• Title/Summary/Keyword: Transformation Heat

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A Study on the Transformation Behaviors of a Multi-phase (Ferrite-Bainite-Martensite) in Ductile Cast Iron (구상흑연주철(球狀黑鉛鑄鐵)의 3상혼합조직(相混合組織)의 변태거동(變態擧動)에 관(關)한 연구(硏究))

  • Kim, Sug-Won;Kim, Dong-Keun;Yo, Seon-Kyung
    • Journal of Korea Foundry Society
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    • v.11 no.5
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    • pp.406-413
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    • 1991
  • Ductile cast iron(DCI) with a multi-phase(ferrite-bainite-martensite) structures was produced by various special heat treatment. Intercritical heat treatment(I. C.), intermediate heat treatment(I. M.) and step quenching(S. Q.) were used to strengthen and toughen the fracture initiation sites such as graphite-marix interfaces and eutectic cell boundaries in DCI. The purpose of this study was to investigate of DCI by the special heat treatment. (I. C., I. M., and S. Q.) At a result, bainite nucleation rate at higher temperature was higher than that of at lower temperature, and shapes of bainite and martensite became bar /spheroidal type with increase of isothermal transformation time.

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Transformation Hardening of High Power Laser (고출력 레이저에 의한 표면 경화)

  • Kim, J.D.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.1
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    • pp.24-31
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    • 1995
  • Heat flow equation and FEM have been used to calculate the hardening section of material in laser transformation hardening. SCM440 used as the diesel engine piston of vessel has been hardened by a $CO_2$ laser with the wavelength of $10.6{\mu}m$. The specimens were inclined from 0 to 70 degree to investigate the characteristics of laser hardening. The geometrical factor of heat flow equation affects the size of hardening area. The case width decreased with increasing travel speed and the case width increased with increasing inclined angle. Maximum case depth was achieved about 1.0mm and maximum hardness of laser hardened area was of 2.8 times than that of base metal. Experimental data show good agreement with the theoretical calculations for given laser hardening conditions.

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Effect of Isochronic Aging on Transformation Behavior in Ti-50.85at%Ni Alloy (Ti-50.85atNi 합금의 변태거동 및 형상기억특성 미치는 시효처리의 영향)

  • Kim, J.I.;Sung, J.H.;Kim, Y.H.;Lee, J.H.;Miyazaki, S.
    • Journal of the Korean Society for Heat Treatment
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    • v.22 no.2
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    • pp.101-107
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    • 2009
  • Effect of isochronic aging on transformation behavior of Ti-50.85at%Ni alloy were investigated by differential scanning calorimeter (DSC). The martensitic transformation temperature increases with increasing annealing temperature until reaching a maximum, and then decreases with further increasing annealing temperature. This can be rationalized by interaction between the distribution of $Ti_3Ni_4$ precipitates and Ni content in the matrix. The R-phase transformation temperature increases with increasing annealing temperature until reaching a maximum, and then decreases with a further increase of annealing temperature. This is attributed to the change of Ni content in the matrix caused by precipitation of $Ti_3Ni_4$. The occurrence of the multiple-stage martensitic and R-phase transformation is attributed to precipitation-induced inhomogeneity of the matrix, both in terms of composition and of internal stress fields.

Phase Transformation and Reversible Shape Memory Effect of Ti-Ni-Cu Alloys (Ti-Ni-Cu 합금의 상변태 및 가역형상기억효과)

  • Hong, S.W.;Lee, O.Y.;Kim, D.K.
    • Journal of the Korean Society for Heat Treatment
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    • v.5 no.3
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    • pp.149-156
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    • 1992
  • Transformation behavior and reversible shape memory effct of Ti-Ni-Cu alloys with various Cu content has been investigated by means of electrical resistivity measurement, differential scanning calorimetry. X-ray diffraction and strain gage sensor. The transformation sequence in Ti-Ni-Cu alloys substituted by Cu for Ni up to 5at.% occurs to $B2{\leftrightarrow}B19^{\prime}$ and it proceeds in two stages by addition of 10 at.%Cu. i.e. $B2{\leftrightarrow}B19{\leftrightarrow}B19^{\prime}$. But the content of Cu increases up to 20at.%, it has been transformed in one stage ; $B2{\leftrightarrow}B19$. The shape change of Ti-40Ni-10Cu alloy which was constrain aged in circular form bended in $B2{\leftrightarrow}B19$ transformation but it spreaded out in $B19{\leftrightarrow}B19^{\prime}$ transformation. The amount of reversible shape change (${\Delta}{\varepsilon}$) of Ti-47Ni-3Cu alloy constrain aged at $400^{\circ}C$ after solution treatment has a maximum value of about $5.6{\times}10^{-3}$, but that of cold rolled and constrain aged specimens exhibits a little value independent of Cu concentrations.

