Notch ductility of steels for automotive components

The aim of this work is to experimentally evaluate the notch ductility of a TWinning Induced Plasticity (TWIP) steel, a Dual Phase (DP) steel and two Quenching and Partitioning (Q&P) steels for automotive components. The notch ductility was investigated by studying the resistance to fracture initiation in tensile specimens with notches of various root radii. Fracture toughness is discussed in terms of the critical J-integral J(c). It was found that J(c) progressively increases with the notch tip radius rho for all the studied steels, demonstrating a high sensitivity of ductility upon notch severity. The relationship between J(c) and rho allowed to calculate the maximum strain at fracture initiation epsilon(max) that is proposed as a deformation limit parameter useful to rank the forming capacity of the steels. It can be considered as the maximum strain that can be sustained ahead of the notch tip up to the onset of fracture advancement. Afterwards, a metallographic analysis by means of light optical microscope and scanning electron microscope was carried on etched specimens. The fracture mechanisms were also investigated by means of scanning electron microscope. (C) 2014 Elsevier Ltd. All rights reserved.