AISI 422 martensitic stainless steels were welded according to the ISO 15792-1 standard with austenitic stainless-steel filler. The effects of tempering and preheating heat treatments were also evaluated. The microstructures of the welds were characterized with optical microscopy. Mechanical properties were determined via microhardness, tensile and fatigue tests, and compared to those of the unwelded AISI 422 steel. X-ray diffraction was used to characterize the phases present in the weld. Chromium carbides were observed at the grain boundaries of the welds. The precipitation was caused mainly by the diffusion of carbon into the austenitic stainless steel during the welding. The microhardness decreased from the base metal to the weld. The tensile-strength and percent-elongation values were improved with preheating and tempering heat treatments. The highest fatigue limit was obtained with preheating.