ADI 의 미세조직과 기계적 특성에 미치는 특수열처리 및 합금원소의 영향

한상원(Sang Won Han),김석원(Sug Won Kim),이의종(Ui Jong Lee),박진성(Jin Sung Park),우기도(Kee Do Woo),김동건(Dong Keun Kim) 한국주조공학회 2002 한국주조공학회지 Vol.22 No.2

N/A The effects of heat treatments and alloying elements on the microstructure and mechanical charaterisitics of specially austempered ADIs containing alloying elements such as Cu, Mo and Ni were investigated. To compare with the effect of conventional and normal(CN) austempering treatment, two kinds of special austempering treatments which are those with pre-quenching and pre-heating were conducted. The hardness and uniaxial fatigue tests were carried out to evaluate the mechanical charateristics. The hardness of ADI treated by CN heat cycles was higher than those of other ADIs. Cu added ADI (Cu-ADI) tempered at 400 after austenitizing exhibited the highest fatigue life cycles. While austempering after prequenching makes the austenite with high carbon stable, which resulted in transformation to highly strengthened bainites from the carbon enriched austenite phases during tempering. The high carbon enriched banites is considered to improve the fatigue strength.

기술강좌 : Semi-Solid Process 법으로 제조된 Al-Si-Mg 주조재의 피로특성

김석원 ( Sug Won Kim ),이의종 ( Ui Jong Lee ),한상원 ( Sang Won Han ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.2

고속도강 압연 Roll 성질에 미치는 응고미세조직 및 합금원소의 영향

김정규,한상원,우기도,김석원 ( Jung Kyu Kim,Sang Won Han,Ki Do Woo,Sug Won Kim ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.5

N/A In this study, Fe-3%C-4%Mo-4%Cr-0,1,5,10%(W,V) were investigated on the kinds of carbides, microstucture, solidification process, hardness and wear resistance properties. In the Fe-3%C-4%Mo-4%Cr-X%W alloy system, eutectic M_7C₃, and eutectoid M₃C carbides were crystallized at the martensite matrix interfaces. With increase of amount of W addition, amount of M, C carbide was decreased but amount of M_7C₃carbide was increased. In the Fe-3%C-4%Mo-4%Cr-X%V alloy system, primary MC, eutectic MC, eutectic M_7C₃eutectoid M₃C carbide were crystallized at the martensite matrix interfaces, excepting case of 10%V addition, matrix of 10%V addition was ferrite. With increase of V addition amount, amount of M₃C, M_7C₃carbides were decreased and amount of MC carbide was increased. Hardness was decreased but wear resistance was increased with increase of amount of W, V addition excepting case of 10%V addition.

Squeeze Casting 에 의한 Al-SiCp 복합재료의 제조 조건에 관한 연구

김석원,우기도,한상원 ( Sug Won Kim,Kee Do Woo,Sang Won Han ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.5

N/A Al-2%Si-2%Mg alloy containing SiC particle in 20, 70㎛ were prepared by mean of squeeze casting with various pressure 50, 100, 150 and 220㎫ respectively. The specimens were made by casting into 50ø×100ℓ mold under various squeeze conditions(pressures, pressurizing temperature, particle sizes). Mechanical properties(hardness, tensile strength, elongation and wear characteristics) were evaluated at room temperature with those various fabrication factors. It became feasible to make favorable Al-SiCp composite free from casting defects by the injection of Ar gas during melting and 100㎫ pressure squeeze casting. However, pressure of 50㎫ was not sufficient to avoid completely porosity formation as a result of precessing and shrinkage during solidification. As the particle size is smaller and the squeeze pressure is higher, the hardness and tensile strength at room temperature are higher. Cell size became smaller gradually with increase of squeeze pressure. With increase of squeeze pressure(㎫), wear behaviors of those composites were changed from adhesive into abrasive wear, and the tendency of above behavior became outstanding with increasing sliding speed. The chemical reaction(4Al+3SiC→Al₄C₃+3Si) is more accelerated at interface between SiCp and matrix with increase of squeeze pressure. Therefore Al₄C₃ intercompound and Si peak intensity is increased at interface.

