• Title/Summary/Keyword: aging treatment

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Effects of Cryogenic Treatment Cycles on Residual Stress and Mechanical Properties for 7075 Aluminum Alloy (극저온 열처리가 7075 알루미늄 합금의 잔류응력과 기계적 특성에 미치는 영향)

  • Kim, Hoi-Bong;Jeong, Eun-Wook;Ko, Dae-Hoon;Kim, Byung-Min;Cho, Young-Rae
    • Korean Journal of Materials Research
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    • v.23 no.1
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    • pp.18-23
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    • 2013
  • In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at $470^{\circ}C$, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.

Microstructural Development of Ferritic 11Cr-3.45W Heat-resistance Steel for Ultra-supercritical Power Plant During Creep and Thermal Aging (크리프와 등온열화에 따른 초초임계압 발전설비용 페라이트계 11Cr-3.45W 내열합금강의 미세조직 변화)

  • Kim, Chung-Seok
    • Journal of the Korean Society for Heat Treatment
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    • v.31 no.3
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    • pp.91-96
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    • 2018
  • Microstructural development of ferritic 11Cr-3.45W heat-resistance steel for ultra-supercritical power plant during creep and thermal aging was investigated using electron microscopy. The test samples were isothermally aged at $700^{\circ}C$ for up to 4000 hours and subjected to creep loading at $700^{\circ}C$ for predetermined periods of lifetime to prepare the damaged materials. In this structural material, a various secondary phases are the primary influence on mechanical properties of ferritic heat-resistance steel. The typical precipitates of $M_{23}C_6$, MX and $M_2X$ secondary phases had been analyzed through qualitative and quantitative manner. Coarsening of precipitates and increase of lath width were observed during creep and thermal aging. This phenomenon was remarkable for creep process compared with isothermal aging process.

Dependence of Damping Capacity on ${\beta}$ Phase Precipitation in Mg Alloy (Mg 합금에서 진동감쇠능의 ${\beta}$상 석출 의존성)

  • Jun, Joong-Hwan
    • Journal of the Korean Society for Heat Treatment
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    • v.20 no.6
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    • pp.306-310
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    • 2007
  • Changes in microstructure and damping capacity with aging time for solutionized Mg-Al alloy have been investigated. Discontinuous ${\beta}\;(Mg_{17}Al_{12})$ precipitates form along the primary grain boundaries, the amount of which increases as the aging time increases. The hardness of the matrix with respect to aging time shows a typical "S" shape, indicating a generation of fine continuous precipitates in the matrix during the aging. The peak level of damping capacity is obtained after 1 hour of aging, over which the damping capacity becomes deteriorated continuously. The formation of optimum density of continuous ${\beta}$ precipitates with fine morphology which would act as pinning points for dislocation lines, might be responsible for the improvement of damping capacity.

Zirconia galvani sensor for the measurement of oxygen activity (용존산소활량 측정용 지르코니아 갈바니 센서)

  • Oh, Young-Jei
    • Journal of Sensor Science and Technology
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    • v.18 no.6
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    • pp.441-448
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    • 2009
  • Magnesia partially stabilized zirconia(Mg-PSZ) solid electrolytes for an improvement of thermal shock resistance, which is suitable for the measurement of oxygen activity in a molten steel, were prepared by post-thermal aging treatment. The steelmaking oxygen sensor elements were formed by an injection molding method, sintered at $1650^{\circ}C$, and then thermal aged ranged from 1250 to $1400^{\circ}C$. Sintered density and porosity were decreased as increasing the magnesia content in a zirconia-magnesia solid solution. Fractions of cubic phase to the synthesized Mg-PSZ solid electrolytes were ranged from 13.13 to 79.54.% after post-thermal aging treatment. Very dense microstructure without voids in the grains was obtained by the post-thermal aging process. Fine tetragonal phase crystallites precipitated on the cubic surface during post-thermal aging up to $1300^{\circ}C$ improve a thermal shock resistance and reappearance of electro motive force(EMF) curve.

EFFECTS OF AGING TREATMENT ON MICROSTRUCTURE AND STRENGTH OF WELD HEAT AFFECTED ZONE OF 6N01-T5 ALUMINUM ALLOY

  • Yoshida, Naoharu;Shibao, Masami;Ema, Mitsuhiro;Sasabe, Seiji;Hirose, Akio;Kobayashi, Kojiro F.
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.59-64
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    • 2002
  • Effects of the aging treatments on the microstructure and strength of heat affected zone(HAZ) in the welds of a age-hardened Al-Mg-Si alloy, 5N01-T5, were investigated. The base metal aging treatments before MIG welding were conducted at 423K to 473K for 28.8ks Post weld heat treatment(PWHT) to recover the HAZ strength was performed at 448K for 28.8ks. Microstructure observations, hardness measurements and tensile tests were conducted to study properties of the MIG weld joints. The position of the softest region in HAZ where the hardness insufficiently recovered after natural aging and PWHT was at a distance of approximately 15mm from the center of the fusion zone. Hardness of the softest regions after natural aging and PWHT decreased with increase in the base metal aging temperature. TEM observation clarified that strengthening ${\beta}$"(Mg$_2$Si) precipitates and coarse ${\beta}$′ precipitates affected the hardnes of HAZ. Incomplete recover of hardness in HAZ after PWHT was caused by the precipitating of non-hardening ${\beta}$′ phase during the weld thermal cycle. In order to examine the effects of weldheat input and welding speed, the laser weld joints were also investigated and compared with the MIG weld ones. Laser welding had the narrower width of the softened regions in HAZ compared with MIG welding. The hardness of the softest regions of the laser welds after PWHT was higher than that of the MIG welds. Quantitative relations between hardness of the softest region and base metal aging temperature were obtained for both welding processes. Accordingly, the equations to estimate the strength of the weld joints after PWHT with varying base metal temperatures were proposed for MIG welding and laser welding.

