• Title/Summary/Keyword: Fine Grained Steel

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Effect of Prior Deformation on the Sliding Wear of Ultra-fine Grained Ferrite-Martensite Dual Phase Steel (초기 소성변형이 초미세 결정립 페라이트-마르텐사이트 이상조직 탄소강의 건식 미끄럼마멸 특성에 미치는 영향)

  • Park, J.K.;Yi, S.K.;Shin, D.H.;Kim, Y.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.05a
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    • pp.521-524
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    • 2008
  • Effect of prior deformation on the sliding wear of the ultra-fine grained (UFG) ferrite-martensite dual phase (DP) steel was investigated. The UFG DP steel was fabricated by the ECAP and subsequent intercritical annealing. The steel was cold rolled before the wear test, and the effect of the prior deformation on the wear was examined. The wear tests were carried out at various loads against a bearing steel ball. The wear rate of the UFG DP steel that did not experience the prior deformation was higher than that of the coarse-grained (CG) DP steel, because of more severe surface shear deformation. The wear rate of the specimens with prior deformation was much higher than that of the specimen without prior deformation. The deformed CG DP specimen showed higher rate than the deformed UFG DP specimen, and the rate-variation of the CG DP steel was much bigger under the same test condition.

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Mechanical Property of Ultra Fine Grained Steel Weld by Hybrid Welding (하이브리드 용접에 의한 세립강 용접부의 기계적 성질에 관한 연구)

  • Dong, H.W.;Ahn, Y.S.
    • Journal of Power System Engineering
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    • v.15 no.1
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    • pp.45-50
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    • 2011
  • The effect of Mn and Ti contents in filler wire on the microstructure and mechanical property of weld metal has been investigated after hybrid welding with ultra fine grained (UFG) steel. The microstructure and distribution of alloy compositions at the top region of weld zone were quite different with those at the bottom region after hybrid welding. The bottom region of weld zone contained higher Mn and Ti contents, and consequently the hardness of bottom region was higher than that of top region. With the increase of Mn and Ti contents in filler wire, the volume percent of acicular ferrite in weld metal decreased, and the weld zone showed higher hardness and better impact property.

Microstructures and Mechanical Properties of Friction Stir Welded High Strength Steels far Shipbuilding (선급용 고장력강 FSW접합부의 미세조직 및 기계적 성질)

  • 장웅성;최기용
    • Journal of Welding and Joining
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    • v.20 no.3
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    • pp.67-73
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    • 2002
  • In an attempt to evaluate the feasibility of friction stir welding(FSW) for joining carbon steels, microstructures and mechanical properties of friction stir welded carbon steels with different grain structures were investigated. In comparison of O-type stir zone(SZ) appeared in various aluminium alloys, configuration of SZ in friction stir welded carbon steels displayed U-type. Plastically deformed pearlite band structure was identified to surround the SZ, indicating the existence of so-called thermo-mechanically affected zone(TMAZ). However, the TMAZ of carbon steels was much narrower than that of Al alloys. The microstructures of both stir zone and TMAZ revealed bainite matrix in a conventional carbon steel for shipbuilding, while, in the same region, ferrite matrix microstructures were formed in a low carbon fine grained steel. The conventional carbon steel showed superior stirring workability to that of the fine grained carbon steel. The yield and tensile strength of the friction stir welded joints were comparable to those of the base metals, and the elongation in welded joints demonstrated excellent ductility. Absorbed energy in SZ of the fine grained carbon steel was ten times higher than that obtained from conventional submerged arc weld metal of the same steel. Based on these results, the application FSW to carbon steels was found to be feasible.

Mechanical properties of fine grained steel weldments formed with low heat input (세립강 저입열 용접부의 기계적 성질)

  • 윤중근;박태동;김광수;박영수
    • Proceedings of the KWS Conference
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    • 2003.11a
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    • pp.227-229
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    • 2003
  • Low heat input welding methods have been investigated in order to minimize the HAZ softening of the 600MPa grade fine grained steel weldment. The welding processes of interest were a high speed FCA welding with a multi-torch welding system, laser welding with filler feeding and hybrid laser welding. No HAZ softening was found for all the weldments formed with low heat input less than 10kJ/cm. Tensile strength of the weldments was high enough to satisfy the required value. Impact toughness of the weldments was also good even at -20$^{\circ}C$.

