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Pascal Jacques - One of the best experts on this subject based on the ideXlab platform.

  • Beneficial influence of an intercritically rolled recovered Ferritic Matrix on the mechanical properties of TRIP-assisted multiphase steels
    Materials Science and Engineering: A, 2015
    Co-Authors: Stéphane Godet, Pascal Jacques
    Abstract:

    Abstract The present study deals with the microstructure and mechanical properties of intercritically rolled TRIP-assisted multiphase steels. It is shown that the occurrence of the TRIP effect in a recovered Ferritic Matrix brings about an improved strength–ductility balance with respect to a fully recrystallised ferrite Matrix. On the other hand, the intercritical deformation does not influence the austenite transformation rate during straining at room temperature. The improvement of the mechanical properties results from the interactions between the transformation strain and the recovered ferrite.

  • on the measurement of the nanohardness of the constitutive phases of trip assisted multiphase steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002
    Co-Authors: Quentin Furnemont, Pascal Jacques, M Kempf, Mathias Goken, Francis Delannay
    Abstract:

    The nanohardness of the phases present in the microstructure of two TRIP (for TRansformation Induced Plasticity)-assisted multiphase steels differing by their silicon content was measured by nanoindentation in an atomic force microscope. It is observed that the softest phase in both steels is the Ferritic Matrix, followed by bainite, austenite and martensite. It is also shown that the silicon content of the steel grades is responsible for an increase of the hardness of the Ferritic Matrix due to solid solution strengthening. Finally, the influence of the preparation mode of the surface prior to the nanoindentation measurements has been investigated. An electropolishing stage after mechanical polishing is acceptable to allow valuable nanohardness measurements. (C) 2002 Elsevier Science B.V. All rights reserved.

  • Effect of the work-hardening of retained austenite on the martensitic transformation in a TRIP-aided steel
    2000
    Co-Authors: Stéphane Godet, Pascal Jacques, Francis Delannay
    Abstract:

    This study deals with the hot deformation of TRIP-assisted multiphase steels. These steels consist typically of bainite and retained austenite grains dispersed in a Ferritic Matrix. The austenite, which is metastable at room temperature, transforms to martensite during straining, bringing about the TRIP effect, which improves the strength-ductility balance of these steels. This work investigates the effect of a prior deformation in the intercritical temperature range on the mechanical properties and work hardening behaviour of these TRIP-assisted multiphase steels. Several deformation levels in the ferrite-austenite domain were applied during the thermo-mechanical scheme. Results show that work-hardening is strongly enhanced when the specimens were sufficiently deformed in the intercritical temperature range. This study also shows that the beneficial influence of the prior deformation is more related to the TRIP phenomenon than to the strain-hardening of the Ferritic Matrix. These experiments prove that a displacive transformation such as the martensitic transformation is highly influenced by the dislocation density within the parent phase.

Francis Delannay - One of the best experts on this subject based on the ideXlab platform.

  • on the measurement of the nanohardness of the constitutive phases of trip assisted multiphase steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002
    Co-Authors: Quentin Furnemont, Pascal Jacques, M Kempf, Mathias Goken, Francis Delannay
    Abstract:

    The nanohardness of the phases present in the microstructure of two TRIP (for TRansformation Induced Plasticity)-assisted multiphase steels differing by their silicon content was measured by nanoindentation in an atomic force microscope. It is observed that the softest phase in both steels is the Ferritic Matrix, followed by bainite, austenite and martensite. It is also shown that the silicon content of the steel grades is responsible for an increase of the hardness of the Ferritic Matrix due to solid solution strengthening. Finally, the influence of the preparation mode of the surface prior to the nanoindentation measurements has been investigated. An electropolishing stage after mechanical polishing is acceptable to allow valuable nanohardness measurements. (C) 2002 Elsevier Science B.V. All rights reserved.

