High-Temperature Deformation Behavior of 718Plus: Consideration of γ′ Effects

Özturk, Utkudeniz; Cabrera, José‐María; Calvo, Jessica; Redjaïmia, A.; Ghanbaja, Jaâfar

doi:10.1520/mpc20190031

Cited by 4 publications

(1 citation statement)

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“…Both the morphology and the variant number of the precipitate, which adopts orientation relationships with the matrix, can be understood in terms of group theory [57,58]. This symmetry concept has been successfully applied to determine the number of variants and to characterize the morphology of precipitates in different alloy systems, and is widely investigated [59][60][61][62][63][64][65][66]. This approach, based on the shared symmetry elements of the two point groups can be applied to explain the habitus and especially the variant number developed by the K-M 23 C 6 in the eutectoid nodule.…”

Section: Symmetry Analysis and Morphology The Equilibrium Shapementioning

confidence: 99%

On the M23C6-Carbide in 2205 Duplex Stainless Steel: An Unexpected (M23C6/Austenite)—Eutectoid in the δ-Ferritic Matrix

Redjaïmia

García

2021

Metals

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This study is focused on isothermal and anisothermal precipitation of M23C6 carbides from the fully ferritic structure of the (γ + δ) austenitic-ferritic duplex stainless steel X2CrNiMo2253, (2205). During isothermal heat treatments, small particles of K-M23C6 carbide precipitates at the δ/δ grain-boundaries. Their formation precedes γ and σ-phases, by acting as highly potential nucleation sites, confirming the undertaken TEM investigations. Furthermore, anisothermal heat treatment leads to the formation of very fine islands dispersed throughout the fully δ-ferritic matrix. TEM characterization of these islands reveals a particular eutectoid, reminiscent of the well-known (γ-σ)—eutectoid, usually encountered in this kind of steel. TEM and electron microdiffraction techniques were used to determine the crystal structure of the eutectoid constituents: γ-Austenite and K-M23C6 carbides. Based on this characterization, orientation relationships between the two latter phases and the ferritic matrix were derived: cube-on-cube, on one hand, between K-M23C6 and γ-Austenite and Kurdjumov-Sachs, on the other hand, between γ-Austenite and the δ-ferritic matrix. Based on these rational orientation relationships and using group theory (symmetry analysis), the morphology and the only one variant number of K-M23C6 in γ-Austenite have been elucidated and explained. Thermodynamic calculations, based on the commercial software ThermoCalq® (Thermo-Calc Software, Stockholm, Sweden), were carried out to explain the K-M23C6 precipitation and its effect on the other decomposition products of the ferritic matrix, namely γ-Austenite and σ-Sigma phase. For this purpose, the mole fraction evolution of K-M23C6 and σ-phase and the mass percent of all components entering in their composition, have been drawn. A geometrical model, based on the corrugated compact layers instead of lattice planes with the conservation of the site density at the interface plane, has been proposed to explain the transition δ-ferrite ⇒ {γ-Austenite ⇔ K-M23C6}.

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