Procedures for microstructurally conditioning an Fe-22Mn-0.6C-1.5Al TWIP steel for optimal mechanical behaviour

BOJA, M.F. SKLATE; GIORDANA, M.F.; MALARRIA, J.; DRUKER, A.V.

MATERIALS CHARACTERIZATION

ELSEVIER SCIENCE INC

Año: 2023

1044-5803

Inthis work, we investigate the development of microstructures during thermomechanicalprocessing of an Fe-22Mn-0.6C-1.5Al TWIP steel designed and manufactured in thelaboratory, using optical microscopy, transmission electron microscopy andX-ray diffraction. The effect of rolling at room temperature, 600 °C and 1000°C followed by annealing at intermediate and high temperatures was related tothe mechanical properties measured with tensile tests. We found that theselected chemical composition controlled the value of the stacking faultenergy, so that the main deformation mechanism was twinning together with dislocationglide, for all sheet-processing conditions. The addition of aluminiumeliminated serrations in the stress-strain curves, guaranteeing stable plasticflow of the material during deformation processes. The accumulation of stackingfaults during rolling facilitated the formation of an abundance of twins in subsequentanneals. Twin boundaries appear distorted due to dislocation interactions, andthese distortions provided nucleation sites for nanometric mechanical twins.This microstructure reduced the mean free path of dislocations, increasing thehardening rate during deformation, which resulted in excellent mechanical properties.Among the thermo-mechanical processes studied, we found that the sheets rolledat 20 °C and annealed at 750 °C gave a total deformation close to 50% and amaximum strength greater than 1100 MPa, with a yield strength of 350 MPa. Thisprocess also produced a small grain size of 7μm, which is capable of developinga high number of twins during heat treatments and load application. Finally,such a process is a simple and economic procedure, easily adapted to industrialpractice.