• Title/Summary/Keyword: secondary hardness

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Effect of Processing Conditions for Atmospheric Plasma Spraying on Characteristics of Ceramic Coatings (상압 플라즈마 용사의 공정조건에 따른 세라믹 피막의 특성)

  • 주원태;최병룡;홍상희
    • Journal of the Korean institute of surface engineering
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    • v.26 no.4
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    • pp.192-202
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    • 1993
  • The characteristics of the high-performance ceramic coatings fabricated on the optimum processings con-ditions for the atmospheric plasma spraying are evaluated by various material tests and analyses. The opti-mum processing parameters for the plasma spraying are determined by using the two-level orthogonal arrays of fractional factorial testing method as a statistical approach. Material tests for the coating specimens are carried out to evaluate microstructure, hardness, adhesion strength, and deposition efficiency. The properties of Al2O3-13%TiO2 coating are discussed with regard to the effective processings parameters. The decarburization effects of WC-12%Co coating is examined by XRD analysis in terms of the arc power and the secondary gas species. The hardness of Al2O2-13%TiO2 coating is increased with the arc power and shows the maximum value at around 40 lpm of Ar gas flowrate, which appears to be the most critical parame-ter on the deposition efficiency. For reducing the decarburization of WC-12%Co coating, the injection of inert He gas instead of reactive H2 gas as a secondary gas is more effective than the dropping of arc power to lessen the plasma enthalpy.

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A Study of Aluminum Reflector Manufacturing in Diamond Turning Machine (다이아몬드 터닝머신을 이용한 알루미늄반사경의 절삭특성)

  • 김건희;고준빈;김홍배;원종호
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.4
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    • pp.1-5
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    • 2002
  • A 110 m diameter aspheric metal secondary mirror for a test model of an earth observation satellite camera was fsbricated by ultra-precision single point diamond turning (SPDT). Aluminum alloy for mirror substrates is known to be easily machinable, but not polishable due to its ductility. A harder material, Ni, is usually electrolessly coated on an A1 substrate to increase the surface hardness for optical polishing. Aspheric metal secondary mirror without a conventional polishing process, the surface roughness of Ra=10nm, and the form error of Ra=λ/12(λ=632.8nm) has been required. The purpose of this research is to find the optimum machining conditions for reflector cutting of electroless-Ni coated A1 alloy and apply the SPDT technique to the manufacturing of ultra precision optical components of metal aspheric reflector.

A Study of Aluminum reflector manufacturing in diamond turning machine (초정밀가공기를 이용한 알루미늄반사경의 절삭특성)

  • 김건희;도철진;홍권희;유병주;원종호;김상석
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.1125-1128
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    • 2001
  • A 110mm diameter aspheric metal secondary mirror for a test model of an earth observation satellite camera was fabricated by ultra-precision single point diamond turning(SPDT). Aluminum alloy for mirror substrates is known to be easily machinable, but not polishable due to its ductility. A harder material, Ni, is usually electrolessly coated on an Al substrate to increase the surface hardness for optical polishing. Aspheric metal secondary mirror without a conventional polishing process, the surface roughness of Ra=10nm, and the form error of Ra=λ/12(λ=632nm) has been required. The purpose of this research is to find the optimum machining conditions for reflector cutting of electroless-Ni coated Al alloy and apply the SPDT technique to the manufacturing of ultra precision optical components of metal aspheric reflector.

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A Study on Temperature Measurement for Quenching of Carbon Steel (탄소강 담금질 공정의 온도 측정방법에 대한 고찰)

  • Kim, D.K.;Jung, K.H.;Kang, S.H.;Im, Y.T.
    • Transactions of Materials Processing
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    • v.19 no.1
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    • pp.25-31
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    • 2010
  • To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.

Effects of Tempering on Tensile Properties of Medium-Carbon Low-Alloy Steels (중탄소 저합금강의 인장성질에 미치는 템퍼링의 영향)

  • Lee, Young-Kook;Krauss, George
    • 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.

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Performance evaluation of plasma nitrided 316L stainless steel during long term high temperature sodium exposure

  • Akash Singh;R. Thirumurugesan;S. Krishnakumar;Revati Rani;S. Chandramouli;P. Parameswaran;R. Mythili
    • Nuclear Engineering and Technology
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    • v.55 no.4
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    • pp.1468-1475
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    • 2023
  • Enhancement of wear resistance of components used in fast reactors is necessary for long service life of the components. Plasma nitriding is a promising surface modification technology to impart high hardness and improved wear resistance of various steel components. This study discusses the characterization of chrome nitrided SS316L casing ring used in secondary sodium pump of fast breeder reactor and its stability under long term sodium exposure. Microstructural and hardness analysis showed that stress relieved component could be chrome nitrided successfully to a thickness of about 100 ㎛. Assessment of in-sodium performance of the chrome nitrided casing ring subjected to long term exposure up to 5000h at 550℃, showed retention of chrome nitrided layer with a case depth almost similar to that before sodium exposure. A slight decrease in the hardness was observed due to prolonged high temperature sodium exposure. Tribological studies indicate very low coefficient of friction indicating the retention of good wear resistance of the coating even after long term sodium exposure.

