Papers by Keyword: Austenitic Heat Resistant Steel

Abstract: In the present study, the recrystallization and grain growth behavior of HR3C austenitic heat resistant steel were studied by scanning electron microscopy and electron backscatter diffraction (SEM/EBSD). The HR3C steel was forged into a plate of 12mm in thickness and then solution treated at 1150-1250°C followed by an annealing treatment at 650-1050°C for 1h. The results show that the recrystalization occurs during the annealing treatment when the steel is solution-treated at 1150°C. Increasing the solution temperature to 1200°C or above, the recrystalization will not occur during the same annealing treatment. EBSD measured results show that the solution temperature has a significant effect on grain boundary character, especially on density of the low angle grain boundaries within the austenitic grain. The mechanism of the recrystallization and effect of annealing treatment on precipitation behavior of second phase were analyzed.

Abstract: The influence of the cooling condition after solution treatment on the high temperature fatigue resistance of 23Cr-26Ni heat resistant steel was investigated. Two different cooling conditions were applied to the steel after solution treatment at 1230oC for 3 hours. One specimen was water quenched immediately after the solution treatment. The other one was furnace cooled at a rate of 0.5oC/min down to 750oC after the solution treatment. Then, both specimens were aged at 750oC for 5 hours. The low cycle fatigue (LCF) test was conducted to investigate the influence of high temperature on the LCF behaviors of the heat-resistant 23Cr26Ni alloy. Under two different heat treatment conditions, the LCF test was performed at total strain amplitudes ranging from ±0.4~0.9% at room temperature (RT) and 600°C. During the test, initial cyclic hardening occurred at both experimental temperatures. This phenomenon was attributed to the increase in the dislocation density due to cyclic deformation, which resulted in the interaction between the newly created dislocations and precipitates. Cyclic softening was observed in the later stages of the LCF test at RT. The formation of precipitates and increase in the dislocation density were observed using TEM. Also, the XRD and EDS techniques were used to verify the type and composition of the precipitates.

Abstract: The effect of nitrogen on creep properties of 22Cr-25Ni austenitic heat-resistant steels with different nitrogen content was studied. The tensile and creep strength increased with increasing nitrogen content. The tensile strength increased due to grain refinement by Nb-rich carbonitride. The creep strength increased with increasing nitrogen content because nitrogen retarded the formation and growth rate of Cr-rich carbide and the growth rate of Nb-rich carbonitride during creep.