• Both Al and C promote κ-carbide precipitation, with C having a stronger effect on size and volume fraction.
• Increasing C content from 0.8 to 1.4 wt.% raises κ-carbide size from 9.6 nm to 38.2 nm and volume fraction from 10.2% to 29.8%.
• Higher Al and C reduce lattice mismatch and Gibbs free energy, enhancing nucleation and driving force for κ-carbide formation.
• Precipitation strengthening reaches 583 MPa, with dislocation interaction transitioning from cutting to bypassing as C content increases.