• Journal of the Korean Society for Heat Treatment
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• v.24 no.6
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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.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.2
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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.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.1
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• pp.25-34
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• 1994

To investigate the effect of austenitizing tempratures on the mechanical properties and corrosion resistance of 0.19%C-13.6%Cr martensitic stainless steel, the changes in martensitic trasformation temperatures, mechanical properties and anodic polarization curve were examined after changing the austenitizing temperatures and tempering temperatures. On increasing heating rate at the same austenitizing temperatures, $A_s$, $A_r$ and $M_s$ increased. And the $M_s$ temperature showed to be decreased with increasing austenitizing temperature. With increasing tempering temperature up to $500^{\circ}C$, strength, hardness and impact value were not changed remarkably, on the other hand the tensile strength and hardness decreased and impact value increased after tempering above $550^{\circ}C$ owing to the $M_{23}C_6$ carbide precipitation. The abrupt decrease in elongation at the tempering temperture of $500^{\circ}C$ proved to the precipitation of $M_7C_3$ carbide. The effect of austenitizing temperature on the mechanical properties of the tempered specimen showed to be decreased in impact value and elongation at the austenitizing temperature of $1150^{\circ}C$. At low tempering temperatures the corrosion resistance of the tempered specimen was not changed obviously with increasing tempering temperature. On the other hand, the resistance decreased above the tempering temperature of $600^{\circ}C$ due to the precipitation of $M_{23}C_6$ carbides. The corrosion resistance showed to be improved with increasing the austenitizing temperature owing to the dissolution of carbides.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.1
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• pp.1-6
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• 2023

In order to process plastic with similar mechanical performance to metal materials, it is necessary to improve the strength and hardness of core parts of the injection equipment in extrusion system. The tempering process is a heat treatment performed to reduce brittleness and improve elongation along with improvement of dimensional defects of martensite formed after quenching. In this study, changes in microstructure and mechanical properties according to temperature were evaluated after quenching and tempering of SM30C material. As a result, the strength and hardness were gradually decreased by tempering at 250~400℃, and the decrease was greatly increased under the tempering condition at 450℃. Under the tempering condition of 200~400℃, the main structure was lath martensite, and the precipitation amount and size of needle-shaped cementite increased along the lath with the increase of the tempering temperature. Most of the shape of cementite has a needle-like structure, and the formation of some spherical cementite is observed. Under the tempering condition of 450℃, a mixed structure of ferrite and martensite was formed according to the decomposition of martensite.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.1
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• pp.29-35
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• 2004

The effect of low tempering in a temperature range of $150{\sim}400^{\circ}C$ on corrosion resistance in 420J2 stainless steel austenitized at $1000^{\circ}C$ was investigated by the application of salt spray test, electrochemical pitting test in 3.5% NaCl solution and DL-EPR test for intergranular corrosion in 0.5M $H_2SO_4$+0.01M KSCN solution. In salt spray test, good corrosion resistance was obtained in a tempering temperature range of $150{\sim}250^{\circ}C$. Pitting potential was increased to the tempering temperature of $250^{\circ}C$, but decreased with the increase of temperature up to $400^{\circ}C$ And it was thought that the degradation of pitting corrosion resistance showed at the tempering temperature of around $400^{\circ}C$ was due to the precipitation of $Cr_7C_3$ of $M_7C_3$ type. The degree of sensitization showed increasing tendency with the increase of tempering temperature, and also Cr depletion phenomena were observed in the vicinity of grain boundary.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.53-56
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• 2003

The disappearance of continuous yielding and the formation of an extended region in engineering stress-strain curves at tempering temperatures of 673-873K is closely related to the reduction of mobile dislocations during tempering and dynamic recovery during tensile deformation. In addition, the occurrence of discontinuous yielding at tempering temperature above 923K would be attributed to the formation of new strain-free polygonal ferrite grain.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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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.

• Journal of Korea Foundry Society
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• v.35 no.4
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• pp.88-98
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• 2015

The effects of quenching and tempering temperatures on the tensile, impact and corrosion properties of A487 alloy cast with different C contents of 0.16, 0.19 to 0.23 wt.% were examined. The impact tests were conducted at $25^{\circ}C$ and $-60^{\circ}C$ and the immersion test was performed using 3.5% NaCl solution for 14 days. The quenching temperature affected the mechanical properties of A487 alloy cast, while the magnitude of change varied depending on the C content. The increase in tempering temperature showed the typical trend of decreasing tensile strength and increasing impact properties. The change in quenching and tempering temperature in this study did not affect the corrosion properties of A487 alloy significantly. The change in mechanical and corrosion properties of A487 with different C contents was discussed based on the microstructural and fractographic observation.

• Korean Journal of Materials Research
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• v.21 no.6
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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.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.327-337
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• 1999

A series of Ni-Cr-Mo alloy steels were austenitized, quenched to martensite, and tempered at various temperature and time conditions. Tensile testing was conducted at room temperature with cylindrical specimens, and hardness was measured using Rockwell hardness tester. In the tempering stage I, high strain hardening and yield strength accounted for the high ultimate strength and hardness. In the tempering stage II, strengths and hardness linearly decreased with increasing tempering temperature. Specimens tempered in the temperin stage III showed incipient discontinuous yielding and tensile strengths only slightly higher than yield strengths. Ductilities decreased slightly in specimens tempered in the tempered martensite embrittlement range, and severely decreased in specimens tempered for 10 hours at $500^{\circ}C$ in the temper embrittlement range. Specimens tempered at $600^{\circ}C$ for 10 hours showed recrystallized microstructures, a number of fine dimples, and increased strain hardening, probably due to the precipitation of alloy carbides. The simple formulae for the mechanical properties of these steels were suggested as a function of carbon content and Hollomon-Jaffe tempering parameter.