Advanced Ultra-Super Critical (AUSC) fossil fired power plants are envisage d to operate at higher steam temperature (983-1023 K) and pressure (32-35 MPa) compared to existing supercritical/Ultra-Supercritical thermal power plants. One of the candidate materials currently considered for boiler tube application for India’s National Mission on AUSC coal-fired power plant (with 993 K, 32 MPa) is 304HCu stainless steel (SS). In the present study, the influence of grain size on the creep properties of 304HCu SS was studied at a temperature of 923 K in the stress range of 180-240 MPa. The grain sizes investigated were 10, 20, 30, 60 and 180 µm. At all the stress levels, the grain size of 30 micron exhibited the lowest value of minimum creep rate and highest rupture life. The microstructures of initial and post tested conditions have been characterized using scanning electron microscope/transmission electron microscope. The creep curves were modelled using, 1) Modified theta projection approach and 2) Physically constitutive continuum damage mechanics approa ch using Genetic Algorithm optimization. The approaches have been modified to consider the effect of grain size. A good agreement between experimental and predicted creep strain was observed.
Keywords: 304HCu SS, AUSC, Creep, Grain size, Theta projection model and Genetic Algorithm – CDM model.