• 열처리공학회지
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• 제20권2호
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• pp.84-93
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• 2007

Microstructural changes during tempering at the temperature range of $300^{\circ}C{\sim}700^{\circ}C$ for the nitrogen-permeated STS 410 and 410L martensitic stainless steels has been investigated. After nitrogen permeation at temperature between 1050 and $1150^{\circ}C$, the surface layer appeared fine $Cr_2N$ of square and rod types in the martensite matrices. Hardness of the nitrogen-permeated surface layer represented 680Hv and 625Hv, respectively, for 410 and 410L steels. It is considered that the fine homogeneously dispersive effect of precipitates by nitrogen caused the increased hardness. Due to the counter current effect of carbon from interior to surface during nitrogen diffusion from surface to interior, the 0.1%C alloyed 410 steel showed the low nitrogen content of 0.025% compared with 0.045% of 410L steel at the distance of $100{\mu}m$ from the surface. Tempering of nitrogen-alloyed 410 and 410L showed the maximum hardness at $450^{\circ}C$. This maximum hardness was considered to be the secondary hardening effect of very fine carbide and nitride. The decrease in hardness at $700^{\circ}C$ was the softening effect of the matrix due to the precipitation of many needle-shaped $Cr_2N$ for 410 steel and the precipitation of coarse nitride of $Cr_2N$ in line with the spherical precipitates with directionality for 410L steel. For 410 steel, the corrosion resistance of nitrogen permeated surface in the solution of 1 N $H_2SO_4$ were nearly unchanged, however the superior corrosion resistance was obtained for nitrogen permeated 410L steel compared to the solution annealed condition.

• 한국생산제조학회지
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• 제20권4호
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• pp.419-426
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• 2011

In this study, an experimental and theoretical program were carried out to determine the cutting forces and chip formation at different cutting speeds using a 0.4mm nose radius ceramic insert and -7 rake angle for non heat-treated AISI 4140 (27HRc) and heat-treated AISI 4140 (45 HRc) steel. The results obtained were compared to show the hardness differences between the materials. The secondary deformation zone thicknesses when comparing the two materials show different physical structure but similar size. These results were also discussed in light of the heat treatment and the effects it had on the machining characteristics of the material. In addition, the Oxley Machining Theory was used to predict the cutting forces for these materials and a comparison made. The predicted cutting performances were verified experimentally and showed good agreement with experimental data.

• Journal of Welding and Joining
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• 제16권1호
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• pp.114-124
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• 1998

The effect of matrix phase (austenite, pearlite, martensite) on the low stress abrasion resistance in the chromium-carbide-type high Cr white iorn hardfacing weld deposites has been investigated. In order to examine matrix phase, a series of alloys with different matrix phase by changing the ratio of Cr/C system by heat treatment were employed. The alloys were deposited twice on a mild steel plate using self-shielding flux cored arc welding process. The low stress abrasion resistance of the alloys against sands was measured by the Dry Sand/Rubber Wheel Abrasion Test(RWAT). Even though formation of pearlite phase in the matrix showed higher hardness than that of austenite, there was no observable difference in wear resistance between the pearlite and austenite phase for the same amount of chromium-carbide in the matrix. On the other hand, the formation of martensitic phase,, from heat treated austenitic alloys (high content of Cr), enhanced wear resistance due to its fine secondary precipitates.

• 한국기계가공학회지
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• 제18권11호
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• pp.69-75
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• 2019

Oil seals have a great effect on transmission performance and durability. In this study, the optimal rubber mix was derived using dispersion analysis to obtain excellent oil-seal rubber properties. ANOVA was performed twice. The factors were polymers, carbon, magnesium oxide, and calcium hydroxide, which were used as four factors in ANOVA. The response factors were four items (hardness, tensile strength, elongation rate, and compression deformation) obtained through an experiment with a confidence level of 95%. In the first ANOVA, 168 tests were performed, and in the secondary ANOVA, 24 physical tests were conducted using polymers and carbon derived from the primary ANOVA. Through the ANOVA, we derived a rubber mixture recipe.

