<p>The non-uniformity of phase transformation between different regions during the cooling process of dual-phase steel is a key factor determining the level of residual stress. In this paper, a new mechanism is revealed through experimental studies and thermal-metallurgical-mechanical coupled simulations, in which austenite-stabilizing elements (Nb, C, and Mn) synergistically regulate phase transformation kinetics, improving the uniformity of phase transformation and thereby suppressing residual stress. It is found that Nb retards ferrite transformation through the solute drag effect and improves its distribution uniformity in a two-phase microstructure. The synergistic effect of Nb-C-Mn significantly reduces the martensite Ms temperature and transformation rate, thereby decreasing the difference in martensite content between the surface and the core. The enhancement of phase transformation uniformity effectively alleviates the phase transformation stress and non-coordinated plastic strain caused by the difference in phase transformation volume expansion, which becomes a key factor in reducing residual stress. In a typical Ferrite/Martensite dual-phase steel, optimizing the alloy composition reduces surface and core residual stress by 35.1 and 35.6%, respectively. This study clarifies the correlation mechanism between alloy composition, phase transformation uniformity, and residual stress, providing a new perspective for the development of low-stress, high-strength steels.</p>