On the m23 c6-carbide in 2205 duplex stainless steel: An unexpected (m23 c6 /austenite)—eutectoid in the d-ferritic matrix
This study is focused on isothermal and anisothermal precipitation of M23C6 carbides from the fully ferritic structure of the (¿ + d) austenitic-ferritic duplex stainless steel X2CrNiMo2253, (2205). During isothermal heat treatments, small particles of K-M23C6 carbide precipitates at the d/d grain-b...
| Autores: | , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/353543 |
| Acceso en línea: | https://hdl.handle.net/2117/353543 https://dx.doi.org/10.3390/met11091340 |
| Access Level: | acceso abierto |
| Palabra clave: | Stainless steel Duplex stainless steels M23C6 carbide Crystal structure (M23C6/¿)-eutectoid Morphology Geometrical model Mechanism Thermodynamic calculations Acer inoxidable Estructura cristal·lina Àrees temàtiques de la UPC::Enginyeria dels materials |
| Sumario: | This study is focused on isothermal and anisothermal precipitation of M23C6 carbides from the fully ferritic structure of the (¿ + d) austenitic-ferritic duplex stainless steel X2CrNiMo2253, (2205). During isothermal heat treatments, small particles of K-M23C6 carbide precipitates at the d/d grain-boundaries. Their formation precedes ¿ and s-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 d-ferritic matrix. TEM characterization of these islands reveals a particular eutectoid, reminiscent of the well-known (¿-s)—eutectoid, usually encountered in this kind of steel. TEM and electron microdiffraction techniques were used to determine the crystal structure of the eutectoid constituents: ¿-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 ¿-Austenite and Kurdjumov-Sachs, on the other hand, between ¿-Austenite and the d-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 ¿-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 ¿-Austenite and s-Sigma phase. For this purpose, the mole fraction evolution of K-M23C6 and s-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 d-ferrite ¿ {¿-Austenite ¿ K-M23C6}. |
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