Osprey Forming 공정으로 제조된 고강도 저합금강의 기계적 특성에 관한 연구

박수정,최답천,이현규 조선대학교 생산기술연구소 2004 生産技術硏究 Vol.26 No.1

High strength low alloy steel was fabricated by Osprey forming process. The billet have been characterized by optical microscopy, scanning electron microscopy. hardness test. tensile test and impact test. High strength low alloy steel is bainite structure. Hardness range of billets was about 300 kgf/㎟ without a part of horizontal and vertical about spray angle. After hot rolling, aged specimen was tensile test in results, meas yield strength 858MPa, tensile strength 985MPa, and elongation ratio was 20.3%. TO absorption energies hot rolling specimen were 17.8J, 32.8J at -90℃, -50℃. energy of respectively but it was very high 92.7J at ambient temperature. after hot rolling, absorbed aged specimen were 102J.

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.

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.

Fe-25at% Al 금속간화합물의 입계부식거동에 미치는 Cr, Mo, Nb 및 B의 영향

최답천,최한철 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.4

Effects of the addition of Cr, Mo, Nb, and B to Fe-25at%Al intermetallic compound on the intergranular corrosion behavior were investigated using potentiostat. The specimens were casted by the vacuum arc melting. The subsequent homogenization and the stabilization led to the homogeneous DO₃ structure of the specimen. After the corrosion tests, the surface of the tested specimens were observed by the optical microscopy and scanning electron microscopy(SEM). For Fe-25at%Al intemetallic compound, the addition of Cr and Mo proved beneficial to decrease the grain boundary attack by decreasing activation current density. Addition of B and Nb resulted in a higher activation current density and also a higher passive current density. These results indicated the role of Cr and Mo in improving the intergranular corrosion resistance of Fe-25at%Al intermetallic compound. Boron and Nb addition to Fe-25at%Al accelerated the granular and also the intergranular corrosion. Fe-25at%Al containing Cr and Mo showed remarkably improved intergranular corrosion resistance in comparison with Born and Nb addition to Fe-25at%Al.

Cr 과 Si 이 복합 첨가된 TiAl 금속간화합물의 미세조직 및 기계적 성질에 관한 연구

최답천,이호종,이병택 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8

In order to investigate the effects of Cr and Si additions in γ-TiAl alloy, the microstructure and mechanical properties before and after heat treatment were studied. Simultaneous additions of Cr and Si were more effective in stabilizing the lamellar structure of TiAl alloys after heat treatment. The stoichiometric composition of the precipitates formed in the alloy with 0.5% Si addition was estimated to be Ti_5(Si, Al)₃, and that with 3%Cr0.5%Si addition to be(Ti, Cr)_5(Si,Al)₃. Good mechanical properties could be achieved by simultaneous addition of Cr and Si. Tensile tests before and after heat treatment showed that maximum yield strength was obtained from the alloy with 1%Cr0.5%Si addition and while the highest elongation was observed by 1%Cr0.25%Si addition before heat treatment. However, the alloy with 2%Cr0.5%Si addition showed the highest elongation after heat treatment.

Fe-38at.%Al 합금의 미세조직과 기계적 성질에 미치는 Cr, Mo, Nb 및 B 의 첨가효과

최답천,최한철,주성민,박광일 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.3

The changes in the microstructure, mechanical properties and Fracture mode were investigated for Fe-38at.%Al alloys when Cr, Mo, Nb and B were added. As the amount of B or Nb addition was increased, the grain size became smaller. The effects of Mo and Cr were not significant. Hardness and yield strength of Fe-38at.%Al alloy were decreased by adding 6%Cr. However Mo, Nb and B additions were increased. The fracture mode of Fe-38at.%A1 binary alloy was the typical intergranular fracture, but it was changed into the quasi-cleavage fracture mode by adding 6%Cr. In Fe-38Al-6Cr+Mo alloy, the fracture mode was changed into cleavage. The typical intergranular mode was observed in Nb added alloys where cracks propagated along the grain boundary precipitates. However, the fracture mode in B added alloys was the quasi-cleavage mode due to strengthening of grain boundaries.

Nd-Fe-B 계 영구자석 제조에 있어서 수소화 반응의 응용

최답천,박충년,최유 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.12

Co-Al-C 3 원계 금속간화합물 Co3AlCx (k 상) 의 특성 : Part 1:(Co) + k 2 상 합금의 기계적 성질 Part 1:Mechanical Property of (Co) + k Two Phase Alloys

최답천,황금연,강창석,명태호,Mishima, Yoshinao 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11

A new class of Co-base superalloy may be developed based on the ternary Co-Al-C system in which two phase alloys could be designed containing E2₁-type intermetallic compound Co₃AlC_x, known as κ-phase, being dispersed in the Co primary solid solution. Strength and ductility of the two phase alloys are evaluated at room to elevated temperatures. It is found that compressive 0.2% flow stress of the two phase alloys at room temperature seems to exhibit a maximum with 30 to 50% volume fraction of the intermetallic phase. Room temperature ductility of the two phase alloys is found to be 5 to 21% varying monotonously with increasing volume fraction of the intermetallic phase. At 1000℃, the 0.2% flow stress of the two phase alloys with κ-phase for more than 30% in volume are about 250 to 280 ㎫ under a strain rate of 1.4 ×10^(-4)s^(-1), which is comparable to that of commercial nickel base superalloy.

Fe-Cr-Al 3 원계 합금의 미세조직, 기계적 성질 및 파괴거동에 미치는 첨가원소의 영향

최답천,이도재,이광민,주성민,최한철 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.2

Fe-Cr-Al alloy has been used in automobiles to meet the social needs for clean exhaust gases and reduced weight for better fuel economy. Various other types of high performance Fe-Cr-Al alloy are now being used in the automobile exhaust system. This paper described the changes in the microstructures, mechanical properties and fracture behaviors for automobile exhaust system parts application. As the amount of 0.05 wt.%B or 0.5 wt.%Zr addition was added, the grain size became smaller. The results of XRD were observed α-ferrite(α-Fe) for Fe-(5∼20)wt.%Cr-(5, 6, 8)wt.%Al alloys. However, Fe-(5∼20)wt.%Cr-10 wt.% Al alloys were observed α-ferrite(α-Fe) and α₁(Fe₃Al). Rockwell hardness was increased by increasing Cr and Al amount. Yield strength was decreased by adding 0.5wt.%Zr. Regardless of Cr amount, fracture behaviors in 5 wt.%Al added alloys revealed quasi-cleavage and ductile fracture mode, and 10 wt.%Al added alloys revealed brittle fracture mode with cleavage and river pattern. However the fracture mode in 0.05 wt.%B and 0.5 wt.%Zr added alloy revealed quasi-cleavage and dimple fracture mode due to strengthening of grain boundaries, respectively.