Extra-long creep rupture life of Alleima 3R60^TM (316/316L) stainless steel

ABSTRACT

Alleima 3R60^TM is 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(Ni_0.5)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.

KEYWORDS:

• Creep
• 316/316L austenitic stainless steel
• fine grain size
• microstructures
• precipitates

Acknowledgments

This work is published by permission of Alleima EMEA AB. The supports of Dr Tom Eriksson, Ms Eva Lindh-Ulmgren and Mr Martin Östlund, assistance of FIBSEM and ECCI investigation by Mr Jerry Lindqvist are acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).