide a comparison. With a treatment time of 4.0 h at $400^{\circ}C$, the nitrogen-rich layer on MSK 420 is 20pm thick and has a hardness about 4.3 times higher than that of the untreated material. The layer thickness is much greater than that obtained on AISI 304 under identical treatment conditions, reflecting the different Cr content of the two alloys. The alloy AlISI 420 is more susceptible than AISI 304 to the formation of CrN and ferrite, and this has a deleterious effect on the hardnes, gain. Below the temperature at which CrN forms, the treated layer retains its martensitic structure, but with a larger lattice parameter than the bulk, a phase that we term expanded martensite, by analogy with the situation with austenitic stainless steel. The fact that the treated layer retains a martensitic structure is interesting in view of previous evidence that nitrogen is an austenite stabilizer.

• 한국자기학회지
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• 제2권3호
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• pp.244-250
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• 1992

고밀도 자기기록 매체인 iron carbonitride는 출발물질인 iron oxalate$(FeC_2O_4{\cdot}2H_2O)$를 암모니아-수소 혼합 분위기 상태에서 질화함으로써 제조되었다. 또한 carbonitride 결정의 형태는 출발물질의 제조조건에 의존하며, 이의 침전반응 조건은 $60^{\circ}C,$ 30분이 가장 적당하였다. Fe일부에 대한 Sn의 치환은 입자성장을 억제하고, 침상성을 증가시키는 효과가 있었다. 전자현미경 관찰결과, 질화철 입자는 많은 미세한 단위입자들이 입체망목적으로 연결되어 있었으며, 이 단위입자는 단자구 정도의 크기로 관찰되었다. 이때 보자력과 포화자화는 각각 500 Oe, 120 emu/g 이었다.

• 한국재료학회지
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• 제19권9호
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• pp.457-461
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• 2009

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature.

• 열처리공학회지
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• 제14권2호
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• pp.103-109
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• 2001

Plasma nitrocarburising and post oxidation were performed on SM45C steel using a plasma nitriding unit. Nitrocarburising was carried out with various methane gas compositions with 4 torr gas pressure at $570^{\circ}C$ for 3 hours and post oxidation was carried out with 100% oxygen gas atmosphere with 4 torr at different temperatures for various times. It was found that the compound layer produced by plasma nitrocarburising consisted of predominantly ${\varepsilon}-Fe_{2-3}(N,C)$ and a small proportion of ${\gamma}-Fe_4(N,C)$. With increasing methane content in the gas mixture, ${\varepsilon}$ phase compound layer was favoured. In addition, when the methane content was further increased, cementite was observed in the compound layer. The very thin oxide layer on top of the compound layer was obtained by post oxidation. The formation of Oxide phase was initially started from the magnetite($Fe_3O_4$) and with increasing oxidation time, the oxide phase was increased. With increasing oxidation temperature, oxide phase was increased. However the oxide layer was split from the compound layer at high temperature. Corrosion resistance was slightly influenced by oxidation times and temperatures.

• 자원리싸이클링
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• 제12권5호
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• pp.29-35
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• 2003

국내의 화력발전소에서 발생되는 Fly ash와 활성탄을 원료로 사용하여 환원질화방법에 의해 $\beta$-Sialon 분말을 합성하였다. 분말합성은 $1,450^{\circ}C$에서 10시간 동안 질소분위기에서 합성하였으며, 또한 소결체 제조는 $1,550^{\circ}C$에서 3시간 동안 관상로에서 소결하였다. 본 실험에서 합성된 $\beta$-Sialon의 z value는 2.15이었으며 XRD 분석결과 $\beta$-Sialon 이외에 소량의 $SiO_2$와 $_FeSi{x}$ 가 일부 확인되었다. $\beta$-Sialon 소결체는 20시간 동안의 고온산화 결과 1,31$0^{\circ}C$까지는 열적으로 매우 안정하나 $1,360^{\circ}C$ 부근에서는 급격한 무게의 증가를 나타냈다. $1,360^{\circ}C$에서 10시간 고온산화 후 산화층은 mullite로 상전이가 일어났다.

