SAVREMENI PRISTUPI OPORAVKU SENZITIZOVANE MIKROSTRUKTURE AUSTENITNIH Cr-Ni ČELIKA ŽARENJEM / MODERN APPROACHES TO THE RECOVERY OF SENSITIZED MICROSTRUCTURE IN AUSTENITIC Cr-Ni STEELS BY ANNEALING

Abstract

It is well known that various damage mechanisms can occur during the service life of austenitic chromium-nickel steels. These steels are prone to sensitization during long-term operation at high temperatures, particularly those with higher carbon content and insufficient stabilizing elements, such as niobium. This paper describes the possibility of stabilizing the microstructure of ASTM A297 HK-40 catalytic steam reformer tubes through annealing. During their exploitation under high operating temperatures and in corrosive environments, these tubes experienced sensitization and cracking. The experiment involved mechanical and metallographic testing of the HK-40 material's properties and structure, both before and after the stabilization treatment. After applying six different annealing regimes (varying temperature and time) to the service-exposed material, the results were compared. The test sample that yielded mechanical properties (hardness) and a microstructure most similar to those of a new catalytic tube of the same material was selected as the optimal regime.