Effect of Microstructure and Texture on the Edge Formability of Light Gauge Strip Steel

Abstract

Twin roll casting (TRC) of low-carbon ultra-thin cast strip (UCS) steel has the potential to deliver significant economic advantages over steels made by conventional processes. Novel microstructures containing intragranularly nucleated acicular ferrite may be produced in UCS products manufactured by the CASTRIP^®* process, however, their mechanical property performance has yet to be fully evaluated. This study compared the mechanical properties and edge formability of UCS steel produced by the CASTRIP process to steel produced by conventional hot rolled (HR) and cold rolled and continuously annealed (CR & CA) process routes. The results revealed an apparent paradox, where recent UCS steel produced by the CASTRIP process was shown to have lower total tensile elongation values, yet higher edge formability than products manufactured by the conventional process routes. The discrepancy was largely attributable to the influence of acicular ferrite microstructure on steel plasticity. Acicular ferrite decreased macro-plasticity by reducing the contribution of yield point elongation (lower volume fraction of pro-eutectoid ferrite) and post uniform elongation (strain localisation to softer pro-eutectoid ferrite) components of the total tensile elongation value. Conversely, the high homogeneity of the acicular ferrite microstructure enhanced micro-plasticity of the UCS steel produced by improving resistance to void initiation and propagation during forming. This study also showed that plastic anisotropy can significantly influence the edge formability of low-carbon sheet steel, with failure occurring along the direction where the resistance to through thickness thinning was the least. * CASTRIP is a registered trademark of Castrip LLC