Effect of high strain rate deformation on microstructure of strip steels tested under dynamic tensile conditions

The correlation between low and high strain rate deformation characteristics and the microstructure of novel strip steel products employed by the automotive industry has been assessed. Research has been carried out to establish whether microstructural changes during high speed deformation could explain the relative attributes of mild steel, carbon manganese steel and novel dual phase steel grades of increasing yield and tensile strength, in relation to their crash behaviour. The results obtained indicate that the dual phase steel grades having similar microstructures, although with varying strength levels, displayed the same response to high strain rate loading conditions. They both exhibited a reduction in the level of hardness at high strain rate compared with low strain rate deformation. The strain rate softening effect observed with the dual phase steel was accompanied by an increase in plastic deformation of the ferrite areas around the martensitic constituent regions.