The effects of microalloy precipitation and (tunnel furnace) dissolution during direct slab production are explored relative to the position within a slab (i.e. thermal profile of the slab) and alloy content. Niobium solute contents and precipitate fractions are quantified using electrochemical extraction and inductively coupled plasma atomic emission spectrometry (ICP-AES) techniques. The locations selected for testing experimental CMn(Nb) steels incorporated the influence of temperature differences between different locations within the slab, differing solidification rates, and alloy segregation. The results show that the greatest amount of alloy precipitation occurred at the slab surface measured along the edges of the continuously cast thin slab. The extent of precipitation appeared greatest in the high niobium steel, where dissolution subsequently occurred during reheating and equalization in the tunnel furnace. There does not appear to be substantial precipitation or dissolution in the tunnel furnace for the low and medium niobium steels. The columnar region represents the bulk of the slab volume and exhibited the lowest amount of precipitated niobium. The precipitation and dissolution behaviors were generally consistent with expectations based on solubility considerations related to applicable thermal and compositional variations.