Microstructure Characteristics of TP304 Steel after Long-time High-temperature Service

Abstract

Abstract The microstructure characteristics of specimens used for 1.5×104 h, 7.8×104 h, and 9×104 h and a burst tube specimen used for 8.5×104 h were analyzed by a metallographic microscope, a scanning electron microscope, and energy spectrum, and the precipitated phase was quantitatively analyzed by ImageJ. The results show that the second phase precipitates at grain boundaries and within grains after service. During operation, chrome-rich carbides precipitate along grain boundaries, which gradually aggregate and grow into chains, forming intergranular corrosion, resulting in intergranular cracking, and the σ-phase precipitates at severe overtemperature.