<p>To develop high-performance Ni-saving Sanicro 25 austenitic heat-resistant steel, the micro-scale control mechanisms governing thermodynamic stability, electronic structure, and mechanical properties of the system are systematically investigated using first-principles calculations, based on the previously optimized Ni-saving reference system Fe₈Cr₄Ni₃Mn. The results show that the formation energies and binding energies of all doped systems are negative. Gibbs free energy analysis further confirms that Cu, Nb, and Co can stably exist in the matrix. Among these results, the Fe₇Cr₄Ni₃MnCo system with 6.25 wt% Co exhibits the highest thermodynamic stability at elevated temperatures. Electronic property analysis reveals that the charge accumulation around atoms is most pronounced at a Co content of 6.25 wt%, corresponding to optimal electrochemical stability and bonding strength. Mechanical property calculations indicate that Nb doping leads to a peak in ductility for the Fe₆Cr₄Ni₃MnNb₂ system, while the Young’s modulus of the Fe₇Cr₄Ni₃MnCo system reaches 393.17 GPa, achieving a synergistic enhancement in both strength and ductility. In a nutshell, Co acts as an ideal doping element for optimizing the Ni-alloying in Sanicro 25 steel, as it simultaneously enhances the thermodynamic stability, electronic structure, and mechanical properties of the system. This study thus provides crucial theoretical support for designing high-performance, Ni-saving austenitic heat-resistant steels.</p> Graphical abstract <p></p>