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

  • designing duplex ultrafine grained fe mn al c steels by tuning phase transformation and recrystallization kinetics
    Acta Materialia, 2017
    Co-Authors: Jiali Zhang, Dierk Raabe, Cemal Cem Tasan
    Abstract:

    Abstract A novel, lightweight Fe-25.7Mn-10.6Al-1.2C (wt.%) steel is designed by exploiting the concurrent progress of primary recrystallization and phase transformation, in order to produce an ultrafine-grained, duplex microstructure. The microstructure consists of recrystallized austenite grains surrounded by submicron-sized ferrite grains, and recovered austenite regions with preferential nano-κ-Carbide Precipitation. This partially recrystallized duplex microstructure demonstrates excellent strength-ductility combinations, e.g. a yield strength of 1251 MPa, an ultimate tensile strength of 1387 MPa, and a total elongation of 43%, arising from the composite response by virtue of diverging constituent strength and strain hardening behaviors.

  • carbon partitioning during quenching and partitioning heat treatment accompanied by Carbide Precipitation
    Acta Materialia, 2015
    Co-Authors: Yuki Toji, Goro Miyamoto, Dierk Raabe
    Abstract:

    Abstract Carbon partitioning from martensite into austenite in the quenching and partitioning (Q&P) process has been suggested to be controlled by the constrained carbon equilibrium (CCE) criterion. It defines an approach for predicting the carbon concentration in austenite under the condition that competing reactions such as Carbide formation and bainite transformation are suppressed. Carbide Precipitation in martensite is, however, often observed during the partitioning step, even in low-carbon steels as well as in high-carbon steels, even when containing a high amount of Si. Therefore, carbon partitioning from martensite into austenite is studied here, considering Carbide Precipitation in martensite. Carbon partitioning was investigated by means of a field-emission electron probe micro analysis (FE-EPMA) and atom probe tomography (APT), using 1.07 wt.% and 0.59 wt.% carbon steels with various martensite volume fractions. Carbon partitioning from martensite to austenite was clearly observed in all specimens, even though a considerable amount of Carbide precipitated inside the martensite. The austenite carbon concentration after the partitioning step was not influenced by either the martensite volume fraction or the bulk carbon content. A modified model for predicting the austenite carbon concentration after the partitioning step was proposed to explain the experimental results by assuming carbon equilibria between austenite, ferrite and cementite under a constrained condition.

M Pouranvari - One of the best experts on this subject based on the ideXlab platform.

  • welding metallurgy of stainless steels during resistance spot welding part i fusion zone
    Science and Technology of Welding and Joining, 2015
    Co-Authors: M Pouranvari, M Alizadehsh, S P H Marashi
    Abstract:

    AbstractWeldability is one of the key requirements for automotive materials. This two-part paper aims at understanding the metallurgical phenomena during resistance spot welding of stainless steels, as interesting candidates for automotive body in white. Part I addresses the phase transformations in the fusion zone of three types of stainless steels including austenitic, ferritic and duplex types. The solidification and solid state phenomena including columnar to equiaxed transition, ferrite–austenite post-solidification transformation, martensitic transformation and Carbide Precipitation are discussed. Particular attention is given to the effect of high cooling rate of resistance spot welding process on the ferrite–austenite transformation. Key factors controlling the hardness of the fusion zone are highlighted.

  • resistance spot welding of aisi 430 ferritic stainless steel phase transformations and mechanical properties
    Materials & Design, 2014
    Co-Authors: M Alizadehsh, S P H Marashi, M Pouranvari
    Abstract:

    Abstract The paper aims at investigating the process–microstructure–performance relationship in resistance spot welding of AISI 430 ferritic stainless steel. The phase transformations which occur during weld thermal cycle were analyzed in details, based on the physical metallurgy of welding of the ferritic stainless steels. It was found that the microstructure of the fusion zone and the heat affected zone is influenced by different phenomena including grain growth, martensite formation and Carbide Precipitation. The effects of welding cycle on the mechanical properties of the spot welds in terms of peak load, energy absorption and failure mode are discussed.