Squeeze Casting 에 의한 SiC 입자강화 Al 합금기 복합재료의 미세조직 특성

김석원,우기도,한상원 ( Sug Won Kim,Kee Do Woo,Sang Won Han ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.6

N/A In this study, the microstructural characteristics such as primary silicon, eutectic silicon, SiC_p dispersion behavior, compound amount and Si solubility in Al/SiC_p composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(㎫) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary α-Al in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting. This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

고온 내산화성 고 Si , Mo 구상흑연주철의 특성에 관한 연구

김석원,우기도,한상원,김정규,김대영 ( Sug Won Kim,Kee Do Woo,Sang Won Han,Jung Ku Kim,Dae Yong Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2

N/A The physical and chemical characteristics of Ductile Cast Iron(DCI) have been well known because of many studies about DCI. So it has a wide application in the field of heavy and automobile industry because DCI has a good combination of excellent castability and good mechanical properties. But its usage has been often restricted to use in parts such as exhaust manifold required high heat resistance in automobile industry. So, in this study, in order to achieve high heat resistance in DCI, DCI with addition of high Si and Mo alloy elements have been researched on mechanical properties, including heat resistances systematically. With the increase of Mo and Si content, the size and number of graphite in matrix of DCI increased and the pearlite in DCI matrix is transferred to ferrite because of Si strong former of ferrite, otherwhile carbide in matrix increased because of Mo carbide former. In the test of oxidation property, Si and Mo played an important role to retard oxidation of DCI. By the: addition of Si and Mo, the Charpy impact energy was decreased, whereas the total hardness was increased. (Received February 20, 1998)

Al-Si-Mg 주조합금의 저 사이클 피로거동에 미치는 미세조직의 영향

韓相元,金錫元 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7

Low cycle fatigue tests were carried out using four kinds of Al-7%Si-0.4Mg cast alloys, i.e., two kinds of sand mold casts, permanent mold cast and semi-solid die cast. They were heat-treated in the condition of under aging and over aging to investigate effects of precipitates on fatigue. All tests were conducted under axial plastic strain amplitude control. Stress level of cyclic hardening curves increased sensitively with needle like eutectic Si particle, refined grain size and dendrite arm spacing(DAS). In particular, the refined grain structure of under aged matrix was more effective encourager for cyclic hardening compared with DAS and eutectic Si particle size. After rapid increase in cyclic hardening during several number of cycles, the stress amplitude kept increasing steadily until fracture in under aged alloys strengthened by shearable G.P. zone. On the other hand, over aged alloys strengthened by non-shearable β' precipitates generated more drastic initial hardening and the stress amplitude reached the saturation state in quite early stage of the fatigue.

Squeeze Casting 에 의한 SiC 입자강화 Al 합금기 복합재료의 마멸 특성

한상원,우기도,김석원 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.1

This study was aimed to investigate influence of microstructure, abrasive heat affected zone(AHAZ), primary silicon and eutectic silicon on abrasive characteristics of AC8A/SiC_p composite fabricated by the squeeze casting under various conditions. The abrasive characteristics was improved by addition of Mg and Ca elements because of improvement of SiC_p wettability and hardness in matrix. It is general theory that abrasive amount is decreased with increase of squeezing pressure. In this study, however, as squeezing pressure applies over a certain limit value(220MPa), the abrasive resistance under the condition of the high abrasive speed(3.67 ㎧) is not increased with increase of squeezing pressure. This is due to the crack by the generation of abrasive heat and fatigue below abrasive surface under the condition of high abrasive speed(3.67 ㎧). In abrasive heat affected zones of AC8A and AC8A/SiC_p composite fabricated by same squeezing pressure(220MPa), eutectic Si of directly below abrasive surface is finer than that of matrix, and abrasive heat affected zone of AC8A/SiC_p composite is thinner than that of AC8A. These reasons are that abrasive heat makes α dendrite and eutectic Si fine in AC8A/SiC_p composite. Therefore, the hardness of heat affected zone of directly below abrasive surface was increased sharply owing to abrasive heat.

주조용 알루미늄 합금의 피로

한상원,김석원 한국주조공학회 2002 한국주조공학회지 Vol.22 No.2

방향성 수지상정조직과 구상 셀조직을 갖는 Al-7%Si-0.4%Mg 주조합금의 일축 찢기특성

한상원,김석원 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.12

Tear resistance behaviors of Al-7%Si-0.4%Mg cast alloys were examined using Kahn-type tear test specimens which are distinguished DCC(directional continuous cast) consisting of a directional and ordinary dendrite structure with SLD(semi-liquid die cast) consisting of globular cells and fine grain structure. Restricted plastic deformation occurs near notch tip of semi-liquid die cast characterized by refinement of grain size. Popin for stress was exhibited in semi-liquid die cast but no pop-in was observed in DCC cast alloy. Tear resistance was evaluated by the energies required for crack initiation, UE_(i) and the crack propagation, UE_(p). An unit propagation energy, UE_(p) can be converted into critical stress intensity factor, K_(c), which in directional dendrite structure improves due to a high plane stress state over thickness-direction and the fracture surface of slant type.