Papers by Author: Jong Kyu Yoon

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Authors: Dong Hee Yeon, Pil Ryung Cha, Jong Kyu Yoon
Authors: Kee Hyun Kim, Benny van Daele, Gustaaf Van Tendeloo, Yong Sug Chung, Jong Kyu Yoon
Abstract: A hot dip aluminising process was carried out with a 1mm steel sheet dipped into the Al-10at.% Si melt in an automatic hot-dip simulator. When steel and liquid aluminium are in contact with each other, a thin intermetallic compound (IMC) is formed between the steel and the aluminium. The analysis and identification of the formation mechanism of the IMC is needed to manufacture the application products. Energy dispersive X-ray spectroscopy (EDX) and electron probe microanalysis (EPMA) are normally used to identify the phases of IMC. In the Al-Fe-Si system, numerous compounds with only slight differences in composition are formed. Consequently, EDX and EPMA are insufficient to confirm exactly the thin IMC with multiphases. In this study, transmission electron microscopy (TEM) analysis combined with EDX was used. The TEM sample was prepared with focused ion beam (FIB) sampling. The FIB lift-out technology is used to slice a very thin specimen with minimum contamination for TEM analysis. It is clearly shown that the IMC consists of Al-27 at. % Fe-10 at. % Si and is identified as Al8Fe2Si with a hexagonal unit cell (space group P63/mmc). The cell parameters are a= 1.2404nm and c= 2.6234nm.
Authors: Kee Hyun Kim, Nong Moon Hwang, Byeong Joo Lee, Jong Kyu Yoon
Abstract: Mechanical properties of line pipe steels used in the deep sea or in the severe cold climate depend on alloying elements and manufacturing processes and many efforts have been made to enhance the properties of the line pipe steels. In this study, for systematic approaches to the process design of line pipe steels, its phase diagram was calculated using a Thermo-CalcTM program. The calculations indicated that A3 is around 840oC. Setting the FRT(Finish Rolling Temperature) above A3 appears to be critical to the increase of strength and toughness of line pipe steels by increasing the amounts of acicular ferrite and at the same time by decreasing the precipitation of proeutectoid ferrite. In the case of the FRT below A3, relatively large amounts of proeutectoid ferrite are precipitated from the matrix with the carbon contents of the austenite phase around ferrite being enriched.
Authors: Kee Hyun Kim, Benny van Daele, Gustaaf Van Tendeloo, Jong Kyu Yoon
Abstract: A hot dip aluminizing process to simulate the continuous galvanizing line (CGL) was carried out in three successive steps by a hot dip simulator: the pre-treatment for removing scales on the 200 × 250 mm2 and 1mm in thickness cold rolled steel sheet, the dipping in 660°C Al-Si melt for 3s and the cooling. In a pre-treatment, the steel specimen was partly coated by Au to confirm the mechanism of intermetallic compound (IMC) formation. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) analyses were followed to observe the cross-section and the distribution of the elements. The specimen was analyzed in the boundary of the dipped-undipped part to see the formation mechanism of the aluminized steel. An intermetallic compound (IMC) is rapidly developed and grown in the steel-liquid interface. It has been usually reported that the IMC was formed by the dissolution of iron in the steel substrate toward the melt and the diffusion of aluminum in an opposite direction. The specimen is covered with aluminum-10 wt.% silicon, forms the IMC in the part that was not Au coated. However, IMC is not formed in the Au-coated part. The interface of the dipped-undipped is also analyzed by EDX. At the interface of the steel-IMC, it is clearly shown that the IMC is only formed in the dipped part and exists in the steel substrate as well, and contributes by iron, aluminum and silicon. The result clearly shows that only aluminum diffuses into the steel substrate without the dissolution of iron and forms the IMC between the steel substrate and the melt. Au coating and the short dipping time prevent the iron from dissolving into the aluminum melt. By TEM combined with focused ion beam (FIB) sample preparation, the IMC is confirmed as Fe2SiAl8, a hexagonal structure with space group P63/mmc.
Authors: Jin You Kim, Jong Kyu Yoon, Yoo Chan Kim, Hyunn Kwang Suck, Ki Bae Kim, Pil Ryung Cha
Abstract: We present a phase field model for coherent phase transition and its application to the self-assembled arrangement of second phase particles in coherent phase transition. The model developed here is free from the interface instability due to the contribution of chemical free energy and correctly describes elastically inhomogeneous system. It is observed that coherent misfit strain and anisotropy of elastic constants induce the interface instability that brings about the particle splitting and the self-assembled alignment of second phase particles. Their arrangement to the elastically soft direction occurs only in the system where the elastic contant of the precipitates is larger than that of the matrix phase.
Authors: Jin You Kim, Dong Hee Yeon, Pil Ryung Cha, Jong Kyu Yoon
Abstract: A phase field model for step dynamics on vicinal surface is presented. Using this model, time dependent, collective motions of steps were investigated. Through numerical simulations, morphological step instabilities induced by ES barrier were analyzed, and it is shown that this model could interpret various phenomena during step flow growth such as step bunching and meandering.
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