Processing an 18Cr-8Ni Austenitic Stainless Steel Without the Dilemma of the Strength and Ductility Trade-Off

The magnitude of the contribution of common strengthening mechanisms in two samples of heterogeneous structured 18Cr-8Ni austenitic stainless steel (γ-SS) was innovatively compared using theoretical calculations and mechanical tests. Cold-rolling (CR) was applied to the commercial 18Cr-8Ni γ-SS (as-received specimen) to obtain a 30% CR specimen (a heterogeneous multiphase structure). The ultra-fine-grained/fine-grained (UFG/FG) specimen (a heterogeneous multimodal structure) was obtained after 90% CR and annealed at 800°C for 100 s. Tensile results elucidated that the yield strengths of the as-received, 30% CR and UFG/FG specimens were 349 ± 23 MPa, 1098 ± 15 MPa and 1008 ± 12 MPa, respectively. Additionally, the elongation of the as-received, 30% CR and UFG/FG specimens was 57.2 ± 2.7%, 25.4 ± 2.2% and 46.3 ± 2.1%, respectively. The static toughness of the as-received, 30% CR and UFG/FG specimens was 35,059, 27,189 and 57,328 MPa %, respectively, indicating superior comprehensive mechanical properties of the UFG/FG specimen. Moreover, average grain size, precipitate and dislocation density significantly influenced the yield strength. Due to the differences in structure, the 30% CR and UFG/FG specimens exhibited stress- and strain-induced transformations during plastic deformation, respectively. The 30% CR specimen had a more uneven dimple size distribution than the UFG/FG specimen, and the 30% CR specimen showed a higher degree of strain concentration during tensile.