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Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.

  • enhanced superplasticity in an al alloyed multicomponent mn si cr c steel
    Acta Materialia, 2014
    Co-Authors: Han Zhang, Konda Gokuldoss Pradeep, Suvendu Mandal, Dirk Ponge, Pyuckpa Choi, Cemal Cem Tasan, Dierk Raabe
    Abstract:

    Abstract Excellent superplasticity (elongation ∼720%) is observed in a novel multi-component (Mn–S–Cr–Al alloyed) ultrahigh carbon steel during tensile testing at a strain rate of 2 × 10 −3  s −1 and a temperature of 1053 K (just above the equilibrium austenite–Pearlite Transformation temperature). In order to understand superplasticity in this material and its strong Al dependence, the deformation-induced microstructure evolution is characterized at various length scales down to atomic resolution, using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy-dispersive X-ray spectroscopy and atom probe tomography. The results reveal that 1 wt.% Al addition influences various microprocesses during deformation, e.g. it impedes Ostwald ripening of carbides, carbide dissolution, austenite nucleation and growth and void growth. As a result, the size of the austenite grains and voids remains relatively fine (

  • enhanced superplasticity in an al alloyed multicomponent mn si cr c steel
    Acta Materialia, 2014
    Co-Authors: Han Zhang, Konda Gokuldoss Pradeep, Suvendu Mandal, Dirk Ponge, Pyuckpa Choi, Cemal Cem Tasan, Dierk Raabe
    Abstract:

    Abstract Excellent superplasticity (elongation ∼720%) is observed in a novel multi-component (Mn–S–Cr–Al alloyed) ultrahigh carbon steel during tensile testing at a strain rate of 2 × 10 −3  s −1 and a temperature of 1053 K (just above the equilibrium austenite–Pearlite Transformation temperature). In order to understand superplasticity in this material and its strong Al dependence, the deformation-induced microstructure evolution is characterized at various length scales down to atomic resolution, using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy-dispersive X-ray spectroscopy and atom probe tomography. The results reveal that 1 wt.% Al addition influences various microprocesses during deformation, e.g. it impedes Ostwald ripening of carbides, carbide dissolution, austenite nucleation and growth and void growth. As a result, the size of the austenite grains and voids remains relatively fine (

S. Van Der Zwaag - One of the best experts on this subject based on the ideXlab platform.

  • High-temperature magnetisation measurements on the Pearlite Transformation kinetics in nearly eutectoid steel
    Journal of Magnetism and Magnetic Materials, 2004
    Co-Authors: N.h. Van Dijk, S.e. Offerman, J.c.p. Klaasse, Jilt Sietsma, S. Van Der Zwaag
    Abstract:

    Abstract The isothermal Transformation kinetics of the austenite to Pearlite Transformation in (nearly) eutectoid steel was studied by in situ magnetisation measurements at high temperatures. In eutectoid steel the high temperature austenite (γ-Fe) phase decomposes into Pearlite, which consists of a lamellar structure of ferrite (α-Fe) and cementite (Fe 3 C). Below the Curie temperature of ferrite T C =1043 K the ferrite phase fraction can be probed by the magnetisation measurements. For our nearly eutectoid steel not only Pearlite but also a small fraction of pro-eutectoid ferrite is formed. The Transformation kinetics of the Pearlite and the pro-eutectoid ferrite is studied by magnetisation measurements as a function of the isothermal Transformation temperature and compared with the results from additional dilatometry measurements. The Transformation kinetics was found to vary over four orders of magnitude over the range of Transformation temperatures and was compared with model predictions.

  • In-situ study of Pearlite nucleation and growth during isothermal austenite decomposition in nearly eutectoid steel
    Acta Materialia, 2003
    Co-Authors: S.e. Offerman, N.h. Van Dijk, Jilt Sietsma, L.j.g.w. Van Wilderen, M.th. Rekveldt, S. Van Der Zwaag
    Abstract:

    The evolution of the microstructure during the isothermal austenite/Pearlite Transformation in a nearly eutectoid steel was studied by the three-dimensional neutron depolarization technique, which simultaneously provides information about the Pearlite fraction, the average Pearlite colony size, and the spatial distribution of the Pearlite colonies during the Transformation. The in-situ measurements show that the Pearlite nucleation rate increases linearly with time with a temperature-dependent slope. The in-situ measured average Pearlite growth rate is accurately described by the Zener-Hillert theory, which assumes that volume diffusion of carbon is the rate-controlling mechanism. The measured overall Transformation rate deviates from the predictions of the theory developed by Kolmogorov, Johnson, Mehl, and Avrami.

