• Korean Journal of Metals and Materials
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• v.60 no.4
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• pp.329-339
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• 2022

The effect of Cu content on the microstructure and mechanical properties of Al-8.0Zn-2.5Mg-xCu (x: 0, 1, 2, 3) aluminum alloys manufactured by the twin-roll casting process was investigated. The Al-8.0Zn-2.5Mg-xCu alloy showed an increase in surface defects with increasing Cu content. This is because the amount of residual liquid in the final solidification region increased from 9.6 wt.% to 18.3 wt.% as the Cu content increased from 0Cu to 3 Cu alloy. For the 3Cu alloy, as the amount of residual liquid in the final solidification region exceeded the critical point, a large number of surface defects and internal shrinkage defect were observed. The main secondary phases of the four alloys were the T(Mg₃₂(Al, Zn)₄₉) and η(MgZn₂) phases, and their fraction increased with Cu content. These secondary phases mainly existed in the center segregation band, and a fine η(MgZn₂) phase was additionally observed. In terms of mechanical properties, as the Cu content increased, the hardness of the center matrix, secondary phase, and overall hardness increased respectively. Although the yield strength increased, the tensile strength and elongation decreased because the center segregation band was widened from 684 ㎛ to 790 ㎛ with increasing Cu content.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.3-9
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• 2006

The phase changes, nitride precipitation and hardness variations of 14%Cr-6.7Ni-0.65Mo-0.26Nb-0.05V-0.03C super martensitic stainless steel were investigated after nitrogen permeation heat treatment at a temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The nitrogen-permeated surface layer was transformed into austenite. The rectangular type NbN, NbCrN precipitates and fine round type precipitate were coexisted in the surface austenite layer, while the interior region that was free from nitrogen permeation kept the martensitic phase. The hardness of surface austenite showed 280 Hv, while the interior region of martensite phase represented 340 Hv. When tempering the nitrogen-permeated steel at $450^{\circ}C$, a maximum hardness of 433 Hv was appeared, probably this is attributed to the secondary hardening effect of the precipitates. The nitrogen concentration decreased gradually with increasing depth below the surface after showing a maximum of 0.3% at the outmost surface. The strong affinity between nitrogen and Cr enabled the substitutional element Cr to move from interiors to the surface when nitrogen diffuse form surface to the interior. Corrosion resistance of nitrogen permeated steel was superior to that of solution-anneaed steel in the solution of 1N $H_2SO_4$.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.1
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• pp.7-13
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• 2013

Vacuum heat treatment(indirect heating method) has long exposure time at high temperature and low quenching rate. Contrarily salt bath heat treatment (direct heating method) has short exposure time at high temperature and fast cooling rate. With these different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study, Salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heat process and secondary hardening with high temperature tempering process. Consequently, It indicates that salt bath heat treatment is better way than vacuum heat treatment for product to have high mechanical properties.

• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.33-37
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• 1999

White cast iron of 3%C-10%Cr-5%Mo-5%W was casted, and then heat treated with three different methods such as homogenizing, austenitizing and tempering to observe its effects on the microstructure, hardness and abrasive wear resistance. In uni-directional soldification, bamboo tree-like $M_7C_3$ carbide grew along with the heat flow direction, and fishbone-like $M_6C$ carbide was dispersed randomly among $M_7C_3$ carbides. While almost pearlitic structures were observed in the as-cast specimen, those of the heat treated specimens consisted of secondary carbide, retained austenite and tempered martensite. In austenitized specimen, the amounts of retained austenite were 60.88% due to the higher cooling rate encountered in forced air cooling. On the other hand, the amounts of retained austenite were reduced from 60.88% to 23.85% in tempered specimen due to the transformation of austenite into tempered martensite. The hardness of tempered specimen showed the highest value, and then decreased in the order of austenitized, as-cast and homogenized specimens. But, the abrasive wear resistance of austenitized specimen was the highest, and then decreased in the order of tempered, as-cast and homogenized specimens.

