The effect of banded microstructures on the hole expansion behavior of hot-rolled steel

Multiphase steels are widely used in automotive components due to their high strength and good local formability. The subtle hardness difference between microstructures makes multiphase steels exhibit excellent hole expansion performance. Our previous work insights that the distribution of microstructures changes the position of the serious plastic damage area on the punching hole edge which positively and decisively influences the hole expansion behavior of 800 MPa grade hot-rolled steels. In this work, two types of banded structures steels were constructed and their hole expansion behavior with and without pre-damage was investigated. The steels with banded ferrite and pearlite have excellent hole expansion performance due to their strong deformation capacity after necking. The cracks extending circumferentially along the direction of the banded structures and the higher toughness of the matrix are responsible for the higher hole expansion performance. The combination of ferrite and pearlite banded structures is an outstanding microstructure that has the potential to inspire the development of advanced high strength and hole expansion requirement multiphase steels.