Effects of Annealing Treatment Prior to Cold Rolling on the Edge Cracking Phenomenon of Ferritic Lightweight Steel

Abstract

Effects of annealing treatment from 923 K to 1023 K (650 A degrees C to 750 A degrees C) prior to cold rolling on the edge cracking phenomenon of a ferritic lightweight steel were investigated. The edge cracking was severely found in the hot-rolled and 923 K (650 A degrees C)-annealed steels after cold rolling, whereas it hardly occurred in the 1023 K (750 A degrees C)-annealed steel. As the annealing temperature increased, lamellar kappa-carbides were dissolved and coarsened, and most of the kappa-carbides continuously formed along boundaries between ferrite and kappa-carbide bands disappeared. Microstructural observation of the deformed region of tensile specimens revealed that the removal of band boundary kappa-carbides reduced the difference in tensile elongation along the longitudinal direction (LD) and transverse direction (TD), which consequently led to the reduction in edge cracking. The 1023 K (750 A degrees C)-annealed steel showed fine ferrite grain size, weak texture, and decomposed band structure after subsequent cold rolling and intercritical annealing, because kappa-carbides actively worked as nucleation sites of ferrite and austenite. The present annealing treatment prior to cold rolling, which was originally adopted to prevent edge cracking, also beneficially mod