Carbon distribution in low temperature bainite
- Autores: Rosalía Rementería Fernández
- Directores de la Tesis: Francisca García Caballero (dir. tes.), Carlos García Mateo (codir. tes.)
- Lectura: En la Universidad Internacional Menéndez Pelayo (UIMP) ( España ) en 2017
- Idioma: inglés
- Tribunal Calificador de la Tesis: Joaquin Rams Ramos (presid.), Mercedes Hernández Mayoral (secret.), Jilt Sietsma (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología por la Universidad Internacional Menéndez Pelayo
- Materias:
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- Resumen
Bainite, defined as neither pearlite nor martensite, but as a mixture of bainitic ferrite and a second phase, is perhaps the most debated microstructure in steel science. Over time, the thermodynamic and kinetic aspects of bainite transformation theory have been progressively adapted to new evidence and concepts as they emerged. The question now is mostly reduced to whether or not bainitic ferrite initially forms with fully supersaturation of carbon.
Previous observations indicate that large quantities of excess carbon persist in body-centered tetragonal (bct) bainitic ferrite in spite of prolonged heat treatment. This work shows that the overall structure in the ferritic phase of low temperature bainite consists of a bct lattice at metastable equilibrium where carbon clusters of a definite composition are embedded in a carbon-depleted matrix. This phase separation is thought to develop as a consequence of a conditional spinodal decomposition mechanism, where initial full (or almost full) supersaturation of the freshly-formed ferrite is needed. The interaction of carbon with point defects and the subsequent formation of C–vacancy complexes would further assist in retaining carbon in the supersaturated matrix.
In addition to tetragonal ferrite and carbon-enriched austenite, cementite and the transient η–carbide are present in low temperature bainite. These two latter compounds together with dislocations are important sinks for carbon, and need to be considered in order to satisfy the mass balance.
