• Nuclear Engineering and Technology
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• v.45 no.6
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• pp.821-826
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• 2013

In the present study, the effects of various heat treatments on the microstructure and mechanical properties of dual phase ODS steels were investigated to enhance the high strength at elevated temperature. Dual phase ODS steels have been designed by the control of ferrite and austenite formers, i.e., Cr, W and Ni, C in Fe-based alloys. The ODS steels were fabricated by mechanical alloying and a hot isostatic pressing process. Heat treatments, including hot rolling-tempering and normalizing-tempering with air- and furnace-cooling, were carefully carried out. It was revealed that the grain size and oxide distributions of the ODS steels can be changed by heat treatment, which significantly affected the strengths at elevated temperature. Therefore, the high temperature strength of dual phase ODS steel can be enhanced by a proper heat treatment process with a good combination of ferrite grains, nano-oxide particles, and grain boundary sliding.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.220-221
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• 2017

In this study, the thermal strain of high strength concrete with the compressive strength of 70, 80, 100MPa were measured under 33% of compressive strength loading condition. As results, it is considered that shrinkage strain of high strength concrete become grater at the elevated temperatures.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.04a
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• pp.35-35
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• 1997

High$\cdot$speed steels (HSS) with a combination of good wear resistance and toughness are finding new, non-cutting applications such as rolls and rollers. In this paper, the research interests are focused on the microstructural evolution of a SMo-6W series high speed steel during HIPping and the effect of HIPping process parameters on its microstructure and properties. HIPping process variables includes; temperature, pressure and hold time. The microstructures of the HIPped HSS were examined by SEM, OM and X-ray diffraction whereas the properties measured were the relative density, hardness, and bend strength at room temperature. In HIPped materials, MC and M6C were the major carbides formed in a matrix of martensite. The effect of powder size on the microstructure and mechanical properties of HIPped materials was insignificant. However, HIPping temperature and hold time strongly affected the carbide size and distribution. The results show that at proper HIPping temperature and pressure conditions, the final products approach the full density ( > 99% RD). The particle boundaries were completely eliminated without an eminent microstructural coarsening. The bend strength was about 2.3 Gpa, which is superior to cast HSS. At excessive HIPping temperatures, rapid carbide coarsening occurred, thus deteriorating the mechanical properties of the P/M steels.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.05a
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• pp.63-64
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• 2012

In case of concrete, it should be deformed by many factors, such as explosive spalling, thermal strain and creep at high temperature. Structural fire design has been proposed to predict fire damage as national standard. It is general safer to use values obtained from tests of unstressed residual test in stead of stressed test. But most of thermal properties on concrete were conducted with normal aggregate. In this study, it evaluated mechanical properties of concrete with aggregate type and loading condition. we use normal and light aggregate to have different thermal properties. Also, we test mechanical properties to use Ø100×200 mm cylinder specimen according to target temperature and 0%, 20%, 40% loading.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1344-1347
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• 2004

Recently, Study on measuring property of a micro thin film(nm ～ hundreds of ) under Thermal Mechanical loading. In this work, We perform tensile test at high temperature(1200 ) to investigate mechanical properties of alumina TGO formed under Thermal Barrier Coating. We used Digital Image Correlation method for measuring displacement, and We presented a method of tensile test for thin film at high temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3234-3242
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• 1996

This paper describes experimental results of modified small punch( MSP) test conducted to evaluate the fracure characteristics and mechanical properties of plasma sparayed zirconia ($ZrO_2$ stabilized with 8wt. % $Y_20_3$ : YSZ) NiCrAlY composite. The mixing ratios of YSZ/NiCrAlY were 0/100, 25/75, 50/50, 100/0 v.%. Test temperatures ranged from 293K to 1473K. This study is directed at development of thermal barrrier coating(TBC) system with superior heat resistance and mechanical properties. The microstructure and fracture process of the composite were examined by SEM and AE method. The mechanical properties of 100% YSZ were nearly independent of the temperatures tested in this study. In contrast, the NiCrAlY-containing composites showed a significant decrease of the mechanical properties above 1273K, showing a ductile- brittle transition behavior up to the temperature. Furthermore, it can seen that 25% YSZ/75% NiCrAlY composite gave the highest fracure strength and fracture energy among the mixing ratio tested over the temperature range.

• Laser Solutions
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• v.12 no.4
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• pp.12-16
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• 2009

The engineering ceramic is one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance, etc. However, due to high strength and high brittleness, ceramic incurs high costs and long time on finishing process required after sintering. So a process for obtaining wanted measurements of them has been studied using the high temperature which makes ceramics softened and heat affected recently. This study makes an estimate of laser-assisted machining (LAM) if an economically practical process for manufacturing precision silicon nitride ceramic parts using laser beam. In this study, mechanical properties of silicon nitride at high temperature were observed. And during the LAM, it was observed that cutting force and tool wear were reduced and oxidation of machined surface was increased according to a increase of laser power.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.4_2
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• pp.621-626
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• 2022

Tungsten is a high melting point metal unlike other steel materials, and it is difficult to manufacture because of its high melting temperature. In this study, pressure sintering process method was applied to manufacture the tungsten materials at low temperature. Therefore, it is necessary to densify the sintered material by using a sintering additive. Studies have been conducted on how the amount of titanium for sintering tungsten affects the mechanical properties of tungsten in this study. In order to secure the densification mechanism of tungsten powder during the sintering process, the characteristics of the sintered tungsten material according to the change of titanium content were evaluated. It was investigated the relationship between sintering parameters and mechanical properties for densification of microstructures. The sintered tungsten materials according to sintering additive content showed high sintered density (about 16.31g/cm³) and flexural strength (about 584 MPa) when the content of sintering additive was 3 wt%. However, as the content of the sintering additive increases, mechanical property of flexural strength is decreased, and the porosity is increased due to the heterogeneous sintering around titanium.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.1
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• pp.60-64
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• 2020

In this study, to develop angle ring pressboards for high voltage transformers, the radius and thickness are modified under the conditions of temperature and humidity. In particular, a pressboard with a thickness of 6 mm and a radius at the angled part were investigated based on the simulation of the principal stress from the angled optimization profile shape. As a result, by the appropriate application of a higher temperature, the solid insulation can be improved to reduce the moisture content for an optimized profile angle of a high voltage transformer. This also results in the improvement of the safety factor by 25%. It is determined that the electrical insulation properties of pressboards in high voltage transformers can be enhanced by improving their properties.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.98-99
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• 2020

This study is aim to assess mechanical properties which is highly related to structural safe and durability of 100MPa high strength concrete mixed with amorphous metallic fiber. All specimens were heated with low velocity heating rate(1℃/min.), residual compressive strength and residual flexural strength was evaluated. The specimens were cooled down to room temperature after heating. As a result, in the case of 100MPa high-strength concrete, the residual compressive strength enhancing effect of amorphous metallic fiber has showed with the mix proportion of fiber. In addition, residual flexural strength showed more regular pattern before 300℃ then residual compressive strength, but simillar decreasing behavior was shown after 300℃ like residual compressive strength. Further study about fiber pull-out behavior and fiber mechanical, chemical property change due to temperature is needed.