• Title/Summary/Keyword: microstructure effect

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Effect of Welding Heat Input and PWHT Cooling Rate on Mechanical Properties of Welded Region at SAW of 1.25Cr-0.5Mo Steel for Pressure Vessel (압력용기용 1.25Cr-0.5Mo 강의 Submerged Arc Welding시 입열 및 PWHT 냉각속도가 용접부 기계적 성질에 미치는 영향)

  • Lee Dong-Hwan;Park Jong-Jin
    • Journal of Welding and Joining
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    • v.22 no.5
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    • pp.26-31
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    • 2004
  • In order to propose the optimum welding condition for field application, the effects of welding heat input and cooling rate at PWHT on the mechanical properties were investigated. Submerged arc welding of 1.25Cr-0.5Mo steel for pressure vessel was conducted at welding heat inputs of 15.2kJ/cm, 30.9kJ/cm, and 44.8kJ/cm, and cooling rates of 184$^{\circ}C$/hr, 55$^{\circ}C$/hr, and 2$0^{\circ}C$/hr at PWHT. From the test results, as the welding heat input increase up to 30.9kJ/cm, the changes of microstructure and impact toughness were small. At the heat input of 44.8kJ/cm, however, toughness decreased obviously due to the coarsening of coarse-grained HAZ and formation of ferrite at bainite grainboundary of weld metal. On the other hand, cooling rates at PWHT did not effect on the changes in microstructure and mechanical properties. Even though tensile strength and impact toughness at all welding conditions of this study were above the minimum specification requirement, it was confirmed that heat input of 30.9kJ/cm was the optimum welding condition to improve welding performance by higher heat input.

Effect of Milling Time on the Microstructure and Phase Transformation Behaviors of Ni-B Powder During Mechanical Alloying Process (Ni-B 분말의 기계적 합금화 과정에서 밀링시간에 따른 미세조직과 상변화 거동)

  • Kim, Jung-Geun;Lee, Wook-Jin;Park, Sung-Kyun;Park, Ik-Min;Park, Yong-Ho
    • Journal of Powder Materials
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    • v.18 no.6
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    • pp.496-501
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    • 2011
  • In this study, the effect of milling time on the microstructure and phase transformation behaviors of Ni-12 wt.%B powders was investigated using vibratory ball milling process. X-ray diffraction patterns showed that the phase transformation of mixed Ni-B elemental powder occurred after 50 hours of milling, with a formation of nickel boride phases. Through the study of microstructures in mechanical alloying process, it was considered that ball milling strongly accelerates solid-state diffusions of the Ni and B atoms during mechanical alloying process. The results of X-ray photoelectron spectroscopy showed that most of B atoms in the powder were linked to Ni with a formation of nickel boride phases after 200 hours of milling. It was finally concluded that mechanical alloying using ball milling process is feasible to synthesize fine and uniform nickel boride powders.

Effect of Microstructure on the Machinability of Cast Iron (주철의 절삭성에 미치는 조직의 영향)

  • Park, Hee-Sang;Lee, Sang-Young;Kim, Jeong-Suk;Park, Ik-Min
    • Journal of Korea Foundry Society
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    • v.21 no.6
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    • pp.350-358
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    • 2001
  • The machinability of cast iron is closely related to its microstructural property. In this study, the effect of graphite mophology and matrix microstructure on machinability in several commercial cast irons(GC 25, GCD 45, GCD 50, GCD 70, GCD HSMo, GCMP) was investigated. To estimate the machinability, turning test was carried out under conditions of spindle speed 80m/min, depth of cut 0.25mm, feed 0.16mm/rev and cutting distance 1 km. Thrust force in turning test decreases in the order of GCMP, GCD 70, GCD 50, GC 25, GCD 45 and GCD HSMo. i.e. machinability increases in this order. The superior machinability of GC 25 is caused by flake type graphite which acts as chip braker and provides lubrication during machining. Consequently, soft ferritic cast irons exhibit superior machinability compared with pearlitic cast irons.

