Kinetics of static recrystallization in the coarse-grained Fe–40 at.%Al–Zr–B alloy

Abstract

The aim of works was to describe mathematically the kinetics of static recrystallization of the alloy type Fe–40at.%Al–Zr–B (with 24.6 Al–0.01 B–0.18 Zr–0.01 C in wt.%) with the coarse-grained structure. The microstructure of the laboratory castings made of this extremely brittle alloy was homogenized by hot rolling of the material in the protective capsules and by the long-term annealing at 1200°C. An initial microstructure with average grain size 0.77±0.27mm was obtained. Based on the isothermal plastic deformation tests and EBSD analysis, the static recrystallization kinetics of the prepared coarse-grained B2 iron aluminide after strain 0.20 was mathematically described. Recrystallized fraction depends on deformation/annealing temperature (900–1100°C) as well as on annealing time. The activation energy of static recrystallization was calculated as 255kJmol−1. Competition between dynamic recovery and static recrystallization was proved after strain 0.35 and annealing temperature 1100°C. Static recrystallization starts relatively easily in the studied alloy, but a very long-term annealing is quite necessary for the complete course of recrystallization. The mean size of recrystallized grains falls with the decreasing annealing temperature (0.47±0.15mm for temperature 1100°C, and 0.22±0.04mm for 900°C). Even at a temperature of 1200°C the annealing after deformation should last approx. 1min for obtaining the fully recrystallized microstructure. That is why the standard hot forming technologies should be combined by an interpass annealing in order to refine sufficiently the coarse grains.