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Fe - Si - C 계 압분체의 소결에 따른 조직 변화
최답천(D . C . Choi),이도재(D . J . Lee),이방식(B . S . Lee),강길원(K . W . Kang) 대한금속재료학회(구 대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.2
Change of microstructure and pore shape during sintering was investigated in Fe-2.5% Si-l.4%C compacts. The compacts were sintered at 1140, 1150, 1160 and 1170℃ in Ar atmosphere for various sintering time. Slow and rapid cooling after sintering allowed to examine the behavior of inter-diffusion between elemental particles, change of microstructure and pore shape of sintered alloy. At early stage of sintering, as-quenched microstructure was fine pearlite and it changed to marten-site with succesive sintering upto 27 hr. This change of microstructure with sintering time seems closely related to the homogenization process of Si. Dissimilarly to the previous reports, two type of pores, surrounded by ferrite or pearlite, were observed in slowly cooled specimen after sintering 27 hr. This result suggests that the local content of carbon and silicon were slightly different due to the sluggish diffusion of Si.
이도재,윤덕용 대한금속재료학회(대한금속학회) 1976 대한금속·재료학회지 Vol.14 No.3
Cu-10% Sn 오일레스 베어링 시편의 소결 과정에서 분말의 크기, 가열 속도 및 소결 시간이 칫수변화, 함유량, 압환강도 및 미세 조직 등에 미치는 영향을 조사하였다. 사용한 구리 분말의 크기는 -150mesh와 -270mesh였고, 주석 분말은 -230+325mesh와 -400mesh이었다. 시편은 수소와 질소의 혼합 gas 분위기에서 797℃와 807℃에서 15분까지 소결하였다. Cu-Sn 혼합 분말 압분체의 소결중 칫수 변화는 대부분 가열 도중에 일어났다. 분말이 클수록, 특히 주석 분말이 클수록, 팽창이 많이 일어났고, 가열 속도가 빠르면 또한 팽창도 많았다. 함유량과 압환강도는 대체로 밀도와 비슷한 변화를 보였다. 본 실험에서 나타난 입도 크기와 가열 속도의 칫수 팽창에 대한 영향은 고상 소결과 액상 소결로 인한 수축현상과 구리 분말 boundary에 액상의 penetration으로 인한 팽창 효과로 설명을 시도하였다. 미세한 혼합 분말로 만든 시편을 15분 소결하여 균일하고 입도가 큰 청동 합금 조직을 얻었다. 본 실험 결과의 실제 공정에 대한 의미도 논하였다. The effects of powder size, heating rate, and sintering time on dimensional change, oil impregnation, radial crushing strength, and microstructure were examined in sintered Cu-10% Sn mixture. The copper powder sizes were -150 mesh and -270 mesh, and tin powders were -230 +325 mesh and -400 mesh. The specimens were sintered in hydrogen-nitrogen atmosphere at 797℃ for sintering time up to 15 minutes. The dimensional change of Cu-Sn mixture compacts occurred mostly during the heating up stage. Larger powder size, in particular, larger tin powder size and faster heating rate caused more expansion. The oil impregnation and radial crushing strength changed in a way similar to the density change. The observed dependence of growth on particle size and heating rate can be explained by densification effects of the solid state and liquid state sintering and the growth due to the penetration of copper particle boundaries by tin rich melt. The specimen of fine powder mixture sintered for 15 minutes showed uniform bronze structure with large grains. The practical implications of the present results are discussed.
이경구,윤동주,기회봉,최답천,이도재 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.1
In the present study, oxidation behavior of 304 and 316 stainless steels Was investigated. After solution treatment, specimens were polished up to 1㎛ Al₂O₃grade and then subjected to oxidation treatment in dry air. The range of temperature was used for oxidation treatment at 300℃∼500℃ and TEM was used for analyzing the components and structure of oxide film. Also, these results were compared with the results of ESCA and TG. According to the results of TEM analysis, it was found that Cr oxide film was formed on top of the surface after room temperature oxidation but amorphous Fe oxide was formed on top of the surface and polycrystalline (Cr,Fe)₂O₃was formed below the amorphous Fe oxide layer after 500℃ oxidation treatment. The oxidized specimens at 500℃ showed that 316 stainless steel resists more strongly to grain and grain boundary oxidation than 304 stainless steel. These results suggested that Mo component resolved in 316 stainless steel matrix suppressed the formation of Cr carbide which may results in local Cr deplete area.