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Sliding Wear Mechanism of Ultra-Fine Grained Low Carbon Dual Phase Steel as n Function of Applied Load (결정립 미세화에 따른 이상조직 탄소강의 하중에 따른 마멸 기구)

  • Yu, H.S.;Yi, S.K.;Shin, D.H.;Kim, Y.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2007.05a
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    • pp.421-424
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    • 2007
  • Dry sliding wear behavior of ultra-fine grained (UFG) plain low carbon dual phase steel, of which microstructure consists of hard martensite in a ductile ferrite matrix, has been investigated. The wear characteristics of the UFG dual phase steel was compared with that of a coarse grained dual phase steel under various applied load conditions. Dry sliding wear test were carried out using a pin-on-disk type tester at various loads of 1N to 100N under a constant sliding speed condition of 0.20m/s against an AISI 52100 bearing steel ball at room temperature. The sliding distance was fixed as 1000m for all wear tests. The wear rate was calculated by dividing the weight loss, measured to the accuracy of 10-5g by the specific gravity and sliding distance. The worn surfaces and wear debris were analyzed by SEM, EDS and profilometer. Micro-vickers hardness of the cross section of worn surfaces were conducted to analyze strain hardening underneath the contact surfaces. The wear mechanism of the UFG dual phase steel was investigated with emphasis on the unstable nature of the grain boundaries of the UFG microstructure.

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Sliding Wear Mechanism of Ultra-Fine Grained Low Carbon Dual Phase Steel as a Function of Applied Load (경정립 미세화에 따른 이상조직 탄소강의 하중에 따른 마멸기구)

  • Yu, H.S.;Yi, S.K.;Shin, D.H.;Kim, Y.S.
    • Transactions of Materials Processing
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    • v.16 no.4 s.94
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    • pp.299-303
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    • 2007
  • Dry sliding wear behavior of ultra-fine grained(UFG) plain low carbon dual phase steel, of which microstructure consists of hard martensite in a ductile ferrite matrix, has been investigated. The wear characteristics of the UFG dual phase steel was compared with that of a coarse grained dual phase steel under various applied load conditions. Dry sliding wear test were carried out using a pin-on-disk type tester at various loads of 1N to 100N under a constant sliding speed condition of 0.20m/s against an AISI 52100 bearing steel ball at room temperature. The sliding distance was fixed as 1000m for all wear tests. The wear rate was calculated by dividing the weight loss, measured to the accuracy of 10-5g by the specific gravity and sliding distance. The worn surfaces and wear debris were analyzed by SEM, EDS and profilometer. Micro-vickers hardness of the cross section of worn surfaces were conducted to analyze strain hardening underneath the contact surfaces. The wear mechanism of the UFG dual phase steel was investigated with emphasis on the unstable nature of the grain boundaries of the UFG microstructure.

Microstructure Evolution of UFG Steel Weld by Hybrid and Laser Welding (하이브리드 용접과 레이저 용접에 의한 세립강 용접부의 미세조직변화에 관한 연구)

  • Dong, H.W.;Lee, M.Y.;Ahn, Y.S.
    • Journal of Power System Engineering
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    • v.14 no.3
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    • pp.58-63
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    • 2010
  • A laser beam welding and an electric arc welding were combined, and the positive points of each welding method are drawn such as high speed, low thermal load, deep penetration, and high productivity. The fiber laser-MIG conjugated welding. namely the hybrid welding has been studied mainly for the automation industry of a pipeline welding. In this study, the MIG welding was combined with a fiber laser welding to make up the hybrid welding. The weld shapes, microstructures and mechanical properties for weld zones after the hybrid welding or only fiber laser welding were investigated on the 700 MPa grade Ultra Fine Grained(UFG) high strength steel. The amount of acicular ferrite in weld metals and HAZ(heat affected zone) was observed larger after hybrid welding compared with after only laser welding. The Vickers hardness of the top area of the fusion zone after fiber laser welding was higher compared with after hybrid welding.

Toward Improving the Dynamic Deformation Properties of Metallic Materials via Role of Microstructure Factor (미세조직 인자의 영향을 고려한 금속 소재의 동적변형 특성 향상에 관한 연구)

  • Kim, Y.G.;Hwang, B.;Lee, D.G.;Ko, Y.G.;Lee, S.
    • Transactions of Materials Processing
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    • v.30 no.5
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    • pp.247-254
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    • 2021
  • This study reviews dynamic deformation behavior of ultra-fine-grained Al alloys, ultra-fine-grained conventional low carbon steel and dual phase steel and Zr-based amorphous alloys. Dynamic tests were conducted using a Kolsky bar then the test data was analyzed in relation to resultant microstructures, mechanical properties and propensity of adiabatic shear band. In addition, deformed microstructures and fracture surfaces were used to investigate the behavior of both the dynamic deformation and fracture, and adiabatic shear banding. As a result, increasing microstructural homogeneity, strain hardenability and forming multiple shear bands could be a better way to increase the fracture resistance under dynamic loading as the formation of adiabatic shear bands was reduced or prevented.