Orientation dependence of transformation induced plasticity in high carbon bainitic steel

Abstract

The crystallographic orientation dependence of the transformation induced plasticity (TRIP) in the high carbon bainitic steel was studied. 0.6% C-2.0% Si-1% Cr steels were austenitized at two conditions to obtain different size of prior-austenite grains. Subsequently, they were austempered to evolve the bainitic structure composed mainly of bainitic ferrite and retained austenite. The characteristic of this sample is that it has much larger amount of carbon content compared with that of the conventional low alloyed TRIP steels. The bainitic steels with different sizes of mean prior-austenite grain show high strength with large ductility. The measurement of electron back scattering diffraction (EBSD) of the samples both before and after the tensile test clarified that much of the retained austenite transformed to ferrite while the austenite grains having the tensile orientation nearly parallel to <111> kept remaining after the fracture. This change indicates that the retained austenite with its tensile axis parallel near to <001> is preferential for the deformation-induced martensitic transformation. This behavior was found in the samples with different prior-austenite grain sizes.