Fe-28at.%Al 합금의 미세조직과 기계적 성질에 미치는 Cr , Mo 및 B 의 영향

최답천,이연오,김관휴,박은식,이호종 ( Dap Chun Choi,Yeon O Lee,Kwan Hyu Kim,Eun Sik Park,Ho Jong Lee ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.5

N/A The effects of Cr, Mo or B additions were investigated on B2↔DO₃structural transition temperature (T_c) and mechanical properties of Fe-28at.%Al. The raw materials were arc-melted in vacuum and then subjected to the following heat-treatments to maximize the DO₃ordered structure : 1000℃/7days, slowly cooled to 500℃ and then held for 5 days. In the effect on the grain refinment, the addition of alloying element B was the most effective. The addition of Cr or Mo had little effect. When 1at.%Mo was added, T_c increase about 30℃, but Cr had a very little effect on T_c. On the contrary, when B was added, T_c was apt to come down minutely. In the additional effect of alloying element on the mechanical properties, Cr was apt to decrease the microvickers hardness and yield strength, Mo and B didn`t have much effect. In the case of compressure strength test, the effect of the environment on the yield strength was contrary to the result of the tensile strength test.

고강도 내마모 금속간화합물 / Al 기지 복합재료의 개발을 위한 기초연구

최답천,이경구,이호종,기회봉 ( Dap Chun Choi,Kyung Ku Lee,Ho Jong Lee,Whe Bong Ghi ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.3

N/A The interfacial phenomena between intermetallic compounds and Al matrix have been studied at 680℃ for various holding time under argon atmosphere. Model experiments were performed using Fe, Ni and Ti wire to observe the interfacial phenomena. The interfacial phenomena between intermetallic compounds and Al matrix were analysed by optical microscope, SEM and EDX. The results of EDX and XRD showed that the interfacial zones of intermetallic compounds/Al matrix were composed of several intermetallic layers. The reaction layer was varied with holding time and heating temperature. The investigation of interfacial zones in the specimen as a function of heat treatment time at 680℃ indicated that the best heat treatment condition for squeeze casting was 680℃ for 5min.

용탕단조법에 의한 금속간화합물 / Al 기지 복합재료 개발을 위한 기초연구

최답천,이경구,이연오 ( Dap Chun Choi,Kyung Ku Lee,Yeon O Lee ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.5

N/A The microvickers hardness and microstructure of Fe/Al composite fabricated by squeeze casting method were investigated. Pure Al and A356 Alloy were chosen for the matrix composition and Fe preform was fabricated with sintered Fe powder at 1000℃ for 30min. under hydrogen atmosphere. Experimental variables were included preheating temperature, melt temperature and applied pressure. Analysing the experimental result concerning microstructure of fabricated composites, Fe/A356 composite showed improved microstructure at 600℃ melt temperature and 350℃ preform preheating temperature in Fe distribution and Infiltrated distance. The results of EDX and XRD showed that the interfacial zones of Fe/Al composite were composed of non-equilibrium intermetallic layers[(Al_5Fe₂)_x, Al_(13)Fe₄m Fe₃Al, FeAl]. The microvickers hardness of Fe/Al composite showed higher value than Fe/A356 composite in interface.

주철의 기지조직에 (基地組織) 미치는 Mischmetal Hydride 의 첨가효과

최답천,진영철 ( Dap Chun Choi,Young Chul Jin ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.4

N/A In this study we have investigated the effects of Mm, MmH and MmH₂ on the matrix development in cast iron, The conclusive summary is as follows : The spheroidal graphite was observed when 0.5wt.% or more of mischmetal was added and the matrix was of ledeburite structure, but hull`s eye structure was not observed. On the other hand, the bulls eye structure was observed when 0.25wt.% of MmH, or 0.25wt.% to 0.5wt.% of MmH₂was added. Above limit of the additives, the matrix changed into ledeburite structure. As the hydrogen content of mischmetal compound increased from MmH, the range of additives to obtain bulls eye structure expanded. This reveals the significant effect of mischmetal hydride on matrix development in cast iron and the possibility of practical use of the additives.

