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김근준(K. J. Kim),김준호(J. H. Kim),석치훈(C. H. Seok),박대규(D. K. Park),최국선(G. S. Choi),김문철(M. C. Kim),하태권(T. K. Ha) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
High temperature deformation behavior of heat-resisting duplex stainless steel for retort used i Pidgeon process for Mg production was investigated in this study. 25Cr-8Ni based duplex stainless steels were cast into rectangular ingots of which the dimension was 350x350x100mm<SUP>3</SUP>. Some amount of Nitrogen and Yttrium was added and phase equilibrium was calculated using the thermodynamic software FactSage® and the database of FSStel. For comparison, 310S steel, widely used heat-resisting austenitic stainless steel, was also casts in this study. On ingotsm dilatometry was carried out in the temperature range from RT to 1200℃ and thermal expansion coefficient were evaluated. Addition of N and Y had no effect on the thermal expansion behavior. High temperature tensile and compression tests were conducted on the ingots at 1230℃, which is operation temperature employed for Mg production by Silicothermic reduction. The steel with N and Y showed much higher strength than 310S in both tensile and compression tests. By thermal exposition at 1230℃ for 64 hrs, hardness of duplex stainless steel containing N and Y was found to increase, while of 310S decreased.
김근준(K. J. Kim),나길환(G. H. Na),하태권(T. K. Ha),정재영(J. Y. Jung) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
Thermodynamic equilibrium of Fe-36Ni-base Invar alloy containing C contents from 0.25 to 0.38 weight percent during solidification has been investigated in this study. From the thermodynamic simulation using FactSage®, it has been revealed that equilibrium phases which can be formed are two kinds of MC-type precipitates, i.e. (Nb, Mo, V)C and MoC, and M₂C carbide. The MoC carbide was expected to be formed at relatively lower temperature below 770℃. Microstructure observation revealed the coarse precipitates in the as-cast ingots, which was Mo-rich non-equilibrium phase and could be resolved by the successive heat treatment. With increasing C contents from 0.25 to 0.38 wt.%, tensile strength of Invar alloy increased from 950 to 1100㎫ after hot rolling and thermal expansion coefficient showed a trivial increase.
정재용(J. Y. Jung),김근준(K. J. Kim),나길환(G. H. Na),하태권(T. K. Ha) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
Superplastic deformation behavior and texture evolution after equal channel angular pressing (ECAP) of Zn-0.3Al alloy were investigated in this study. ECAP was conducted at temperatures form 40℃ to 160℃ on the plate type specimens of 5 mm thickness and 20 mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED. A series of compression and tensile tests was carried out at temperatures from RT TO 200℃ under the strain rate from 0.03 to 10/s. After ECAP of the Zn-Al alloy, elongation was dramatically increased up to 1000% at above 60℃. The effects of ECAP on the texture and anisotropy in the superplastic deformation bebavior were found to be negligible.
하태권(T. K. Ha),김근준(K. J. Kim),나길환(G. H. Na) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
In the present study, the effect of initial microstructure, cold reduction ratio, and annealing temperature on the spherodization rate of SK85 high carbon steel sheet was investigated. High carbon steel sheet fabricated by POSCO was soaked at 800℃ for 2 hr in a box furnace and then treated at 570℃ for 5 min in a salt bath furnace followed by water quenching to obtain a fine pearlite structure. Cold rolling was conducted on the sheets of fine pearlite by reduction ratios of 20, 30, and 40% and heat treatment for spheroidization was carried out at 600 and 720℃ for the various time intervals from 0.1 to 32 hrs. Area fraction of spheroidized cementite was measured with an image analyzer as a function of cold reduction ratios and duration times.