Steel alloys with high Mn and low C, low Cr wt.%, were designed based on the composition system for traditional high toughness, creep resistance, and longevity for high-temperature applications. In terms of energy resource utilization during production and refining, CALPHAD strategical optimization is preferable for all steel alloys. Thermo-Calc software calculates the phase diagrams α-BCC (Ferrite), and M23C6 (carbide) phases. The vital temperatures which are highlighted in this work are Ac3 (threshold temperature at which ferrite is fully transformed into austenite (α→γ)), and A4 (the threshold temperature at which austenite is fully transformed into Delta ferrite (γ→δ)) are essential for phase transformations. JMatPro software is used to predict the mechanical properties of steel alloys. The interfacial energies with regards to alloying elements for M23C6 are calculated to be between ~0.272 J/m-2 to ~0.328 J/m-2 for α-BCC) matrix, while γ-FCC has interfacial energy ranges to be between ~0.132 J/m-2 to ~0.168 J/m-2. This paper focuses on investigating the effect of alloying elements on phase transformations, interfacial energy, coarsening rate of carbides, and many other mechanical properties such as toughness at high-temperature applications using CALPHAD strategies.