Michal Cagala

Homogenization of Microstructure of Castings from the Alloy Fe-40at.%Al-Zr-B

The samples intended for the study of static recrystallization on plastometer Gleeble were prepared from the laboratory castings of iron aluminide containing 24.6 Al 0.17 Mn 0.16 Zr 0.026 B 0.004 C (in wt. %, remainder Fe). Nevertheless, the structure analysis discovered that the results were excessively influenced by the huge heterogeneity of the as-cast microstructure, mostly of the grain size. Combination of the hot forming and recrystallization process during the long-term high-temperature annealing was selected for the necessary structure homogenization. As the tested intermetallic alloy is extremely brittle and susceptible to surface cracking, the original method was applied for its processing. The method consists in hot rolling in the protective capsules welded from the ferritic stainless steel sheet. The castings were rolled to 2/3 of their thickness by 4 reductions with the inter-stage heating, and then annealed at the temperature of 1200 °C in the vacuum furnace for several periods. Metallographic analysis revealed that annealing lasting 7 hours was essential for the uniform coarsening of the recrystallized grains. Material processed in this way proved successful for the subsequent metallographical study of static recrystallization.