Advanced microstructural characterization of a lean duplex stainless steel cryorolled at 77K and isothermally annealed up to 800ºC

• Grant number: 23/13092-2
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: March 04, 2024
• End date: July 03, 2024
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Maria Jose Ramos Sandim
• Grantee: Rafael José Vieira Mesquita
• Supervisor: Dirk Ponge
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil
• Institution abroad: Max Planck Society, Dusseldorf, Germany
• Associated to the scholarship: 23/05852-7 - Study on austenite reversion and its influence on the magnetic properties of a duplex stainless steel cryorolled at 77K, BP.IC

Abstract

Duplex stainless steels (DSSs) have a microstructure comprised of approximately equal amounts of fcc austenite (g) and bcc ferrite (±), arranged in alternate lamellae. These steels have good mechanical properties and high corrosion resistance, which allow their use in chemical and oil and gas industries. The so-called lean duplex stainless steels (LDSSs) possess lower contents of nickel and molybdenum in comparison to conventional DSSs. The austenite phase is metastable in LDSSs and exhibits the transformation-induced plasticity (TRIP) effect. Two types of strain-induced martensite (SIM) can be formed: hcp µ-martensite or bcc ±2- martensite. It is well known that ±'-martensite results from a complex interplay involving dislocations, stacking faults, nanotwins and/or e-martensite. The SIM is strongly dependent on applied strain and stacking fault energy (SFE). With the decrease of temperature, the SFE decreases, and it is difficult to predict the deformation mechanism of metastable austenite at cryogenic temperatures. In this work, we will investigate the deformation behavior of cryorolled UNS S32304 lean duplex steel deformed to 10% and 50% reduction in thickness at 77 K. Representative annealed samples will be also probed to understand the mechanisms of austenite reversion. To resolve fine details of the microstructure, it is crucial the use of high-resolution techniques such as EBSD (including cross-correlation EBSD) and ECCI, which are available at the Max-Planck-Institut für Eisenforschung (MPIE) in Düsseldorf (Germany). There are only a few works in the literature on this topic. Cryorolling followed by austenite reversion is a potential route to obtain fine-grained steels with superior mechanical properties. (AU)