• 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.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.2
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• pp.69-78
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• 2008

Differences in hardness and microstructure between surface and area at 0.3 mm below the surface after quenching and tempering of ductile cast iron for rear planet carrier of automotive transmission have been investigated. Microstructure of ductile cast iron consisted of ferrite, pearlite, and nodular graphite. The amount of pearlite increased with going down to the half-thickness area. It was found that Cr and Mo segregated to the pearlite and the pearlite transformed to the harder martensite during quenching. The martensite was more resistant to the decomposition to ferrite and cementite during tempering because of segregation of Cr and Mo, resulting in the harder tempered martensite. Consequently, the hardness of the surface with less amount of pearlite, corresponding to the harder martensite in the quenched and tempered microstructure, was lower than that of the area at 0.3 mm below the surface.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.1
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• pp.26-31
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• 2003

Decarburized zone of metal tongue which is used in seat belt for automobiles was carbon-restoration quenched and tempered using nitrogen-methanol gaseous atmosphere. The effects of microstructure and mechanical properties of metal tongue on the effectiveness of carbon-restoration during tempering was studied. Metal tongue showed $20{\sim}30{\mu}m$ decarburized zone. However, after carbon-restoration, it has uniform microstructure and thus hardness without decarburized zone. Carbon-restoration quenching and tempering process resulted in better wear and corrosion resistances than quenching and tempering process.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.4
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• pp.189-198
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• 2008

The production of automotive chassis parts requiring both high hardness and good shape-holdability is better realized by using press quenching technology, comprising the austenitizaton and the subsequent press quenching in a specially designed stamping tool. The effect of press quenching mold shape on the hardness distribution, bending height, and degree of planeness of automotive flexible plate during press quenching and tempering has been investigated. The preferable shape of the projections of punch and die in contact with the flexible plate was close to oval to improve the flow of cooling oil, leading to the higher hardness. The press quenching mold with three separate parts was more effective to control the dimensional change due to thermal deformation during press quenching. Some decrease in the bending height during tempering may be related to some recovery of the residual stress at $400^{\circ}C$.

• 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.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.666-671
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• 2015

In this study, we investigated the effect of the residual carbides and tempered carbides precipitated by tempering treatment after quenching on the pitting corrosion of mod. 440A martensitic stainless steel. In quenched specimens and tempered specimens after quenching of mod. 440A martensitic stainless steel, the volume fraction of the residual carbides and total carbides decreased with the increase of the austenitizing temperature. Pitting resistance increased with the increase of austenitizing temperature. With the increase of the volume fraction of the residual and total carbides, the pitting resistance of mod. 440A martensitic stainless steel was decreased. The pitting resistance of mod. 0.5C-17Cr-0.5Ni 440A martensitic stainless steel had stronger affected by residual carbides than precipitated carbides produced by tempering.

• 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 Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.69-76
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• 2018

This study examined the effect of the heat treatment and alloying elements (B, Ti) on the microstructures and mechanical properties of API J55 steel. The experiments were carried out using various austenization temperatures ($880^{\circ}C$, $910^{\circ}C$, $940^{\circ}C$), cooling methods (water quenching, oil quenching) and tempering temperatures (none, $550^{\circ}C$, $650^{\circ}C$) with J55 and J55+B,Ti steels. The phase diagram and CCT curve were simulated based on the chemical compositions of the J55 and J55+B,Ti steels to predict the microstructures. The results showed that the A1 and A3 temperatures decreased and, as a result, the noses of the ferrite and bainite parts of the CCT curve moved to the right. Various microstructures were formed, namely martensite, bainite, ferrite and pearlite, in accordance with the heat treatment, which had an effect on the hardness, tensile strength and toughness. Martensite was formed after water quenching, but bainite and ferrite appeared after oil quenching with the J55 specimens. On the other hand, martensite was formed, regardless of the cooling method (water quenching, oil quenching), with the J55+B,Ti specimens, because of the improvement of the hardenability caused by the addition of boron. Therefore, the J55+B,Ti specimens exhibited much higher mechanical properties than the J55 specimens, even after the tempering treatment, since the addition of Ti caused fine precipitates to be formed, which inhibited grain growth at the recrystallization temperature.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.48-53
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• 2000

The effects of added elements, such as Co or Nb, on wear properties of high speed steel by powder metallurgy(PM-HSS) had been evaluated in previous paper. The wear properties of materials, in fact, have been a]so influenced by heat-treating conditions. In this paper, the effects of heat-treating conditions on wear properties of PM-HSS have been evaluated. The wear tests have been performed as same conditions as previous paper using PM-HSS(5%Co-1%Nb) heat-treated under different quenching and tempering temperature. The result of this paper shows that wear resistance of PM-HSS is improved with relatively high quenching temperature. However tempering temperature is not sensitve to the wear resistance in range of high quenching temperature. It may be deduced by the fact that the shear strength of matrix by strengthening mechanisms of quenching aging in addition to dispersion-hardening is improved.

• 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.