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DUPLEX stainless steels (DSSs) are a category of high-alloyed steels characterized by a biphasic austenoferritic (c/a) microstructure obtained from a proper solution treatment after the forming operations. The presence of an equal volume fraction of the phases provides the best combination of mechanical and corrosion-resistance properties, making DSSs very interesting materials, especially for structural and special applications in aggressive environments.[1] However, owing to the presence of the metastable austenitic phase and to the instability of ferrite at high temperatures, these steels are sensitive to diffusive and diffusionless phase transformations. The eutectoidic decomposition of ferrite in the temperature range of 523 K to 1273 K (250 C to 1000 C) and its nitrogen-supersaturated condition are the main causes for precipitation of dangerous secondary phases,[1–5] limiting the employment of DSS at high

MARCO BREDA and KATYA BRUNELLI, Post-Doc Researchers, and IRENE CALLIARI, Researcher, are with the Industrial Engineering Department (DII), University of Padova, Via Marzolo 9 int. 4, 35131 Padova, Italy. FRANCESCO GRAZZI, Researcher, is with the Consiglio Nazionale delle Ricerche (CNR), Istituto dei Sistemi Complessi, Via Madonna del Piano 10, Sesto Fiorentino, 50019 Florence, Italy. Contact e-mail: [email protected] ANTONELLA SCHERILLO, Instrument Scientist, is with the Science and Technology Facility Council, ISIS Neutron Source, Didcot OX11 0QX, U.K. Manuscript submitted July 23, 2014. Article published online November 19, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A

temperatures. Further, the possibility of strain-induced martensite (SIM) formation from cold-worked austenite cannot be neglected if the phase is not adequately stabilized. Secondary phase precipitation from ferrite has been the subject of several studies,[1–5] but less attention has been paid to SIM formation from DSS austenite. Conversely, kinetics and mechanisms of SIM have been extensively investigated in metastable austenitic stainless steels (ASSs), in which it was found to occur at relatively low strains at a wide range of temperatures.[6–15] Recently, the austeniteto-SIM transformation was studied in low-alloyed DSSs grades (lean DSSs), in order to quantitatively describe SIM formation[16,17] and improve the mechanical characteristics by inducing the onset of the transformation induced plasticity (TRIP) effect.[18,19] On the other hand, in the higher-alloyed DSS grades, austenite is more stable and SIM has been more or less directly observed.[20–22] Austenite stability depends on the amount of solubilized alloying elements, and the involved deformation mechanisms can be associated with its staking fault energy (SFE), which is related to the chemical composition of the phase at a fixed temperature;[6] in isothermal conditions, the tendency to SIM formation increases with the decrease of SFE.[8] At room temperature, the martensitic transformation is governed by strain-induced mechanisms; therefore, its onset can be primarily rel