• 대한기계학회논문집A
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• 제35권10호
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• pp.1145-1153
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• 2011

본 연구의 목적은 극저온 열처리를 통해 Al6061 의 열처리 잔류응력을 제거하는 것이다. 이를 위해 유한요소해석을 이용하여 열처리 잔류응력을 예측하였으며, 열처리 조건에 따른 각 단계별 대류 열전달계수를 T6 와 극저온 열처리 실험을 수행하여 결정하였다. 예측된 잔류응력 결과는 X 선회절법(XRD)으로 측정된 잔류응력 결과와 비교하여 유한요소해석 결과의 타당성을 확인하였다. 또한 T6 와 극저온 열처리에 대해 각각 전기 전도도와 경도를 측정하여 기계적 특성을 평가하고 TEM 관찰과 XRD 회절 분석을 통해 석출물의 크기 및 성분을 파악하였다. 이를 통해 Al6061 의 T6 열처리와 비교하여 극저온 열처리를 적용함에 따른 잔류응력, 기계적 특성 및 미세조직변화를 조사하였다.

• Advances in materials Research
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• 제13권3호
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• pp.183-194
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• 2024

D3 tools steel and 440C stainless steel (SS) are normally being employed for application such as knife blade and cutting tools. These steels are iron alloys which have high carbon and high chromium content. In this study, lab work focused on the microstructural and corrosion behavior of D3 tools steel and 440C SS after went through heat treatment processes. Heat treatments for both steels were started with normalizing at 1020 ℃, continue with hardening at 1000 ℃followed by oil quenching. Cryogenic treatment was carried out in liquid nitrogen for 24 hours. The addition of cryogenic heat treatment is believed to increase the hardness and corrosion resistance for steels. Both samples were then tempered at two different tempering temperatures, 160 ℃ and 426 ℃. For corrosion test, the samples were immersed in NaCl solution for 30 days to study the corrosion behavior of D3 tool steel and 440C SS after heat treatment. The mechanical properties of these steels have been investigated using Rockwell hardness machine before heat treatment, after heat treatment (before corrosion) and after corrosion test. Microstructure observation of samples was carried out by scanning electron microscopy. The corrosion rate of these steels was calculated after the corrosion test completed. From the results, the highest hardness is observed for D3 tool steel which tempered at 160 ℃(54.1 HRC). In terms of microstructural analysis, primary carbide and pearlite in the as-received samples transform to tempered martensite and cementite after heat treatment process. From this research, for corrosion test, heat treated 440C SS sample tempered with 426 ℃possessed the excellent corrosion resistance with corrosion rate 0.2808 mm/year.

• 한국생산제조학회지
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• 제21권5호
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• pp.824-829
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• 2012

The purpose of this study is to evaluate the proposed jig for turning process of large-scale aluminum tube of D500mm through Finite Element Analysis (FEA). Also, a machining evaluation is conducted with general heat-treated and cryogenic heat-treated tubes. Dimensions of the specimens are determined to be suitable for collet appearance. The characteristics of equivalent stress and strain according to the expansion of the collet are evaluated by FEA. The aluminum tubes which are heat-treated by T4/T6 condition and cryogenic condition are machined by using a large-scale lathe machine and the roundness of machined tube is evaluated by using a 3D measuring machine. Through the results of this study, effects of each heat treatment and residual stress on the roundness are established.

• 한국생산제조학회지
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• 제22권5호
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• pp.865-870
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• 2013

In recent years, aluminum processing has been increasing in the aerospace, vehicle, airplane industries etc., because aluminum has abundant resources and has a high specific strength. Aluminum alloys have a high coefficient of thermal expansion therefore, it is necessary to consider the temperature problem in the cutting process. The objective of this research is to investigate the machinability of a hardened aluminum alloy Al7075-T6 by using cryogenic heat treatment. The machining test is conducted by comparing the cutting force and surface roughness, corresponding to various cutting conditions of depth of cut, cutting speed, and feed rate, with those of Al7075-T0.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.215-218
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• 2005

For the production of cold forged parts with near-net-shape attributes, the quality of the tool system is responsible for an essential portion of costs fer the finished components. Therefore, a tool lift is one of the important issues on cold forging industry. There are many complicated variables related with tool life, such as material, heat-treatment, coating, lubricant, process design. In this study, heat-treatment of tool material and lubricant are investigated to improve the tool life. Deep cryogenic treatment of tool steel is very efficient to improve the wear resistance due to the fine carbide. And, friction factor of lubricants for cold forging are measured by the ring compression test. Zinc-Phosphate and $MoS_2$ lubricant is effective to sustain the friction factor under 0.1.

