• Journal of the Korean Society for Heat Treatment
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• v.24 no.3
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• pp.149-155
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• 2011

Residual stress relief by pulse magnetic treatment is attractive because the process is carried out at room temperature and magnetic fields that are easy to produce and control can be used. This study shows that strong pulse magnetic treatment can lead to stress relaxation of structural steels instead of a conventional heat treatment process. And it makes a comparative study about pulse magnetic treatment and tempering by using Larson-Miller equation. When the specimen was subjected to a pulse magnetic treatment process the residual stress in the specimen was reduced by about 13.8%. It could be compared with tempering at $200^{\circ}C$ for 2hours by using thermal effect of Larson-Miller equation. As a result, it is considered that the pulsed magnetic treatment have an effect of the stress relation by tempering at $200^{\circ}C$ for 2 hours.

• Journal of Power System Engineering
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• v.5 no.2
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• pp.63-70
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• 2001

To obtain the optimal condition of heat treatment of wear-resistant alloy, hardness and Charpy V-notch test have been performed with Co-based Stellite No.4, No.6 and Tribaloy 800 alloys, following by heat treatment at the various conditions. Heat treatment at $1250^{\circ}C$ for 1 hours caused the as-casted Tribaloy 800 with FCC crystal structure to transform to HCP structure and lamellar eutectic structure was disappeared, which did not influence on the hardness. Aging at $800^{\circ}C$ for 20 hours, following by $1250^{\circ}C$ for 2 hours heat treatment has enhanced hardness significantly, which is due to the precipitation of large amounts of Laves-phase. The hardness of Stellite alloys was increased by the aging at $800^{\circ}C$ to 5 hours, and was nearly constant by the aging over 5 hours. The toughness of Stellite alloys was a few influenced by the aging treatment.

• Journal of Power System Engineering
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• v.7 no.4
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• pp.55-60
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• 2003

This paper is to investigate the fatigue crack growth of plasma-sprayed coating steels according to heat treatments. The experimental materials are carbon steels(substrate: S45C) with plasma-sprayed coating layers of Ni-4.5%Al and $TiO_2$. The fatigue test is conducted on compact tension specimen by a servo-hydraulic fatigue testing machine. The specimens are heat-treated at $400^{\circ}C\;and\;800^{\circ}C$, respectively. Loading condition is a constant amplitude sinusoidal wave with a frequency of 10Hz and a load ratio of 0.1. The fatigue crack growth length is automatically measured by a compliance method. In the case of non-heat treated specimens, the fatigue crack growth rates of both substrate and coating specimen are almost same. The crack growth rates of substrates and coating steels by heat treatment are larger than those of the non-heat treated one, because the ductile property increase by heat treatment. In ${\Delta}K<18MPa{\cdot}m^{1/2}$, the crack growth rates of the heat-treated specimens are slightly taster than non-heat treated one. But the both heated and non-heated one are almost same in ${\Delta}K>18MPa{\cdot}m^{1/2}$.

• Journal of Power System Engineering
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• v.15 no.2
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• pp.49-54
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• 2011

Effect of tempering treatment on the mechanical properties of 12Cr heat resistant steel with ferrite phase was investigate in this study. As time and temperature of tempering treatment were increase, C and Cr contents in matrix structure were decreased. Due to increase of the amount of Cr26C6 type carbides. It was confirmed in mechanical properties experimental that tensile strength and hardness were decreased, while elongation and impact value were, increased with increasing the time and temperature.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.5
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• pp.51-60
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• 2006

In order to examine the heat transfer characteristic of a soil warming system and effects of soil warming on the greenhouse heating load, control experiments were performed in two greenhouses covered with double polyethylene film. One treated the soil warming with an electric heat wire and the other treated a control. Inside and outside air temperature, soil temperature and heat flux, and heating energy consumption were measured under the set point of heating temperature of $5,\;10,\;15,\;and\;20^{\circ}C$, respectively. Soil temperatures in a soil warming treatment were observed $4.1\;to\;4.9^{\circ}C$ higher than a control. Heating energy consumptions decreased by 14.6 to 30.8% in a soil warming treatment. As the set point of heating temperature became lower, the rate of decrease in the heating energy consumptions increased. The percentage of soil heat flux in total heating load was -49.4 to 24.4% and as the set point of heating temperature became higher, the percentage increased. When the set point of heating temperature was low in a soil warming treatment, the soil heat flux load was minus value and it had an effect on reducing the heating load. Soil heat flux loads showed in proportion to the air temperature difference between the inside and outside of greenhouse but they showed big difference according to the soil warming treatment. So new model for estimation of the soil heat flux load should be introduced. Convective heat transfer coefficients were in proportion to the 1/3 power of temperature difference between the soil surface and the inside air. They were $3.41\;to\;12.42\;W/m^{2}^{\circ}C$ in their temperature difference of $0\;to\;10^{\circ}C$. Radiative heat loss from soil surface in greenhouse was about 66 to 130% of total heating load. To cut the radiation loss by the use of thermal curtains must be able to contribute for the energy saving in greenhouse.

