The SM-4 is a JIS-compliant machine structural material, equivalent to former JIS SMF4030, suitable for general mechanical components. It supports post-treatments like steam treatment, carburizing, quenching, and tempering. Composed mainly of Iron (Bal.), Copper (≤5%), and Carbon (≤1%), it offers a density of 6.4 g/cm³, hardness ≤100 HV, tensile strength ≤300 MPa, and a Young's Modulus of 80 GPa. Steam treatment, which forms a bluish-black magnetic iron oxide (Fe3O4) layer at 400-600°C, significantly improves surface hardness, wear resistance, and corrosion resistance. Environmental testing, including a 500-hour humidity resistance test at 60°C and 95% RH, showed no degradation, confirming its durability.