• 소성∙가공
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• 제19권1호
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• pp.25-31
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• 2010

To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.

• Journal of Welding and Joining
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• 제20권1호
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• pp.62-68
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• 2002

This study investigated the feasibility of penetration depth measurement using infrared temperature sensing on the weld surface. The detection point was optimized by FEM analysis in the laser keyhole welding. The profile of the weld surface temperature was measured using infrared detector array. Surface temperature behind the weld pool is proportional or exponentially proportional to penetration depth and bead width. From the results, the monitoring device of surface temperature using infrared detector array was applicable fur real time penetration depth control.

• 한국해양공학회지
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• 제35권1호
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• pp.59-74
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• 2021

To validate the fire safety assessment of structures, many structural experiments under fire load have been conducted. However, most of these experiments were conducted in restricted environments, such as inside a furnace, and experiments were seldom carried out in open space. In this study, an experimental study on H-beams, frequently used as structural reinforcements, was carried out for validating the thermal-structural analysis method under development. A 1.8 MW burner fire was adopted with each end of the H-beam fixed without a mechanical load. Gas temperature, steel surface temperature, and displacements were then measured. During the experiment, gas and steel temperatures were obtained at 9 and 17 points near the H-beam, respectively. In addition, the vertical and horizontal displacements of the H-beam under fire load at 6 points were obtained. Furthermore, it was verified that the stable displacement measurements via the contact and non-contact methods were feasible in harsh environments where flames and smoke were both present.

• Journal of Welding and Joining
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• 제20권1호
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• pp.69-75
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• 2002

This study investigated the effect of the system parameters on penetration depth measurement using infrared temperature sensing system. The distance from focusing lens to detector was varied to diminish the error in measuring weld bead width. The effect of bead surface shape on measured surface temperature profile was evaluated using specimen heated by electric resistance. The measuring distance from laser beam was changed to optimize the measuring point. The results indicated that the monitoring device of surface temperature using infrared detector array was applicable to real time penetration depth control.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.757-762
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• 2002

Many reports have been shown that the buoyancy, electromagnetic force, surface tension, and gas shear stress are the driving forces of weld pool circulation in arc welding. Among them, the surface tension of molten metal plays an important role in the flow in weld pool, which are clarified by the specially designed experiments with small particles as well as the numerical simulations. The surface tension is also related to the penetration in arc welding. Therefore, a quantitative evaluation of surface tension is demanded for the development of materials and arc process control. However, there are few available data published on the surface tension of molten metals, since it depends on the temperature and the composition of materials. In this study, a new method was proposed for the evaluation of surface tension and its temperature dependence, in which it is evaluated by the equilibrium condition of acting forces under a given surface geometry, especially back surface. When this method was applied to the water pool and to the back surface of molten pool in the stationary gas tungsten arc welding of thin plate, following results were obtained. In the evaluation of surface tension of water, it was shown that the back surface geometry was very sensitive to the evaluation of surface tension and the evaluated value coincided with the surface tension of water. In the measurement of molten pool in the stationary gas tungsten arc welding, it was also shown that the comparison between the surface tension and temperature distribution across the back surface gave the temperature dependent surface tension. Applying this method to the mild steel and stainless steel plates, the surface tension with negative gradient for temperature is obtained. The evaluated values are well matched with ones in the published papers.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.134-137
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• 2008

The effects of residual stress and surface defects on the mechanical properties of the high carbon steel filament used for the automotive tire have been experimentally investigated. The samples were fabricated with annealing temperature. The residual stress was measured by focused ion beam and strain mapping software which has advantages, such as data with high accuracy and fast data acquisition time. Mechanical properties, such as tensile strength and fatigue resistance, were gradually increased up to $200^{\circ}C$ and then slightly decreased. From the measurement of residual stress and level of surface defect, it was revealed that the critical factor was varied with different temperature region. That is, the fatigue resistance increased due to decreasing the residual stress and decreased due to increasing the size and distribution of surface defect.

