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Dendritic precipitates in AS-CAST Nb-Ti-V microalloyed steel

Abstract:

The present research work deals with the analysis of dendritic precipitates present in a commercially produced Nb-Ti-V steel. The study was performed by scanning electron microscopy on precipitates extracted by chemical dissolution of a microalloyed steel matrix in the as-cast condition. Well-ramified dendritic precipitates of the (Ti,Nb,V)(C,N) type, rich in Ti or Nb of micrometric size, growing by faceted mechanisms were observed. The growth of primary and secondary arms look like laths when rich in Ti. This morphology is less accentuated in dendritic regions rich in Nb, which showed larger ramification. Dendrites with four-fold symmetry, with primary and secondary branches, were also found, but the well-ramified dendrites predominate. Computational thermodynamics was used to simulate the segregation during the solidification, and the results obtained both with the Scheil model and with a simple model including diffusion during solidification, are consistent with the observations.