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W-Cu와 Cu의 고속 충돌에 의한 연강의 미세조직 변화
이성,홍문희,백운형,Lee, Seong,Hong, Moon-Hee,Baek, Woon-Hyung 한국분말야금학회 1999 한국분말재료학회지 (KPMI) Vol.6 No.1
The microstructure of the reagion of carters, created by Cu and W-Cu shaped charge jets, in a 1020 mild steel target has been intestiaged. The region ahead of the crater created by the Cu shaped charge jet, reveals dramatic grain refinement implying the occurrence of a dynamic recrystallization, while that of W-Cu one dose a martensitic transformation indicative of heating up to an austenitic region followed by rapid cooling.The impacting pressure calculated when the W-Cu shaped charge jet encounters the target is higher than that of the Cu one. The micro-hardness of the region ahead of the crater created by the W-Cu shaped charge jet is also higher than that of the Cu one. The microstructure of W-Cu slug remained in the inside of the craters depicts the occurrence of the remarkable elongation of W particles during the liner collaphse. From these results, the microstructural variation of the region ahead of the crater with Cu and W-Cu shaped charge jets is discussed in trems of the pressure dependency of the transformation region of ferrite and austenite phases.
ESR法에 의한 Fe-18Ni Maraging 銅의 2次 精鍊에 關한 硏究
申璟煥,白雲炯 國立 昌原大學校 産業技術硏究所 1989 産技硏論文集 Vol.3 No.-
The primary objective of this study has been to develop the production scale technique of appling the ESR(Electro Slag Remelting) process to the secondary refining of Fe-18 Ni Maraging steels. Through this study, 60% Ca F2-20% Al2 O3-20% Ti O2 slag was proved to be useful in reducing the segregation between top and bottom of ingot and in stabilizing the recovery of oxidizing elements. Furthermore, ESR refining improved the mechanical properties of 250 and 300 grade Maraging steels, including the tensile strength and fracture toughness. These improvements were believed to be due to the reduction in non-metallic inclusions, particularly those of larger than 8㎛, and reduction in macro and micro-segregation. As a result, VIM+ESR process was proved to be a process which can be substituted for the VIM+VAR in the manufacturing of Fe-18 Ni Maraging Steel.
홍준표,백운형 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.8
A two dimensional mathematical model was developed to analyze the heat flow involving phase change during welding of thin plates. A modified finite difference method was adopted for computer simulation. Latent heat of fusion or freezing during welding was treated by the temperature recovery method. Radiative and convective heat losses from the surface and the dependence of the relevant physical properties on temperature were also taken into account. The effects of welding speed, heat input, preheating temperature, and plate thickness on the thermal history and isotherms of the welding zone were quantitatively demonstrated by computer simulation based on 7020 aluminum alloy and l.5% Mn steel.
W-Ni-Fe 중합금에서 바인더 조성에 따른 미세조직 및 기계적 성질의 변화
이성,백운형,김은표,송흥섭,노준웅,천길성 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.8
W heavy alloys with different composition of matrix were sintered at various temperatures to investigate the microstructure and mechanical properties. The Ni/Fe ratios in the composition of 93W-7 (Ni-Fe) heavy alloys were varied from 7/3 via 8/2 to 9/1 by weight. The results showed that, with increased in Ni contents, the volume fraction of matrix was increased due to increased solubility of W in the matrix. In trun, it lowered dihedral angle and facilitated matrix peneratration along the grains to lower contiguity. The increased volume fraction of ductile matrix and decreased contiguity contributed to a higher ductility and toughness. The specimen with 9/1 of Ni/Fe ratio showed the lowest impact energy even though it had the largest volume fraction of matrix and the lowest contiguity. This was attributed to the highly dissolved W in the matrix. The optimum composition in the matrix is 80% Ni and 20Fe.
기계적으로 혼합된 WO3-CuO 복합분말의 환원 분말 형상 및 소결 거동에 미치는 환원온도의 영향
이성,천병선,백운형 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.12
It is known fact that the presence of each element in insoluble system like W-Cu does not influence the mutual reduction process. Therefore, reduction is generally carried out at lower temperature in order to gain smaller particle size. However, in a nano sized mechanically mixed WO₃-CuO system, grain growth of tungsten particle and distinct solid state sintering are observed during reduction process. This implies the possibility of change of powder morphology by diffusion during reduction. This study is focused on scanning electron microscopy and dilatometry in order to investigate the effects of reduction temperature not only on the reduced powder morphology but also on the sintering behavior. It is observed that powder gets smaller and more round upto reduction temperature 980℃ due to breakage of composite powder and solid state sintering. As reduction temperature exceeds 980℃, the powder begins to grow once again. These results are well in agreement with the dilatometry experiments. In W-Cu system, sintered density is almost always determined by the rearrangement stage, which is determined by the powder size and its morphology. This dilatometry experiments show that the densification of reduced W-Cu powder is largely depended on the reduction temperature and shows the best at 980℃.