Ex-situ and in-situ S/TEM study of bainitic ferrite nucleation and martensite transformation for various heat treatment scenarios
Dynamics in matter and processes observed using in-situ microscopy methods provide an immense capability for direct revealing phenomena in the nanoscale. As a part of this work, Fe-7.9Ni-2.8Al-0.77Cu-0.4C wt.% bainitic steel (named BainNiAlCu), designed for (Ni, Al)-rich particles formation, was inv...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/403154 |
| Acceso en línea: | http://hdl.handle.net/10261/403154 |
| Access Level: | acceso abierto |
| Palabra clave: | Dynamic microscopy Bainitic transformation Martensite Bainite nucleation Nial Kappa carbide Intercritical annealing |
| Sumario: | Dynamics in matter and processes observed using in-situ microscopy methods provide an immense capability for direct revealing phenomena in the nanoscale. As a part of this work, Fe-7.9Ni-2.8Al-0.77Cu-0.4C wt.% bainitic steel (named BainNiAlCu), designed for (Ni, Al)-rich particles formation, was investigated using ex-situ and in-situ Scanning Transmission Electron Microscopy (S/TEM), dilatometry and X-ray diffraction (XRD). The bainitic and martensitic transformation was conducted inside a microscope column. The progress of austenite-to-ferrite transformation in the annealing step at 670 °C has generated dislocations in the adjacent austenite to accommodate the volume misfit between ferrite and austenite. The dynamic recovery of these dislocations has introduced numerous sub-grains and twin boundaries in the austenite, which act as nucleation sites for bainitic ferrite accelerating significantly this transformation during isothermal annealing at 250 °C. On the other hand, the B2-NiAl phase expected from the theoretical calculations was not revealed either in the in-situ or ex-situ microstructural studies, nor in the XRD patterns. The bainitic structure contained Kappa carbide resulted from ordering reaction of a NiAl-enriched FCC phase formed from the spinodal decomposition of the austenite, which would suppress the formation of B2 precipitates at 650 °C. The insight into the nucleation of bainitic ferrite considering various factors was revealed. |
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