<p>This study investigates the influence of twin spacing and twin thickness on the tensile behavior of Fe-Cr-Ni alloys using molecular dynamics simulations. Microstructural features such as twin planes and stacking faults significantly impact the mechanical properties and deformation mechanisms of metals and alloys. The presence of twin planes guides the formation and evolution of stacking faults and dislocations during tensile deformation. Stress–strain analyses reveal distinct deformation stages, with twin spacing playing a crucial role in determining yield strength and plasticity. Alloys with nanotwins exhibit increased strength as twin spacing decreases, reaching a critical spacing at <i>d</i> = 1.25&#xa0;nm. Additionally, the analysis indicates that larger stacking fault areas correlate with enhanced plastic flow. The study also explores the effects of twin thickness on mechanical properties and phase transitions, finding that greater twin thickness enhances yield strength but reduces ductility. These insights underscore the importance of strategically designing twin boundaries and controlling their spacing to develop advanced materials with optimized strength, ductility, and deformation resistance. This research provides a foundational understanding for tailoring the mechanical performance of Fe-Cr-Ni alloys through microstructural engineering.</p>