Jeong E.H.,Hanyang University |
Jeong E.H.,SeAH Besteel Corporation |
Nam C.W.,Korea Institute of Geoscience and Mineral Resources |
Park K.H.,Korea Institute of Geoscience and Mineral Resources |
Park J.H.,Hanyang University
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2016
Calcium sulfate (CaSO4) is proposed as an alternative sulfur source to convert the Fe-Ni-Cu-Co alloy to the matte phase. Solid carbon was used as a reducing agent and the influence of oxide fluxes on the sulfurization efficiency at 1673 K (1400 °C) in a CO-CO2-SO2-Ar atmosphere was investigated. When CaSO4 was equilibrated with the Fe-Ni-Cu-Co alloy without any reducing agent, it was reduced by Fe in the liquid alloy, resulting in the formation of FeS. The sulfurization efficiency was about 56 pct, even though an excess amount of CaSO4 (gypsum equivalent, Geq = 1.7) was added. Adding solid carbon as the reducing agent significantly shortened the equilibration time from 36 to 3.5 hours and increased the sulfurization efficiency from 56 to 91 pct, even though the amount of carbon was lower than the theoretical equivalent for carbothermic reduction of CaSO4, viz. Ceq = 0.7. Although CaS (not FeS) was formed as a primary reaction product, it continuously reacted with CaSO4, forming CaO-rich slag. Neither the carbothermic reduction time nor the sulfurization efficiency were affected by the addition of Al2O3 (-SiO2) fluxes, but the equilibration time fell to 2.5 hours with the addition of Al2O3-Fe2O3 flux because the former systems produced primarily calcium silicate and calcium aluminate, which have relatively high melting points, whereas the latter system produced calcium ferrite, which has a lower melting point. Consequently, calcium sulfate (waste gypsum) can replace expensive pure sulfur as a raw material in the sulfurization of Fe-Ni-Cu-Co alloy with small amounts of iron oxide (Fe2O3) as a flux material. The present results can be used to improve the recovery of rare metals, such as Ni and Co, from deep sea manganese nodules. © 2016 The Minerals, Metals & Materials Society and ASM International
Kim T.H.,SeAH Besteel Corporation |
Cho K.J.,Chungnam National University |
Hong S.I.,Chungnam National University
Journal of Korean Institute of Metals and Materials | Year: 2010
Effects of the surface modification on the deposition behaviors of apatite crystals in Zr-1Nb plates were studied. Zr-1Nb alloy plates were polished with abrasive papers to have different roughness and some of them were treated in NaOH or coated with collagen before deposition of apatites in the simulated body fluid (SBF). The weight gain due to the deposition of apatite crystals increased as the surface roughness increased in Zr-1Nb. The size of granular apatite crystals were found to be smaller in Zr-1Nb roughened by 162 μm abrasive paper than in Zr-1Nb roughened by 8.4 μm paper, suggesting the nucleation rate increased with increase of surface roughness. After, 10 days immersion in a SBF, NaOH-treated Zr-1Nb was completely coated with apatite with the deposited apatite weight comparable to that in Ti-6Al-4V. The deposition rate of Zr-1Nb was not appreciably influenced by NaOH treatment unlike the significant influence of NaOHtreatment on the deposition rate of apatite in Ti-6Al-4V. One significant observation in this study is an appreciable increase of the apatite deposition rate after collagen coating both on Zr-1Nb and TI-6Al-4V plate, which may be caused by the interaction between collagen and Ca+2 ions.
