Effect of aging on microstructure and precipitated phase of wear-resistant plate
Austenitic wear-resistant plate has high thermal strength and oxidation resistance, widely used in the boiler superheater and reheater high temperature section of more than 600℃, the maximum use temperature can reach 760℃, the use of wear-resistant plate, to a certain extent, solve the overtemperature explosion caused by the furnace flue gas temperature difference, significantly improve the safety of boiler operation. However, the wear-resistant plate is prone to structural transformation during long-term high temperature operation, resulting in aging of the material. Therefore, the study of the microstructure transformation of austenitic wear-resistant plate steel under high temperature conditions and its influencing factors is of great significance for arranging the running time of the material reasonably, monitoring the damage degree of the pipeline online and improving the material itself. Therefore, the effects of aging temperature and time on the structure and precipitated phase of wear-resistant plate were studied through high temperature aging simulation test, which can provide reference for the safe service of wear-resistant plate.
The supply condition of the material is solid solution treatment, that is, after holding at 1060 ~ 1070℃ for 15 ~ 30min, air cooling or air cooling, and the organization is single-phase austenite. In this experiment, the aging temperature of the wear-resistant plate was accelerated by increasing the temperature. The aging temperature was 650, 700 and 750℃, and the aging time was 30, 60 and 150d, respectively. The characteristics of the microstructure change of the wear-resistant plate during long-term operation were studied by aging simulation.
After grinding, polishing and aqua regia corrosion of the simulated samples and original samples at high temperature aging, the grain size of the samples was observed by optical microscope, and the microstructure was analyzed by QUANTA 400 scanning electron microscope. The microstructure was quantitatively analyzed by Image-Pro Plus software, and the distribution and characteristics of precipitated phase were compared. The component analysis was carried out by the energy spectrometer attached to SEM. The existence of σ phase after aging of the wear-resistant plate was determined by observing whether there were orange spots on the surface of the sample under metallography microscope by etching the sample with alkaline potassium permanganate solution. The results show that:
(1) The original structure of the wear-resistant plate is austenite, and the twin boundary is clearly visible; After high temperature aging, grain size gradually increases, grain boundary coarsening, twin crystals decrease and abnormal grain growth increase.
(2) During the aging process of wear-resistant plates at 650, 700 and 750℃, the total precipitated phase increases as a power function with the extension of time, and the area fraction of precipitated phase, that is, the total precipitated phase, complies with the functions S650=0.084t0.454, S700=0.281t0.327, S750=0.313t0.338, respectively.
(3) After aging at 650 ℃ and 700℃ respectively for 30 days, the precipitated phase is mainly carbide, and after aging for 60 days, the precipitated phase has a very small amount of σ phase in addition to carbide, and the main components are Fe and Cr; After aging at 750℃ for 30 days, the amount of precipitated phase increased significantly, mainly carbide, and a small amount of σ phase.
