Daejeon, South Korea
Daejeon, South Korea

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Seol J.-B.,Pohang University of Science and Technology | Choi J.-M.,Jinhap Inc. | Kim J.H.,Hanbat National University
Science of Advanced Materials | Year: 2016

A heat-treatment method for A286 stainless steels has been designed which combines the advantages of the precipitation-hardened strengthening with the simplicity of a solid-solution treatment. One-step solid-solution treated samples, designed in this context, are seen to exhibit higher yield strength and relatively lower fatigue strength than those of conventional samples subjected to two-step solid solution treatments. The two step solidsolution treated samples contain an ordered structure of γ'-Ni3(Al,Ti), while with the one-step treated samples, a considerable amount of η phase is observed along the grain boundaries. Experimental results conclude that, although leading to lower fatigue strength, the one-step solid-solution treatment of A286 samples promotes yield strength via an increase in the density of dislocations, and enables a significant cost-reduction in the production of A286 steels. © 2016 by American Scientific Publishers All rights reserved.


Lim J.-H.,Pohang Institute of metal Industry Advancement | Kim J.-S.,Pohang Institute of metal Industry Advancement | Park B.-H.,Pohang Institute of metal Industry Advancement | Lee J.-H.,Pohang Institute of metal Industry Advancement | Choi J.-M.,Jinhap Inc.
Korean Journal of Materials Research | Year: 2011

The effect of heat treatment on the micro-structures and the mechanical properties of 0.002% boron added low carbon steel was investigated. The tensile strength reached the peak at about 880-890°C with the rising quenching temperature and then the hardness decreased sharply, but the tensile strength hardly decreased. The tensile and yield strength decreased and the total elongation increased with a rising tempering temperature, but the tensile and yield strength sharply fell and the total elongation prominently increased from above a 400-450°C tempering temperature. Tempered martensite embrittlement (TME) was observed at tempering condition of 350-400°C. In the condition of quenching at 890°C and tempering at 350°C, the boron precipitates were observed as Fe-C-B and BN together. The hardness decreased in proportion to the tempering temperature untill 350°C and dropped sharply above 400°C regardless of the quenching temperature.


Kim M.S.,Hanbat National University | Jung H.D.,Hanbat National University | Park H.Y.,Jinhap Inc. | Choi J.M.,Jinhap Inc. | And 2 more authors.
Korean Journal of Materials Research | Year: 2015

The mechanical properties and microstructures of Aluminum 6056 alloys were investigated for their use in the fabrication of a piton block. The EN-AW6056 alloys exhibited a tensile strength of 375 MPa for a solution treatment temperature of 550 °C for 2 h followed by an aging treatment at 190 °C for 4 h. The microstructures of the heat treated specimen showed that the Mg2Si phase with a size of 3~5 um was dispersed throughout the aluminum matrix when the heat treatment was done. Moreover, in order to identify the forgeability of the specimen, upsetting tests were done. For up to 80 % of the upsetting ratio, the specimen maintained its original shape, and at above 80 % of the upsetting ratio, the specimen underwent crack development. The specimen was successfully forged without any defects with the examined material conditions. The material conditions together with the forging conditions are discussed in terms of the microstructures and mechanical properties. © Materials Research Society of Korea, All rights reserved.


Lim J.H.,Hyundai Motor Company | Choi J.M.,Jinhap Inc.
Korean Journal of Materials Research | Year: 2013

A study on the corrosion behavior of Inconel alloys and Incoloy 800H in molten salt of LiCl-Li2O was investigated at 650 oC for 24-312 hours in an oxidation atmosphere. The order of the corrosion rate was Inconel 600 < Inconel 601 < Incoloy 800H < Inconel 690. Inconel 600 showed the best performance suggesting that the content of Fe, Cr and Ni are the important factor for corrosion resistance in hot molten salt oxidation conditions. The corrosion products of Inconel 600 and Inconel 601 were Cr2O3 and NiFe2O4, In case of Inconel 690, a single layer of Cr2O3 was formed in the early stage of corrosion and an outer layer of NiFe2O4 and inner layer of Cr2O3 were formed with an increase of corrosion time. In the case of Incoloy 800H, Cr2O3 and FeCr2O4 were observed. Most of the outer scale of the alloys was observed to be spalled from the results of the SEM analysis and the unspalled scale which adhered to the substrate was composed of three layers. The outer layer, the middle one, and the inner one were Fe, Cr, and Ni-rich, respectively. Inconel 600 showed localized corrosion behavior and Inconel 601, 690 and Incoloy 800H showed uniform corrosion behavior. Ni improves the corrosion resistance and too much Cr and/ or Fe content deteriorates the corrosion resistance. © Materials Research Society of Korea, All rights reserved.


Lim J.H.,Hyundai Motor Company | Choi J.M.,Jinhap Inc.
Korean Journal of Materials Research | Year: 2013

The electrolytic reduction of a spent oxide fuel involves liberation of the oxygen in a molten LiCl electrolyte, which is a chemically aggressive environment that is too crosive for typical structural materials. Therefore, it is essential to choosethe optimum material for the process equipment for handling a molten salt. In this study, the corrosion behavior of pyro-carbon made by CVD was investigated in a molten LiCl-Li2O salt under an oxidation atmosphere at 650 oC and 750 oC for 72 hours. Pyro-carbon showed no chemical reactions with the molten salt because of its low wettability between pyro-carbon and the molten salt. As a result of XRD analysis, pyro-carbon exposed to the molten salt showed pure graphite after corrosion tests. As a result of TGA, whereas the coated layer by CVD showed high anti-oxidation, the non-coated layer showed relatively low anti-oxidation. The stable phases in the reactions were C(S), Li2CO3(S), LiCl(l), Li2O at 650 oC and C(S), LiCl(l), Li2O(S) at 750 oC. Li2CO(S) was decomposed at 750 oC into Li2O(S) and CO2(g). © Materials Research Society of Korea, All rights reserved.


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