Influence of Strain Rate on Grain Size Dependence of Strength of Sheet Steel

Abstract

Influence of strain rates on the grain size dependence of tensile deformation behavior was investigated on a mild steel and solid-solute hardened 440MPa and 590MPa grade steels. The grain size of these steels was ranged from 0.005mm to 0.2mm in diameter. Tensile tests were performed at strain rates of 0.02/s and 2/s with an Instron tensile machine, and at 2000/s with a split-Hopkinson pressure bar apparatus. The relationships between yield strength and grain size of the steels investigated were well represented by the Hall-Petch relationship, and the energy absorbed during deformation at the strain rate of 2000/s increased for finer grain size. The grain size dependence of the yield strength of the 440MPa and 590MPa grade steels was intensified with increase in strain rate, while, those of the mild steel were almost independent of the strain rate. The n-value of the mild steel was remarkably reduced with an increase of the strain rate. The grain size, however, didn't affect the n-value.