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Heat Treatment Effects on the Phase Evolutions of Partially Stabilized Grade Zirconia Plasma Sprayed Coatings

  • Park, Han-Shin;Kim, Hyung-Jun;Lee, Chang-Hee
    • Journal of the Korean institute of surface engineering
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    • v.34 no.5
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    • pp.486-493
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    • 2001
  • Partially stabilized zirconia (PSZ) is an attractive material for thermal barrier coating. Zirconia exists in three crystallographic phases: cubic, tetragonal and monoclinic. Especially, the phase transformation of tetragonal phase to monoclinic phase accompanies significant volume expansion, so this transition generally results in cracking and contributes to the failure of the TBC system. Both the plasma sprayed ZrO$_2$-8Y$_2$O$_3$ (YSZ) coat and the ZrO$_2$,-25CeO$_2$,-2.5Y$_2$O$_3$ (CYSZ) coat are isothermally heat -treated at 130$0^{\circ}C$ and 150$0^{\circ}C$ for 100hr and cooled at different cooling rates. The monoclinic phase is not discovered in all the CYSZ annealed at 130$0^{\circ}C$ and 150$0^{\circ}C$. In the 150$0^{\circ}C$ heat-treated specimens, the YSZ contains some monoclinic phase while none exists in the 130$0^{\circ}C$ heat-treated YSZ coat. For the YSZ, the different phase transformation behaviors at the two temperatures are due to the stabilizer concentration of high temperature phases and grain growth. For the YSZ with 150$0^{\circ}C$-100hr annealing, the amount of monoclinic phase increased with the slower cooling rate. The extra oxygen vacancy, thermal stress, and c to t'phase transformation might suppress the t to m martensitic phase transformation.

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Finite Element Analysis for Pearlite Transformation of Carbon Steel (탄소강의 펄라이트 변태에 대한 유한요소 해석)

  • 탄소강
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.9 no.3
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    • pp.69-75
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    • 2000
  • The object of the research is to estimate for pearlite structure of quenched carbon steels. The effects of temperature on physical properties metallic structures and the latent heat by phase transformation were considered. In this study a set of constitutive equations relevant to the analysis of thermo-elasto plastic materials with pearlite phase transformation during quenching process way presented on the basis of continuum thermo-dynamics. The iso-thermal transformation curve of the SM50C was formlated by cubic spline curve. The formulated equations of evolution in pearlite transformation was used for structure analysis. The volume fraction of pearlite was obtained from the results of calculated metallic structure by Finite element equation.

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An Analysis Finite Element for Elasto-Plastic Stresses Considerating Phase Transformation at the Quenching Process(I) - From Austenite to Pearlite - (퀜칭과정에서 상변태를 고려한 탄소성 열응력의 유한요소해석(I) -오스테나이트에서 퍼얼라이트로의 변태-)

  • Kim, Ok-Sam;Koo, Bon-Kwon
    • Journal of the Korean Society for Heat Treatment
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    • v.7 no.4
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    • pp.233-243
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    • 1994
  • Constitutive relation of thermoelasto-plastic material undergoing phase transformation during quenching process were developed on the basic of continuum thermodynamics. The metallic structure, temperature and residual stresses distributions were numerically calculated by the finite element technique. The metallic structure were defined by transformation from austenite to pearlite and characterized as a fuction of thermal history and mixture rule of phase. On the distribution of thermal stress along the radial direction, axial and tangential stresses are compressive in the surface, and tential in the inner part. Radial stress is tensile in the whole body. The reversion of residual stress takes plase at 11.5~15.5mm from the center.

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Residual Stress Analysis of Hot Rolled Strip (열연 강판의 잔류 응력 해석)

  • 구진모;김홍준;이재권;황상무
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.172-175
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    • 2003
  • Run-Out-Table is the region between EDT and CT. Hot killed strip is cooled by air and water in ROT. In this procedure, phase transformation and shape deformation occur due to temperature drop. Because of un-ideal cooling condition, deformation of strip and non-uniform phase distribution come into existence. This phenomenon affects the strip property and lead th the existence of residual stress. And it exerts effects on the Coiling process, Coil Cooling process, and Un-coiling process. Through these process, the residual stresses of strip are more larger and unbalance of these stresses become more severe. Finite element (FE) based models for the analysises of non-steady state heat transfer and elastoplastic deformation are described in this investigation. The analysises of thermodynamics and phase transformation kinetics are suggested also. Using the ROT simulation result coiling process and coil cooling process simulations are carried out.

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Effects of Annealing Treatments on Microstructure and Mechanical Property of co-sputtered TiNi Thin Film (Co-sputtering에 의해 증착된 TiNi 박막의 미세조직 및 기계적성질에 미치는 어닐링 열처리 효과)

  • Park, S.D.;Baeg, C.H.;Hong, J.W.
    • Journal of the Korean Society for Heat Treatment
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    • v.21 no.1
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    • pp.26-32
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    • 2008
  • Effects of annealing treatment on microstructure and mechanical property of co-sputtered TiNi thin films were studied. As-deposited films showed amorphous state. However, above annealing temperature of $500^{\circ}C$ martensite phase (B19'), precipitate phase ($Ti_2Ni$) and a small amount of parent phase ($B_2$) were present, and phase transformation behaviors were three multi-step phase transformations $B19^{\prime}{\rightarrow}B_2$ and $B_2{\rightarrow}R-phase$ and $R-phase{\rightarrow}B19^{\prime}$. Increase of martensite transformation temperature, increase of microhardness and Young's modulus of TiNi films annealed above $500^{\circ}C$ were discussed in terms of precipitate phase.

Effects of Alloy Additions and Annealing Parameters on Microstructure in Cold-Rolled Ultra Low Carbon Steels (극저탄소 냉연강판에서 합금원소 및 어닐링조건이 미세조직에 미치는 영향)

  • Jeong, Woo Chang
    • Journal of the Korean Society for Heat Treatment
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    • v.17 no.2
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    • pp.78-86
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    • 2004
  • Effects of the annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.