  • Effect of the work-hardening of retained austenite on the martensitic transformation in a TRIP-aided steel
    2000
    Co-Authors: Stéphane Godet, Pascal Jacques, Francis Delannay
    Abstract:

    This study deals with the hot deformation of TRIP-assisted multiphase steels. These steels consist typically of bainite and retained austenite grains dispersed in a Ferritic Matrix. The austenite, which is metastable at room temperature, transforms to martensite during straining, bringing about the TRIP effect, which improves the strength-ductility balance of these steels. This work investigates the effect of a prior deformation in the intercritical temperature range on the mechanical properties and work hardening behaviour of these TRIP-assisted multiphase steels. Several deformation levels in the ferrite-austenite domain were applied during the thermo-mechanical scheme. Results show that work-hardening is strongly enhanced when the specimens were sufficiently deformed in the intercritical temperature range. This study also shows that the beneficial influence of the prior deformation is more related to the TRIP phenomenon than to the strain-hardening of the Ferritic Matrix. These experiments prove that a displacive transformation such as the martensitic transformation is highly influenced by the dislocation density within the parent phase.

A. Redjaïmia - One of the best experts on this subject based on the ideXlab platform.

  • A proper assessment of Tem diffraction patterns originating from CrN nitrides in a Ferritic Matrix
    Materials Characterization, 2018
    Co-Authors: Olivier Skiba, A. Redjaïmia, Jacky Dulcy, Jaafar Ghanbaja, Grégory Marcos, Nancy Caldeira-meulnotte, Thierry Czerwiec
    Abstract:

    Abstract Upon nitriding of a Fe-3%Cr alloy at 550 °C during 48 h at a nitriding potential KN = 5 atm−1/2, finely dispersed CrN grains precipitate. Considering that the nitrides developing within the nitrided layer adopt a cubic, rock-salt structure, Transmission Electron Microscopy (TEM) investigations revealed the Bain orientation relationships (also called Baker-Nutting) existing between the Matrix and the precipitates. Given the latter and the structures of both ferrite (bcc) and nitrides (fcc), we have shown that group theory predicts the existence of three nitrides variants, orthogonal to each other, developing in ferrite along the 〈001〉α-Fe directions, which is in agreement with our experimental observations. The nitrides adopt a very thin platelet-like morphology, energetically corresponding to an absolute extremum. Diffraction patterns obtained along the [001]α-Fe result from the simultaneous diffraction of the Ferritic Matrix and the three nitrides variants. The platelet-like nitride precipitates give birth to diffuse intensity lines, originating from the two families developing along the (100) and (010) ferrite planes, as well as possible appearance of additional reflections, located at the forbidden positions {100}α-Fe and {110}CrN of the remaining variant, driving the interpretation of such diffraction patterns complicated. Foil thickness has proven to play a key role in the occurrence of this phenomenon. When the geometric diffraction conditions are favorable (i.e. very thin foil along the zone axis and very fine precipitates platelets), TEM analysis permitted to attribute these extra reflections to the nodes located in the first layer of the third variant's reciprocal space.

  • Morphology, crystallography and defects of the intermetallic χ-phase precipitated in a duplex (δ + γ) stainless steel
    Journal of Materials Science, 2004
    Co-Authors: A. Redjaïmia, A. Proult, Patricia Donnadieu, J. P. Morniroli
    Abstract:

