• 열처리공학회지
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• 제24권3호
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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.

• 열처리공학회지
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• 제26권3호
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• pp.120-125
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• 2013

In this study, the effect of tempering treatment on the mechanical properties in modified 440A steel has been investigated. The amount of remaining carbide decreased with increasing the austenitizing treatment temperature, and all carbides were completely dissolved at $1250^{\circ}C$. The amount of remaining carbide decreased with increasing the time of austenitizing, but the carbide remained insoluble up to 120 minutes at $1050^{\circ}C$. With increasing the tempering temperature, tensile strength decreased, and elongation increased slowly, while hardness rapidly decreased, and impact value unchanged and then rapidly increased over $500^{\circ}C$. The strength and hardness slowly decreased, while the elongation and impact absorbed energy increased with increasing the tempering time. $Cr_{23}C_6$ type carbide was precipitated and sharp decrease of elongation and toughness by tempering did not appear.

• 열처리공학회지
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• 제36권6호
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• pp.396-401
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• 2023

Aus-tempering heat treatment is suitable for thin and small-sized in precision parts. However, the heat treatment process relies on the experience and skill of the operator, making it challenging to produce precision parts due to the cold forging process. The aims of this study is to explore suitable machine learning models using data from the aus-tempering heat treatment process and analyze the factors that significantly impact the mechanic properties (e.g. hardness). As a result, the study analyzed, from a machine learning perspective, how hardness prediction varies based on the quenching temperature, carbon (C), and copper (Cu) contents.

• 한국재료학회지
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• 제21권6호
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• pp.303-308
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• 2011

The effect of heat treatment on the micro-structures and the mechanical properties of 0.002% boron added low carbon steel was investigated. The tensile strength reached the peak at about $880-890^{\circ}C$ with the rising quenching temperature and then the hardness decreased sharply, but the tensile strength hardly decreased. The tensile and yield strength decreased and the total elongation increased with a rising tempering temperature, but the tensile and yield strength sharply fell and the total elongation prominently increased from above a $400-450^{\circ}C$ tempering temperature. Tempered martensite embrittlement (TME) was observed at tempering condition of $350-400^{\circ}C$. In the condition of quenching at $890^{\circ}C$ and tempering at $350^{\circ}C$, the boron precipitates were observed as Fe-C-B and BN together. The hardness decreased in proportion to the tempering temperature untill $350^{\circ}C$ and dropped sharply above $400^{\circ}C$ regardless of the quenching temperature.

• 열처리공학회지
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• 제10권4호
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• pp.266-277
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• 1997

Near-threshold fatigue crack growth characteristics was investigated on the Ni-Cr-Mo-V low alloy steel, which has the different microstructure obtained by tempering at various temperature. The specimens were austenized at $950^{\circ}C$ and then followed by tempering at $200^{\circ}C$, $530^{\circ}C$ and $600^{\circ}C$. Strain rate was obtained from strain gauge attached on the crack tip and crack opening point was observed through load-strain curve. Threshold stress intensity range(${\Delta}K_{th}$) was increased with increasing tempering tempuerature, but the effective threshold stress intensity rage (${\Delta}K_{eff,\;th}$) was not affected with the increasing temperature. Grain size increased with increasing tempering temperature.

• 열처리공학회지
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• 제33권2호
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• pp.65-71
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• 2020

To study the effects of tempering on microstructure and mechanical property of Cu-22 wt.%Sn alloy, tempering was carried out for 30 sec, 1 min, 5 min, 30 min, 3 h, 5 h, and 10 h at 325, 370, 500, and 570℃, which are in the (α+ε), lower (α+δ), higher (α+δ), and (α+γ) region of Cu-Sn phase diagram, respectively. Overall, the hardness value increased and decreased over time at all tempering temperatures, and the time to reach the maximum hardness value beccame shorter as the tempering temperature increases. At the beginning of tempering at each temperature, a portion of the β' phase was decomposed into a fine (α+δ) phase or (α+γ) phase, so that the Cu-22Sn alloy had a high hardness value. However, as the tempering time increases, the hardness value of the alloy decreased due to the growth of the decomposed phases.

• 열처리공학회지
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• 제36권1호
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• pp.7-14
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• 2023

We investigated the effect of multiple tempering on the microstructure and mechanical properties of AISI 4340 steel. The austenitized and quenched AISI 4340 steels were tempered at 550, 600, and 650℃ for 1, 2, and 4 h by single-tempering (ST). The multiple tempering was conducted for 4 h by double-tempering (DT, 2 h + 2 h), and quadruple-tempering (QT, 1 h + 1 h + 1 h + 1 h). As tempering temperature increases, yield strength and ultimate tensile strength decrease and elongation increases due to recovery and recrystallization of martensite and coarsening of carbides. At 550℃, as the number of tempering cycles increases, the yield strength and tensile strength decrease at the expense of fracture elongation. At 600 and 650℃, the yield strength and tensile strength increase with increasing the number of tempering cycles while fracture elongation maintains similar values. The multiple tempering at the same tempering time of 4 h improves the modulus of toughness at all tempering temperatures, which is presumed to be due to the change in carbide precipitation behavior by multiple tempering.

• 열처리공학회지
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• 제24권6호
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• pp.327-337
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• 2011

Effects of microstructural change, tensile properties and impact property according to the change of austenitizing temperature and tempering temperature of AISI 51B20 steel were examined. Regardless of austenite grain size, lath martensite with needle and packet shapes was found at tempering temperature of $300^{\circ}C{\sim}400^{\circ}C$. The needles of lath martensite changed to parallel packet at tempering temperature of $450^{\circ}C{\sim}600^{\circ}C$. As tempering temperature increased, tensile strength, yield strength and hardness decreased, while elongation, ratio of reduction area and Charpy impact energy increased. Grain size increased when quenching temperature was $930^{\circ}C$. Grain size had prominent effect on the mechanical properties of AISI 51B20 steel. Ratio of tensile strength/yield strength and yield strength autenitized at $880^{\circ}C$ followed by tempering at $350^{\circ}C{\sim}450^{\circ}C$ showed higher values than that of autenization at $930^{\circ}C$ due to fine grain size.

• 한국분말재료학회지
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• 제4권3호
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• pp.222-229
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• 1997

A P/M high speed steel of ASP 30 grade was austenitized, gas quenched and tempered at various conditional. The mechanical properties such as hardness, bend strength and fracture toughness were evaluated after heat treatment. The microstructure and the type and volume fraction of carbides were analyzed by an optical microscope, image analyzer and XRD. The primary carbides after the heat treatment were MC and $M_6C$ type. The volume of the total carbide varied from 10 to 15% depending on the austenitizing and tempering temperature. The tempering temperature for maximum hardness was at around 52$0^{\circ}C$. But the maximum bend strength was obtained at about 55$0^{\circ}C$. The fracture toughness was largely affected by the presence of retained austenite after gas quenching and secondary hardening during tempering.

• 열처리공학회지
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• 제26권1호
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• pp.7-13
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• 2013

Vacuum heat treatment(indirect heating method) has long exposure time at high temperature and low quenching rate. Contrarily salt bath heat treatment (direct heating method) has short exposure time at high temperature and fast cooling rate. With these different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study, Salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heat process and secondary hardening with high temperature tempering process. Consequently, It indicates that salt bath heat treatment is better way than vacuum heat treatment for product to have high mechanical properties.