2014 年 63 巻 6 号 p. 467-472
Fracture behavior transition due to strain rate change in Fe-5%Si alloy with dislocation microstructures was studied to investigate the effect of pre-deformation on toughness. The Fe-5%Si alloy was multi-passed rolled (pre-deformed) at 1073K to various reductions up to 50% to introduce dislocation microstructure. The room temperature tensile deformation was conducted at various strain rates from 10-5 to 100/s. Electron backscattering diffraction measurements clarified that the dislocations were successfully introduced within the grains. All rolled alloys were fractured with local elongation (necking) at slower strain rate. When strain rate was faster, the local elongation disappeared and the fracture manner was turned to brittle. The strain rate at which fracture behavior changed increased with increasing of the reduction. On the other hand, the almost fully recrystallized Si steel was fractured in the brittle manner at any strain rate and the transition strain rate was not found. The fractured tensile specimen with no local elongations contains deformation twins ; however, these deformation twins were not observed in the fractured specimen with local elongations. This result indicates that the dislocation structure evolved during rolling suppressed the twinning and that the dislocation structure is effective for the enhancement of both ductility and toughness in Fe-5%Si alloy.