• 한국재료학회지
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• 제19권12호
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• pp.692-698
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• 2009

Inconel 718 alloy has excellent mechanical properties at room temperature, high temperature and cryogenic conditions. UTS of base metal is about 900MPa at room temperature; this is increased up to 1300MPa after heat treatment & aging-hardening. Mechanical properties of Inconel 718 Alloy were similar to those shown in the the results for tensile test; mechanical properties of Inconel 718 alloy's GTAW were similar to those of base metal's properties at room temperature. Mechanical properties at cryogenic conditions were better than those at room temperature. Heat-treated Inconel 718, non- filler metal GTAW on Inconel 718 and GTAW used filler metal on Inconel 718's UTS was 1400MPa at cryogenic condition. As a result, the excellent mechanical properties of Inconel 718 alloy under cryogenic conditions was proved through tensile tests under cryogenic conditions. In addition, weldability of Inconel 718 alloy under cryogenic conditions was superior to that of its base-metal. In this case, UTS of hybrid joint (IS-G) at -100$^{\circ}C$ was 900MPa. Consequently, UTS of Inconel 718 alloy is estimated to increase from -100$^{\circ}C$ to a specific temperature below -100$^{\circ}C$. Therefore, Inconel 718 alloy is considered a pertinent material for the production of Lox Pipe under cryogenic conditions.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.125-126
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• 2006

The characteristics of the tool system give many effects into the costs and qualities for the finished components. Therefore, a tool life is one of the important issues on cold forging industry. However, since variables related with tool life are many complicated, the studies for solution should be investigated by the systematic research approach. In this study, heat-treatment of tool material is investigated to improve the tool life. Deep cryogenic treatment of tool steel is very efficient to improve the wear resistance due to the fine carbide. And, it is investigated that the shape and dimension of tool give effect into both tool life and quality of forged product.

• 열처리공학회지
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• 제15권4호
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• pp.166-171
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• 2002

The effects of Ni and N addition to 304 stainless steel on mechanical properties and microstructure were investigated within temperature ranged from $-196^{\circ}C$ to $25^{\circ}C$. The addition of nickel and nitrogen induced the stability against the formation of provide significantly enhanced ductility at $-196^{\circ}C$ and reduce the Md temperature. Fe-18Cr-10Ni-0.2N alloy showed the ${\gamma}$ phase in deformed structure which it was beneficial to enhance the tensile strength and elongation at $25^{\circ}C$ and $-196^{\circ}C$.

• 한국재료학회지
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• 제34권1호
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• pp.44-54
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• 2024

High-Manganese (Mn) austenitic steel, with over 24 wt% Mn content, offers outstanding mechanical properties in cryogenic settings, making it a potential replacement for existing cryogenic materials. This high manganese steel exhibits high strength, ductility, and wear resistance, making it promising for applications like LNG tanks, flanges, and valves. To operate in cryogenic environments, hot forging and heat treatment processes are vital, especially in flange production. The cooling rate during high-temperature cooling after hot forging plays a critical role in influencing the microstructure and mechanical properties of high manganese steel. The rate at which cooling occurs during this process influences the size of the grains and the distribution of manganese and consequently has an impact on mechanical properties. This study assessed the microstructure and mechanical properties based on different cooling rates during the hot forging of High-Mn steel flanges. Comparing air and water cooling after hot forging, followed by heat treatment, revealed notable differences in grain size. These differences directly impacted mechanical properties such as tensile strength, hardness, and Charpy impact property. Understanding these effects is crucial for optimizing the performance and reliability of High-Mn steel in cryogenic applications.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.42-47
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• 2007

The characteristics of the tool system give many effects into the costs and qualities for the finished components. Therefore, a tool life is one of the important issues on cold forging industry. However, since variables related with tool life are many complicated, the studies for solution should be investigated by the systematic research approach. The shape and process changes of die, the hardness changes of material and the tolerance of dies to decrease the die stress are analyzed by the FEM software. The heat-treatment of tool material is investigated to improve the tool life. Deep cryogenic treatment of tool steel is very efficient to improve the wear resistance due to the fine carbide. And, it is investigated that the shape and dimension of tool give effect into both tool life and quality of forged product..