Modified rolled homogeneous armor (RHA) steels were designed and produced to characterize the effects of niobium additions and accompanying heat treatments on microstructure and mechanical properties. This study combines in-house steel production and property analysis to advance the understanding of niobium on enhanced hardenability and weldability in a chemistry-process-structure-property relationship paradigm. For steel production, designed alloys were cast in a vacuum induction melting furnace and thermo-mechanically processed. Optimal heat treatment conditions were determined by utilizing a thermo-mechanics calculation software. Microstructures were investigated by optical and electron microscopy while hardenability was characterized by Jominy end-quench tests. Mechanical tests were performed at various stress states, strain rates, and temperatures to understand deformation behavior under complex loading conditions. Encouraging results in performance were observed in the micro-alloyed armor steels as compared to reference materials from earlier studies.