• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.496-504
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• 2005

The thermal and mechanical properties of an electro-slag cast steel of a similar chemical composition with an AISI-6F2 steel are investigated and compared with a forged AISI-6F2 steel. AISI-6F2 is a hot-working tool steel. Electro-slag casting (ESC) is a method of producing ingots in a water-cooled metal mold by the heat generated in an electrically conductive slag when current passes through a consumable electrode. The ESC method provides the possibility of producing material for the high quality hot-working tools and ingots directly into a desirable shape. In the present study, the thermal and mechanical properties of yield strength, tensile strength, hardness, impact toughness, wear resistance, thermal fatigue resistance, and thermal shock resistance for electro-slag cast and forged steel are experimentally measured for both annealed and quenched and tempered heat treatment conditions. It has been found that the electro-slag cast steel has comparable thermal and mechanical properties to the forged steel.

• Korean Journal of Human Ecology
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• v.24 no.2
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• pp.285-295
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• 2015

To identify optimized thermal properties of mold brassiere cup for improved thermal comfort during summer, we compared the thermal resistance and the water vapor permeability of Polyurethane (PU) foam, 3D spacer fabric and the two combined materials of the PU foam and the 3D spacer fabric. Four experimental mold brassieres were made of the materials for wearing test. Six women in their twenties evaluated the wearing sensation in the hot and humid environment. The changes in microclimate temperature and humidity while wearing test brassiere cups were measured. Results indicate that thermal resistance increased as more PU foam were combined, while the water vapor permeability was higher as the content of the 3D spacer fabric increased at thickness of 18mm and over. However, in the wear test, the PU foam brassiere was the most preferred in all ambient conditions due to its soft, flexible and smooth texture, despite its high thermal resistance and low water vapor permeability. This indicates that the textures of mold foams are more dominant properties than thermal properties for mold foams in determining the wear comfort of mold brassieres.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1026-1029
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• 2006

Particulate reinforced titanium composites were produced by PM rout. Differents volumetric percentages of TiN reinforcements were used, 5,10,15 vol%. Samples were uniaxial pressed and vacuum sintered at differents temperatures between $1200-1300^{\circ}C$. Density, porosity, shrinkage, mechanical properties and microstructure were studied. Elastic properties and strength resistance were analysed by flexural strength and tension tests, and after the test, fractured samples were analysed too, obtaining a correlation between the fracture, interparticulated or intraparticulated, and the reinforcement addition.. Hardness and microhardness test were applied too, in order to complete the study about mechanical properties. In order to study wear resistance pin-on-disc test were used. In addition, the temperature influence, the reactivity between matrix and reinforcement, and the microstructures developed were observed by optical and electron microscopy.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.5
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• pp.239-249
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• 2015

Various amount of NbC carbide was intentionally formed in a matrix-type cold-work tool steel by controlled amount of Nb and C addition. And the effect of NbC addition on the mechanical properties was investigated. Four alloys with different Nb and C contents were cast by vacuum induction melting, then hot forging and spheroidizing annealing were conducted. The machinability of the annealed specimens was examined with 3 different cutting tools. And tensile tests at room temperature were conducted. After quenching and tempering, hardness and impact toughness were measured, while wear resistance was evaluated by disk-on-plate type wear test. The increasing amount of NbC addition resulted in degraded machinability with increased strength, whereas the absence of NbC also led to poor machinability due to high toughness. After quenching and tempering, the additional NbC improved wear resistance with increasing hardness, whereas it deteriorated impact toughness. Therefore, it could be found that a moderate addition of NbC was desirable for the balanced combination of mechanical properties.

• Korean Journal of Materials Research
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• v.30 no.9
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• pp.465-473
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• 2020

For surface hardening of a continuous casting mold component, a fundamental metallurgical investigation on dissimilar laser clads (Cu-NiCrBSi) is performed. In particular, variation behavior of microstructures and mechanical properties (hardness and wear resistance) of dissimilar clads during long-term service is clarified by performing high-temperature post-clad heat treatment (temperature range: 500 ~ 1,000 ℃ and isothermal holding time: 20 ~ 500 min). The microstructures of clad metals (as-clads) consist of fine dendrite morphologies and severe microsegregations of the alloying elements (Cr and Si); substrate material (Cu) is clearly confirmed. During the post-clad heat treatment, the microsegregations are totally homogenized, and secondary phases (Cr-based borides and carbides) precipitated during the short-term heat treatment are also almost dissolved, especially at the heat treatment conditions of 950 ℃ for 500 min. Owing to these microstructural homogenization behaviors, an opposite tendency of the surface mechanical properties can be confirmed. In other words, the wear resistance (wear rate) improves from 4.1 × 10^-2 ㎣/Nm (as-clad condition) to 1.4 × 10^-2 ㎣/Nm (heat-treated at 950 ℃ for 500 min), whereas the hardness decreases from 453 HV (as-clad condition) to 142 HV (heat-treated at 950 ℃ for 500 min).

