Effect of annealing treatment on microstructures and properties of austenite-based Fe-28Mn-9Al-0.8C lightweight steel with addition of Cu

The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich and kappa-carbide particles. The Fe-28Mn-9Al-0.8C-(0,3)Cu (wt.%) strips were near-rapidly solidified and annealed in the temperature range from 500 degrees C to 700 degrees C. The microstructure evolution and mechanical properties of the steel under different annealing processes were studied. Microstructural analysis reveals that nanoscale kappa-carbides and Cu-rich particles precipitate in the austenite and ferrite of the steel in this annealing temperature range. Co-precipitation of nanoscale Cu-rich particles and kappa-carbides provides an obvious increment in the yield strength. At the annealing temperature of 600 degrees C, both the yield strength and ultimate tensile strength of Fe-28Mn-9Al-0.8C-3Cu (wt.%) steel strip are the highest. The total elongation is 25%, which is obviously higher than that of Cu-free steel strips, for the addition of Cu reduces the large sized kappa-carbides precipitated along austenite/ferrite interfaces. When the annealing temperature rises to 700 degrees C, the strength and ductility of the two steel strips deteriorate due to the formation of massive intergranular kappa-carbides precipitated along austenite/ferrite interfaces. It can be concluded that a proper co-precipitation of Cu-rich particles and kappa-carbides would improve the properties of austenite-based Fe-Mn-Al-C steel.