Effect of the Combined Addition of Niobium and Boron on Static Recrystallization in Hot Worked Austenite

Four low carbon bainitic steels were compression tested under interrupted and continuous loading conditions. These materials were made from a base steel containing 0.026% C, to which were added one or both of 0.055% Nb and/or 30 ppm of B. In this way, the influence on the rate of recrystallization of additions of: (i) Nb; (ii) B ; and (iii) Nb + B was assessed independently.The recrystallization kinetics of the hot worked austenite were determined for prestrains of 0.12, 0.25 and 0.50 in the temperature range 900–1100°C. The results are presented in the form of percentage softening vs log time plots and of RTT (recrystallization-time-temperature) diagrams. The observations indicate that the addition of B is most effective in retarding recrystallization in the presence of Nb. Furthermore, the degree of retardation is influenced by both the prestrain and the temperature. The kinetics of recovery and recrystallization are characterized in terms of the Avrami equation; the influence of prestrain, temperature and alloy composition on the coefficients and exponents is described.