Some Physical Metallurgy Aspects of Niobium- and Vanadium- Microalloyed Steels for Structural Beams

摘要

The paper describes a comparative study of the precipitation behavior in Nb- and V- microalloyed steels characterized by pearlite-ferrite microstructure. In both the microalloyed steels, coarse carbides/carbonitrides precipitate preferentially along the grain boundaries, whereas fine carbides precipitate in the ferrite matrix. The niobium and vanadium carbides cause ordering in the ferrite lattice that is displayed by the diffraction pattern as 'chemically sensitive or 'superlattice' reflection. Interestingly, Nb- and V-microalloyed steels exhibit similar superlattice diffraction patterns. The different precipitates exhibit orientation relationship with the ferrite matrix and their partitioning is not observed in the pearlite. The effect of carbon content on the resulting microstructure is also discussed.