    The Ferritic Matrix in the Fe-22Cr-5Ni-3Mo-0.03C Ferritic-austenic duplex stainless steel undergoes a variety of decomposition processes when aged in the temperature range 650–750°C. These processes involve the precipitation of the austenite and of the σ and χ Frank-Kasper phases. The intermetallic χ-phase is found at both the grains boundaries (homo and heterophase interfaces) and inside the Ferritic grains where it adopts an unexpected hexagonal shape. At the early stage of its precipitation, it nucleates at the δ/γ and δ/σheterophase interfaces and then grows by expanding exclusively in the Ferritic Matrix. This study is basically focused on this intermetallic χ-phase. The crystal structure and the chemical composition are respectively studied by electron diffraction and energy dispersive X-ray spectroscopy. The χ-phase exhibits rational orientation relationships with the austenite and the σ-phase with which it is in contact and an invariably cube-on-cube orientation relationship with the Ferritic Matrix into which it grows. Based on the orientation relationship, the morphology and the number of variants of this χ-phase are understood in terms of the group theory. The planar defects present in a large density in the χ-phase, are roughly parallel to {0 1 1}_χ//{0 1 1}_δ. The fault vectors are determined as: $$\frac{1}{3}$$ 〈110〉_χ and $$\frac{1}{4}$$ 〈111〉_χ, the latter corresponding for a bcc structure to a π phase shift, the defects can be simply described as π boundaries. Based on the obtained results, a structural proximity between the χ-phase and a super-cell derived from the Ferritic Matrix has been brought to light. This super-cell is described as a stacking of corrugated and planar layers obeying the following parallelism {0 1 1}_χ//{0 1 1}_δ. Indeed this super-cell approach provides an interpretation for several microstructural features such as the χ/δ interface plane, the planar defects in the χ-phase and their related fault vectors. It has been also stated that Mo is an efficient χ-phase forming element. Upon these considerations a detailed characterization provided valuable insights into the precipitation mechanism associated with the χ-phase formation.

  • Morphology, crystallography and defects of the intermetallic χ-phase precipitated in a duplex (δ + γ) stainless steel
    Journal of Materials Science, 2004
    Co-Authors: A. Redjaïmia, A. Proult, Patricia Donnadieu, J. P. Morniroli
    Abstract:

    The Ferritic Matrix in the Fe-22Cr-5Ni-3Mo-0.03C Ferritic-austenic duplex stainless steel undergoes a variety of decomposition processes when aged in the temperature range 650–750°C. These processes involve the precipitation of the austenite and of the σ and χ Frank-Kasper phases. The intermetallic χ-phase is found at both the grains boundaries (homo and heterophase interfaces) and inside the Ferritic grains where it adopts an unexpected hexagonal shape. At the early stage of its precipitation, it nucleates at the δ/γ and δ/σheterophase interfaces and then grows by expanding exclusively in the Ferritic Matrix. This study is basically focused on this intermetallic χ-phase. The crystal structure and the chemical composition are respectively studied by electron diffraction and energy dispersive X-ray spectroscopy. The χ-phase exhibits rational orientation relationships with the austenite and the σ-phase with which it is in contact and an invariably cube-on-cube orientation relationship with the Ferritic Matrix into which it grows. Based on the orientation relationship, the morphology and the number of variants of this χ-phase are understood in terms of the group theory. The planar defects present in a large density in the χ-phase, are roughly parallel to {0 1 1}χ//{0 1 1}δ. The fault vectors are determined as: \(\frac{1}{3}\)〈110〉χ and \(\frac{1}{4}\)〈111〉χ, the latter corresponding for a bcc structure to a π phase shift, the defects can be simply described as π boundaries. Based on the obtained results, a structural proximity between the χ-phase and a super-cell derived from the Ferritic Matrix has been brought to light. This super-cell is described as a stacking of corrugated and planar layers obeying the following parallelism {0 1 1}χ//{0 1 1}δ. Indeed this super-cell approach provides an interpretation for several microstructural features such as the χ/δ interface plane, the planar defects in the χ-phase and their related fault vectors.

  • Identification and characterization of a novel Mn-N nitride formed in Fe-Mn-N alloy
    Journal of Applied Crystallography, 2003
    Co-Authors: Mohamed Gouné, A. Redjaïmia, Thierry Belmonte, H. Michel
    Abstract:

    An unexpected phase, formed throughout the Ferritic Matrix of an Fe–Mn (1.62 wt% Mn) alloy during a nitriding treatment at 843 K for 8 h, is analysed. This new phase, labelled θ′, is a metastable Mn nitride. It adopts the form of plates, with length 200 nm and width 20 nm. Its crystal structure is established by electron microdiffraction in conjunction with group-theory analysis. This nitride crystallizes in the tetragonal system and belongs to the space group P 42/m 2/m 2/c with the following lattice parameters: a_{\theta'} = 2.876 A and c_{\theta'} = 5.752 A. The θ′-phase crystal lattice is oriented with respect to the surrounding Ferritic Matrix according to the cube-on-cube orientation relationship, namely: (100)_{\theta'} || (200)_\alpha, (010)_{\theta'} || (020)_\alpha and (002)_{\theta'} || (002)_\alpha.

