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In-situ observation of the delta-ferrite to austenite phase transition in Fe-C alloys

Conference Paper


Abstract


  • During continuous casting of steel, the delta-ferrite to austenite phase transition occurs following solidification in the meniscus region of the solidifying strand. It is of great industrial significance to gain a better understanding of the nature and mechanism of this reaction because product quality is in large measure determined by events occurring during and shortly following solidification. Moreover, the exact way in which delta-ferrite transforms to austenite may influence the subsequent transformation of austenite to ferrite, by which much of the mechanical properties of the steel is determined. Relatively little attention has been devoted to the delta-ferrite to austenite phase transition in the past, in part because of the difficulty of making in-situ observations at the high temperature at which this phase transition occurs. The recent development of high-temperature laser-scanning confocal microscopy has provided new opportunities to observe in-situ high temperature phase transformations and this technique has been employed in the present study. In order to limit grain boundary pinning by alloying elements and alloy compounds during growth of delta-ferrite grains and their influence on the δ-to-γ phase transition, the solid-state phase transformation was firstly studied in pure iron-carbon alloys and subsequently in low-carbon steel. Experimental observations of the effect of cooling rate on the δ/γ phase transformation are discussed in terms of three different morphologies that have been observed. At low cooling rates the newly formed austenite phase that nucleated at triple points grow by an advancing planar interface but at higher cooling rates the transformation occurs by a massive kind of transformation. Computer simulations have been used in an attempt to better explain the experimental observations.

Publication Date


  • 2007

Citation


  • Niknafs, S., & Dippenaar, R. (2007). In-situ observation of the delta-ferrite to austenite phase transition in Fe-C alloys. In AIST Steel Properties and Applications Conference Proceedings, Combined with Ms and T'07, Materials Science and Technology 2007 (pp. 669-678).

Scopus Eid


  • 2-s2.0-37349057497

Web Of Science Accession Number


Start Page


  • 669

End Page


  • 678

Abstract


  • During continuous casting of steel, the delta-ferrite to austenite phase transition occurs following solidification in the meniscus region of the solidifying strand. It is of great industrial significance to gain a better understanding of the nature and mechanism of this reaction because product quality is in large measure determined by events occurring during and shortly following solidification. Moreover, the exact way in which delta-ferrite transforms to austenite may influence the subsequent transformation of austenite to ferrite, by which much of the mechanical properties of the steel is determined. Relatively little attention has been devoted to the delta-ferrite to austenite phase transition in the past, in part because of the difficulty of making in-situ observations at the high temperature at which this phase transition occurs. The recent development of high-temperature laser-scanning confocal microscopy has provided new opportunities to observe in-situ high temperature phase transformations and this technique has been employed in the present study. In order to limit grain boundary pinning by alloying elements and alloy compounds during growth of delta-ferrite grains and their influence on the δ-to-γ phase transition, the solid-state phase transformation was firstly studied in pure iron-carbon alloys and subsequently in low-carbon steel. Experimental observations of the effect of cooling rate on the δ/γ phase transformation are discussed in terms of three different morphologies that have been observed. At low cooling rates the newly formed austenite phase that nucleated at triple points grow by an advancing planar interface but at higher cooling rates the transformation occurs by a massive kind of transformation. Computer simulations have been used in an attempt to better explain the experimental observations.

Publication Date


  • 2007

Citation


  • Niknafs, S., & Dippenaar, R. (2007). In-situ observation of the delta-ferrite to austenite phase transition in Fe-C alloys. In AIST Steel Properties and Applications Conference Proceedings, Combined with Ms and T'07, Materials Science and Technology 2007 (pp. 669-678).

Scopus Eid


  • 2-s2.0-37349057497

Web Of Science Accession Number


Start Page


  • 669

End Page


  • 678