Microstructure, Crystallographic Texture, and Stretch-Flangeability of Hot-Rolled Multiphase Steel

The microstructure, crystallographic texture, strain hardening in the hole edge-punched and stretch-flangeability of hot-rolled multiphase sheet steel is investigated by scanning electron microscopy, electron backscatter diffraction, and microhardness measurements. The results show that the strain hardening in the hole edge-punched is not the main factor that influences the hole expansion ratio. The bainite fraction, average grain area, and kernel average misorientation distribution mean are microstructure factors that improve the hole expandability and reduce the effect of strain hardening in the hole edge-punched on the hole expansion ratio. The crystallographic texture affects the hole expandability. The high intensity of {332}(alpha) and {111}(alpha) components that have higher normal anisotropy (r over bar ) also reduces the effect of strain hardening at the hole edge-punched. The cracks propagate through the interfaces following the banded microstructure direction at the hole edge-punched during the punching process. The gamma distribution analysis of the kernel average misorientation distribution indicates that there are different energy transfer (beta parameter) and dislocation densities due to different cooling rates.