Shin J.-H.,Seahbesteel Co. |
Shin J.-H.,Chonbuk National University |
Lee W.-J.,Seahbesteel Co. |
Kim Y.-P.,Dongwoo Heat Treating Co. |
Ko I.-Y.,Chonbuk National University
Journal of Korean Institute of Metals and Materials | Year: 2012
In this study, a super carburizing treatment was applied to improve roller pitting fatigue life. It produced excellent properties of surface hardness and temper softening resistance by forming precipitation of fine and spherodized carbides on a tempered marstensite matrix through the repeated process of carburization and diffusion after high temperature carburizing step 1. The cycle II performed two times carburizing/diffusion cycle (process) after super carburization at 1, 000 °C had fine and spherodized carbides to subsurface 200 μm. In this case, the carbide was (Fe, Cr) 3C and there was not any massive carbides. In the case of Cycle II, the roller pitting fatigue life had a 6.15 million cycles. It was improved 48% compared to normal gas carburizing treatment. copyright © 2012 The Korean Institute of Metals and Materials.
Hyundai Motor Company and SeAH Besteel Corporation | Date: 2014-11-06
A material for high carburizing steel and a method for producing a gear using the material are provided. The material includes C of about 0.13 to 0.3 wt %, Si 0.7 to 1.3 wt %, Mn of about 0.3 to 1 wt %, P of about 0.02 wt % or less, S of about 0.03 wt % or less, Cr of about 2.2 to 3.0 wt %, Mo of about 0.2 to 0.7 wt %, Cu of about 0.3 wt % or less, Nb of about 0.03 to 0.06 wt %, V of about 0.1 to 0.3 wt %, Ti of about 0.001 to 0.003 wt %, a balance of Fe and other inevitable.
Park J.-S.,Chonbuk National University |
Lim C.-H.,SeAH Besteel Corporation |
Cho Y.-K.,Chonbuk National University |
Yu Y.-T.,Chonbuk National University
Metals and Materials International | Year: 2015
P-type Cu-TiN composites sensitive to CO gas, CuO-TiN and CuO-TiN-TiO2, were synthesized by ball milling Cu33Ti67 and Cu15Ti85 alloys for 25 h in a pressurized N2 atmosphere. The sensing materials of CuO-TiN and CuO-TiN-TiO2 were prepared via a two-step oxidation process following an investigation of their CO gas-sensing properties. Their sensing responses for CO gas were compared; typical for p-type semiconductors, the resistances of both sensing materials increased as CO was introduced. The CuO-TiN-TiO2 powder had a greater response than the CuO-TiN powder at all temperatures tested. The highest responses shown by the two materials were to 1000 ppm CO at 250 °C: a response of 5.4 by CuO-TiN-TiO2 and 3.1 by CuO-TiN. During the first oxidation step of CuO-TiN-TiO2, micropores were formed that significantly increased this material’s specific surface area. Therefore, we believe that the superior response of the CuO-TiN-TiO2 sensing material was due to this surface area enlargement during the oxidation treatment. © 2015, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.
Shin J.-H.,Seahbesteel Co. |
Shin J.-H.,Chonbuk National University |
Ryu Y.-J.,Seahbesteel Co. |
Kim B.-O.,Seahbesteel Co. |
And 3 more authors.
Korean Journal of Materials Research | Year: 2012
Recently, automobile parts have been required to have high strength and toughness to allow for weight lightening or improved stability. But, traditional micro-alloyed steel cannot be applied in automobile parts. In this study, we considered the influence of quenching temperature and cooling rate for specimens fabricated by vacuum induction furnace. Directly quenched micro-alloyed steel for hot forging can be controlled according to its micro structure and the heat-treatment process. Low carbon steel, as well as alloying elements for improvement of strength and toughness, was used to obtain optimized conditions. After hot forging at 1,200°C, the ideal mechanical properties (tensile strength ≥ 1,000MPa, Charpy impact value ≥ 100 J/cm2) can be achieved by using optimized conditions (quenching temperature: 925 to 1,050°C, cooling rate: ≥ 5°C/sec). The difference of impact value according to cooling rate can be influenced by the microstructure. A fine lath martensite micro structure is formed at a cooling rate of over 5°C/sec. On the other hand, the second phase of the M-A constituent microstructure is the cause of crack initiation under the cooling rate of 5°C/sec.