• Journal of Powder Materials
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• v.22 no.3
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• pp.157-162
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• 2015

SKD11(ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. Adding of CNTs increased the performance of mechanical properties more. 1, 3 vol.% CNTs was dispersed in SKD11 matrix by mechanical alloying. SKD11 carbon nanocomposite powder was sintered by spark plasma sintering process. FE-SEM, HR-TEM and Raman analysis were carried out SKD11 carbon nanocomposites.

• Journal of Powder Materials
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• v.20 no.4
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• pp.291-296
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• 2013

SKD11 (ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. The CNTs was good additives to improve the mechanical properties of metal. In this study, 1, 3 vol% CNTs was dispersed in SKD11 matrix by mechanical alloying. The SKD11+ CNT hybrid nanocomposites were investigated by FE-SEM, particle size distribution, hardness and wear resistance. The CNT was well dispersed in the SKD11 matrix and the mechanical properties of the composite were improved by CNTs addition. It shows good feasibility as cold work die tool.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.13-15
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• 2012

Stainless steels is widely used in various industries due to its high strength and excellent corrosion resistance. However, in the case of fusion welding for stainless steel, chromium deficiency layer produced by chromium carbide precipitation during welding process causes corrosion-resistance to be lower and formation of intergranular corrosion. It requires a inevitable complex procedure such as pre-heating and post-heating process etc. to prevent such weld defects. From this viewpoint, the new welding process such as a solid state welding method is suited for welding of stainless steels due to its advantages over the fusion welding. Therefore this paper intends to investigate the research trend on friction stir welding, one of solid state welding processes for stainless steels.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.8-16
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• 2013

As the energy consumption increases rapidly, power generation needs the high energy efficiency continuously. To achieve the high efficiency of power generation, the materials used have to endure the higher temperature and pressure. The 9-12%Cr steels possess good mechanical properties, corrosion resistance, and creep strength in high temperature due to high Cr contents. Therefore, the 9-12%Cr steels are widely used for the high-temperature components in power plants. Even though the steels usually have a fully martensitic microstructure, they are susceptible to the formation of ${\delta}$-ferrite specifically during the welding process. The formation of ${\delta}$-ferrite has several detrimental effects on creep, ductility and toughness. Therefore, it is necessary to avoid its formation. As the volume fraction of ${\delta}$-ferrite is less than 2% in microstructure, it has the isolated island morphology and causes no significant degradation on mechanical properties. For ${\delta}$-ferrite above 2%, it has a polygonal shape affecting the detrimental influence on the mechanical properties. The formation of ${\delta}$-ferrite is affected by two factors: a chemical composition and a welding heat input. The most effective ways to get a fully martensite microstructure are to reduce the chromium equivalent less than 13.5, to keep the difference between the chromium and nickel equivalent less than 8, and to reduce the welding heat input.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.2
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• pp.58-65
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• 1997

Work rolls used in cold rolling mills must have outstanding wear resistance and very little plastic defor- mation. Thus, these rolls require a higher surface hardness and harding to a greater depth. To meet these requirements, the rolls, in general, have basic chemical composition of 0.7 to 1.0% carbon and 1.0 to 5.0% Cr(chromium), plus a small amounts of special elements, and are subjected to intensive water quenching and tempering at low temperature to provide a surface hardness of over 90 shore. This test results are as follows. Deflection and fracture load of 5% Cr material are than those of 3% Cr material and show flat curve from surface to subsurface. It will be clear that 5% Cr work roll has a superior resisti- bility against wear and abrasion comparing with 3% Cr work roll. The improvement of wear and abrasion in 5% Cr work roll will be achieved by the large amount of wpheroidal carbide. In grindability and polish, 5% Cr work roll will be a little inferior comparing with 3% Cr work roll.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.5
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• pp.678-685
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• 2010

GTAW was carried out to the austenitic 304(STS 304) and 22 APU stainless steels. In this case, difference of the corrosion characteristics of welded zone with STS 304 and 22APU mentioned above was investigated with electrochemical methods. Vickers hardness of weld metal in case of STS 304 (Hv-250) showed a relatively higher value than this of 22 APU(Hv-217). The corrosion current densities of weld metal of 22APU and heat affected zone of STS 304 were observed at the highest value compared to those of other welding zone respectively. This is probably because chromium depletion field due to chromium carbide formed to weld metal of 22APU and to heat affected zone of STS 304 can preferentially easily be corroded with more active anode than other fields. Consequently it is thought that application of the other welding methods like as laser welding or using of the optimum filler metals is necessary to improve the corrosion resistance of welding parts of these steels.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.328-331
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• 2012

With the recent development of super-precision optical instruments, camera modules for devices, such as portable terminals and digital camera lenses, are increasingly being used. Since an optical lens is usually produced by high-temperature compression molding methods using tungsten carbide (WC) alloy molding cores, it is necessary to develop and study technology for super-precision processing of molding cores and coatings for the core surface. In this study, Rhenium-Iridium (Re-Ir) thin films were deposited onto a WC molding core using a sputtering system. The Re-Ir thin films were prepared by a multi-target sputtering technique, using iridium, rhenium, and chromium as the sources. Argon and nitrogen were introduced through an inlet into the chamber to be the plasma and reactive gases. The Re-Ir thin films were prepared with targets having a composition ratio of 30 : 70, and the Re-Ir thin films were formed with a 240 nm thickness. Re-Ir thin films on WC molding core were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and Ra (the arithmetical average surface roughness). Also, adhesion strength and coefficient friction of Re-Ir thin films were examined. The Re-Ir coating technique has received intensive attention in the coating processes field because of promising features, such as hardness, high elasticity, abrasion resistance and mechanical stability that result from the process. Re-Ir coating technique has also been applied widely in industrial and biomedical applications. In this study, WC molding core was manufactured, using high-performance precision machining and the effects of the Re-Ir coating on the surface roughness.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.154-165
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• 1997

Abrasive wear characteristics of high Cr white cast iron-based hardfacing were investigated using the rubber wheel abrasion wear test method according with the ASTM G65-85. Mild steel was also tested for comparison with high Cr cast iron hardfacing. Wear experiments, where the applied force, wheel revolution rate and abrasive powder feed rate were selected as test valuables, were planned and analyzed by response surface method to evaluate wear statistically and quantitatively. Weight loss of high Cr cast iron hardfacing was mostly affected by the applied force and wheel revolution rate, and little by the powder feed rate. Weight loss of mild steel was greatly affected by the wheel revolution rate and powder feed rate, and slowly and steadily increased with the applied force. Abrasive wear mechanism of high Cr cast iron and mild steel was discussed in the light of the wear test results.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.4
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• pp.262-269
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• 1994

This study has been carried out to evaluate effects of alloying elements and nitrocarburizing on rolling contact fatigue life. Manganese has a significant influence on the distribution of retained carbides and microstructural changes after rolling contact fatigue test. The effect of the manganese addition stabilized fine retained carbide particles during rolling contact fatigue life test, and so increased fatigue life markedly. High carbon chromium bearing steel with different matrixes were nitrocarbunzed by austenitic nitrocarburizing process at $850^{\circ}C$ for 4hrs. Rolling contact fatigue life of the nitrocarburized specimen was increased 2 times than full hardening treated.