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김대환 ( Dae-hwan Kim ),임수근 ( Su-gun Lim ) 한국주조공학회 2017 한국주조공학회지 Vol.37 No.1
The microstructure, electrical conductivity and hardness variation of an AZ91-5wt%Sn Mg alloy sample during a solid-solution and aging heat treatment were instigated by optical microscopy, scanning electron microscopy, X-ray diffraction and by Rockwell hardness techniques in this study. The XRD result shows that the main phases in the as-casted alloy are α-Mg, Mg<sub>17</sub>Al<sub>12</sub> and Mg<sub>2</sub>Sn. From the SEM images of the AZ91-5wt%Sn Mg alloy after the solution treatment, the Mg<sub>17</sub>Al<sub>12</sub> phases in the alloy were found to have dissolved into the matrix with an increase in the holding time during the solution treatment, but Mg<sub>2</sub>Sn phases were clearly observable. The highest peak hardness of the AZ91-5wt%Sn Mg alloy is 82HRE at an aging temperature of 200 ℃.
셀 몰드 주조한 SSC13 엘보우 피팅 주강의 고용화율에 따른 델타 페라이트 분율 변화와 내부식특성
김국진 ( Kuk Jin Kim ),임수근 ( Su Gun Lim ),주형규 ( Heong Kyu Ju ),박성준 ( Sung Joon Pak ) 한국주조공학회 2015 한국주조공학회지 Vol.35 No.5
In this study, the measurement of FN (ferrite volume fraction) and the solution annealing ratio at a temperature of 1130oC were determined with 15A elbow fittings of shell cast SSC13, and the corrosion resistance with and without austenitizing solution annealing were investigated in comparison with AISI304. The delta ferrite phase was observed in the material due to the slow cooling effect of the shell mold casting. However, the delta ferrite phase decreased gradually with the solution annealing at a temperature of 1130oC. The hardness generally decreased with a heat treatment; however, its corrosion resistance was improved with the heat treatment.In addition, when a passivation treatment was applied, its corrosion ratio showed the lowest value. The pattern of general corrosion decreased due to the decrease in the delta ferrite phase with the solution annealing treatment. Consequently, it is suggested that the corrosion resistance of SSC13 elbow fittings can be improved by increasing the ratio of any solution annealing treatment used and by decreasing the ferrite phase. The relationship between the ratio of solution annealing and delta ferrite is expressed as follows: SA (solution annealing ratio,%) = 98 - FN (ferrite volume fraction, %).
분말 사출성형법으로 제조된 T42 고속도 공구강의 소결거동
박동욱,김혜성,권영삼,조권구,임수근,안인섭,Park, Dong-Wook,Kim, Hye-Seong,Kwon, Young-Sam,Cho, Kwon-Koo,Lim, Su-Gun,Ahn, In-Shup 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.2
Tool steels serve a large range of applications including hot and cold workings of metals and injection mouldings of plastics or light alloys. The high speed steels (HSS) are specifically used as cutting tools and wear parts because it has high strength, wear resistance and hardness along with appreciable toughness and fatigue resistance. From the view of HSS microstructure, it can be described as metallic matrix composites formed by a ferrous with a dispersion of hard and wear resistant carbides. The experimental specimens were manufactured using the PIM with T42 powders (50~80 vol.%) and polymer (20~50 vol.%). The green parts were debinded in n-hexane solution at $60^{\circ}C$ for 8 hours and thermal debinded at an $N_2-H_2$ mixed gas atmosphere for 8 hours. Specimens were sintered in high vacuum ($10^{-5}$ Torr) and various temperatures.
SSC13 주강품의 내부식특성에 미치는 고용화 열처리 영향
김국진 ( Kuk Jin Kim ),임수근 ( Su Gun Lim ),박성준 ( S. J. Pak ) 한국부식방식학회(구 한국부식학회) 2015 Corrosion Science and Technology Vol.14 No.2
Recently, Stainless steels have been increasingly selected as the fitting or the valve materials of water pipes as the human health issue is getting higher and higher. Therefore, the connectors attached at pipes to deliver water are exposed to more severe environments than the pipes because crevice or galvanic corrosion is apt to occur at the fittings or the valves. Effects of the solid solution annealing, cooling rate after this heat treatment, and passivation on the corrosion properties of the shell mold casted SSC13 (STS304 alloy equivalent) were studied. The heating and quenching treatment more or less reduced hardness but effectively improved corrosion resistance. It was explained by the reduction of delta ferrite contents. Independent of heat treatment, the chemical passivation treatment also lowered corrosion rate but the improvement of corrosion resistance depended on temperature and time for passivation treatment indicating that the optimum conditions for passivation treatment were the bath temperature of 34 oC and operating time of 10 minutes. Therefore it is suggested that the corrosion resistance of SSC13 can be effectively improved with the heat treatment, where SSC13 is heated for 10 minutes at 1120 °C and quenched and passivation treatment, where SSC13 is passivated for at least 10 seconds at 34 °C nitric acid solution.