• 한국해양환경ㆍ에너지학회지
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• 제16권4호
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• pp.227-238
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• 2013

본 연구의 목적은 해수담수화 과정 중 황산이온과 염소이온은 제거하고 유용미네랄인 마그네슘, 칼슘은 잔존 시키는 미네랄 수질 조정 기술로 먹는물 수질기준에 맞는 고경수 제조 공정 개발에 있다. 역삼투막(RO)에 통과시켜 농축수(Concentrated deep seawater)와 탈염수(desalted deep seawater)를 제조하고, 나노여과막(NF)를 사용하여 염화나트륨이 제거되지 않은 1차 미네랄 농축수(Mineral enriched deep seawater)를 제조하여, 전기투석 이온교환막(ED)을 가동하여 염화나트륨을 제거한 탈염 미네랄농축수(Mineral enriched desalted water)를 제조하여 이를 RO 탈염수와 희석하여 고경도 먹는해양심층수를 제조하였다. 역삼투막은 해수(해양심층수) 원수에서 용존물질과 담수를 분리할 수 있으며, 2차에 걸쳐 역삼투막을 사용하면, 용존성분 중 99.9% 이상 제거되고, 경도 1이하, 염소이온의 농도 2.3 mg/L인 용존물질이 완전히 제거된 탈염수(순수)를 제조할 수 있었다. 나노여과막 (NF 막)의 간극은 $10^{-9}$ m으로 마그네슘과 칼슘은 50%정도 통과시키며, 염소이온과 나트륨 같은 일가이온은 95%이상 통과한다. 나노여과막은 마그네슘과 칼슘과 같은 경도 성분과 나트륨과 염소이온과 같은 염분성분을 분리 농축할 수 있지만, 완벽하게 분리하지는 못한다. 전기투석막(ED)은 전기전도도에 따라 경도성분의 이가이온과 염분성분인 일가이온이 분리된다. 전기전도도 20 mS/cm 이상에서 경도성분(마그네슘이온, 칼슘 이온 등)은 제거되지 않는 반면, 염분성분 (나트륨이온, 염소이온 등)은 지속적으로 제거되었다. 따라서, 나노여과막을 이용하여 마그네슘과 칼슘과 같은 경도 성분을 농축하고, 전기투석막을 이용하여 경도농축수에서 염분성분을 분리하여 경도농도 12,600 mg/L, 염소이온 농도 2,446 mg/L의 염분성분이 배제된 고경도 농축수를 제조할 수 있었다. 이러한 고경도수를 역삼투막을 이용하여 용존물질이 모두 제거된 2차 RO 생산수로 10배 희석하면 염소이온 농도 244 mg/L 로 먹는물 수질기준에 적합하면서 경도농도 1,260 mg/L 인 고경도 수 제조도 가능하였다. RO/NF/ED 또는 NF/ED 연계공정은 해수의 증발 없이 역삼투막, 나노여과막과 전기투석막만을 이용하여 염소이온과 나트륨, 칼륨, 황산이온과 같은 염분성분을 제거하면서 마그네슘과 칼슘과 같은 경도성분은 농축할 수 있어서 먹는물 수질기준에 적합한 고경도수 제조가 가능하였으며, 이 과정 중 소모되는 에너지를 줄일 수 있었다.

• 열처리공학회지
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• 제30권6호
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• pp.279-284
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• 2017

Mechanical properties of titanium alloy can be improved by controlling microstructure through heat treatment. In this study, Ti-3Al-8V-6Cr-4Mo-4Zr metastable beta titanium alloy, was controlled for excellent mechanical property and sound formability through various high temperature heat treatment and aging conditions and the optimum heat treatment conditions were determined. The specimens were heat-treated at $950^{\circ}C$, followed by various aging treatments from $430^{\circ}C$ to $500^{\circ}C$ for 1 to 24 h. As aging temperature and holding time increased, hardness increased by ${\beta}^{\prime}$ phase formation and precipitation of secondary ${\alpha}$ phase in ${\beta}$ matrix. However, the optimum aging temperature and holding time for mechanical properties were at $450{\sim}470^{\circ}C$ for 8~16 hr. Hardness values of the specimen aged at $450^{\circ}C$ for 8 h were found to be the highest. These results can be effectively applied to fabrication of spring with better formability and mechanical property.