  • Microstructural and analytical study of heavily faulted Frank-Kasper R-phase precipitates in the ferrite of a duplex stainless steel
    Journal of Materials Science, 2002
    Co-Authors: A. Redjaïmia, Patricia Donnadieu, J. P. Morniroli, G. Metauer
    Abstract:

    The Ferritic Matrix in the Fe-22Cr-5Ni-3Mo-0.03C Ferritic-austenitic duplex stainless steel can undergo a variety of decomposition processes when aged in the temperature range 550–650°C. These processes are the precipitation of the γs austenitic bi-crystal, the α′-BCC ferrite, the τ-phase and the heavily faulted R-phase. The latter is a Frank-Kasper phase, which nucleates on the dislocations in the Ferritic δ-Matrix and adopts a lenticular shape. This study is basically focused on this intermetallic R-phase. The crystal structure and the chemical composition are respectively studied by electron microdiffraction and energy dispersive X-ray spectroscopy. The R-phase is oriented with respect to the surrounding Ferritic Matrix by developing a rational orientation relationship such that: (0 0 0 1)R//(1 1 1)δ with [1 $$\bar 3$$ 2]δ//[2 $$\bar 1\bar 1$$ 0]R. This orientation relationship is here examined in term of lattice matching. Based on this orientation, the morphology and the variant number of this R-phase are understood in terms of the group theory. The defects, present in a large density in the R-phase, are identified as planar faults, which are grouped in two families parallel respectively to {1 3 9}δ and {11 13 23}δ lattice planes of the Ferritic δ-Matrix. Based on the obtained results, a structural proximity between the R-phase and a supercell derived from the Ferritic Matrix has been brought to light. It has been stated that Mo is an efficient R-phase forming element. The results provide valuable insights into the precipitation mechanism associated with the R-phase formation.

Stéphane Godet - One of the best experts on this subject based on the ideXlab platform.

  • Beneficial influence of an intercritically rolled recovered Ferritic Matrix on the mechanical properties of TRIP-assisted multiphase steels
    Materials Science and Engineering: A, 2015
    Co-Authors: Stéphane Godet, Pascal Jacques
    Abstract:

    Abstract The present study deals with the microstructure and mechanical properties of intercritically rolled TRIP-assisted multiphase steels. It is shown that the occurrence of the TRIP effect in a recovered Ferritic Matrix brings about an improved strength–ductility balance with respect to a fully recrystallised ferrite Matrix. On the other hand, the intercritical deformation does not influence the austenite transformation rate during straining at room temperature. The improvement of the mechanical properties results from the interactions between the transformation strain and the recovered ferrite.

  • Effect of the work-hardening of retained austenite on the martensitic transformation in a TRIP-aided steel
    2000
    Co-Authors: Stéphane Godet, Pascal Jacques, Francis Delannay
    Abstract:

    This study deals with the hot deformation of TRIP-assisted multiphase steels. These steels consist typically of bainite and retained austenite grains dispersed in a Ferritic Matrix. The austenite, which is metastable at room temperature, transforms to martensite during straining, bringing about the TRIP effect, which improves the strength-ductility balance of these steels. This work investigates the effect of a prior deformation in the intercritical temperature range on the mechanical properties and work hardening behaviour of these TRIP-assisted multiphase steels. Several deformation levels in the ferrite-austenite domain were applied during the thermo-mechanical scheme. Results show that work-hardening is strongly enhanced when the specimens were sufficiently deformed in the intercritical temperature range. This study also shows that the beneficial influence of the prior deformation is more related to the TRIP phenomenon than to the strain-hardening of the Ferritic Matrix. These experiments prove that a displacive transformation such as the martensitic transformation is highly influenced by the dislocation density within the parent phase.

V Baltazar H Hernandez - One of the best experts on this subject based on the ideXlab platform.