Recrystallization and mechanical behavior of high Mn and low C cold rolled and annealed steel with TWIP effect

Increasing demand for automotive vehicles with reduced weight, improved crashworthiness and passengers safety has steamed the research of new Twinning Induced Plasticity (TWIP) steels. In this work the effect of annealing between 400 and 900oC on the microstructure and mechanical properties of hot and cold rolled 0.06C-24Mn-3Al-2Si-1Ni (wt%) steel with TWIP effect was investigated. The results have shown that steel exhibits fast recrystallization kinetics with a low amount of recovery, which results in a high driving force for the former. Mechanical properties were determined using Vickers microhardness and tensile tests. Tensile strength of 670 MPa with 54% of total elongation, and strain hardening exponent of 0.57 were reached after annealing at 900°C

Effect of Uniaxial Tension on the Microstructure and Texture of High Mn Steel

Cold-rolled to 42% thickness reduction and annealed at 500, 625, and 700 C, an Fe-17Mn-3Al-2Si-1Ni-0.06C wt% steel is subjected to uniaxial tension and characterized via digital image correlation and electron back-scattering diffraction. The cold-rolled and 500 C samples return similar microstructures comprising predominantly α0-martensite and remnant e-martensite fractions and a trace fraction of untransformed austenite (γ) before and after uniaxial tension. For the 625 and 700 C samples, uniaxial tension results in the transformation of the initially reverted and recrystallized γ into e and α0- martensite via strain localization. The γ shows the formation of h111iγ, h100iγ double-fiber texture, whereas the e and α0-martensite show the development of the {hkil}e and h110iα0 || ND fibers, respectively. 1012gh1011ie extension twinning is also observed in e-martensite upon uniaxial tension. The cold-rolled sample exhibits a mixed brittle and ductile fracture mode. The fracture of the 500 C sample is similar to that of the cold-rolled sample, whereas the 625 and 700 C samples display a ductile fracture mode

Microstructure evolution during isochronal annealing of a 42% cold rolled TRIP-TWIP steel

A high manganese TRIP-TWIP steel was cold rolled to 42% thickness reduction and isochronally annealed between 600 to 900 °C for 300 s. The microstructural evolution during annealing was studied by high resolution electron back-scattering diffraction. After cold rolling, the steel comprised predominant fraction of α′-martensite, a small fraction of blocky ε-martensite and a trace fraction of retained austenite (γ). During annealing, the reversion of ε and α′ martensite to γ was followed by the recrystallisation of γ. While the processes of reversion to and recrystallisation of γ were completed by 700 °C, further annealing between 750 to 900 °C led to γ grain growth. A novel method to delineate the γ-γ grain boundaries was developed in order to accurately quantify γ grain size and subsequently the activation energy for γ grain growth

Effect of the cold rolling reduction on the microstructural characteristics and mechanical behavior of a 0.06%C-17%Mn TRIP/TWIP steel

High Mn steels, alloyed with Si and Al, present large plasticity when deformed due to the TRIP/TWIP effect. The present work studies the microstructural evolution and its influence on the mechanical behavior of a steel containing 17%Mn and 0.06%C after cold rolling to 45 and 90% reduction and subsequent annealing at 700 degrees C for different times. The microstructural analysis is performed by X-ray diffraction (XRD), scanning electronmicroscopy (SEM)-electron backscatter diffraction (EBSD), and transmission electronmicroscopy (TEM). It is observed that cold reduction induces the formation of epsilon- and alpha'-martensite. The material exhibits yield and tensile strength around 700 and 950 MPa, respectively, with a total elongation around 43% and a work hardening exponent of around 0.30 after 45% cold rolling and subsequent annealing and a yield and tensile strength of 750 and 950 MPa, respectively, with a total elongation of almost 50% when 90% cold rolling and subsequent annealing. The austenite texture contains brass, copper, and Goss components, while the alpha'- and epsilon-martensite textures mainly consist of rotated cube and prismatic and pyramidal fibers, respectively