• Journal of Welding and Joining
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• v.23 no.5
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• pp.20-24
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• 2005

Due to the difficulties associated with the supply of steel plates, hot rolled coil (Steel grade: SM490A) is considered fur structural materials in replace of the existing SWS50A-M1. However, it is found that SM490A exhibits a significant anisotropy in terms of impact energy with respect to transverse and longitudinal directions. In this study, an experimental investigation is carried out to examine the relationship between the anisotropy in impact values and the fatigue strengths of SM490A with respect to the rolling direction of test specimens. All test specimens failed around 1,500,000 cycles regardless of the test specimen direction. Therefore, it is found that the anisotropy in impact energy is not related to the fatigue strength of the materials considered in this study. However, the transverse direction specimen showed more rapid brittle fracture mode compared to that of longitudinal direction specimen, and this appears to be related to the lower impact values in transverse direction.

• Journal of the Korean institute of surface engineering
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• v.36 no.6
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• pp.466-474
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• 2003

To develop a method of detecting dross in coating layer on hot-dip galvanizing steel, chemical etching behavior of the artificial coating layers with top and bottom dross were investigated. After chemical etching with the mixture of picric acid and sodium thiosulfate, each of the top and bottom dross take its distinct color, and alloy layer in coating is also observed. Defects in the coating layers of HGI(hot rolled galvanized iron), CGI(continuous galvanized steel sheet) and GA(galvannealed steel) were analysed, and methods of dross detection which can be applied to inspection process in manufacture were suggested.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.223-230
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• 2004

In order to improve the productivity and quality of the hot rolled products, many morden mills have continuously required advanced roll materials. The introduction of HSS rolls in early stands of the Hot Strip Mill brought the excellent performance in wear resistance and surface roughness. Ni-grain rolls used in the later stands was needed to improve the roll performance. Therefore, the carbide reinforced Ni-grain roll was developed. The present paper will describe the development of carbide reinforced rolls made by INI STEEL and the results of mill tests. The wear resistance was increased upto $40\%$ and the anti-accident ablility was remarkably improved compared to the normal Ni-rain roll.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.307-316
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• 2004

This study examined the cause of the wrinkle defect which is frequently encountered in wire rod rolling of low carbon steel$(C0.08\~0.13wt.\%)$. Even a small defect on the surface of rolled bars can easily develop into fatal cracks during cold heading process of low carbon steel, and it is therefore necessary to minimize inherent defects on the surface of hot rolled bars. Hot rolling process of low carbon steel was analyzed to identify the cause of the wrinkle defect in conjunction with FE analysis. The integrated analysis revealed that the wrinkle defect initiated in the first stage of rolling, and it was at the billet edge where severe deformation and drastic temperature drop were present. To elucidate the micro-mechanical mechanism of the wrinkle defect, hot compression tests were carried out at various temperatures and strain rates using Gleeble-3800. The surface profile of the each other compressed specimens was compared, and rough surface lines were observed at relatively low temperatures. Those surface defects can develop into wrinkles during multi-pass rolling. To control the wrinkle defect in rolling, it is necessary to design an adequate caliber which can minimize the loss of ductility, and thereby prevent flow localization. To use the result of this study fur other steels, the quantitative measure of the wrinkle defect and flow localization parameter should be proposed.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.487-493
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• 2012

To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and $500^{\circ}C$, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at $650^{\circ}C$ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe-Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature $650^{\circ}C$.

• Korean Journal of Metals and Materials
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• v.46 no.3
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• pp.150-158
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• 2008

The temperature distribution of high speed tool steel rod has been studied during high speed hot rolling procedures. The tool steel rod shows severe temperature gradient during rolling procedures and the temperature at the center of rod are much higher than that at the surface of rod. This temperature gradient accumulated after every rolling procedure and the center of rolled rod could be remelt in some procedures to cause inside defects. In this study, the temperature distribution was simulated using finite element method and the processing parameters such as rolling speed, cooling condition, have been discussed to prevent the temperature increases at the center of rod.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.88-90
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• 2005

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.353-353
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• 2009

It is an important task to construct a recycling society with a low damage on the environment in our century. Magnetic separation is expected to be applied for the industrial waste treatment as an important supporting technology. In the magnetic separation of dry condition, the cohesive force between particles is strong compared with that in the wet condition's magnetic separation. The use of high magnetic field by the superconducting magnet enhances the powder's magnetic substance capture ability of the magnetic separation. In this study, the POSCO's coolant sludge of hot rolled steel was used for the superconducting magnetic separation of dry condition. Cryo-cooled NB-Ti superconducting magnet with 100 mm room temperature bore and 600 mm of height was used for magnetic separator.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.4
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• pp.326-332
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• 1995

Using natural frequency measurement method, which is one of NDT method, natural frequency of the hot-rolled mild steel plate(specimen) under fatigue loading was measured. Between the degradation of the specimen under fatigue loading and the variation of the natural frequency of the specimen was investigated. As a result, the degradation of the specimen was described and monitored as variation of natural frequency of specimen. The natural frequency of specimen decreased gradually under fatigue loading. This means the variation of material properties of specimen. Especially. It means the variation of Young's modulus of specimen.

• Steel and Composite Structures
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• v.4 no.1
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• pp.23-36
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• 2004

The inelastic lateral-distortional buckling of doubly-symmetric hot-rolled I-section beam-columns subjected to a concentric axial force and uniform bending with elastic restraint which produce single curvature is investigated in this paper. The numerical model adopted in this paper is an energy-based method which leads to the incremental and iterative solution of a fourth-order eigenproblem, with very rapid solutions being obtained. The elastic restraint considered in this paper is full restraint against translation, but torsional restraint is permitted at the tension flange. Hitherto, a numerical method to analyse the elastic and inelastic lateral-distortional buckling of restrained or unrestrained beam-columns is unavailable. The prediction of the inelastic lateral-distortional buckling load obtained in this study is compared with the inelastic lateral-distortional buckling of restrained beams and the inelastic lateral-torsional buckling solution, by suppressing the out-of-plane web distortion, is published elsewhere and they agree reasonable well. The method is then extended to the lateral-distortional buckling of continuously restrained doubly symmetric I-sections to illustrate the effect of web distortion.