Process for pretreatment of the surface of an alloy containing chromium

A process for pretreatment of cold-worked or machined alloys containing chromium, intended to make them receptive to protective refractory oxide coatings, and to a process for depositing such coatings on the pretreated alloy, is described. The pretreatment consists in reheating the alloy to a temperature above 200 DEG C, cooling the reheated alloy to a temperature below 200 DEG C and finally preoxidising the reheated, now cooled, alloy by raising its temperature above 200 DEG C in the presence of an oxidising gas. Representative types of such alloys are niobium steels and a representative protective oxide coating is that of silica. Alloys pretreated and coated in this manner are capable of withstanding a hostile environment at high temperatures and in the presence of oxidising gases and are resistant to corrosion, to carbonisation and to coke deposits.