Tadashi Furuhara - One of the best experts on this subject based on the ideXlab platform.

  • volume fractions of proeutectoid ferrite Pearlite and their dependence on prior austenite grain size in hypoeutectoid fe mn c alloys
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2013
    Co-Authors: Goro Miyamoto, Zhenqing Liu, Zhigang Yang, Tadashi Furuhara
    Abstract:

    It has been generally believed that Pearlite Transformation in hypoeutectoid steels starts when the average carbon concentration in untransformed austenite reaches the Acm line after the formation of proeutectoid ferrite. To test this concept experimentally, volume fractions of proeutectoid ferrite/Pearlite and carbon contents in the austenite being transformed into Pearlite were measured for the Fe-2Mn-0.3C alloy isothermally transformed in the temperature range 848 K to 898 K (575 °C to 625 °C). It was found that lamellar Pearlite can form even when the average carbon content in untransformed austenite is much lower than the Acm line. This peculiar observation is probably due to the two-dimensional diffusion of carbon, i.e., parallel to and normal to the austenite/Pearlite interface, which enables lamellar cementite to grow continuously by supplying carbon atoms to its growth front. This results in proeutectoid ferrite fractions with respect to Pearlite being much lower than those predicted by the lever rule. With decreasing prior austenite grain size, proeutectoid ferrite fractions with respect to Pearlite were found to increase, but the thickness of proeutectoid ferrite was constant within the range of grain size investigated. This is due to the existence of the critical α/γ interface velocity only below which Pearlite (actually cementite) can be nucleated at the migrating α/γ interface. Furthermore, the upper limit temperatures for Pearlite formation in the Fe-1Mn-0.33C and Fe-2Mn-0.3C alloys were found to be well between the PLE/NPLE and PE Ae1 temperatures.

  • Interphase Boundary Precipitation of VC Accompanying Ferrite and Pearlite Transformation in Medium Carbon Steels
    Solid State Phenomena, 2011
    Co-Authors: Goro Miyamoto, Poorganji Behrang, Tadashi Furuhara
    Abstract:

    Demands for medium carbon steels with high strength used for forging parts in automobile have been increasing. V addition to such steels leads to interphase boundary precipitation (IBP) of VC and thus an increase of strength. However, mechanism and strengthening effect of IBP have not been clarified in detail. In this study, precipitation of VC accompanying ferrite and Pearlite Transformations and its effect on hardness have been examined in medium carbon steels microalloyed with 0.3%V. Specimens transformed in a temperature range between 873 and 973K consist of Pearlite and small amount of proeutectoid ferrite. Hardness increase by the V addition becomes larger by lowering Transformation temperature at these temperatures. Meanwhile the alloying effect of V on the hardness remarkably decreases at 823K where bainite Transformation takes place partly. TEM characterization has revealed that VC are precipitated in both of proeutectoid and pearlitic ferrites in the manner of fine rows parallel to the austenite / ferrite interphase boundary. The size of VC decreases and its number density increases by lowering Transformation temperature, corresponding to the larger hardness increase. Orientation relationship analyses between ferrite and austenite in the V-added specimen based of EBSD measurements reveals that proeutectoid ferrite grows preferentially towards an austenite grain with which ferrite does not hold a specific orientation relationship, indicating that classical ledge mechanism does not play a role for interphase boundary precipitation of VC in this alloy.

