Magnetic properties of a 17.6 Mn-TRIP steel: Study of strain-induced martensite formation, austenite reversion, and athermal alpha '-formation

Author(s)

Souza Filho, I. R. ; Sandim, M. J. R. ; Cohen, R. ; Nagamine, L. C. C. M. ; Sandim, H. R. Z. ; Raabe, D.

• Document type: Journal article
• Source: Journal of Magnetism and Magnetic Materials; v. 473, p. 10-pg., 2019-03-01.

Abstract

Strain-induced martensite (SIM) formation was evaluated upon cold-rolling of a 17.6 wt.%Mn-TRIP steel by means of magnetic measurements, X-ray diffraction, and high-resolution electron backscatter diffraction (EBSD). alpha'-martensite formation was observed to be dependent on the presence of prior epsilon-martensite. Upon deformation, the coercivity of the ferromagnetic alpha'-martensite is characterized by strong magnetic shape anisotropy. Austenite (gamma) reversion was evaluated by means of in situ magnetic measurements during continuous annealing. The experimental results were compared to thermodynamic simulations. It turned out that y-reversion was not completed in the regime where a gamma-single phase field is expected, which suggests the splitting of alpha' -> gamma transformation into two stages. The Curie temperature of remaining a'-martensite was determined as being similar to 620 degrees C. Magnetic properties presented an annealing time-dependence within the temperature range of 500-600 degrees C, suggesting long-range diffusional alpha' -> gamma transformation. With the aid of electron channeling contrast image technique (ECU), we noticed that the formation of gamma-nanograins in the early stages of reversion is sufficient to induce strong magnetic shape anisotropy in this steel. After full austenitization at 800 degrees C, further in situ magnetic measurements were also used to track the magnetic response of the material upon controlled cooling. Athermal formation of alpha'-martensite within the prior athermal epsilon-phase was clearly observed for temperatures lower than 100 degrees C. Using thermodynamic modeling we also calculated the start temperature for epsilon-formation (M-s(epsilon)). Results showed that epsilon-martensite is indeed expected to form before alpha', which was confirmed in all cases by means of EBSD. (AU)

• FAPESP's process: 17/04444-1 - Study of microstructural stability and magnetic properties of Fe-Mn-C TRIP/TWIP steels
• Grantee: Maria Jose Ramos Sandim
• Support Opportunities: Regular Research Grants
• FAPESP's process: 17/17170-7 - Advanced microstructural characterization of two Fe-Mn-C steel grades (1.5 Mn wt-perc. and 17 Mn wt-perc.) in different metallurgical conditions
• Grantee: Isnaldi Rodrigues de Souza Filho
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate