The adhesion/cohesion (A/C) of coatings onto metallic substrates is an important property for most service conditions. Preheating the substrate before spraying the powder is a way to improve its A/C. It results in a surface oxidation of the substrate due to the high temperature of the gas close to the substrate surface and consequently to the high level of atomic oxygen. This study is devoted to the estimation of the influence of this oxide layer onto the A/C values. A precise monitoring of the preheating process by presetting values of the heating rate, temperature level and heating time allows to produce oxide layers with controlled composition and thickness. In the studied case of low carbon steel a specific choice in the heating rate and temperature leads to the production of an oxide layer with a low or high content of hematite layers in a duplex layer of hematite and magnetite iron oxides.