Prof. Yong-Shin Lee
Kookmin University, Korea
Biography: Prof. Yong-Shin Lee received his BS from Seoul National University in Korea, MS from Korea Advanced Institute of Science and Engineering (KAIST) in Korea, and Ph. D. from Cornell University in the United States of America. He worked at Samsung Engineering Co., and Korea Institute of Science and Engineering (KIST), before he joined the School of Mechanical Engineering, Kookmin University in 1992. Since then, he served as a Dean in the College of Engineering, as a Dean in the Graduate School of Engineering, Kookmin University. He also served as a President of Korean Society for Technology of Plasticity (KSTP). He has been working on the process design for metal forming such as rolling, extrusion/drawing, forging, and so forth. The specialty in his process model is the incorporation of micro structural developments such as texture development and damage evolution. He also developed a damage evolution model, a new penalty contact model, a new diffusion bonding model in terms of temperature and plastic work dissipation, and a constitutive relation for powder metallurgy.
Abstract: Pearlitic steel wires have been widely used for a main cable of a suspension bridge, a reinforcement wire of concrete or tire, and other structural wires requiring high strength. The mechanical properties, such as strength and ductility, of a pearlitic steel wire depend strongly on its microstructures. The high strength of pearlitic steel wire is obtained by the band-shaped cementite, which exist between the matrix of ferrite just like a laminated structure. Previous works reported that the most important microstructural parameters, affecting the strength of pearlitic steel most, are generally the thickness, shape and orientation of a cementite, and interlamellar spacing or the distance between cementite bands in a laminated structure of pearlitic steel wires.
Although there have been many works on finding the relation between the microstructure of a pearlitic steel and its mechanical properties in a drawn pearlitic steel wire, no works has been reported on the micro deformation of cementite band during wire drawing of pearlitic steel. In general, a wire drawing process changes not only the orientation of cementite but also its shape and dimension. In high carbon steels, the decrease of interlamellar spacing causes the reduction of cementite thickness. In order to control the strength of drawn pearlitic steel wire, it is necessary to trace the microstructural evolutions, such as micro deformation of a cementite band, during wire drawing.
The current author proposed a new simulation model, which can predict the micro-deformation behaviors of cementite bands using a finite element analysis in a micro scale. In his simulation model, a macro-deformation behavior at a material point during macro wire drawing of pearlitic steel could be represented by an averaged response of a unit problem. The material behavior in this unit model is assumed as rigid viscoplastic. Then, the unit model problem could be completed by defining the boundary conditions based on the macro velocity gradient that is obtained by performing the macro finite element simulation for wire drawing. Micro structural deformation of a cementite band would be predicted by micro finite element simulations with the above unit problem. Eventually, effects of various parameters such as the orientation and location of cementite on its micro deformation behaviors are studied.