Effect of microstructural evolution and fractographic properties on hole expandability of hot rolling complex phase steel with different coiling temperature

Hole expansion is one of the most important properties describing the formability of steel sheets, especially those used in automotive industry. In this paper, the effect of microstructure evolution and fractographic properties on hole expansion ratio has been studied and reported. The hole expansion test has been carried out for complex phase steel with different coiling temperature. Hole expansion ratio is strongly influenced by the microstructure of the steel. With the change of different mechanical properties, regular changes have also taken place in hole expansion rate. Besides, the fractographic factors, such as crack characteristic in the cross section of the vicinity of the hole expansion surface, void formation mechanisms, average dimple size, dimple density affect the hole expansion ratio. Among them the steel coiled at 520 degrees C has the best hole expansion ratio.