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Effects of Aging Period Prior to Freezing on Meat Quality of Hanwoo Muscle (Longissimus dorsi)

  • Kim, Hyun-Wook;Lee, Eui-Soo;Choi, Yun-Sang;Choi, Ji-Hun;Han, Doo-Jeong;Kim, Hack-Youn;Song, Dong-Heon;Choi, Seul-Gi;Kim, Cheon-Jei
    • Food Science of Animal Resources
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    • v.31 no.6
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    • pp.799-806
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    • 2011
  • This study was conducted to evaluate the effect of the aging period prior to freezing on the meat quality of Hanwoo longissimus dorsi (LD) muscle. Three different combinations of aging and freezing periods (0/90, 20/70, and 40/50) were examined using LD muscle at 24 h postmortem under an identical storage time of 90 d. The pH and lightness slightly increased with increasing aging period. However, there were no significant (p>0.05) differences in redness and yellowness. The solitary freezing treatment (0/90) had the significantly (p<0.05) lowest moisture content. The un-aged treatment had a significantly (p<0.05) higher total loss than the aged treatments due to an increase in thaw drip loss. The aging significantly improved the myofibrillar fragmentation index and shear force of Hanwoo LD muscle (p<0.05). In addition, the aged treatments produced a higher flavor, tenderness, juiciness, and overall acceptability relative to un-aged treatment. However, there was no significant (p>0.05) difference in shear force and sensorial properties between 20 and 40 d aging prior to freezing. Therefore, 20 d aging prior to freezing may be a sufficiently effective strategy to improve the tenderness and sensorial properties of Hanwoo LD muscle.

Effects of Cr content and Thermomechanical Treatment on Tensile Strength and Electrical Conductivity of Cu-Cr Alloys (Cu-Cr 합금의 인장강도와 전기전도도에 미치는 Cr 첨가량 및 가공열처리의 영향)

  • Kim, Ki-Tae;Jung, Woon-Jae;Shin, Han-Chul;Choi, Chong-Sool
    • Journal of the Korean Society for Heat Treatment
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    • v.14 no.1
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    • pp.17-21
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    • 2001
  • The effects of Cr content above its solubility limit and thermomechanical treatment on tensile strength and electrical conductivity of Cu-Cr alloys were studied to obtain optimum Cr content exhibiting a high tensile strength without degradation of electrical conductivity. The increase in Cr content above the solubility limit increased tensile strength of Cu-Cr alloys without deterioration of the electrical conductivity. The electrical conductivity was not affected by cold rolling. The electrical conductivity of a Cu-3.5%Cr alloy subjected to cold rolling ${\rightarrow}$ aging treatment ($450^{\circ}C{\times}1hr$) ${\rightarrow}$ cold rolling was equal to that of the alloy subjected to cold rolling ${\rightarrow}$ aging treatment. However, the tensile strength of the alloy subjected to the former thermomechanical treatment was superior to that of the alloy subjected to the latter thermomechanical treatment at all the deformation degrees.

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Medical Treatment Service for the Housing Welfare of Elderly People- Laying stress on Aging in Place concept - (노인주거복지 향상을 위한 의료서비스 지원방안 연구 - Aging in Place 개념을 중심으로 -)

  • Lee, Joon-Min;Park, Nam-Hee;Shin, Hwa-Kyoung
    • Proceeding of Spring/Autumn Annual Conference of KHA
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    • 2005.11a
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    • pp.367-370
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    • 2005
  • Offer of medical treatment service for recovery or preservation of physical spiritual function of elderly people by sudden population graying developing is essential. Therefore, according to increase of elderly's medical treatment demand, medical treatment service request is augmented. Number of medical treatment service utilization wishes to grope medical treatment service support way for elderly residing cloth elevation laying stress on elderly's Aging in Place in increase trend in this research. If decide, is as following : First, national hospital and public health center were concentrated most on Seoul and kyonggi, and there were many hospitals to south of a river nine, Songpagu, Seochogu, and public health center was expose that is one by one to each nine. Second, in the case of Seoul, elderly population ratio was expose that comparatively high Yeongdeungpo, Chongno, Yongsan, west passage nine is few hospital number relatively in elderly's residential area. Third, need that establish elderly full text clinic on part of general hospital or university hospital equipment. Fourth, must do so that can use access as is easy little more in local community to all elderly who need medical treatment service of visit nursing, visit medical examination and treatment etc.. that consist in present public health center.

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Effect of σ-phase on Intergranular Corrosion of Super Duplex Stainless Steel Weld Metal (슈퍼듀플렉스강 용접금속의 입계부식에 미치는 σ 상의 영향)

  • Lee, Jae-Hyoung;Jung, Byong-Ho;Seo, Gi-Jeong;Kang, Chang-Yong
    • Journal of the Korean Society for Heat Treatment
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    • v.26 no.6
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    • pp.293-299
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    • 2013
  • A specimen of weld metal was prepared by GTA welding with weld wire of super duplex stainless steel. Aging treatment was conducted for the sample at the temperature range of 700 to $900^{\circ}C$ for 5 to 300 minutes. The effect of volume fraction of ${\sigma}$-phase to intergranular corrosion of weld metal has been investigated and the results were derived as follows. The volume fraction of ${\sigma}$ phase tends to increase with an increase of aging temperature and time and intergranular corrosion of weld metal was increased by an increase of ${\sigma}$ phase. Degree of sensitization representing intergranular corrosion was found to tend to increase with an increase of aging time at 700 to $800^{\circ}C$, while it decreased by an increase of aging time at $900^{\circ}C$.