• Proceedings of the Korean Society of Postharvest Science and Technology of Agricultural Products Conference
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• 2003.10a
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• pp.167.1-167
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• 2003

To maintain high quality and to extend the shelf life of intact and minimally processed apple cubes, the effect of heat shock on the texture and color of apple cubes (Fuji) was evaluated in this study. After peeled and cored, the apples were cut into cubes of 1.5 cm. The heat shock was immersion in heated water from 25$^{\circ}C$ to 95$^{\circ}C$ in 10$^{\circ}C$ increments for 2 min and cooling to storage temperature as soon as possible after heat treatment. The effect of heat treatment in terms of color and texture measurements with respect to time was investigated, respectively during 7 days storage at in LDPE film bags without sealing at 4$^{\circ}C$, and 95% relative humidity air. Results suggest that heat shock (55$^{\circ}C$, 2 min) may have effectively delayed browning, and there were significant changes in color of apple cube when the temperature of heat shock is above 75$^{\circ}C$. And hardness, stiffness and firmness, which were used to describe texture, behaved similarly in the textural qualities. It was shown that the texture of the apple cubes was decreased with temperature increase. The value of them were most decreased to 70% of the initial ones after treated with 85$^{\circ}C$ and 95$^{\circ}C$ on the lust day.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.1
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• pp.29-33
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• 2014

Recently, Difficult-to-cut materials are used in many manufacturing industry. But the difficult-to-cut materials are difficult-to-cutting process. So difficult to cut material cutting process was used after heat treatment through preheating for easy cutting process. In this study, Inconel 625 was preheating using laser heat source in computer simulation. Laser heat source temperature applied $1290^{\circ}C$ that suitable preheating temperature for Inconel 625. And temperature effects such as temperature distribution for moving heat source studied apply to similar actual process condition. Simulation results for heat treatment effects through temperature distribution verified.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.84-91
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• 2010

Heat treatment with carburized quenching process is widely used for automotive helical gear to improve its surface properties of hardness and strength. However, the gear can be deformed with the process over the allowable tolerance, which possibly makes noise, vibration and heat problems in operation. In this study, deformation of helical gear during heat treatment of carburized quenching was analyzed with a numerical method, incorporating coupled calculations of thermal conduction, carbon diffusion, phase transformation and thermal stresses. With the analysis, the effect of coolant temperature in quenching on the deformation was investigated. The result of the analysis revealed that the higher the coolant temperature became, the more change of helix angle and the more compressive stresses in the surface generated, because of delayed generation of martensite in the part.

• Corrosion Science and Technology
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• v.13 no.1
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• pp.28-35
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• 2014

Recently, the fuel oil of diesel engines of marine ships has been increasingly changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the spiral gear attached at the motor of the oil purifier which plays an important role to purify the heavy oil is also easy to expose at severe environmental condition due to the purification of the heavy oil in higher temperature. Thus, the material of the spiral gear requires a better mechanical strength, wear and corrosion resistance. In this study, the heat treatment(tempering) with various holding time at temperature of $500^{\circ}C$ was carried out to the alloy of Cu-7Al-2.5Si as centrifugal casting, and the properties of both hardness and corrosion resistance with and without heat treatment were investigated with observation of the microstructure and with electrochemical methods, such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and a.c. impedance. in natural seawater solution. The ${\alpha}$, ${\beta}^{\prime}$ and ${\gamma}_2$ phases were observed in the material in spite of no heat treatment due to quenching effect of a spin mold. However, their phases, that is, ${\beta}^{\prime}$ and ${\gamma}_2$ phases decreased gradually with increasing the holding time at a constant temperature of $500^{\circ}C$. The hardness more or less decreased with heat treatment, however its corrosion resistance was improved with the heat treatment. Furthermore, the longer holding time, the better corrosion resistance. In addition, when the holding time was 48hrs, its corrosion current density showed the lowest value. The pattern of corroded surface was nearly similar to that of the pitting corrosion, and this morphology was greatly observed in the case of no heat treatment. It is considered that ${\gamma}_2$ phase at the grain boundary was corroded preferentially as an anode. However, the pattern of general corrosion exhibited increasingly due to decreasing the ${\gamma}_2$ phase with heat treatment. Consequently, it is suggested that the corrosion resistance of Cu-7Al-2.5Si alloy can be improved with the heat treatment as a holding time for 48 hrs at $500^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.2
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• pp.80-87
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• 2009

Effects of retained austenite contents on ductility of medium carbon spring steels according to steel alloy compositions and heat treatment conditions were studied. Contents of retained austenite varied with steel compositions and heat treatment conditions, and some retained austenite were found to transform to martensite on stress. Reduction of area (RA) increased with contents of retained austenite, then saturated through its maximum, and subsequently decreased. Increase in RA with retained austenite contents could be due to crack blunting effect by retained austenite on stress, however, more contents of martensite transformed from retained austenite in its higher contents could cause decrease in RA.