Shuai Hu - One of the best experts on this subject based on the ideXlab platform.

G. M. Michal - One of the best experts on this subject based on the ideXlab platform.

  • Carbide Precipitation in austenitic stainless steel carburized at low temperature
    Acta Materialia, 2007
    Co-Authors: F. Ernst, G. M. Michal, A H Heuer
    Abstract:

    Abstract Low-temperature gas-phase carburization can significantly improve the surface mechanical properties and corrosion resistance of austenitic stainless steel by generating a single-phase “case” with concentrations of interstitially dissolved carbon exceeding the equilibrium solubility limit by orders of magnitude. Upon prolonged treatment, however, Carbides (mostly χ, M5C2) can precipitate and degrade the properties. High-resolution and spatially resolved analytical transmission electron microscopy revealed the precise Carbide–austenite orientation relationship, a highly coherent interface, and that Precipitation only occurs when (i) the carbon-induced lattice expansion of the austenite has reached a level that substantially reduces volume-misfit stress and (ii) diffusional transport of nickel, chromium, and iron – enhanced by structural defects – can locally reduce the nickel concentration to the solubility limit of nickel in χ-Carbide.

  • colossal carbon supersaturation in austenitic stainless steels carburized at low temperature
    Acta Materialia, 2003
    Co-Authors: F. Ernst, G. M. Michal
    Abstract:

    A novel, low-temperature (470 °C) gas-phase carburization treatment, developed by the Swagelok Company, increases the surface hardness of 316 austenitic stainless steels from ≈200 to ≈1000 HV25 and improves the corrosion resistance. While normally the Precipitation of Carbides restricts the carbon concentration in the austenite of 316 steels to <0.015 at%, the Swagelok treatment generates a colossal supersaturation of up to 12 at% carbon in solid solution. Only upon extended treatment, does Carbide Precipitation eventually occur, but the colossal carbon supersaturation of the austenite is maintained. Unusual for austenitic stainless steels, the precipitates are Hagg Carbide (M5C2).

F. Ernst - One of the best experts on this subject based on the ideXlab platform.

  • Carbide Precipitation in austenitic stainless steel carburized at low temperature
    Acta Materialia, 2007
    Co-Authors: F. Ernst, G. M. Michal, A H Heuer
    Abstract:

    Abstract Low-temperature gas-phase carburization can significantly improve the surface mechanical properties and corrosion resistance of austenitic stainless steel by generating a single-phase “case” with concentrations of interstitially dissolved carbon exceeding the equilibrium solubility limit by orders of magnitude. Upon prolonged treatment, however, Carbides (mostly χ, M5C2) can precipitate and degrade the properties. High-resolution and spatially resolved analytical transmission electron microscopy revealed the precise Carbide–austenite orientation relationship, a highly coherent interface, and that Precipitation only occurs when (i) the carbon-induced lattice expansion of the austenite has reached a level that substantially reduces volume-misfit stress and (ii) diffusional transport of nickel, chromium, and iron – enhanced by structural defects – can locally reduce the nickel concentration to the solubility limit of nickel in χ-Carbide.

  • colossal carbon supersaturation in austenitic stainless steels carburized at low temperature
    Acta Materialia, 2003
    Co-Authors: F. Ernst, G. M. Michal
    Abstract:

    A novel, low-temperature (470 °C) gas-phase carburization treatment, developed by the Swagelok Company, increases the surface hardness of 316 austenitic stainless steels from ≈200 to ≈1000 HV25 and improves the corrosion resistance. While normally the Precipitation of Carbides restricts the carbon concentration in the austenite of 316 steels to <0.015 at%, the Swagelok treatment generates a colossal supersaturation of up to 12 at% carbon in solid solution. Only upon extended treatment, does Carbide Precipitation eventually occur, but the colossal carbon supersaturation of the austenite is maintained. Unusual for austenitic stainless steels, the precipitates are Hagg Carbide (M5C2).