  • kinetics and crystallography of intragranular Pearlite Transformation nucleated at mns vc complex precipitates in hypereutectoid fe mn c alloys
    Isij International, 2002
    Co-Authors: Zhenghong Guo, Tadashi Furuhara, N. Kimura, S. Tagashira, Tadashi Maki
    Abstract:

    Kinetics and crystallography of intragranular Pearlite nucleated at the surface of (MnS+VC) complex precipitate were studied in hypereutectoid Fe-Mn-C steels. The incoherent MnS embedded in the austenite does not act as a strong nucleation site of Pearlite unless the Transformation time is prolonged. The intragranular Pearlite Transformation is promoted effectively by the addition of vanadium (V). EPMA analysis showed that the intragranular Pearlite nucleates on the (MnS+VC) complex precipitate in the V-added alloy. As the Transformation temperature decreases, the intragranular Pearlite formation occurs more frequently. A single intragranular Pearlite is composed of several colonies, indicating that multiple Pearlite colonies nucleate on a (MnS+VC) complex precipitate for intragranular Pearlite Transformation. There is no specific orientation relationship (OR) between ferrite in intragranular Pearlite and austenite matrix while there is a specific OR (Pitsch-Petch OR) between pearlitic ferrite and cementite in the intragranular Pearlite.

  • the influence of mns vc complex precipitate on the crystallography of intergranular Pearlite Transformation in fe mn c hypereutectoid alloys
    Scripta Materialia, 2001
    Co-Authors: Zhenghong Guo, Tadashi Furuhara, Tadashi Maki
    Abstract:

    Abstract Vanadium addition to a hypereutectoid Fe–Mn–C alloy decreases the proportion of specific orientation relationship between ferrite in intergranular Pearlite and the adjacent austenite grains because many Pearlite grains nucleate at (MnS+VC) or VC precipitates formed at austenite grain boundaries, whereas Pearlite grows from the proeutectoid cementite at austenite grain boundaries in the vanadium-free alloy.

Tadashi Maki - One of the best experts on this subject based on the ideXlab platform.

Han Zhang - One of the best experts on this subject based on the ideXlab platform.

  • enhanced superplasticity in an al alloyed multicomponent mn si cr c steel
    Acta Materialia, 2014
    Co-Authors: Han Zhang, Konda Gokuldoss Pradeep, Suvendu Mandal, Dirk Ponge, Pyuckpa Choi, Cemal Cem Tasan, Dierk Raabe
    Abstract:

    Abstract Excellent superplasticity (elongation ∼720%) is observed in a novel multi-component (Mn–S–Cr–Al alloyed) ultrahigh carbon steel during tensile testing at a strain rate of 2 × 10 −3  s −1 and a temperature of 1053 K (just above the equilibrium austenite–Pearlite Transformation temperature). In order to understand superplasticity in this material and its strong Al dependence, the deformation-induced microstructure evolution is characterized at various length scales down to atomic resolution, using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy-dispersive X-ray spectroscopy and atom probe tomography. The results reveal that 1 wt.% Al addition influences various microprocesses during deformation, e.g. it impedes Ostwald ripening of carbides, carbide dissolution, austenite nucleation and growth and void growth. As a result, the size of the austenite grains and voids remains relatively fine (

  • enhanced superplasticity in an al alloyed multicomponent mn si cr c steel
    Acta Materialia, 2014
    Co-Authors: Han Zhang, Konda Gokuldoss Pradeep, Suvendu Mandal, Dirk Ponge, Pyuckpa Choi, Cemal Cem Tasan, Dierk Raabe
    Abstract:

    Abstract Excellent superplasticity (elongation ∼720%) is observed in a novel multi-component (Mn–S–Cr–Al alloyed) ultrahigh carbon steel during tensile testing at a strain rate of 2 × 10 −3  s −1 and a temperature of 1053 K (just above the equilibrium austenite–Pearlite Transformation temperature). In order to understand superplasticity in this material and its strong Al dependence, the deformation-induced microstructure evolution is characterized at various length scales down to atomic resolution, using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy-dispersive X-ray spectroscopy and atom probe tomography. The results reveal that 1 wt.% Al addition influences various microprocesses during deformation, e.g. it impedes Ostwald ripening of carbides, carbide dissolution, austenite nucleation and growth and void growth. As a result, the size of the austenite grains and voids remains relatively fine (