Effects of Al and C content on κ-carbide precipitation and strengthening in high-Mn low-density steels: A quantitative study

Fe-28Mn-(10-12)Al-(0.8-1.4)C (wt.%) steels were designed to investigate the influence of varying Al and C content on precipitation behavior of kappa-carbide and its contribution to the strength of high-Mn low-density steels. Results reveal that both Al and C elements promote kappa-carbide precipitation, with C having a more pronounced effect. In near-rapidly solidified 10Al steel strips, increasing C content from 0.8wt.% to 1.4wt.% raises the kappa-carbide size from 9.6 nm to 38.2 nm, accompanied by volume fraction increase from 10.2vol.% to 29.8vol.%. In comparison, the average size and volume fraction of kappa-carbides in 12Al0.8C steel are only 11.4 nm and 17.8vol.%, respectively. Higher Al and C content reduces the lattice mismatch between austenite and kappa-carbides, thus promoting nucleation of kappa-carbides. Notably, the increase in C content results in a greater reduction in the Gibbs free energy of kappa-carbide, leading to a stronger driving force for kappa-carbide formation. Consequently, as the C content increases from 0.8wt.% to 1.4wt.%, the interaction between kappa-carbides and dislocations transforms from particle cutting to bypassing, and the maximum precipitation strengthening of kappa-carbides reaches 583 MPa. The construction of the relationship between Al and C contents and kappa-carbide precipitation in this study would provide valuable insights for alloy design of high-Mn steels.