Effect of a combined addition of boron and niobium on the dynamic recrystallization kinetics of boron‐containing micro‐alloyed low carbon steel

The effect of a combined addition of boron and niobium on the dynamic recrystallization kinetics of boron‐containing micro‐alloyed low carbon steel has been studied by measuring the flow curves of three different (i.e., niobium, boron‐niobium, boron) micro‐alloyed steels at various temperatures and strain rates and by modeling the recrystallization kinetics in an Avrami expression. The results show that the recrystallization kinetics and flow stress can be modeled in a single function of temperature‐compensated strain‐rate (Z) using Avrami kinetics by applying, not the conventional t 1/2 ‐method, but recently proposed ε 1/2 ‐method. Detailed analysis of the Avrami kinetics together with secondary ion mass spectrometry (SIMS) and drag force calculation show that non‐equilibrium segregation of boron and boron‐niobium complex occurs up to 1100 °C and its intensity increases with the strain rate. The non‐equilibrium segregation decreases both the growth and nucleation rates of dynamic recrystallization by lowering the mobilities of the grain‐ and subgrain‐ boundaries. Combined addition of boron and niobium to boron‐bearing carbon steels leads to more intense segregation on grain‐ and subgrain‐ boundaries, which delays the recrystallization rate more strongly at an early stage but rather accelerates it at an intermediate stage of deformation by forming iron (boron, carbon) (Fe(B, C)) aggregates.