Effect of Different Thermal Schedules on Ductility of Microalloyed Steel Slabs during Continuous Casting

Abstract

Ductility is the important indicator of transverse surface cracking susceptibility of slabs of microalloyed steels during continuous casting. Welding structure steel HG785 is selected to study the effect of different thermal schedule on ductility of microalloyed steel slabs during continuous casting in this paper. Surface Structure Control (SSC) cooling process parameters of HG785 microalloyed steel were confirmed by the aid of thermomechanical simulation experiment of Gleeble 3500. Results of tensile tests show that the ductilities of slabs under traditional thermal schedule and temperature fluctuation thermal schedule are very low in the III brittleness zone, and the reductions of area reach 29.7% and 26.0% at 800 °C, respectively. The ductility of slabs under SSC thermal schedule is obviously improved, since the pro-eutectoid ferrite film and aggregation of precipitates along the austenite grain boundary has not been discovered.

Nitrogen and nitride non-metallic inclusions in steel

“…Niobium carbo-nitride precipitates are known to decrease hot ductility. 40,50,51 Niobium nitrides and carbo-nitrides delay the onset of dynamic recrystallization during hot working, inhibit austenite grain growth during high-temperature annealing and therefore play an important role in grain refinement. 37,52 Figure 10 shows an example of a niobium nitride inclusion from an industrial sample of X19CrMoNbVN11-1 creep-resistant steel.…”