Performance of Cr oxide coatings on 304 steel against metal dusting

The response to metal dusting of Cr/Cr₂O₃ thin films deposited on 304L stainless steel substrates by reactive magnetron sputtering (RMS) under various deposition conditions was investigated. Selected coated samples and bare substrates were exposed to an atmosphere of CH₄+H₂+residual oxygen at 800°C for up to 20h via thermogravimetric analysis (TGA). The results indicate that the presence of the Cr/Cr oxide film resulted in a clear improvement in resistance against metal dusting of the 304L steel. The protective behavior of the Cr/Cr oxide coatings arises from several effects: decrease of catalytic deposition of carbon on the Cr oxide surface (and expected prevention of inward diffusion of carbon through the Cr oxide), and hindrance of outward Cr and Fe diffusion which were identified as important events in the metal dusting of the bare 304L steel. The structural differences among the various Cr/Cr oxide films prepared in the present conditions played a lesser role in their protective behavior than the presence of the outer Cr oxide layer.