Al-6.3Zn-2.4Mg 합금의 수소충전에 따른 기계적 특성 연구
김대환 ( Dae Hwan Kim ),최태영 ( Tae Young Choi ),심성용 ( Sung Young Shim ),임수근 ( Su Gun Lim ) 한국주조공학회 2014 한국주조공학회지 Vol.34 No.2
In this study, the extruded Al-6.3Zn-2.4Mg alloys were selected among the 7000 series aluminum alloys sensitive to hydrogenenvironment in order to examine the effects of both the aging conditions and the length of hydrogen charging period on themechanical properties of the alloy. The specimens were aged for 24hours at 100oC (under aging (UA)), 120oC (peak aging (PA)),and 160oC (over aging (OA)), respectively. Charging tests were performed at RT for 12, 24, 36 hours under potentiostatic conditions(?2000 mV vs (Ag/AgCl)) for 12, 24 and 36 hours in 1M H2SO4 and 0.1%NH4SCN solution. The fracture surface was examined byscanning electron microscopy (SEM). X-ray diffraction (XRD) pattern in peak aged sample was obtained before and after hydrogencharging from extruded Al-6.3Zn-2.4Mg alloys. The decreasing rate of tensile strength and elongation is represented in order ofover aging < under aging < peak aging, and it is believed that the hydrogen recharge is more sensitive to elongation than tensilestrength. The formation of AlH3 in hydrogen charged Al-6.3Zn-2.4Mg alloys has been confirmed by X-ray diffraction studies.
김대환 ( Dae Hwan Kim ),김희경 ( Hee Kyung Kim ),엄정필 ( Jeong Pil Eom ),임수근 ( Su Gun Lim ) 한국열처리공학회 2013 熱處理工學會誌 Vol.26 No.4
Abstract In the present study, the microstructure and solution treatment response of Al-Zn-Mg alloys bars by thixo-extrusion was investigated. The alloy bars were solution treated at 400, 430, 460 and 490oC for various times. In order to examine the microstructures and phase analysis of the samples after solution treatment, it was performed by optical and scanning electron microscopy. And, Vickers hardness and electrical conductivity was measured on the solution treated samples for each condition to investigate the solution treatment response of extruded bars during solution treatment. The results show that the optimum solution heat treatment conditions of thixo-extruded Al-Zn-Mg alloy for minimization of the grain growth and degradation promotion of the second phase is a temperature of 460oC and holding time of 0.5 to 2 h.
김대환 ( Dae Hwan Kim ),정현주 ( Hyun Ju Jung ),심성용 ( Sung Yong Shim ),임수근 ( Su Gun Lim ),이상용 ( Sang Yong Lee ) 한국주조공학회 2014 한국주조공학회지 Vol.34 No.4
This work presents the results of a thixo-extrusion process applied to aluminum alloy and and reheating characteristics of semisolid A356 Alloy using have been discussed. The reheating experiment was performed using an electric resistance furnace and multistage heating for uniform reheating. The thixo-extrusion was performed at the optimal reheating conditions of the semi-solid A356 alloy, the the extrusion conditions were an extrusion ratio of 33 and ram speed of 6 mm/sec. The results showed that the thixoextrusion of semi-solid A356 alloy fabricated by the cooling slope reduced the extrusion pressure by 180% in comparison with hot extrusion, and that a sound extrusion could be obtained in spite of the same extrusion ratio and strain rate.
AM80-xSn 마그네슘 합금의 반응고 주조 및 압출에 따른 미세조직 및 기계적 특성
김대환 ( Dae-hwan Kim ),임인택 ( In-taek Im ),( Qinlin Jin ),임수근 ( Su-gun Lim ) 한국주조공학회 2016 한국주조공학회지 Vol.36 No.6
In a recent study, the microstructures and mechanical properties of AM80-xSn magnesium alloys with semi solid casting and hot extrusion process were investigated. With increasing Sn content, the amount of β(Mg2Sn) phase increased, while the α-Mg dendritic size decreased. The hardness was increased by the Mg2Sn as the Sn content increased. With increasing Sn content, permanent mold cast and semi solid cast AM80 Mg alloy showed less reduction of hardness and also of extruded AM80 Mg alloy after annealing. In the case of the mechanical properties, the extruded semi solid casting AM80 Mg alloy showed higher tensile strength and yield strength with increasing Sn content compared to the extruded permanent mold cast AM80 Mg alloy at room temperature.