Microstructural evolution of a cryorolled duplex stainless steel followed by isothermal annealing

• Grant number: 25/05060-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2025
• End date: May 31, 2026
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Maria Jose Ramos Sandim
• Grantee: Ian Vicente Tavares
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

Duplex stainless steels have a microstructure composed of alternating austenite and ferrite lamellae, with approximately equal volume fractions. Due to the combination of good mechanical properties and corrosion resistance, these steels are used in a range of applications in the chemical and petrochemical industries. Compared to austenitic stainless steels, few works report on the microstructural evolution in lean duplex steels deformed at cryogenic temperatures. In this project, the material to be investigated is the UNS S32304 lean duplex stainless steel, which presents strain-induced martensite. The focus of this project is the investigation of the microstructural evolution of this steel after cryorolling (50% reduction at 77K), followed by isothermal annealing at ¿ 1085oC, for several annealing times from 1 min up to 240 min. At this temperature, thermodynamic equilibrium predicts 50% austenite and 50% ferrite for the investigated steel. As control samples, the same steel will be cold-rolled at room temperature and annealed at the same conditions. For cold rolling (at room temperature), much less ¿' martensite is formed and microstructural fragmentation is also lower. Annealing under the proposed conditions will result in the ¿'- martensite -to -austenite reversion, in addition to recrystallization and, eventually, grain growth in the material. The microstructural characterization of the material will involve Vickers hardness tests and the use of optical microscopy (OM) and scanning electron microscopy (SEM) techniques. Representative samples will be mapped via EBSD (electron backscatter diffraction). The samples will also be characterized using magnetic measurements. For this purpose, hysteresis loops will be obtained at room temperature, from which the magnetic parameters MS (saturation magnetization) and HC (coercive field) will be obtained. (AU)