• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.138-139
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• 2006

Sintered steels are materials characterized by residual porosity, whose dimension and morphology strongly affect the fatigue crack growth behaviour of the material. Prismatic specimens were pressed at $7.0\;g/cm^3$ from Astaloy CrM powder and sintered varying the sintering temperature and the cooling rate. Optical observations allowed to evaluate the dimensions and the morphology of the porosity and the microstructural characteristics. Fatigue tests were performed to investigate the threshold zone and to calculate the Paris law. Moreover $K_{Ic}$ tests were performed to complete the investigation. Both on fatigue and $K_{Ic}$ samples a fractographic analysis was carried out to investigate the crack path and the fracture surface features. The results show that the Paris law crack growth exponent is around 6.0 for $1120^{\circ}C$ sintered and around 4.7 for $1250^{\circ}C$ sintered materials. The same dependence to process parameters is not found for $K_{Ith}$.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 춘계학술발표 개요집
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• pp.60-61
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• 1997

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2001년도 춘계학술발표회요약집
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• pp.328.1-328
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• 2001

• 열처리공학회지
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• 제30권4호
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• pp.156-163
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• 2017

In the present study, we investigated the optimal austenitizing temperature of high-alloyed tool steels from an industrial point of view. Austenitizing temperatures for manufacturing 25 commercial tool steels were surveyed with their alloy compositions. The relationship between the austenitizing temperatures and the critical equilibrium temperatures by thermodynamic-based calculation was analyzed and a correlation was found. Based on the austenitizing temperatures of 25 commercial tool steels and the thermodynamic calculation results, we proposed a simple equation to predict an optimal austenitizing temperature to achieve superior mechanical properties of high-alloyed tool steels. The applicability of the proposed equation was experimentally validated with a new developed tool steel.

• 한국주조공학회지
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• 제15권3호
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• pp.242-251
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• 1995

Highly alloyed high speed tool steels(ASP steels) were rapidly solidified by melt spinning process, and the microstructures of melt spun tool steel ribbons were examined by optical microscopy and transmission electron microscopy with energy dispersive x-ray spectroscope. The microstructure of melt spun tool steel ribbon was found to be consisted of ${\delta}-ferrite$ cells surrounded by austenite and V-rich MC carbides. The size of ${\delta}-ferrite$ cells and intercellular MC carbides were about $0.4{\mu}m$ or less and 30nm or less, respectively. From the melt spun tool steel ribbons, only the MC type carbide phase was observed, instead of $M_2C$, $M_{23}C_6$ and $M_6C$ carbides which were generally observed in other rapidly solidified high speed steels. Such a change in type of carbide phase formed could be attributed to the increase in alloying content of vanadium and carbon. However, changes in microsturcture of melt spun tool steels with alloying content of cobalt, vanadium and carbon were not observed.

• 한국분말재료학회지
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• 제28권5호
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• pp.375-380
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• 2021

In this study, we investigate the effect of the duration of mechanical alloying on the microstructures and mechanical properties of ODS ferritic/martensitic steel. The Fe(bal.)-10Cr-1Mo pre-alloyed powder and Y₂O₃ powder are mechanically alloyed for the different mechanical alloying duration (0 to 40 h) and then constantly fabricated using a uniaxial hot pressing process. Upon increasing the mechanical alloying time, the average powder diameter and crystallite size increased dramatically. In the initial stages within 5 h of mechanical alloying, inhomogeneous grain morphology is observed along with coarsened carbide and oxide distributions; thus, precipitate phases are temporarily observed between the two powders because of insufficient collision energy to get fragmented. After 40 h of the MA process, however, fine martensitic grains and uniformly distributed oxide particles are observed. This led to a favorable tensile strength and elongation at room temperature and 650℃.

• 열처리공학회지
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• 제10권1호
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• pp.71-78
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• 1997

This work was to investigate suitable tool steels for hardening using laser beam, and was studied on carbon tool steels and alloyed tool steels such as STC3 steel, STS3 steel, STD11 steel and SKH51 steel. The surface hardness of HV700-1000 and the hardening depth of 2-2.5mm were obtained on STC3 steel and STS3 steel, and HV800-1000 was obtained on SKH51 steel, but STD11 steel was not enough. Except STD11 steel, all steels used in this study can be hardened by laser quenching or laser rapid melting.

• Structural Engineering and Mechanics
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• 제78권1호
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• pp.67-75
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• 2021

This work studies the behaviour of a steel portal frame selection under fire exposure, considering both span lengths and fire exposure times as variables. Such structures combine carbon steel (S275), fireproof micro-alloyed steel (FR), and coatings of intumescent paint with variable thicknesses, improving thereby the flame retardant behaviour of the steel structure. Thus, the main contribution of this study is the optimization of the portal frames by combining both steels, analysing the resulting costs influence on the final dimensions. Besides, the topological optimization of each steel component within the structure is also defined, in accordance with the following variables: weather conditions, span, paint thickness, and cost of steel. The results mainly confirmed that using both FR and S275 grades with intumescent painting is the Pareto optimum when considering performance, feasibility and costs of such portal frames widely used for industrial facilities.

• 소성∙가공
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• 제19권4호
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• pp.210-216
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• 2010

The importance and interests for saving of energy and cost in industry has grown up. Therefore, process optimization to reduce the process and energy become one of the most important things. The non-heat treated steel, post-heat-treated is no necessary, has attractive points as structural materials. However, establishment of mechanical properties is necessary to apply non-heat-treated steel to structural parts. In this study, for non-heat-treated steel and pre-heat-treated steel, we have investigated microstructure, hardness, the tensile strength, compressive strength. And the FE analysis technology to predict the hardness value of forged part is developed on micro-alloyed steel forged part.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.177-179
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• 2005

As rail steel at a crossing area must undergo much higher loading than those at regular railway, Mn-containing casting steel is normally used for its high load-carrying capability and reduced wear rate. However, as these Mn-containing casting steel is tend to have casting defects, manufacturing cost to produce defect-free Mn-containing casting steel becomes quite expensive. Therefore, in order to investigate the possibilities of replacing expensive Mn-containing casting steel with a mild steel with a surface build-up using a Mn-alloyed steel electrode.