Effect of Ferrite Grain Size on Dynamic Tensile Properties of Ultrafine Grained Low Carbon Steels with Various Chemical Compositions

The effects of ferrite grain size on dynamic tensile properties of low carbon steels with various chemical compositions are shown. The strain rate dependence of flow stress, represented by the difference between flow stresses at high and low strain rates, Delta sigma, was the highest in the interstitial free (IF) steel having ferrite single-phase microstructure and the 0.1% C-steel having ferrite-cementite (FC) microstructure. The Delta sigma-decreased when P and Mn were added. In all the steels used, the Delta sigma was almost constant or decreased only slightly when the ferrite grains were refined down to 2-4 mu m, and it decreased significantly by further grain refinement down to sub-micrometer region. The FC and ferrite single-phase microstructures strengthened mainly by grain refinement of ferrite showed higher dynamic absorbed energy compared with the other steels strengthened by alloy addition.