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Si 첨가강의 연속주조공정 신뢰성 향상을 위한 고온변형특성에 관한 연구
옥명렬(Myoung-Ryul Ok),서진유(Jin-Yoo Suh),심재혁(Jae-Hyeok Shim),홍경태(Kyung-Tae Hong),이주동(Joo-Dong Lee),임창희(Chang-hee Yim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
A study was made on the high temperature deformation behavior of Si steel to increase the reliability of continuous casting process. In continuous casting process, the cast slab experiences cooling and deformation simultaneously, and various sources for defect formation exist. Of all these defects, cracking has the most deleterious effect on the property of the cast slab. To avoid or minimize transverse cracking, unbending temperature should be chosen carefully. In general, transverse cracks can easily be formed when unbending temperature lies within the ductility minimum temperature range of hot tensile test. Relative ratio of austenite-ferrite and their distribution or morphology have significant effect on the reliability of unbending process. Moreover, inhomogeneous deformation can be the source of defect formation. So, to produce Si steel by continuous casting, deformation behavior of Si steel as well as the relative ratio of austenite-ferrite or phase transformation temperature(Ar₃) should be known. We carried out hot tensile and hot compression test to evaluate the mechanical properties of the Si steel at high temperature. Hot ductility minimum temperature was not found with all Si contents, but inhomogeneous deformation occurred in high Si(1.17% and 3.21%) samples. It can be concluded that to minimize inhomogeneous deformation is the key to the successful unbending process of silicon steel. To analyze the effect of the silicon on the strength of silicon steel, a model was established, by using rule of mixture.
이재철(Jae Chul Lee),서진유(Jin Yoo Suh),안재평(Jae Pyung Ahn) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
Commercially pure Al alloy sheets were processed using high strain rate dissimilar channel angular pressing(DCAP) as many as 100 passages through the channel with φ= 120˚ in order to investigate the work hardening and the work softening behaviors caused by extremely high strain level (~58). The hardness of the alloy increased significantly by a factor of 2 at strains less than ~2.0, while a gradual decrease in the hardness was observed at strains greater than ~2.0. The work hardening and the work softening behaviors observed from the Al alloy were analyzed by correlating the measured properties with microstructural evolutions observed by transmission electron microscopy(TEM). A detailed microstructural evolution sequence occurring at successive strain stages was also demonstrated.
Equal-Channel Angular Pressing 에서의 변형거동해석
김희수,박종우,서진유 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.9
Numerical and experimental studies of equal-channel angular pressing was carried out to verify theoretical deformation models. Finite element method was used to calculate the grid deformation and the effective plastic strain field with various die shapes. When the curvature angle is zero, a homogeneous shear deformation occurs on the cross section of the specimen, which is well predicted by the theoretical models. As the curvature angle increases, the shear deformation is found to be comparatively uniform at the upper part of the specimen, and the effective plastic strain is in a good agreement with the theoretical value. However, the shear deformation at the lower part of the specimen becomes smaller, and the effective plastic strain is considerably different from the theoretical result. Model experiments using plexiglass molds and plasticine billets supported well with the results of the finite element analysis.
이재철,이호인,석현광,서진유 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.11
Deformation history of the materials during equal channel angular pressing(ECAP) is calculated by FEM. The deformation behavior during ECAP is presented in terms of stretch ratio and shear angle with respect to those of simple shear deformation. Although many researchers have presented that the uniform and simple shear deformation during ECAP can be achieved, the material subjected through the ECAP die is shown to experience not a simple shear deformation but a complex deformation in this FEM analysis.