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오스템퍼드 구상흑연주철의 기계적 성질에 미치는 Si 의 영향
이상인,오영근,전기찬 ( Sang In Lee,Young Kun Oh,Ghi Chan Jun ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.3
N/A Influence of Si contents on the mechanical properties and microstructure of austempered ductile iron was investigated. Four different Si contents between 2.0 and 2.9% were used. Austenitizing was performed at 890℃ for 2hrs and austempering temperatures were both 340 and 380℃ for 0.5, 1, and 2hrs. Nodule content was more than 300/㎟ and nodularity was more than 90%. Microstructure was revealed using nital and retained austenite was measured by x-ray diffractometer. Tensile test, no-notch Charpy impact test and wear test were performed. Tensile strength was improved as Si content increased and both elongation and impact toughness had peak at 2.6%Si. The specimen austempered at 380℃ showed lower tensile strength than that of 340℃, but showed higher elongation. However, austempering temperature of 380℃ was desirable because that of 340℃ was close to lower bainite transformation. As austempering time increased, tensile strength and elongation were improved and optimum condition was obtained for 2hrs heat treatment.
최현진,오영근,전기찬,이승춘,이경환 ( Hyun Jin Choi,Young Kun Oh,Ghi Chan Jun,Sung Chun Lee,Gyung Whan Lee ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.6
N/A Coating materials for Evaporative Pattern Casting (EPC) process have been developed to investigate the effect of refractories on coating material properties. Three types of developed and one foreign coating materials were used. The former designated as A, B, C and the latter named S.K. The refractory of coating material A is spherical shape of zirconia, and the ones of B, C and S.K. is flake shape of mica. Strength, permeability at room and elevated temperature, anti-sand attachability and carbon residuary were evaluated at each coating materials. Permeability measurement device for elevated temperature was also designed. The zirconia type of coating material had excellent permeability, on the other hand the mica type had good strength and anti-sand attachability. It was found that the refractories were not broken during casting, so permeability indicated same trend at both room and elevated temperature. Based on results, coating material contained small size of mica which is designated as B has the best combination for cast iron. (Received September 29, 1997)
FDM 에 의한 응고해석시 계산기간 단축을 위한 Algorithm 연구
이재경,전주매,전기찬 ( Jae Kyung Lee,Ju Mae Jeon,Ghi Chan Jun ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.5
N/A Efficient algorithm for the solidification simulation by FDM is described from the practical point of views. If a proper time step Δt is selected, the calculation is accelerated by implicit algorithm with the temperature recovery method of latent heat method. The implicit routine in the calculation is processed by SOR method(relaxation factor=1.5, truncation error=l0^(-4)). The calculation is more accelerated by linear-interpolated explicite algorithm with a time step larger than the minimum value of the time step. This explicit method, which is applicable to the practical casting simulation problems, produces almost same results with about 40% faster calculation speed compared with the conventional explicit method.
전기찬,Hosford, William F. 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.1
Three sheet steels were uniaxially prestrained and tension tested in 15˚intervals to the prestrain axis In the subsequent tests after prestrains higher than about 7%, the residual uniform strains were very small in orientations beyond 30˚ to the prestrain axis. Total strains to failure also decreased in these noncoaxial orientations but the tendency was not as marked as in the uniform strain. The subsequent flow curves in the noncoaxial directions skewed no sharp yield points. The work-hardening rate was initially very high but decreased rapidly, which resulted in a large decrease in uniform strain.
전기찬,Hosford,W. F. 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.11
Several new test procedures were tried to measure flow behavior of sheet metals under combined stress stales utilizing a normalized aluminum-killed steel which was nearly isotropic. Equibiaxial stress condition was obtained From a through-thickness compression test on a disk-slacked circular cylinder. Plane strain and pure shear conditions were obtained by plane strain compression tests, in which one of in-plane strains or the thickness strain is zero. Experimental Flow stresses of the steel were slightly higher in the equibiaxial loading path, and slightly lower in the plane-strain path than the expected values from the Mises theory. Experimental flow stresses in the pure shear path fitted well with the theoretical values.
Hosford,William F.,전기찬 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.12
Physical effects resulting from strain-path changes from cold rolling to uniaxial tension were studied on two sheet steels; a aluminum-killed steel and a normalized aluminum-killed steel. Cold rolling caused a unusually large decrease in uniform strain and in total strain to failure in all orientations in subsequent tension. The prestrained sheets showed three stages of deformation; initial rapid work hardening, work softening and low-work hardening stage.