PURPOSE:To enhance the corrosion resistance of nickel maraging steel to UF6 gas and to prevent the leakage rupture, etc. by heating the steel in a CO2 gas atmosphere at a specific temp. to form an oxide film on the surface. CONSTITUTION:18% Nickel maraging steel is surface cleaned by ultrasonic washing or the like and heat treated in a CO2 atmosphere at 450-550 deg.C to form an oxide film which has very good corrosion resistance and does not undergo corrosion even in a UF6 gas atmosphere. Occurence of troubles such as hydrogen rupture is prevented which is due to residual hydrogen in steel treated with superheated steam. The oxide film is dense and has good adherence to the base metal. When the steel is heated at above 550 deg.C, the strength is lowered remarkably. In case the heating temp. is below 450 deg.C, the resulting oxide film has good corrosion resistance but predetermined mechanical characteristics can not be held.

Yamazaki Daizou

Papers

Improving method for corrosion resistance of nickel maraging steel