Comprehensive understanding of effective parameters on edge cracking sensitivity of hot-rolled complex phase steels

Abstract

Good stretch-flangeability is an essential property for forming complex press-formed automotive parts such as chassis, suspension and control arm components. Continuous research is ongoing in developing materials that could improve the performance of Advanced High Strength Steels (AHSS) during industrial stretch-flangeable operations. Consequently, there is a great interest in investigating the sheared edge stretchability and determining the factors, critically influencing the product edge formability. The objective of the present research is to obtain a comprehensive understanding of effective parameters on the cut-edge behaviour of Hot-Rolled (HR) stretch-flangeable Complex Phase (CP) steels. The role of microstructural damage on the edge stretchability of CP steels was evaluated employing hole punching and Hole Expansion (HE) tests. The influence of product microstructure and inclusions were highlighted. A correlation between the Lankford coefficients ('r' value), strain hardening exponent ('n' value) and Hole Expansion Rate (HER) was investigated. Finally, a new specific testing procedure combining a shearing test followed by tensile test is proposed to correlate with hole punching and HE operations and to develop in-depth understanding.