Investigation On The Microstructure And Properties Of Austenitic Heat Resistant Steel HR3C

HR3C austenitic heat resistant steel plate of12mm in thickness was prepared by melting and hot working treatment. The effect of various heat treatment on the microstructure and properties of the steel has been studied by the scanning electron microscope (SEM) equipped with energy dispersive spectrum analysis (EDS), electron backscatter diffraction (EBSD), transmission election microscopy (TEM), X-ray diffraction (XRD), hardness and creep tests in the paper. The conclusion can be drawn as follows:The microstructure of the HR3C steel after solution treatments at1150,1200and1250℃for1h consists of austenite and NbCrN particles (Z-phase) distributed in austenite grains. High dense dislocations are found within gains when the steel is solution treated at a lower temperature of1150℃. The number of NbCrN particles and dislocation density reduce with increasing of the solution temperature. The hardness of the HR3C steel decreases with the increase of solution temperature.M23C6-type carbides precipitate along austenite grain boundaries after aging treatments at650-1050℃for lh. Nanometer-sized Z-phases precipitate within austenite grains when aging at800～900℃. The density of the nanometer-sized Z-phase particles increases with the increase of solution temperature. During the short-term aging treatment, recrystallization occurs because of the high dense dislocations within gains in HR3C steel solution-treated at a low temperature of1150℃, however, it does not occur after1200-1250℃solution treatments. The hardness of the HR3C steel decreases at first, then increases with increasing the aging temperature and reaches a maximum value when aging temperature is850℃. The variation of hardness of the HR3C steel is attributed to the precipitation strengthening of nanometer-sized Z-phase.For the1250℃solution-treated HR3C steel, M23C6-type carbide particles grow gradually and gather more and more continuously along austenite grain boundaries during the650℃aging process. A high density of nanometer-sized Z-phase precipitates after aging for860h. Whisker-like clusters, which are consisted of nanometer sized precipitates, are formed within gains after1900h aging. The nanometer-sized Z-phases precipitated when aged at850℃for1h after1250℃solution-treated are stable and grow very slowly. With the help of strengthening effect of the nanometer-sized Z-phases, the hardness increases gradually with increasing the aging time.Creep test results at700℃under218MPa have illustrated that the HR3C steel cracks in an intergranular mode. The creep fracture life of the HR3C steel aged at85O℃for lh is shorter than that of the solution-treated HR3C steel.