Influence of microstructure and strain rate on the strain partitioning behaviour of dual phase steels

Abstract

Two dual phase steels with varying martensite content (∼ 10 and 33%) have been deformed in tensile mode at various strain rates (0.001–800/s). The microstructural parameters after deformation have been studied in detail using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The minute details of deformation features within the ferrite matrix have been investigated using EBSD based misorientation analysis. The influence of metallurgical parameters like ferrite grain size and its spatial distribution, the size and fraction of martensite on the deformation at different strain rates have also been investigated along with evolution of crystallographic texture. It has been found that strain rate influences the gradient in deformation in the ferrite grains between the interface and the grain interiors. Increase in martensite although enhances the dislocation density in the ferrite grains, but it also restricts the rotational ability of ferrite, which led to restricted sub-structural recovery at high strain rates. By observing the misorientation development ahead of the interphase boundaries, the failure mechanisms of these dual phase steels have been explained.