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Effect of Weld Elastic Modulus on Simulation of Stress Concentration and Fatigue Life for Boiler Vessel (ADINA & WINLIFE 활용한 압력용기 용접부 피로파괴 해석)

  • Choe, Byung Hak;Lee, Bum Gyu;Shim, Jong Heon;Park, Chan Sung;Kim, Jin Pyo;Park, Nam Gyu
    • Journal of Welding and Joining
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    • v.34 no.5
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    • pp.47-53
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    • 2016
  • The aim of this study is to consider effect of weld elastic modulus on simulations of stress concentration and fatigue life for pressure vessel. The investigations include analysis with ADINA and WINLIFE softwares for whole body model about using condition of the boiler vessel. Values of weld elastic modulus were divided by 5 steps in butt weld area of the boiler vessel body. The stress concentration of the butt weld more was increased in case of higher elastic modulus of weld area because of higher difference of material properties between matrix and weld. It was concluded that the fatigue lives were decreased along increasing stress concentration due to high elastic modulus of weld. The matrix microstructure was estimated as pearlitic structure of ${\alpha}$ ferrite and pearlite. And the microstructures of welds along 5 steps of elastic modulus were estimated as bainitic fine pearlite and martensite as increasing elastic modulus.

Effect of additional heat-treatment temperature on chemical, microstructural, mechanical, and electrical properties of commercial PAN-based carbon fibers

  • Cho, Dong-Hwan;Yoon, Sung-Bong;Cho, Chae-Wook;Park, Jong-Kyoo
    • Carbon letters
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    • v.12 no.4
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    • pp.223-228
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    • 2011
  • In this present work, the effect of additional heat-treatment (AHT) in the range from $1800^{\circ}C$ to $2400^{\circ}C$ on the chemical composition, morphology, microstructure, tensile properties, electrical resistivity, and thermal stability of commercial polyacrylonitrile (PAN)-based carbon fibers was explored by means of elemental analysis, electron microscopy, X-ray diffraction analysis, single fiber tensile testing, two-probe electrical resistivity testing, and thermogravimetric analysis (TGA). The characterization results were in agreement with each other. The results clearly demonstrated that AHTs up to $2400^{\circ}C$ played a significant role in further contributing not only to the enhancement of carbon content, fiber morphology, and tensile modulus, but also to the reduction of fiber diameter, inter-graphene layer distance, and electrical resistivity of "as-received" carbon fibers without AHT. The present study suggests that key properties of commercial PAN-based carbon fibers of an intermediate grade can be further improved by proprietarily adding heat-treatment without applying tension in a batch process.

Analysis of Toughening Mechanism of Ceramic Composites by Acoustic Emission (AE(Acoustic Emission)에 의한 세라믹 복합재료의 고인성화 기구 분석)

  • 장병국
    • Journal of the Korean Ceramic Society
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    • v.34 no.11
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    • pp.1129-1138
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    • 1997
  • Al2O3/20 vol%YAG composite containing equiaxed grains and Al2O3/20 vol%LaAl11O18 composite containing elongated grains were fabricated using Al2O3-Y2O3 composition and Al2O3-La2O3 composition, respectively, by hot-pressing. In order to investigate the influence of microstructural control of second phase on toughening effect of toughened ceramic composites, AE (acoustic emission) measurements have been coupled with fracture toughness experiments(SENB and SEPB method). A separation of the fracture toughness and analysis of toughening mechanism was possible using the AE technique. The fracture toughness of hot-pressed materials was estimated to be 3.2 MPam0.5 for monolithic alumina, 4.7 MPam0.5 for Al2O3/20 vol%YAG composite and 6.2 MPam0.5 for Al2O3/20 vol%LaAl11O18 composite. In monolithic Al2O3, toughening does not occur as a result of either microcracking or grain bridging, whereas, composites exhibit toughening effects by both microcracking in the frontal zone and gain bridging in the wake zone, resulting in an improvement of fracture toughness as compared with monolithic Al2O3. The fracture toughness of Al2O3/20 vol%LaAl11O18 composite is higher than that of Al2O3/20 vol%YAG composite. It may be attributed to the elongated microstructure of Al2O3/20 vol%LaAl11O18 composite, resulting relatively greater bridging effect.

