Producing of oxide films on the surface of chromium-nickel steel tubes

Conditions of treatment of tubes from corrosion-resistant chromium-nickel steel providing their purification from contaminations and simultaneous producing of oxide film on the surface are studied. Different variants of tube surface preparation before chemical heat treatment are tested. Oxide coating is carried out in the NaOH and H2SO4 solutions with K2Cr2O7 or CrO3 additions. In the result of investigations it is established that oxide film of the metals is formed more quickly under labricant oxidation products. Oxide coating of the tube surface in the acid solutions of chromium anhydride is more efficient for tubes having rolling labricant on the surface. On the samples without labricant treatment in the solutions with chromium anhydride leads to intensive process of the metal dissolving, and formation of oxide film is observed only after 3-hr holding