Effect of niobium on microstructure and mechanical properties of high carbon Fe–10.5 wt.% Al alloys

The effect of niobium on the microstructure and mechanical properties of high carbon Fe–10.5 wt.% Al alloys has been investigated. The alloys were prepared by a combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot-forged and hot-rolled at 1373 K. The hot-rolled alloys were characterized. The ternary Fe–10.5 wt.% Al–(0.7 and 0.9 wt.%) C alloys exhibited two-phase microstructure of large volume fraction of Fe3AlC0.5 precipitates in Fe–Al (α) matrix. Addition of niobium to Fe–10.5 wt.% Al–(0.7 and 0.9 wt.%) C alloys resulted in the precipitation of small volume fraction of niobium carbide precipitates in Fe–Al (α) matrix in addition to large volume fraction of Fe3AlC0.5 precipitates. The addition of up to 2 wt.% Nb to high carbon Fe–10.5 wt.% Al alloys has no effect on the yield strength at both room temperature and 873 K as well as creep properties at 140 MPa and 873 K, but it has reduced the room temperature tensile elongation at higher (2 wt.%) concentration. In the present work, it has also been observed that alloys containing high (0.9 wt.%) carbon, exhibited higher yield strength at room temperature as compared to alloys containing low (0.7 wt.%) carbon. The increase in strength with small increase in carbon may be attributed to the significant increase in volume fraction of Fe3AlC 0.5 precipitates.