Effect of Low Aging Temperature and Reversion of α′-martensite on the Fracture Behavior of a 2304 Lean Duplex Stainless Steel

The effects of cold rolling, leading to strain-induced alpha'-martensite transformation and its subsequent reversion during annealing treatment, were investigated based on the microstructural evolution, mechanical properties, and fracture behavior of a lean duplex stainless steel (LDSS) 2304. Hot-rolled sheets 4 mm thick were cold-rolled up to 1.08 mm, with a 74% reduction, followed by isochronal annealing at 400 degrees C to 600 degrees C for 1800 s. In this range of temperature, an increase in strength occurred, leading to an increase in microhardness and tensile strength. The volume fraction of alpha'-martensite during cold rolling reached a value of 52% and, after reversion, 36%, meaning a 16% of volume fraction of austenite reverted. After tensile testing, all samples showed a brittle fracture due to work hardening and aging process of the microstructure, alpha'-martensite formation, and its respective low reversion volume fraction. An increase in the aging temperature enhanced the ductility with a decrease in the yield and tensile strength. Analyzed fractured surfaces reveled cleavage, quasi-cleavage and intergranular features in the aged conditions.