Advanced microstructural characterization of two Fe-Mn-C steel grades (1.5 Mn wt-perc. and 17 Mn wt-perc.) in different metallurgical conditions

• Grant number: 17/17170-7
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: October 02, 2017
• End date: August 01, 2018
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Maria Jose Ramos Sandim
• Grantee: Isnaldi Rodrigues de Souza Filho
• Supervisor: Prof. Dr.-Ing. Dierk Raabe
• 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: 15/26409-8 - A comparative study of the microstructural stability and magnetic properties of two Fe-Mn-C (1,5%Mn and 17%Mn) steels, BP.DR

Abstract

In the last decades, advanced high strength steels (AHSS) have been widely used in automotive industries due to their outstanding mechanical properties. These steels are based on Fe-Mn-C system and combine good strength and ductility. During deformation, Fe-Mn-C steels present several complex work hardening mechanisms, which are closely related to their metallurgical parameters. Among such mechanisms, transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects are the most important. Fe-Mn-C steels have been extensively investigated, however many issues still demand attention. In situ high-energy synchrotron radiation studies focused on the micromechanical behavior of low-Mn TRIP-assisted steels. However, similar studies for high-Mn steels are scarce in the literature. Austenite and epsilon-martensite are both paramagnetic, while alfa'-martensite has a ferromagnetic character. Consequently, magnetic measurements are employed to determine strain-induced martensite (SIM) content in TRIP steels. Contrastingly, the behavior of coercive field of these materials are much less investigated. Depending on chemical composition, Fe-Mn-C steels can also present athermal martensitic transformation. In this context, in situ magnetic measurements taken during annealing and cooling can be a useful tool to evaluate such transformation. In this ongoing PhD work, martensitic transformation have been investigated for two Fe-Mn-C steels with different Mn content (viz. 1.5% and 17%). For TRIP effect evaluation, these steels were deformed by means of uniaxial tensile testing as well as cold rolling. Concerning uniaxial tensile testing, it was carried out during in situ synchrotron radiation diffraction at the Brazilian Synchrotron Light Laboratory (LNLS, Campinas-SP). The 1.5%Mn-TRIP steel was deformed up to failure. After that, samples were prepared for further microstructural characterization. Regarding the 17%Mn-TRIP steel, it was deformed up to an equivalent strain of 0.22. After deformation, the unloaded material was annealed up to 800oC (3oC/min) and cooled down to room temperature at the same rate. During deformation and annealing processes, in situ X-Ray synchrotron diffraction was performed as well. For the cold rolled specimens, the formation of SIM and its reversion were also evaluated using both in situ and ex situ magnetic measurements. For the 17%Mn steel the influence of parent austenite grain size on the athermal martensitic transformation has also been evaluated using both in situ and ex situ magnetic measurements. In the present stage of the work, microstructural evolution of Fe-Mn-C steels involves the formation of micron- and submicron-size features. Therefore, the aim of this proposal is to perform an advanced microstructural characterization of Fe-Mn-C steels, using the high-resolution techniques available at Max Planck Institut für Eisenforschung (MPIE) - Düsseldorf-Germany - in particular electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques. High-resolution EBSD maps will be collected using a step size of 20 nm. Representative samples from the cold rolled steels will also be investigated by means of SEM-ECCI in a Zeiss Merlin microscope to resolve fine microstructural details, such as dislocation substructures, stacking faults, micromechanical twinning, and martensite.

Scientific publications

(6)

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

SOUZA FILHO, I. R.; DUTTA, A.; ALMEIDA JUNIOR, JR., D. R.; LU, W.; SANDIM, M. J. R.; PONGE, D.; SANDIM, H. R. Z.; RAABE, D.. The impact of grain-scale strain localization on strain hardening of a high-Mn steel: Real-time tracking of the transition from the gamma -> epsilon -> alpha ` transformation to twinning. ACTA MATERIALIA, v. 197, p. 123-136, SEP 15 2020. (17/17170-7, 15/26409-8)

SOUZA FILHO, I. R.; DA SILVA, A. KWIATKOWSKI; SANDIM, M. J. R.; PONGE, D.; GAULT, B.; SANDIM, H. R. Z.; RAABE, D.. Martensite to austenite reversion in a high-Mn steel: Partitioning-dependent two-stage kinetics revealed by atom probe tomography, in-situ magnetic measurements and simulation. ACTA MATERIALIA, v. 166, p. 178-191, MAR 2019. (17/04444-1, 15/26409-8, 17/17170-7)

SOUZA FILHO, I. R.; DUTTA, A.; ALMEIDA JUNIOR, D. R., JR.; LU, W.; SANDIM, M. J. R.; PONGE, D.; SANDIM, H. R. Z.; RAABE, D.. The impact of grain-scale strain localization on strain hardening of a high-Mn steel: Real-time tracking of the transition from the gamma -> epsilon -> alpha ' transformation to twinning. ACTA MATERIALIA, v. 197, p. 14-pg., 2020-09-15. (15/26409-8, 17/17170-7)

SOUZA FILHO, I. R.; SANDIM, M. J. R.; COHEN, R.; NAGAMINE, L. C. C. M.; SANDIM, H. R. Z.; RAABE, D.. Magnetic properties of a 17.6 Mn-TRIP steel: Study of strain-induced martensite formation, austenite reversion, and athermal alpha '-formation. Journal of Magnetism and Magnetic Materials, v. 473, p. 10-pg., 2019-03-01. (17/04444-1, 17/17170-7)

SOUZA FILHO, I. R.; SANDIM, M. J. R.; COHEN, R.; NAGAMINE, L. C. C. M.; SANDIM, H. R. Z.; RAABE, D.. Magnetic properties of a 17.6 Mn-TRIP steel: Study of strain-induced martensite formation, austenite reversion, and athermal alpha `-formation. Journal of Magnetism and Magnetic Materials, v. 473, p. 109-118, MAR 1 2019. (17/04444-1, 17/17170-7)

SOUZA FILHO, I. R.; SANDIM, M. J. R.; PONGE, D.; SANDIM, H. R. Z.; RAABE, D.. Strain hardening mechanisms during cold rolling of a high-Mn steel: Interplay between submicron defects and microtexture. MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, v. 754, p. 636-649, APR 29 2019. (17/04444-1, 15/26409-8, 17/17170-7)