<p>The application of austenitic stainless steel weld cladding on Cr-Mo steels is widely used in petrochemical components operating under high-temperature and corrosive environments, where control of microstructure and ferrite content is critical for service performance. The stainless steel cladding on carbon steel is characterized by different temperature gradients and microstructural changes. The correct selection and control of shielding gases play a key role in mitigating metallurgical issues in the deposited material and welding process. This work evaluated the metallurgical characteristics of gas metal arc welded stainless steel weld claddings produced with AISI 309L and 347L as filler material on a 2.25Cr-1Mo steel substrate, analyzing the influence of shielding gas mixtures based on argon with different carbon dioxide contents on chemical composition and ferrite formation in the microstructure of the arc cladding. The layers were characterized by Vickers microindentation, optical microscopy, scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy, and measurement of the amount of ferrite using a digital ferrite content meter. It was observed that increasing carbon dioxide content in the shielding gas leads to a systematic reduction in ferrite percentage in the final arc cladding layer, while maintaining a ferrite–austenite microstructure with ferrite as the primary phase and austenite as the secondary phase. In addition, an increase in arc cladding hardness was observed, with higher microhardness values associated with higher carbon dioxide concentrations in the shielding gas mixture. These results demonstrate that the shielding gas composition is an effective parameter for controlling ferrite content and hardness in stainless steel weld claddings on Cr-Mo steels, contributing to improved metallurgical stability and suitability for petrochemical service conditions.</p>