Papers by Author: You Hwan Lee

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Authors: You Hwan Lee, Sang Yoon Lee, Duk Lak Lee
Abstract: In order to save natural resources and to reduce production costs, many industries have conducted studies on new developed steels and manufacturing processes. For instance, the use of high-strength bolts can decrease the number, size and weight of bolts used in a car, thereby decreasing fuel consumption. For this reason, steel makers are developing boron-added steel for high-strength bolts, which eliminates production processes. However, it has been pointed out that this boron-added steel is sensitive to austenite grain coarsening. The austenite grain coarsening does not occur uniformly, hence it can affect mechanical properties such as tensile, fatigue and so on. Therefore, the aim of this study is to investigate the abnormal behavior of grain growth and to determine the optimum amount of alloying elements in boron-added steel for use in making high-strength bolts.
Authors: J.S. Kim, You Hwan Lee, Young Won Kim, Chong Soo Lee
Abstract: In this study, high-temperature deformation behavior of newly developed beta-gamma TiAl alloys was investigated in the context of the dynamic-materials model (DMM). Processing maps representing the efficiency of power consumption for microstructure evolution were constructed utilizing the results of compression test at temperatures ranging from 1000oC to 1200oC and strain rates ranging from 10-4/s to 102/s and Artificial Neural Network simulation method. With the help of processing map and microstructural analysis, the optimum processing condition for the betagamma TiAl alloy was investigated. The role of β phase was also discussed in this study.
Authors: You Hwan Lee, Chong Soo Lee, T.J. Shin, Sang Moo Hwang, In Ok Shim
Authors: Won Seung Cho, You Hwan Lee, Myeong Woo Cho, Eun Sang Lee, J.H. Lee, Y.C. Hong, Dong Soo Park
Authors: You Hwan Lee, T.J. Shin, Jong Taek Yeom, Nho Kwang Park, S.S. Hong, In Ok Shim, Sang Moo Hwang, Chong Soo Lee
Abstract: Prediction of final microstructures after high temperature forming of Ti-6Al-4V alloy was´attempted in this study. Using two typical microstructures, i.e., equiaxed and Widmanstätten microstructures, compression test was carried out up to the strain level of 0.6 at various temperatures (700 ~ 1100°C) and strain rates (10-4 ~ 102/s). From the flow stress-strain data, parameters such as strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equations for both microstructures. Then, finite element analysis was performed to predict the final microstructure of the deformed body, which was well accorded with the experimental results.
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