Fe-25at%Al 합금의 DO3↔B2 천이온도 , 미세조직 및 부식거동에 미치는 B , Si 의 영향 ( Research Papers : Effects of B and Si Additions on the DO3↔B2 Transition Temperature , Microstructure and Corrosion Behavior of Fe-25at%Al Alloys )

최답천,황금연 ( Dap Chun Choi,Keum Yeon Hwang ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.2

The effects of B additions, alone or in combination with Si, on the microstructure, DO₃⇔B2 transition temperature(Tc) and corrosion behavior of Fe-25at%Al alloys were investigated. The raw materials were arc-melted in vacuum and then subjected to the following heat treatments to maximize the DO₃order : homogenized at 1000℃ for 48hrs, slowly cooled to 500℃, and held at that temperature for 24hours. Results showed that the B addition to Fe-25at%Al alloys does indeed refine the grain and change from intergranular to transgranular fracture mode at room temperature, indicating a strengthening of grain boundaries. The Fe-25at% Al-1at% B-3at% Si alloy showed the highest Tc(△Tc=150℃) in this work. However, the effectiveness of Si in raising Tc decreased with more than 5at% Si additions combined with B. Since the preferential corrosion occurs at the precipitates, the corrosion resistance decreased due to the increased amount of precipitates with alloying additions.

Fe-30at.%A1 합금의 압연성에 미치는 Cr, B, Ti 및 Si 첨가효과

최답천 ( Dap Chun Choi ),이지성 ( Ji Sung Lee ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.2

N/A Some alloying elements such as Cr, B, Ti and Si were added individually or as a mixture to Fe-30 at.%Al alloys. The alloys were melted using an arc furnace and then heat-treated for homogenization at 1000℃ for 7 days and followed by rolling at 1000℃. The alloying elements on rolling characteristics were investigated by the microstructures and fracture mode before and after rolling. The microstructures before rolling showed that all of the alloys had equiaxed grains. On the other hand, the microstructures of rolling plane as well as its perpendicular plane became elongated after rolling. The alloys such as Fe-30Al, Fe-30Al-3Ti, Fe-30Al-0.5B, Fe-30Al-5Cr and Fe-30Al-3Ti-0.5B revealed better rolling behaviour from the point that intergranular and cleavage fractures were not fundamentally occurred. But the addition of 5Ti or 3Si to Fe-Al alloys had detrimental effects. The Ti-added alloy system such as Fe-30Al-5Ti, Fe-30Al-5Ti-5Cr, Fe-30Al-3Ti-5Cr and Fe-30Al-5Ti-0.5B were cracked through grain and showed cleavage fracture. The Si-added alloy system such as Fe-30Al-5Si, Fe-27Al-3Si and Fe-27Al-5Cr-3Si were cracked along the grain boundary and showed intergranular fracture. DO_3 ↔ B_2 transition temperature of Fe-30at.%Al alloy was 520℃, whereas the addition of 3Ti and 3Ti+0.5B comparably increased the temperature to 797 and 773℃, respectively.

Ni-Al-Fe 3원계합금의 미세조직 및 기계적 특성

최답천 ( Dap Chun Choi ),배대성 ( Dae Sung Bae ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.6

N/A Mechanical properties and microstructures of the Ni-Al-Fe and Ni-Al-Fe-(B, Zr) alloys which containing 10~30at.%Fe, 0.1at.%B and/or 0.1at.%Zr have been investigated. The experimental results showed that the microstructures of Ni25Al were changed from a single phase γ to dual phase γ and β by addition of 27at.%Fe. Ni45Al, however, kept the single β phase even though Fe was added upto 30at.%. The hardness of Ni25Al were increased from H_(R)B 70 to H_(R)C 39 by addition of 27at.%Fe. In the case of Ni45Al which have H_(R)C 37, the hardness was decreased by 10at.%Fe addition, but increased with 30at.%nFe. The yield strength and ultimate compressive strength in the compressive test have showed a similar trend with the hardness change. The strain to fracture was 14% at maximum and achieved in Ni25Al-27at.%Fe and Ni25Al-27at.%Fe-0.1at.%B alloys. The Ni45Al showed a relatively low strain to fracture as 4%. The impact absorption energy of Ni25Al increased from 0.74 kg-m to 1.81 kg-m by addition of 27at.%Fe. In case of Ni45Al, the addition of 10at.%oFe and 10at.%Fe with small amounts of B and Zr did not change significantly the impact absorption energy of 0.60 kg-m, whereas the addition of 30at.%Fe with small amounts of B and Zr increased it slightly. In fracture tests, both of two basic materials showed the same intergranular fracture but by adding Fe it changed to the cleavage fracture mode or co-existing of cleavage and intergranular fractures.

