Mechanical and microstructural behavior of a heterogeneous austenitic stainless steel processed by Equal Channel Angular Sheet Extrusion (ECASE)

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 792; p. 139779
• Main Authors: Muñoz, Jairo Alberto, Komissarov, Alexander, Avalos, Martina, Bolmaro, Raúl E.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.08.2020; Elsevier BV
• Subjects: Austenitic stainless steels; Deformation; Dislocation density; Dislocations; Equal channel angular extrusion; Heterogeneity; Heterogeneous microstructure; Heterogeneous structure; Martensite; Phase transformation; Plastic deformation; Plastic instability; Stainless steel; Strain; Tensile strength; Tensile tests; Thickness; Phase transformation; Heterogeneous microstructure; Tensile strength; Strain; Dislocations
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.139779

A sheet-shaped austenitic stainless steel (ASS) was processed by one ECASE pass. In this way, larger deformations were introduced close to the sheet edge vicinities, while the middle zone remained less affected by the deformation. The heterogeneous deformation produced larger amounts of deformation induced martensite (DIM) at the sheet edges, resulting in a heterogeneous structure along the sheet thickness. Tensile tests revealed that after the deformation process the material increased its yield strength more than 3 times from 200 MPa in its initial state to ~690 MPa after one ECASE pass. Tensile tests for the processed material in different zones of sheet thickness revealed the existence of two types of materials, one more resistant and less ductile (near the edges) and other more ductile, but less resistant (in the middle zone). Because of the heterogeneity, higher dislocation densities were found in the edges than in the middle of the sheet, giving rise to a plastic deformation gradient in which the region near the edge is capable of withstanding greater plastic deformations by generating a plastic instability as soon as the deformation starts. Through a rule of mixtures, it was found that the greatest strength contribution of the heterogeneous material came from the dislocations on the bcc martensite developed near the sheet edges. •Equal channel angular sheet extrusion process induces microstructure heterogeneity at room temperature.•Martensite grains around the edges and austenite grains on the sheet core make up the heterogeneous microstructure.•Heterogeneous strain distribution with the formation of a shear band in the hard region.•Plastic deformation gradient due to larger GNDs grouping close to the edges neighbor areas than in the sheet core.•Dislocations located around the edges apport the highest strength contribution.