Surface engineering is unavoidable for most high-performance components manufacturing. Frequently when very specific properties are required duplex treatments are necessary. In the case of diffusion-based treatments, like nitriding and chromizing, the substrate composition plays an important role in the obtained results. Consequently, for duplex treatments, the second treatment will be influenced by the first one. Putting these aspects in evidence, Deutsches Institut für Normung (DIN) CK15, DIN C45Pb, and DIN X40CrMoV5-1 steels were exposed to pack chromizing followed by plasma nitriding and plasma nitriding followed by pack chromizing. Results showed that the treated surface features are very sensitive to the steel composition and treatment sequence. In nitrided and chromized surfaces, the iron nitrides formed during the first treatment are dissolved and replaced by chromium nitrides (CrxNy) during chromizing. The inverse sequence resulted in surfaces containing chromium carbide (Cr7C3) formed during chromizing with CrxNy and iron nitrides formed during nitriding. The higher measured hardness (1,499 Vickers hardness [HV]) was obtained for the chromized and nitride DIN X40CrMoV5-1 steel. Salt spray tests showed that treatments ending by chromizing are the most promising for enhancing the surface corrosion resistance, except for the low carbon steel.