• 한국재료학회지
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• 제4권1호
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• pp.24-30
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• 1994

가공열처리한 7075Al합금을 $170^{\circ}C$에서 퇴화처리하여도 GP대는 완전히 분해되지 않았으며 초기의경도저하는 부분적인 GP대의 분해에 기인하고 $\mu '$의 생성으로 강도는 증가하다가 $\mu '$의 성장 및 $\mu$의 생성으로 강도는 다시 저하한다. 퇴화처리시 경도 곡선의 극소점이나 2차 피크점(극대점)에서 RRA처리한 시편의 응력부식 특성은 T6재에 비하여 상당히 개선되며 강도의 저하를 수반하지 않는다. 또한 저온인 $170^{\circ}C$에서 퇴화처리시 기지조직의 변화가 크지 않아 퇴화처리시 경도곡도의 극소점과 2차 피크점에서의 특성차이는 거의 없었다.

• 열처리공학회지
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• 제27권6호
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• pp.281-287
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• 2014

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for engine mount bracket prepared by gravity casting (as-cast) and die-casting (as-diecast) process have been investigated. For the microstructural characterization, the inductively coupled plasma mass spectrometry (ICP-MS), optical microscope (OM), scanning electron microscope (SEM) and electron probe microanalysis (EPMA) analyses are conducted. For the intermetallic phases, the X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are also conducted with quantitative and qualitative analysis. Micro Vickers hardness and static tensile test are achieved in order to measure mechanical properties of alloys. Secondary dendrite arm spacing (SDAS) of as-cast and as-diecast show 37um and 18um, respectively. A large amount of coarsen eutectic Si, $Al_2Cu$ intermetallic phase and Fe-rich phases are identified in the Al-6Si-2Cu alloy. Mechanical properties of gravity casting alloy are much higher than those of die-casting alloy. Especially, yield strength and elongation of gravity casting alloy show 2 times higher than die-casting alloy. After shot peening, shot peening refined the surface grains and Si particles of the alloys by plastic deformation. The surface hardness value shows that shot peening alloy has higher value than unpeening alloy.

• 한국재료학회지
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• 제18권8호
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• pp.422-426
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• 2008

The effects of an addition of $ZrO_2$ on the microstructure and electrical properties of MgO films as a protective layer for AC plasma display panels were investigated. MgO + a 200 ppm $ZrO_2$ protective layer prepared by e-beam evaporation exhibited a secondary electron emission coefficient ($\gamma$) that was improved by 21% compared to that of a pure MgO protective layer. The relative density and Vickers hardness increased with a further addition of $ZrO_2$. These results suggest that the discharge properties and optical properties of MgO protective layers are closely related to the relative density and Vickers hardness. The good optical and electrical properties of $\gamma$, at 0.080, a grain size of $19\;{\mu}m$ and an optical transmittance of 91.93 % were obtained for the MgO + 200 ppm $ZrO_2$ protective layer sintered at $1700^{\circ}C$ for 5 hrs.

• 대한영양사협회학술지
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• 제24권1호
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• pp.19-30
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• 2018

The primary objective of this study was to develop an optimal composite recipe for ginger extract candy with Salicornia herbacea L., for consumption during the first trimester of pregnancy. The secondary objective was to examine quality characteristics of the candy. The physical and mechanical properties and sensory properties for pregnant women in were measured, and these values were applied to mathematical models. Time of stirring water solution, saltiness, pH, and redness of the candy increased as concentrations of ginger juice did, but variations in pH were not significant. The hardness values of the candy ranged from 3,063.90 to $5,681.65dyne/cm^3$. The average values of sweetness and time stirring the water solution were 5.36% and 14.1 minutes, respectively. However, hardness and sweetness stirring water solution were not significant. The range of sensory values of color (P<0.01), flavor (P<0.05), sweetness, saltiness, spiciness, and overall quality (P<0.05) ranged from were 3.73~5.32, 4.05~5.05, 3.67~5.14, 3.59~5.09, 3.55~5.15, and 3.32~5.45, respectively. Results suggest that ginger extract candy with Salicornia herbacea L. should be comprised of 7.37 g of ginger juice and 1.77 g of salt. Consequently, it could be a functional candy for pregnant women.