Interpretation of the role of forest dislocations and precipitates in high-temperature creep in a Nb-stabilised austenitic stainless steel

The creep response of type 347 austenitic stainless steel was investigated by means of short-term constant-load tests at 750 degrees C. The material w as tested in annealed condition or after annealing and 10% prestraining. Th e results clearly show that cold working significantly increases creep stre ngth at 750 degrees C only at applied stresses larger than 150 MPa. Data we re compared with results available in the literature for type 304 steel. Th e differences between the two materials are discussed in the light of the c urrent theories of dislocation creep. In particular, the marked increase in creep strength observed in Nb-containing steels after testing the two mate rials in annealed condition was attributed to a fast precipitation of NbC n ucleated on dislocations. The different creep response of prestrained steel s are also attributed to the different kinetics of the precipitation of sec ond-phase particles (M23C6 in type 304 and NbC in type 347). (C) 2000 Elsev ier Science S.A. All rights reserved.