Multiphase Strengthening of Nanosized Precipitates in a Cost-Effective Austenitic Heat-Resistant Steel

A newly developed austenitic heat-resistant steel Fe-22Cr-15Ni (SP2215) is aged at 700 degrees C for different times, which presents good mechanical properties. The stress rupture strength can be maintained at 78 MPa by extrapolating to 105 h at 700 degrees C. Transmission electron microscopy (TEM) analysis reveals the multiphase composites strengthening mechanism. Three types of precipitates, the coherent Cu-rich particles, Nb-rich carbonitrides and NbCrN phase, are found in the austenitic matrix. The fine Cu-rich particles are the first to precipitate, most densely and homogeneously distributed, as is illustrated by atom probe tomography (APT). It is concluded that it is the multiphase nanoprecipitate strengthening and the high thermal stability of the precipitates that render the excellent mechanical properties at high temperature. With the significant advantages of high strength at 700 degrees C and cost-effective, the novel austenitic heat-resistant steel SP2215 is recommended to be a promising material for high-efficiency superheaters/reheaters of ultra-supercritical unit boiler at steam temperature from 620 to 650 degrees C.