This study evaluates the microstructure development and mechanical properties of friction-welded dissimilar steels. Rod type steel materials of S20C and SCM415H with a size of 12 mm diameter and 100 mm length were friction welded at a rotation speed of 2000 rpm and an upset force of 30 kg/cm². Electron backscattering diffraction method was used to study the grain boundary characteristics. The mechanical properties of the welds were evaluated by Vickers microhardness and tensile tests. The application of friction welding led to grain refinement of the welds, and the average grain size at the welded zone significantly refined to 4.9 μm comparing with those of the base material zone (66.8 μm at S20C and 19.8 μm at SCM415H). The grain refinement contributed to an increase in the mechanical properties such as hardness and strength. Consequently, the Vickers microhardness increased by 20 and 15%, respectively, when compared to those of the base material. Moreover, fracture occurred at the base material zone and not at the welded zone, which confirmed the soundly welded state of the steel materials.