마그네슘 합금주물

윤의박 한국주조공학회 1987 한국주조공학회지 Vol.7 No.5

초급냉응고한 Al-Cr 계 합금의 석출거동에 관한 연구

윤의박,조순형 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.1

The purpose of this paper was observation of and kinetic analysis of the precipitation process in heat-resistant alloys to improve the mechanical properties and the thermal properties. Al-Cr alloys were rapidly solidified into a ribbon shape by a melt spinner. The decomposition process of rapidly solidified Al-Cr alloys were examined by means of TEM, X-ray diffraction and micro-Vickers hardness. As a result of an isothermal aging of massively transformed Al-3.43wt.%Cr alloy at 450℃, subgrains formed by polygonization process. With more aging, precipitation occurred on the subgrain boundaries. The decomposition process of massively transformed Al-3.43wt%Cr alloy was analyzed by the cylindrical precipitation model. In the initial stave, n in the Johnson-Mehl-Avrami equation is 2.98 corresponding to the characteristics of the interface-controlled growth of a fixed number of particles. In the middle and the final stage, n is 1.85 corresponding to the characteristics of the diffusion-controlled growth of a fixed number of particles.

비평형제2상의 용체화거동에 미치는 응고조직의 영향

윤의박,안갑우,서창제,허태수 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.5

偏析型 2元系合金의 溶體化末期에 있어서 非平衡第2相의 固溶擧動에 대해서는 아직까지 理論的으로 정립되어 있지 않았다. 本 論文에서는 主로 dendrite element의 境界에 晶出된 非平衡第2相의 유효擴散距離로써 1次arm 間隔을 考慮한 擴散 model인 尹의 近似解에 의해 이들 擧動을 調査하였다. 이를 위해 天然가스등의 輸送材料로 囑望되는 高濃度 Al-8%Mg合金을 사용하였다. 實驗結果, 理論的인 尹의 近似解의 實驗値는 近似的으로 一致되었고, 특히 溶體化末期에서는 完全히 一致됨을 알 수 있다. 結局 從來의 Flemings의 解析値보다 더욱 實驗値에 近似하였다. The solution kinetics of nonequilibrium second phase of a segregated binary alloy in the later stages of solution treatment have not yet been made theoretically clear. This paper attempted mainly to investigate this behaviour by Yoon's approximate analysis given by a simple model based upon primary arm spacing as an effective diffusion distance of the second phase which has crystallized at the boundary of dendrite element. For this purpose, we used the high magnesium Al-8% Mg alloy which is expected to be used for transport of liguified natural gas. The theoretically calculated results are in the approximate agreement with that of experiments for complete dissolution time and solution kinetics (expecially at the later stages) of β-phase. The Yoon's approximate analysis was in better agreement with the present experimental results than the Flemings conventional analysis

계장화충격시험법 (計裝化衝擊試驗法) 에 의한 구조용강용접부의 동적파괴인성에 관한 연구 (3) : 선체구조용 고장력강용접부의 인성을 중심으로 on the fracture Toughness of Hull Structural Steel Simulated Welds

윤의박,김기철 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.4

Dynamic fracture toughness of a hull structural steel has been investigated. Thermal cycles simulation and instrumented impart testing technique were employed to obtain the dynamic fracture toughness of welds utilizing small size specimens. Microstructural change of nomnmetallic inclusions during cooling process was also discussed. Experimental results showed that the dynamic fracture toughness of simulated welds, which displayed relatively lower toughness values compared with that of the base metal, was decreased as the critical cooling time was increased. Sulfide-type nonmetallic inclusions in the welds microstructure were observed, and their elongated morphology had been changed into spherical shape during the welds thermal cycling.

전산기를 이용한 주물의 (鑄物) 응고해석에 관하여

윤의박,조순형 ( Eui Pak Yoon,Soon Hyoung Cho ) 한국주조공학회 1983 한국주조공학회지 Vol.3 No.2

In this paper analytical and numerical methods fur analysis of solidification of castings are described, and the matrix method, one of numerical method, where the nodal point is designated on the element boundary was adapted. The cooling curve obtained by experimental values, when cast steel (0.29%C. 0.62%Si) was poured into CO₂mold, is compared with that of computed values by exploiting computer (V77-600 Data Proceeding System, UNIVAC). The computed value is nearly approximation to the experimental. But the computed value shows a tendency that is a little higher than the experimental in solid-liquid coexisting temperature ranges and much lower than the experimental after solidification. It is considered to result from the lacks and difficulties of ultimately appropriate adaptation of various physical properties and also air cap between castings and mold.