Estimation of Mechanical Properties of Tungsten-Fiber-Reinforced Ti-MMCs by Hot Isostatic Pressing (HIP 처리 티타늄기 MMC 의 기계적 특성평가)

  • Son, Sun-Young;Nishida, Shin-Ichi;Lee, Jong-Hyung;Kim, Young-Tae;Lee, Do-Kyung;Son, Yong-Jea;Jang, Hyun-Duck
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.4
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    • pp.407-412
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    • 2010
  • The objective of this study is the estimation of the mechanical properties of HIP-treated MMCs by an optimized manufacturing process. The Ti-MMCs were fabricated by HIP and rotary swaging (RS) for secondary processing. The Ti-MMCs with different tungsten fiber contents of 0, 6, 9, and 12 vol% were subjected to tensile tests, fatigue tests, and hardness tests. The results show that the hardness values of Ti-MMCs increased with the increasing volume percent of tungsten fibers, the tensile strength increased by approximately 50% (specific strength: 38%) at the 9 vol%. The value of tungsten-fiber orientation F affects the tensile strength. The fatigue strengths of the Ti-MMCs did not improve. HIP is a useful manufacturing method for Ti-MMCs and RS is an important process for improving fiber orientation during secondary processing.

A Study on Characteristics of Dissimilar Welds between Super Duplex Stainless Steel UNS S32750 and Carbon Steel A516-70 with FCAW (슈퍼듀플렉스 스테인리스강 UNS S32750과 탄소강 A516-70의 이종금속 FCA 용접 특성에 대한 연구)

  • Moon, In-June;Jang, Bok-Su;Kim, Se-Cheol;Koh, Jin-Hyun
    • Journal of Welding and Joining
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    • v.32 no.4
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    • pp.26-33
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    • 2014
  • The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.

A Study on Correlation of Microstructural Degradation and Mechanical Properties of 9-12%Cr-Steel for Ultra-Super Critical Power Generation (초초임계압 발전용 소재의 장시간 열처리에 따른 미세조직 변화와 기계적 특성의 상관관계 연구)

  • Joo Sungwook;Yoo Junghoon;Shin Keesam;Hur Sung Kang;Lee Je-Hyun;Suk Jin Ik;Kim Jeong Tae;Kim Byung Hoon
    • Korean Journal of Materials Research
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    • v.15 no.1
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    • pp.19-24
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    • 2005
  • For the good combination of high-temperature strength, toughness and creep property, $9-12\%$ chromium steels are often used for gas turbine compressors, steam turbine rotors, blade and casing. In this study, the correlation of microstructural evolution and mechanical properties was investigated fur the specimens heat-treated at 600, 650 and $700^{\circ}C$ for 1000, 3000 and 5000 hrs. The microstructure of as-received specimen was tempered martensite with a high dislocation density, small sub-grains and fine secondary phase such as $M_23C_6$. Aging for long-time at high temperature caused the growth of martensite lath and the decrease of dislocation density resulting in the decrease in strength. However, the evolution of secondary phases had influence on hardness, yield strength and impact property. In the group A specimen aged at $600^{\circ}C\;and\;650^{\circ}C$, Laves phase was observed. The Laves phase caused the increase of the hardness and the decrease of the impact property. In addition, the abrupt growth of secondary phases caused decrease of the impact property in both A and B group specimens.

A Study on Nitrogen Permeation Heat Treatment of Super Martensitic Stainless Steel (수퍼 마르텐사이트계 스테인리스강의 질소침투 열처리)

  • Yoo, D.K.;Sung, J.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.19 no.1
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    • pp.3-9
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    • 2006
  • The phase changes, nitride precipitation and hardness variations of 14%Cr-6.7Ni-0.65Mo-0.26Nb-0.05V-0.03C super martensitic stainless steel were investigated after nitrogen permeation heat treatment at a temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The nitrogen-permeated surface layer was transformed into austenite. The rectangular type NbN, NbCrN precipitates and fine round type precipitate were coexisted in the surface austenite layer, while the interior region that was free from nitrogen permeation kept the martensitic phase. The hardness of surface austenite showed 280 Hv, while the interior region of martensite phase represented 340 Hv. When tempering the nitrogen-permeated steel at $450^{\circ}C$, a maximum hardness of 433 Hv was appeared, probably this is attributed to the secondary hardening effect of the precipitates. The nitrogen concentration decreased gradually with increasing depth below the surface after showing a maximum of 0.3% at the outmost surface. The strong affinity between nitrogen and Cr enabled the substitutional element Cr to move from interiors to the surface when nitrogen diffuse form surface to the interior. Corrosion resistance of nitrogen permeated steel was superior to that of solution-anneaed steel in the solution of 1N $H_2SO_4$.