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Effect of Al Amount on the Sintering Behavior and Mechanical Properties of Reaction Bonded Alumina (반응 소결 Alumina의 소결거동과 기계적 성질에 미치는 Al 첨가량의 영향)

  • 장복기;문종하;이종호
    • Journal of the Korean Ceramic Society
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    • v.34 no.5
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    • pp.519-527
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    • 1997
  • The effect of Al content and heating rate on the sintering behavior, microstructure, and mechanical properties of reaction bonded alumina (RBAO) was investigated. As the heating rate became slower a critical Al content which could be added to RBAO increased. The weight gain and linear shrinkage of RBAO containing of 55 vol% Al were 28% and 6.5%, respectively. The relative density of RBAO decreased from 96 to 94%, as the amount of Al increased from 15 to 55 vol%. The hardness of RBAO increased from 17.8 to 19.9 GPa and the bending strength enhanced from 370 to 570 MPa, as the amount of Al increased from 15 to 55 vol%. On the other hand, the wear rate of RBAO degraded from 6.7 to 3.39$\times$10-5 $\textrm{mm}^2$/kg and the fracture toughness decreased from 4.1 to 3.6 MPa.m1/2, as the amount of Al increased from 15 to 55 vol%. Fracture modes were shown to the mixed mode of inter/transgranular. However, transgranular fracture was dominant with increasing the content of Al.

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Effect of Ca/P Mole Ratio on the Sintering of Hydroxyapatite Powders Synthesized by the Wet Method and its Microstructure (습식법으로 제조한 수산화아파타이트 분말의 소결과 그 미세구조에 미치는 Ca/P몰비의 영향)

  • 신용규;정형진;김병호
    • Journal of the Korean Ceramic Society
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    • v.26 no.1
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    • pp.123-131
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    • 1989
  • Hydroxyapatite powders were syntehsized by the reaction of Ca(NO3)2.4H2O and (NH4)2HPO4 in aqueous solution. The effect of the Ca/P mole ratio in the starting solution on the sintering of the powders and its microstructure was studied. When the Ca/P mole ratio in the starting solution was 1.69, the relative density of the sintered bodies was more than 95%. The sinterability was decreased as the Ca/P mole ratio in the starting solution was increased (Ca/P mole ratio >1.67). Hydroxyapatite sintered bodies obtained from the Ca/P mole ratio=1.69 had very excellent bending strength. The best bending strength was obtained at 110$0^{\circ}C$ and its value was 1220kg/$\textrm{cm}^2$. The average grain size was 0.277${\mu}{\textrm}{m}$. Most of sintered bodies were almost shown 100% hydroxyapatite phase. However, in case of the Ca/P mole ratio=1.64 hydroxyapatite was decomposed to $\alpha$-whitlockite above 120$0^{\circ}C$.

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Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Gravity Cast Superchargers Housing Using A356 Aluminum Alloy (A356 알루미늄 합금 슈퍼차저 하우징의 미세조직과 기계적 성질에 미치는 열처리의 영향)

  • Kim, Dae-Hwan;Van, Guen-Ho;Seong, Bong-Hak;Cho, Bok-Hwan;Eom, Jeong-Pil;Park, Seong-Gi;Lim, Su-Gun
    • Journal of Korea Foundry Society
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    • v.32 no.5
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    • pp.231-240
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    • 2012
  • In present study, the effect of heat treatment on the microstructure and mechanical properties of the gravity cast superchargers housing using A356 alloy were investigated. In order to identify the characteristics of superchagers housing casting with heat treatment, Vickers hardness test, electrical conductivity test, opical and scanning electron microscopy were performed. And also, to investigate their mechanical properties, the T6 treated superchagers housing casting in optimum heat treatment condition were carried out tensile test using UTM (Universal Testing Machine).

Effects of Fiber Arrangement Direction on Microstructure Characteristics of NITE-SiC Composites (NITE-SiC 복합재료의 미세구조 특성에 미치는 섬유배열방향 영향)

  • Lee, Young-Ju;Yoon, Han-Ki;Park, Joon-Soo;Kohyama, A.
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2006.11a
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    • pp.158-161
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    • 2006
  • SiC materials have been extensively studied for high temperature components in advanced energy conversion system and advanced gas turbine. However, the brittle characteristics of SiC such as law fracture toughness and law strain-to fracture impose a severe limitation on the practical applications of SiC materials. SiC/SiC composites can be considered as a promising candidate in various structural materials, because of their good fracture toughness. In this composite system, the direction of SiC fiber will give an effect to the mechanical properties. It is therefore important to control a properdirection of SiC fiber for the fabrication of high performance SiC/SiC composites. In this study, unidirection and two dimension woven structures of SiC/SiC composites were prepared starting from Tyranno SA fiber. SiC matrix was obtained by nano-powder infiltration and transient eutectoid (NITE) process. Effect of microstructure and density on the sintering temperature in NITE-SiC/SiC composites are described and discussed with the fiber direction of unidirection and two dimension woven structures.

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