Study of the formation of strain-induced martensite and subsequent reversion to austenite of the UNS S32304 duplex stainless steel cryorolled at 77 K

• Grant number: 23/16898-8
• Support Opportunities: Regular Research Grants
• Start date: May 01, 2024
• End date: April 30, 2026
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Maria Jose Ramos Sandim
• Grantee: Maria Jose Ramos Sandim
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

Duplex stainless steels (DSSs) are used in the chemical and petrochemical industries due to their good mechanical properties and high corrosion resistance. Lean duplex steels contain lower nickel and molybdenum contents compared to conventional DSSs and present strain-induced martensite transformation (SIM). In this project, UNS S32304 lean duplex steel will be investigated, cryorolled at 77 K up to 50% of thickness reduction (epsilon = 0.7). For cryorolled steel with low deformation (epsilon = 0.1), the mechanisms acting in the first stages of SIM formation will be investigated. For steel with epsilon = 0.7, the austenite reversion mechanisms will be investigated. For this last purpose, the steel will be isothermally annealed at different temperatures up to 800oC and will be subjected to continuous heating up to 700oC to obtain dilatometry and calorimetry curves. The microstructural characterization of the material will involve Vickers hardness tests, X-ray diffraction and scanning electron microscopy. Representative samples will be investigated via EBSD (electron backscatter diffraction) and ECCI (electron channeling contrast imaging). Magnetic measurements will be carried out by obtaining hysteresis loops at room temperature. Studies on cryorolled duplex steels (77 K), combining microstructural, magnetic, dilatometric and calorimetric characterization, focusing on the strain-induced martensite and austenite reversion, have not been found in the literature to date. (AU)