Creep characteristics of austenitic stainless steel foil at elevated temperature

Abstract

High efficiency and compact recuperator with thin foil corrugated air cell as the primary surface is employed in clean and efficient microturbine system (100 kW). Current primary surface recuperators are made of AISI 347 austenitic stainless steel foils that operate at gas inlet temperature of less than 650 °C and attain approximately 30 percent of efficiency. Efficiency of greater than 40 percent is possible with the increase in turbine inlet temperature to 1230 °C, and as a result recuperator inlet temperature increase to 843 °C. This study establishes base line creep rupture behaviour of AISI 347 austenitic stainless steel foils at operating temperature of 700 °C and applied stress of 100 MPa. Creep behaviour of the foil shows that the primary creep stage is short and creep life of the foil is dominated by tertiary creep deformation. The time to rupture for the foil specimen is 184 hours with the corresponding rupture strain of 8.6 percent. Creep curves for AISI 347 austenitic stainless steel foil at 700 °C, 100 MPa are represented by the modified Theta-Projection concept model with hardening and softening terms. The creep coefficients, ?1 and ?3, and the exponent a are -0.6849, 0.6726 and 0.0038 respectively. Theta-Projection parameters values of experimental creep at temperature of 700 °C and applied stress of range 54-221 MPa shows a sudden gradient change at applied stress of 150 MPa possibly due to different mechanism of dislocation movements and microstructure changes. Two different creep failure mechanisms for austenitic stainless steel foils are possible since the creep failure data falls very close to the boundary of dislocation and diffusion creep regions in the creep mechanism map for bulk material