Seoul, South Korea
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Park S.,Chonnam National University | Min D.,Dongbu Steel Co. | Lim H.,Chonnam National University | Yoon D.J.,Sunchon National University | Lee K.,Chonnam National University
Journal of Nanoscience and Nanotechnology | Year: 2011

The purpose of this study was to investigate the effects of heat treatment on the cystallinity of titanium nanotubes. The titanium nanotubes had diameters ranging from 90-95 nm, lengths between 400-500 nm, and thicknesses of 11 nm. After heat treatment at high temperatures, the diameter and length of the nanotubes decreased, whereas the thickness increased. The titanium nanotubes exhibited amorphous+anatase phases at 300 °C, anatase+rutile phases at 500 °C and a rutile phase at 800 °C. Copyright © 2011 American Scientific Publishers All rights reserved.

Lee K.,Chonnam National University | Min D.,Dongbu Steel Co. | Jeong S.,Chonnam National University | Yun K.-D.,Chonnam National University | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2011

The purpose of this study was to investigate the dimensional changes and phase transition of nano-tubular titanium oxide arrays after heat treatment under an oxygen-containing atmosphere. The thermodynamic background for the oxidation of titanium to titanium oxide was theoretically investigated as a function of the oxygen partial pressure. The anodized titanium nanotubes had lengths between 400 and 500 nm, thicknesses of 11 nm and an amorphous structure. The specimens heat-treated at higher oxygen partial pressures preferentially had rutile phase rather than anatase phase. The thickness of the TiO 2 nanotubes was increased at a lower oxygen partial pressure. © 2011 American Scientific Publishers.

Lho S.H.,Korea University | Park M.-W.,Dongbu Steel Co | Ju Y.K.,Korea University | Kim S.-D.,Korea University
Applied Mechanics and Materials | Year: 2014

Plate girders with corrugated webs with angles were developed in order to promote the flange local buckling strength of conventional plate girders with corrugated webs. The width to thickness ratio of flanges can be reduced with angles. However corrugated webs cannot contribute to the flexural stiffness and strength of PGCW, corrugated webs of PGCW-A can. A full-scale test was conducted to evaluate the flexural capacity of PGCW-A. As a result, the flexural capacity of a specimen of PGCW-A increased by 163% compared to a specimen of PGCW. © (2014) Trans Tech Publications, Switzerland.

Lee Y.S.,Dongbu Steel Co. | Jung C.,Dongbu Steel Co. | Jiang Y.,Dongbu Steel Co. | Im J.-T.,Dongbu Steel Co. | And 4 more authors.
Materials Science Forum | Year: 2010

The surface cracking behaviors of Cu-bearing steels were studied under similar conditions of the direct hot charging processes. Several specimens with various Cu contents from 0.11 to 0.38% were prepared, the oxidation tests were performed at the temperature of 1100, 1150 and 1200°C, and the hot compression tests were conducted at 1050°C using the Gleeble 3500 in order to examine the Cu induced surface cracks. The surface cracks increased gradually as the Cu-rich phase above the critical level increased. The critical level of Cu-rich phase for the specimens of high Cu contents (0.38%) reaches with a thin scale layer. However, the specimens with lower Cu content (0.13%) the critical level of Cu-rich phase occurred with a thick scale layer. The oxidation potentials of steel were affected by temperature, time, atmosphere and other elements. The oxidation rates of Cu bearing steels decreased with increasing Cu contents. It is suggested that the oxidized scale thickness is the one of important factors inducing the surface cracks by Cu contained steels in direct hot charging process. © (2010) Trans Tech Publications.

Cho H.S.,Dongbu Steel Co. | Hahm J.H.,Dongbu Steel Co. | Lee Y.H.,Dongbu Steel Co.
Transactions of the Korean Society of Mechanical Engineers, A | Year: 2012

Cold drawn(CD) bars feature superb surface roughness, dimensional precision, and straightness. They are used in the manufacture of automotive parts and home electrical appliances. Two cross-roll straighteners have been used to manufacture CD bars for these industries. This study investigated the variation of the gap size between the two cross-rolls. It was found that changes in the gap size have a large influence on the residual stress and plastic deformation. Finite element method(FEM) simulations were performed to study the influence of the gap size on the residual stress in CD bars, and experiments were performed to verify the FEM results. The residual stresses were measured with X-ray diffraction in both the axial and the hoop directions. © 2012 The Korean Society of Mechanical Engineers.

Dongbu Steel Co. | Date: 2011-08-23

Steel in sheet, rod, bar and/or billet form; Steel in the form of sheets, plates, foils and coils; Wire.

Dongbu Steel Co. | Date: 2017-01-24


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