• Journal of Advanced Marine Engineering and Technology
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• 제35권5호
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• pp.600-607
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• 2011

고탄소강은 사용자가 요구하는 특성을 만족시키기 위해 침탄, 질화, 고주파담금질 등에 의해 표면처리 되어져 왔다. 그러나 기존의 처리 방법은 모두 처리물 전체를 가열하거나 균일한 가열을 하지 못하여 표면처리 후 변형의 문제와 처리후의 후가공의 경비문제, 그리고 극히 일부분만 경화가 필요한 부품에는 적용하기 어려운 문제점이 있었다. 이러한 문제를 해결할 수 있는 표면처리법으로로써 레이저열처리 방법이 대두대고 있으며, 레이저열처리는 레이저 빔을 피처리물의 표면에 조사하고 적당한 속도로 이동을 하게 되면 레이저조사부위가 급속하게 가열되고 레이저 빔이 통과한 후에는 표면의 열이 내부로 열전도 되어 급속히 자기냉각(self-quenching)됨으로써 표면에 새로운 기계적 성질을 갖게 하는 열처리법이다. 본 연구에서는 기존의 CW Nd:YAG 레이저 열원보다 효율이 좋은 HPDL을 이용한 고효율, 고기능의 고탄소강 열처리 후 재료적 물성을 평가하였다. 그 결과 레이저빔의 조사속도 및 온도변화에 따른 열처리부 및 모재 부분에 대한 경도특성 및 미세조직의 특성을 명확히 할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제36권1호
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• pp.78-84
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• 2012

금형의 공정 과정에서 금형과 성형품 사이에서 발생하는 마찰로 인해 발생하는 금형의 마모가공차로 작용하여 성형 품질을 저하시킬 수 있다. 따라서 금형의 내마모성을 향상시키기 위해 질화나 침탄처리, 화염 및 고주파 표면처리 등의 방법들이 적용되어 왔다. 하지만 형상의 제한이나 제품의 변형 등과 같은 문제점을 수반하고 있기 때문에, 이러한 문제점을 해결할 수 있는 표면처리 방법으로써 레이저 표면처리 기술이 검토되고 있다. 따라서 본 연구에서는 고출력 다이오드 레이저를 이용, 금형재료용 주철의 표면처리를 시도하였다. 앞서 제1보와 제2보의 논문에서는 금형의 재료 및 형상의 차이에 따른 열처리 특성을 비교하였다면, 본 논문에서는 열처리 후 생성되는 경화부, 경계부위 및 모재의 조직적 차이를 분석하기 위해 광학 현미경 및 전자 현미경을 이용하여 미세조직을 관찰하고, EDS를 통해 조직의 상태를 파악하였다. 미세조직 관찰 결과, 경화부는 침상의 마르텐사이트 조직이 형성되어 있었다.

• 열처리공학회지
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• 제15권2호
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• pp.57-64
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• 2002

The 22%Cr-5%Ni-3%Mo duplex and 18%Cr-8%Ni austenitic stainless steels have been nitrogen permeated under the $1Kg/cm^2$ nitrogen gas atmosphere at the temperature range of $1050^{\circ}C{\sim}1150^{\circ}C$. The nitrogen-permeated duplex and austenitic stainless steels showed the gradual decrease in hardness with increasing depth below surface. The duplex stainless steel showed nitrogen pearlite at the outmost surface and austenite single phase in the center after nitrogen permeation treatment, while the obvious microstructural change was not observed for the nitrogen-permeated austenitic stainless steel. After solution annealing the nitrogen-permeated stainless steels(NPSA treatment) at $1200^{\circ}C$ for 10 hours, the hardness of the duplex and austenitic stainless steels was constant through the 2 mm thickness of the specimen, and the ${\alpha}+{\gamma}$ phase of duplex stainless steel changed to austenite single phase. Tensile strengths and elongations of the NPSA-treated duplex stainless steel remarkably increased compared to those of solution annealed (SA) duplex stainless steel due to the solution strengthening effect of nitrogen and the phase change from a mixture of ferrite and austenite to austenite single phase, while the NP-treated austenitic stainless steel displayed the lowest value in elongation due to inhomogeneous deformation by the hardness difference between surface and interior.

• 열처리공학회지
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• 제12권3호
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• pp.221-230
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• 1999

The surface nitrogen permeation of Al alloyed 0.14%C-13%Cr stainless steels was investigated after heat treating at $1050^{\circ}C{\sim}1150^{\circ}C$ in the nitrogen gas atmosphere. The strong affinity between Al and nitrogen permeates the nitrogen through the interior of the steels. Two precipitates of round type and needle type are observed at the surface layer. These precipitates mainly consist of AlN containing plenty of aluminum. The surface layer of 0.53%Al alloyed specimen shows ferrite phase, while the surface layers of 1.65%Al and 2.27%Al alloyed specimens appear ${\gamma}$ plus ${\alpha}$ phases. The depth of nitrogen permeation depends upon the Al content and microstructure of the matrix. The 1.65%Al alloyed specimen representing ${\alpha}+{\gamma}$ matrix phases at the nitrogen permeation temperature shows the maximum case depth in this experiment. Although the surface hardness increases by raising the Al content of the specimen owing to the increase of nitride precipitation density, the nitride precipitation deteriorates the corrosion resistance in the solution of HCl, $H_2SO_4$, and $FeCl_3$.