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김영희,김도경 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.4
This study has been conducted to develope the combined heat treating technique of gas carburising-gas nitriding and gas carburising to improve the hot working performance of type H3 hot work tool steel. Case depth and carbrides coarsening were increased with increasing carburising temperature and time, respectively. Surface hardness showed decreasing tendency with increasing 2nd tempering temperature after carburising treatment. After carburising, 2nd treatment at 500 to 600 was chosen according to a hardness demand of final product. High temperature tempering resistance showed more excellent quality during such carburising-nitriding or carburising than complex treatment as after conventional hardening.
급냉응고 Al-Fe 합금에서 TEM 에 의한 Al13Fe4 결정상과 정10면체 준결정상간의 구조 유사성 연구
김도경 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.1
Quasicrystalline and quasicrystal-related crystalline phases in rapidly solidified Al-Fe alloys have been investigated by a detailed TEM(transmission electron microscopy). Rapidly solidified Al-10at %Fe mainly consists of α-Al and microquasicrystalline phase. The decagonal phase particles with a dendritic shape are also present as a primary solidification product in the relatively slowly cooled region of the ribbon. Rapidly solidified Al-20at%Fe consists of α-Al and Al_(13)Fe₄ phase. The Al_(13)Fe₄ phase particles have a dendritic shape with ten branches due to (201) and (100) ten fold twinning of Al_(13)Fe₄ monoclinic structure. Detailed SADP(selected area electron diffraction pattern) analysis has shown that there exists a close similarity between the diffraction characteristics of the decagonal phase and Al_(13)Fe₄. The present study also shows that the quasicrystalline structure of the decagonal phase decomposed into ten fold twinned Al_(13)Fe₄ structure with heat treatment.
김영희,김도경 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.4
For the purpose of investigating the growth characteristics and composition of nitrides, gas nitridings of the austenitic stainless steel, STR 36 heat resisting steel and martensitic stainless steel are investigated at the temperature ranges between 500℃ and 675℃ for 5hours under the 75%NH₃+5%CO₂+20%Air gas atmosphere. When gas nitriding the austentic stainless steel and STR 36 heat resisting alloy, the abnormal growth behavior of compound layer deviating from the conventional diffusion law with increasing temperature appears, while the compound layer of martensitic stainless steel shows the normal diffusional growth behavior. From the examination of microstructure, X-ray diffraction and hardness test, it is concluded that the abnormal growth behavior of compound layer with increasing temperature induces from the formation and dissolution of CrN and γ'-Fe₄N at the nitriding temperature ranges of 600∼650℃.
급냉응고 Mg-Nd-X (X= Al, Si) 합금의 미세 조직 및 상분해 거동
박현,김낙준,박우진,김도경 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.12
The microstructural characteristics and decomposition behaviour of rapidly solidified Mg-Nd-X(X=Al, Si) alloys have been investigated by using a detailed transmission electron microscopy. Rapid solidification of Mg-8Nd, Mg-8Nd-1Al and Mg-8Nd-1Si produces various types of solidification microstructure depending upon the alloy composition, i.e. fine Mg₃Nd precipitates and α-Mg in as-melt-spun Mg-8Nd, α-Mg cellular structure with secondary solidification phase particles at cell boundaries in as-melt-spun Mg-8Nd-1Al and supersaturated α-Mg grains with fine particles at the grain boundaries in as-melt-spun Mg-8Nd-1Si. Annealing of as-rapidly solidified Mg-8Nd and Mg-8Nd-1Si up to 300℃ results in coarsening of Mg₃Nd precipitates. However, no significant change occurs in Mg-8Nd-1Al with annealing up to 300℃. With annealing at 400℃, the pre-existing phase decomposes forming new phases stable at 400℃, i.e. a fcc phase(a=5.4Å) in Mg-8Nd, a fcc phase(a=8.0Å, Al₂Nd) in Mg-8Nd-1Al and Mg_9Nd in Mg-8Nd-1Si.