Control of inter/intra-granular κ-carbides and its influence on overall mechanical properties of a Fe-11Mn-10Al-1.25C low density steel

In this study, a novel ultra-high yield strength Fe-11Mn-10Al-1.25C low density steel was developed with aiming to fundamentally understand the formation of inter/intra-granular kappa-carbides and its influence on the overall mechanical properties by varying cooling patterns, e.g. air cooling (AC), water quenching (WQ) and intensive quenching (IQ). The results show that the IQ microstructure is almost fully austenitic with very fine intragranular kappa-carbides of less than 13 nm, which is totally different from the chain-like ferrite and coarse inter granular kappa-carbides of 0.6-2.6 mu m in both cases of AC and WQ. In contrast, the IQ sample exhibits similar high YS and UTS values (similar to 1.1 GPa) to the others but significantly an enhanced ductility of similar to 29.3%, revealing an excellent balance of strength and ductility, i.e. the product of strength and ductility (PSE) can reach as high as 32.1 GPa%. The improved overall performance and continuously increasing strain hardening are dominated by planar glide, which is mainly attributed to the uniform distribution of nano-sized and shearable kappa-carbides in the austenitic matrix. These results may provide theoretical supports for the kappa-carbides-related alloy design and microstructural modification of ultra-high-strength medium Mn low density steels.