• 한국표면공학회지
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• 제50권6호
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• pp.504-509
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• 2017

In order to improve corrosion resistance for cast stainless steel in seawater, the characteristics of corrosion resistance after plasma ion nitriding was investigated. Plasma ion nitriding process was conducted in a mixture of nitrogen of 25% and hydrogen of 75% at substrate temperature ranging from 350 to $500^{\circ}C$ for 10 hours using pulsed-DC glow discharge plasma with working pressure of 250 Pa in vacuum condition. Corrosion tests were carried out for as-received and plasma ion nitrided specimens. The corrosion characteristics were investigated by measurement of weight loss and observation of surface morphology. In anodic polarization experiment, relatively less damage depth and weight loss were presented at a nitrided temperature of $400^{\circ}C$, attributing to the formation of S-phase.

• 열처리공학회지
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• 제35권5호
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• pp.246-254
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• 2022

The high-temperature oxidation behavior of Cr-Mo steel AISI 4115 in air at different temperatures (600, 850, 950℃) for 120 min was studied by mass gain analysis, phase analysis (optical microscopy, electron probe micro-analysis, x-ray diffraction) and hardness measurement of each iron oxide-phase. The oxidation scales that formed on oxidation process consisted outer layer (Hematite), middle layer (Magnetite) and the inner layer (Chromite). In the case of 850 and 950℃, the oxidation mass gain per unit area of AISI 4115 steel increased according to the logarithmic rate as atmospheric pressure increased. Especially, It has been observed that with an increase in the atmospheric pressure at 600℃, the oxidation mass gain per unit area changed from a linear to logarithmic relationship.

• 비파괴검사학회지
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• 제30권5호
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• pp.484-488
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• 2010

적외선 열화상 카메라를 이용하여 온도를 측정할 때는 측정 대상물질의 적외선 방사율이 중요하다. 적외선 방사율은 흑체와 물체의 적외선 방사 강도비로 구할 수 있으나, 상온에서는 배경의 영향으로 인해 측정하는 것은 용이하지 않다. 따라서 FT-IR를 이용하여 반사법에 의해 강판 및 강판에 코팅된 도료의 적외선 반사율을 측정하고 적외선 방사용을 구하였다. 연마된 강판은 0.06 ~ 0.10의 적외선 방사율을 나타내고 있으며, 비연마 강판은 표면조도에 의해 광학적 특성의 변화로 인한 적외선 방사율 측정에 오차가 발생하였다. 강판에 코팅된 투명도료는 적외선 흡수로 인해 방사율은 0.50 ~ 0.84 정도로 높아졌으며, 도료의 적외선 흡수 밴드에 의해 파장에 따라 방사율도 변한다. 이 실험을 통해 재료표변의 재질, 두께, 조도 등 표면 상태에 따라 적외선의 광학적 특성이 변하는 것을 확인할 수 있었다. 또한 반사법은 금속 및 금속에 코팅된 도료의 적외선 방사율 측정에 유용한 것으로 판단되며, 측정된 적외선 방사율을 적외선 열화상에 제공함으로서 측정온도의 오차를 줄일 수 있다.

• 한국표면공학회지
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• 제29권5호
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• pp.443-448
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• 1996

In order to plasma-sulfnitride by combining ion-nitriding of a steel and sputtering of MoS$_2$, chromium-molybdenum steel was plasma-sulfritrided using hollow cathode discharge with parallel electrodes which are a main of the steel and a subsidiary cathode of $MoS_2$. The treatment was carried out at 823K for 10.8ks under 665Pa in a 30% $N_2$-70% $H_2$ gas atmosphere. Plasma-sulfnitriding layers formed of the steel were characterized with EDX, XRD, micrographic structure observation and hardness measurement. A compound layer of 8-15$\mu\textrm{m}$ and nitrogen diffusion layer of about 400$\mu\textrm{m}$ were formed on the surface of plasma-sulfnitrided steel. The compound layer consisted of FeS containing Mo and iron nitrides. The nitrides of $\varepsilon$-$Fe_2_3N$ and $\gamma$'-$Fe_4N$ formed under the FeS. The thickness of compound layer and surface hardness were different with the gaps between main and subsidiary cathodes even in the same sulfnitriding temperature. The surface hardnesses after plasma-sulfnitriding were distributed from 640 to 830Hv. The surface hardness was higher in the plasma-sulfnitriding than the usual sulfnitriding in molten salt. This may be due to Mo in sulfnitriding layer.