• Journal of Powder Materials
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• v.4 no.3
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• pp.222-229
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• 1997

A P/M high speed steel of ASP 30 grade was austenitized, gas quenched and tempered at various conditional. The mechanical properties such as hardness, bend strength and fracture toughness were evaluated after heat treatment. The microstructure and the type and volume fraction of carbides were analyzed by an optical microscope, image analyzer and XRD. The primary carbides after the heat treatment were MC and $M_6C$ type. The volume of the total carbide varied from 10 to 15% depending on the austenitizing and tempering temperature. The tempering temperature for maximum hardness was at around 52$0^{\circ}C$. But the maximum bend strength was obtained at about 55$0^{\circ}C$. The fracture toughness was largely affected by the presence of retained austenite after gas quenching and secondary hardening during tempering.

• Journal of Surface Science and Engineering
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• v.30 no.6
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• pp.365-373
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• 1997

316L and 420 Stainless steels were deposited onto AZ9ID commercial magnesium alloy by plasma spray process with various gas flow rate of, TEX>$H_2$ secondary gas. And hardness as well as were track volume, coefficient of friction also had been measured. wear and hardness were measured by using reciprocal configuration tribometer and microghardness tester, respectively. Also, the microstructure of the coatings surface the cross sectional area of coating surface and cross sectional area of coaing/Substrate interface had been analyzed with Scanning Electron Microscope(SEM) and Optical microscope(OM). Finally, optimal process parameters for the improvement of coating efficiency such as mechanical property and wear behavior were examined.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.1029-1032
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• 2021

WC-Co cemented carbides were consolidated using spark plasma sintering in the temperature 1400℃ with transition metal carbides addition. The densification depended on exponentially as a function of sintering exponent. Moreover, the secondary (M, W) C_x phases were formed at the grain boundaries of WC basal facet. Corresponded, to increase the basal facets lead to the plastic deformation and oriented grain growth. A higher hardness was correlated with their grain size and lattice strain. We suggest that this is due to the formation energy of (M, W)C_x attributed to inhibit the grain growth and separates the WC/Co interface.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1597-1600
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• 2003

Fine-Blanking is an advanced and precision stamping process, by which a component with precise geometry and smooth cut surface can be produced without any further major secondary operations. By applying the Fine-Blanking technology, the significant improvement of the component should be obvious. As the components are with good shape, smooth surface and precise size, they can be ready for assembly without any further secondary operations. The productivity is increased, the production cycle time and the component cost are significantly reduced. We apply the fine-Blanking for chain sprocket. And do Mecanical test for compress strenth. impaact, roughness, Brinell hardness, dimensional stability.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.107-108
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• 2006

The effect of WC or NbC addition on various properties of Ti(C0.7N0.3)-Ni cermets was investigated. The microstructure oj Ti(C0.7N0.3)-xWC-20Ni showed a typical core/rim structure, irrespective of the WC content, whereas the structure oj Ti(C0.7N0.3)-xNbC-20Ni was different and was dependent on the NbC content. The hardness (HV) and the fracture toughness (KIC) had a tendency to increase marginally, while the coercive force (HC) and the magnetic saturation $(4{\pi}{\sigma})$ decreased gradually with an increase in WC or NbC content in the systems studied. In addition, increasing WC content in Ti(C0.7N0.3)-xWC-20Ni system, decarburization was retarded, while denitrification was accelerated

• Design & Manufacturing
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• v.17 no.2
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• pp.42-46
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• 2023

Currently, fossil resources are depleting rapidly. We are looking for energy to replace fossil fuels. They are trying to use electricity to replace internal combustion locomotives. Secondary battery raw materials and chemical additives are pulverized by the high-speed rotation of the grinding disc of the Classifier Separator Mill. Grinding Disc Assembly requires characteristics to withstand abrasion, corrosion, high-speed rotational force and impact. Domestic and foreign grinding discs were analyzed through abrasion resistance, hardness, bending strength, and tensile adhesion strength tests.