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.728-733
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• 2009

Cu based amorphous ($Cu_{54}Zr_{22}Ti_{18}Ni_{6}$) powders were deposited onto Al 6061 substrates by cold spray process with different powder preheating temperatures (below glass transition temperature: $350^{\circ}C$, near glass transition temperature: $430^{\circ}C$ and near crystallization temperature: $500^{\circ}C$). The microstructure and macroscopic properties (hardness, wear and corrosion) of Cu based amorphous coating layers were also investigated. X-ray diffraction results showed that cold sprayed Cu based amorphous coating layers of $300{\sim}350{\mu}m$ thickness could be well manufactured regardless of powder preheating temperature. Porosity measurements revealed that the coating layers of $430^{\circ}C$ and $500^{\circ}C$ preheating temperature conditions had lower porosity contents (0.88%, 0.93%) than that of the $350^{\circ}C$ preheating condition (4.87%). Hardness was measured as 374.8 Hv ($350^{\circ}C$), 436.3 Hv ($430^{\circ}C$) and 455.4 Hv ($500^{\circ}C$) for the Cu based amorphous coating layers, respectively. The results of the suga test for the wear resistance property also corresponded well to the hardness results. The critical anodic current density ($i_{c}$) according to powder preheating temperature conditions of $430^{\circ}C$, $500^{\circ}C$ was lower than that of the sample preheated at $350^{\circ}C$, respectively. The higher hardness, wear and corrosion resistances of the preheating conditions of near $T_{g}$ and $T_{x}$, compared to the properties of below $T_{g}$, could be well explained by the lower porosity of coating layer.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.6
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• pp.284-291
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• 2016

High temperature alloy steel such as Ni-Cr-Mo-V material has excellent properties of high strength and high heating resistance. It has been used for several military weapon components such as gun barrel of a warship, turbine rotor and turbine disk for nuclear power plant. Being curious about this material required excellent wear resistance and durability in extreme environmental conditions. A dry wear test at the ambient air and Ar gas conditions in the room temperature were performed in this study. What's more a lubricant wear test at different temperature was conducted. In addition that DLC was coated on Ni-Cr-Mo-V alloy steel substrate with a thickness of $3{\mu}m$, a property of it was compare with lubricant conditions. All the coefficient of friction and wear volume, comparing with DLC coated specimens. The test parameters were selected as follows: 10 N for normal load; 80 rpm for sliding wear speed; and 300 m for the sliding wear distance.

• Journal of Powder Materials
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• v.25 no.1
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• pp.36-42
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• 2018

In order to expand the application of oxide dispersion-strengthened (ODS) steel, a composite material is manufactured by adding mechanically alloyed ODS steel powder to conventional steel and investigated in terms of microstructure and wear properties. For comparison, a commercial automobile part material is also tested. Initial microstructural observations confirm that the composite material with added ODS steel contains i) a pearlitic Fe matrix area and ii) an area with Cr-based carbides and ODS steel particles in the form of a $Fe-Fe_3C$ structure. In the commercial material, various hard Co-, Fe-Mo-, and Cr-based particles are present in a pearlitic Fe matrix. Wear testing using the VSR engine simulation wear test confirms that the seatface widths of the composite material with added ODS steel and the commercial material are increased by 24% and 47%, respectively, with wear depths of 0.05 mm and 0.1 mm, respectively. The ODS steel-added composite material shows better wear resistance. Post-wear-testing surface and cross-sectional observations show that particles in the commercial material easily fall off, while the ODS steel-added material has an even, smooth wear surface.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.147-152
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• 2010

Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

• Elastomers and Composites
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• v.44 no.3
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• pp.299-307
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• 2009

The effects of reinforcing materials on durability and mechanical properties of V-rib belt were investigated. Cotton fiber and ZnO were used as a filler for CR, and cotton and aramid fiber were used for EPDM rubber compounds. These materials were prepared as a specimen and V-rib belt for heat resistant and mechanical test. High contents of ZnO give improved wear resistance, and higher contents of cotton fiber showed higher durability in high rotation speed but lower wear resistance for CR rubber compounds. Using the aramid and cotton fiber together in EPDM rubber compounds, thermal and wear resistance were improved simultaneously. The material containing EPDM matrix showed better durability and wear resistance than those of containing CR matrix comparing in the same cotton fiber contents.