High temperature corrosion and microstructure deterioration of KHR35H radiant tubes in continuous annealing furnace

High temperature corrosion and microstructure deterioration phenomenon of KHR35H radiant tubes had been investigated after a service life of approximately 2 years in annealing process. Analyses revealed that deterioration in mechanical properties of the radiant tube was caused primarily by significant growth of precipitates during high temperature service. Internal oxidation and simultaneously in situ carbides dissolution were responsible for the formation of large number of voids and microcracks at the inner wall of the tubes, which brought the reduction of effective thickness of the tube wall and may act as crack sources under either thermal shock or creep deformation.

► We examine corrosion and microstructure status of KHR35H radiant tubes in use.
► Growth of precipitates causes deterioration in mechanical properties.
► Internal oxidation and in situ carbide dissolution form voids at subsurface.
► Voids reduce effective tube thickness and act as crack sources under strains.