Effect of Dendritic Morphology and Central Segregation of Billet Castings on the Microstructure and Mechanical Property of Hot-Rolled Wire Rods

Abstract

Microscopic dendritic morphology and central macrosegregation in continuously cast high carbon steel billets with a cross section 150 × 150 mm2 are investigated to elucidate their effect on the microstructure and mechanical property of the following hot-rolled wire rods, whose diameters are 10 and 6.5 mm, respectively. Experimental observations and numerical simulations for the steel billets under different casting conditions are carried out. It is found that the secondary dendrite arm spacing (SDAS) in the billets increases with the increase of superheat temperature, while decreases with the increasing specific water flow. Smaller SDAS in the billet center leads to lower segregation index of carbon (rC) and manganese (rMn) due to the low permeability in the final solidification stage. The measured rMn and rC in billets are in an approximately linear relationship. In addition, for the same rolling and cooling process, the severer carbon segregation in the center of the billets is, the lower the sorbite rate of the rods and the worse stability in the mechanical property of the rods. The tensile strength of wire rods can be improved by adjusting the casting parameters to decrease the SDAS and reduce the central carbon segregation of the billets.