Deformation and recrystallization behavior of a Fe-30Mn-4Si-3Al-0.097C steel

It is fundamentally important to understand the influence of strain on the density of deformation twins in TWIP steel because twinning is its dominant deformation mechanism.The deformation behavior of a Fe -30Mn - 4Si-3Al-0.097C steel has been investigated by X -ray diffraction(XRD),electron backscatter diffraction (EBSD) and transmission electron microscopy(TEM) techniques.Sample with an average grain size of 10μm was deformed in cold - rolling with a reduction of 10%,20%,30%,40%,50%,60%and 70%,respectively. The mechanical properties of the cold - rolled samples were further investigated by tensile tests.The yield strength (σy) and ultimate - tensile - strength(σUTS) of the as - prepared sample is 480 MPa and 850 MPa, respectively.However,under cold rolling deformation,the tensile strength obviously increases with an increase in rolling reduction.The sample with a rolling reduction of 10%exhibitsσy of 610 MPa andσUTS of - 1000 MPa. The yield strength and tensile strength are further enhanced up to 1320 MPa and 1 378 MPa for the specimen with a rolling reduction of 70%,regardless of the poor ductility of 6.7%.The deformation microstructures were studied by EBSD and TEM observations.It is found that,with increasing rolling reduction,the average distance between deformation twins decreases gradually while the density of deformation twins(the length of twin boundary in unit area) exhibit a maximum value at 40%cold-rolling + tension.Carefully statistics analysis reveals grain orientation is closely related to the deformation twins and the underlying mechanism governing the twinning is discussed.