Thermal Aging of High-Strength Corrosion-Resistant Austenitic Stainless Steel and its Thermal Stability

Unstabilized nitrogen-containing silicon steel 03Kh18N13S2AM2VFBR-Sh (EP 302M-Sh), intended for heat exchanger tubes operating in contact with heavy liquid-metal coolants and water at temperatures of 350 to 550°С, is prone to prolonged thermal aging and sensitization, initiating local metal corrosion in water at 350°С. Changes in the chemical composition of steel and the production of pilot batches of heat exchanger tubes did not lead to an increase in their thermal stability. One of the reasons for this is the factor of nitrogen solubility in austenite, which was neglected during the development of chemical compositions of metal. The principles of alloying and the conceptual chemical composition of unstabilized austenitic steel (EP 302M1-Sh), not prone to thermal aging and sensitization at a temperature of 350°С, have been developed, which excludes the possibility of local corrosion of the heat exchanger tubes during long-term operation in water. A 25% increase in yield point at 350°С compared to steel 08Kh18N10T and the absence of susceptibility to pitting, crevice, and hideout corrosion make thermally stable steel the preferred candidate material for producing heat exchanger tubes for innovative water-cooled power reactors. A possibility of creating economically alloyed austenitic steel, characterized by thermal stability at 350 to 550°С and corrosion resistance in liquid-metal coolants and supercritical steam-water medium, is shown.