구상흑연주철의 Bainite 변태과정에서 Bainitic Ferrite 의 형상변화

최답천 ( Dap Chun Choi ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.5

N/A The growth characteristics of bainite at early stage in the fast quenched spheroidal graphite cast irons containing 0.06%Mn and 0.45%Mn during austempering process, was investigated with optical and scanning electron microscope. The following results regarding the effects of Mn and isothermal heat treatment on the morphological variation of bainitic ferrite were obtained. The morphology of bainite varies from acicular below 350℃ to feather shape above 350℃. The period of isothermal treatment also affects the shape of bainite at the fixed temperature. At 350℃, bainite is bamboo leaf-like up to 200 secs of isothermal holding time and with further increasing time up to 300 secs, changes to a mixed structure consisting of both feather and bamboo leaf and, finally becomes all feather shape at 900 secs. The morphology of bainitic ferrite formed at early stage of 300℃ isothermal treatment is similar to that of bainitic ferrite formed at 250℃ or 350℃ with unbranched, linear ferrite. However, bainitic ferrite divides into branches with increasing isothermal treatment, which occurs more fast at 400℃ than at 350℃. The difference in adding amount of Mn influences the morphology of bainitic ferrite in upper bainite. The bainitic ferrite with 0.45%Mn is observed to be more stable than that with 0.06%Mn, remaining unbranched for a longer period at the same temperature.

반응합성용탕단조법에 의해 제조된 Fe-Al 계 금속간화합물 / Al 기지 복합재료의 마모특성

신왕식,최답천 ( Wang Shik Shin,Dap Chun Choi ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.4

N/A Wear behavior of AC4C and 4 composites under dry condition has been investigated with variations of applied pressure and sliding velocity at the room temperature. Wear volume loss was measured and worn surfaces, its cross sectional views and wear debris were observed to characterize the properties and the wear mechanism of AC4C and 4 composites. Results showed that AC4C and 2 composites fabricated with mixed powder of Al-10, and 20wt%Fe were observed mechanically severe wear, but Al-30, 40wt%Fe did stable wear pattern in the change of wear volume loss on the variation of contact pressure and sliding velocity. The behavior of wear is the transition from mild to severe wear accompanied by surface-layer removal as a result of melting Al matrix because of friction heat at the localized spot between specimen and counterface.

주철의 흑연구상화에 미치는 기포의 영향

박실라,최답천,김관휴 ( Shil La Park,Dap Chun Choi,Kwan Hyu Kim ) 한국주조공학회 1989 한국주조공학회지 Vol.9 No.6

N/A The aim of this research is to investigate the effects of gas bubbles on the formation of spheroidal graphite in cast iron, Fe-Si-8%Mg alloy, mischmetal hydride(MmH₂) and CaCO₃, which discharge various amounts of Mg, H₂and CO₂gases, were added to Fe-3.9% C-2.0%Si melt and the melt was innoculated with 0.3wt% of 75%Fe-Si. The spheroidal graphites and/or compacted vermicular graphites were produced with more than 0.625㏄/g of Mg gas or more than 0.3125㏄/g of H₂gas while CO₂gas did not contribute to graphite spheroidization. Nodule counts increased with the amount of Fe-Si-Mg added ; but they decreased with the amount of MmH₂added because the number of effective gas bubbles decrease with the increase in Mm residual. The bull`s eye structure was revealed with 0.625㏄/g, 1.25㏄/g of Mg and 0.3125㏄/g of H₂; the ledeburite structure was revealed with more than 0.625㏄/g of H₂.