Two welding process parameters (the amplitude and frequency of the pulsed current) were varied in order to investigate their influence on the microstructure of the weld region and the mechanical properties of the joints. This investigation and the subsequent discussion were made based on the results of metallographies, tensile tests, and Vickers microhardness tests. The introduction of pulsed current at ultra-high frequencies resulted in a significant reduction in the size of the heat-affected zone (HAZ) for both materials: up to 54% for carbon steel and up to 73% for stainless steel. An increase in the grain size in the carbon steel HAZ was also noted. There are indications that the pulsed current at ultra-high frequencies has accelerated the atomic diffusion process of alloying elements from the fusion zone (FZ) to the carbon steel HAZ. Martensitic grains were observed in the FZ and the microhardness test verified this finding, once the microhardness values measured were around 400 HV0.3. The tensile strength was around 450 MPa and the rupture occurred on the carbon steel side, for all samples.