Effect of Grain Size on the Deformation Properties of a High-Purity Fe–50Cr Alloy at 293 and 773 K

The effect of grain size on the deformation properties of a high-purity Fe–50Cr alloy at 293 and 773 K was investigated by tensile tests and microstructural observations. Due to grain coarsening, the deformation mode at 293 K is changed from dislocation slips based on Lüders deformation to twinning. Due to grain coarsening, the deformation mode at 773 K is changed from dislocation slip based on P-L (Portevin-Le Chatelier) mechanism to twinning. The yield stress in each of the deformation modes at 293 and 773 K obeys the following equation (i.e. Hall-Petch relation): σy=σ0+kyd−1⁄2. The coefficient kS, which is ky in the deformation mode due to dislocation slips, is different from the coefficient kT due to twinning; kS(293 K)=158, kT(293 K)=1597 in kN·m−3⁄2 and kS(773 K)=266, kT(773 K)=1995 in kN·m−3⁄2.