Extra-long creep rupture life of Alleima 3R60TM(316/316L) stainless steel

ABSTRACTAlleima 3R60TMis an AISI 316/316 L type of stainless steel. This alloy shows extra-long creep lives. At 700°C with an applied stress of 45 MPa, the specimen broke first after 240 131 hours, a 140% longer creep life than the predicted. The reasons have been studied using SEM/EDS, EBSD, ECCI and TEM. Two unexpected phenomena have been observed. One is the presence of homogeneously dispersed small Mo2Fe4CrSi(Ni0.5)f063type of precipitates in the matrix. According to the thermodynamic calculation, this phase should not form in this alloy at 700°C. The other is the fine grains formed in the matrix during the creep-testing at 700°C for such an extra-long time. It is believed that both small precipitates and fine grain size contribute to this extra-long creep life of the steel. With the microstructural study and thermodynamic simulation, the mechanisms to form precipitates and fine grains have been discussed.