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-40 at.%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 degrees C. An initial microstructure with average grain size 0.77 +/- 0.27 mm 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 degrees C) as well as on annealing time. The activation energy of static recrystallization was calculated as 255 kJ mol(-1). Competition between dynamic recovery and static recrystallization was proved after strain 0.35 and annealing temperature 1100 degrees 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 +/- 0.15 mm for temperature 1100 degrees C, and 0.22 +/- 0.04 mm for 900 degrees C). Even at a temperature of 1200 degrees C the annealing after deformation should last approx. 1 min 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.