급냉응고한 Al-Cr 계합금의 용질거동에 관한 연구

윤의박,조순형 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.12

The microstructure of rapidly solidified Al-Cr alloys was investigated by scanning transmission electron microscopy (STEM), X-ray diffraction and micro-Victors hardness test. The temperature mariation during rapid solidification was studied to interpret the results. From the thermal analysis, the relationship between the cooling rate and the dendritic cell size was found to correspond to a previous theory which was obtained from an extrapolation of the measurements at slow cooling rate. The relatinship between the growth rate and the dendritic ceil size, however, was shown to be lower than those of general Al alloys, because the rate of the primary phase formation was suppressed by the increased fooling rate. By detailed composition measurements, the possible solubilily range of the complete supersaturation was found to be 3.43 wt% Cr. Above this concentration, the microstructure changed to a cellular structure by recoalescence in the last stage of solidification.

계장화 충격시험에 의한 구상흑연 주철의 동적파괴인성의 고찰

윤의박,김기철,고광필 ( Eui Park Yoon,Ki Chol Kim,Kwang Pill Ko ) 한국주조공학회 1989 한국주조공학회지 Vol.9 No.2

N/A Microstructures and fracture toughness of the weld heat-affected zone of the ductile cast iron have been investigated. With increasing the cooling time from 800℃ to 500℃, the matrix structure of the heat-affected zone was transformed to martensite, martensitet pearlite, pearlite and pearlite including small amount of ferrite. The use of a proper preheat temperatures prevented the formation of martensite. These welding conditions corresponded to the preheat temperature of 200℃, heat input of 30KJ/㎝. And the instrumented charpy impact test has been carried out on a welded ductile cast iron. Result showed that the dynamic fracture toughness, K_(Id) was increased slightly with preheat temperature and heat input. In this work, it was shown that apparent impact energy includes contributions other than that of the true deflection of specimen. We found that a compliance energy correction was always needed to determine the true specimen energy. For this purpose, elastic compliance value of testing machine was measured dynamically by the low blow test to correct the apparent impact energy. From these results, the true specimen energy was nearly 62 percent of an apparent impact energy value. There, in instrumented impact testing, machine compliance corrections must be adapted to load-deflection curve.

2상혼합조직을 (相混合組織) 가진 구상흑연주철의 기계적 성질에 관한 연구

윤의박,이영호 ( Eui Pak Yoon,Young Ho Lee ) 한국주조공학회 1982 한국주조공학회지 Vol.2 No.2

N/A This paper is concerned with the improvement of impact and tensile Properties of spheroidal graphite cast iron of the following duplex matricess which were heat treated in the eutectic transformation temperature range (that is, (α+γ) coexisting range) ; ferrite-martensite, ferrite-bainite and ferrite-pearlite. The absorbed energy and maximum load was measured by recording the load-deflection curve with instrumented Charpy impact testing machine in the temperature range from +100℃ to -196℃. It was found the ferrite-bainite duplex matrix showed the highest toughness among the above matrices in the room temperature and the low temperature range. Comparison of this matrix to ferrite-pearlite matrix(that is, as east) showed a lowering of 27 ℃ in the nil-ductility transition temperature (NDT) and a lowering of 40 ℃ in the ductile-brittle transition temperature (TrE), Which seems to result from the finner dimple pattern observed using miorofractography.

자동차용 경량화 합금 주물 전망

윤의박 한국주조공학회 1996 한국주조공학회지 Vol.16 No.7

계장화충격시험법 (計裝化衝擊試驗法) 에 의한 구조용강용접부의 동적파괴인성에 관한 연구 (1) : 計裝化衝擊試驗法에 의하여 측정한 결과의 유용성 On the Validity of the Test Result

윤의박,김기철 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.8

Dynamic fracture toughness of a structural steel has been estimated by employing instrumented impact testing method with small size specimens. One of the pendulum type impact testing machines equipped with semiconductor strain gage block in the tup, was used in this study. Signal from the dynamic transducer was multiplied by a dynamic strain amplifier and then stored in a digital memory before analyzing. Experimental results demonstrated that the toughness obtained from the instrumented impact testing agreed well with theoretical value, but several factors were appeared to play an important role when converting the test results into dynamic fracture toughness based on linear elastic theory. They were (1) the crack initiation point which would occur prior to maximum impact load, Pm, on the load-deflection curve, (2) compliance correction and (3) elastic inertial wave effect which had nothing to do with the specimen toughness.