Influence of loading direction on tensile deformation behavior of a lean duplex stainless steel sheet: The role of martensitic transformation

In this work, the tensile deformation behavior of a hot-rolled lean duplex stainless steel with metastable austenite (named as present TLDX) was studied at 20 °C along the loading directions of 0°, 45° and 90° to the rolling direction (corresponding to the L-oriented, D-oriented and T-oriented specimens, respectively). The initial microstructure, martensitic transformation characteristics, damage and fracture behavior were clarified through microstructure observations. The intrinsic mechanism of anisotropy in tensile deformation behavior was comprehensively discussed referring to the microstructure characteristics. The present TLDX exhibited remarkable mechanical anisotropy at 20 °C, characterized by the highest values of ultimate tensile strength (σu = 853 MPa) and plasticity (et = 70.6%, eu = 62.3%) for the L-oriented specimen and the lowest values (i.e., σu = 790 MPa, et = 53.3%, eu = 50.4%) for the T-oriented specimen, although the yield strength is comparable (σs∼524 MPa) for different loading directions. Strain-induced martensitic transformation (SIMT) with a sequence of γ→ε→α′ was detected for all specimens. The L-oriented specimen is most favorable for SIMT, followed by the D-oriented specimen, and finally the T-oriented specimen, which, caused by the different strain partitioning response, is the main factor contributing to the mechanical anisotropy at 20 °C. Different damage and fracture characteristics for different loading directions were also identified, which are closely associated with the initial microstructure.