Effect of ultrafine-grained microstructure on creep behaviour in 304L austenitic steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 785; p. 139383
• Main Authors: Kral, Petr, Dvorak, Jiri, Sklenicka, Vaclav, Horita, Zenji, Takizawa, Yoichi, Tang, Yongpeng, Kvapilova, Marie, Svobodova, Marie
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 21.05.2020; Elsevier BV
• Subjects: Austenitic stainless steels; Creep behaviour; Creep tests; Creep-resistant steels; Grain boundaries; Grain size; Martensite; Microstructure; Misalignment; Plastic deformation; Precipitates; Room temperature; Sigma phase; Sigma phase precipitation; Size reduction; Tensile creep; Ultrafine-grained materials; Ultrafines; Ultrafine-grained materials; Creep behaviour; Creep-resistant steels; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.139383

The austenitic stainless steel 304 L was subjected to severe plastic deformation using high-pressure torsion technique at room temperature. The severe plastic deformation led not only to the grain size reduction but also to the transformation of austenite into deformation-induced martensite. At high imposed strains the martensitic boundaries disappeared and misorientation distribution exhibited nearly random misorientation distribution. The thermal exposure and tensile creep tests under constant load performed at 923 K and stresses ranging from 50 to 150 MPa revealed that austenitic microstructure contains σ phase. The ultrafine-grained microstructure coarsens during creep testing but the mean grain size is significantly finer than the predicted stationary subgrain. The results demonstrate that during creep testing new grains at precipitates of σ phase are formed and texture changes. The formation of new grains during creep keeps the microstructure of being ultrafine-grained and thus grain boundary mediated processes are enhanced in this steel.