Effect of Carbon Content on Cracking Phenomenon Occurring during Cold Rolling of Three Light-Weight Steel Plates

Abstract

Effects of carbon content on cracking phenomenon, which often occurred in cold-rolled light-weight steel plates, were investigated in this study. Three steels were fabricated by varying carbon content, and their microstructures and tensile properties were investigated. The steel containing low carbon content of 0.1 wt pct consisted of thin kappa-carbide bands, coarse band boundary kappa-carbides, and ferrites. As the carbon content increased, volume fractions of kappa-carbide bands and total kappa-carbides increased, and band boundary kappa-carbides were finely distributed in relatively wide band boundary areas. Microstructural observation of the deformed region of tensile specimens revealed that coarse kappa-carbides continuously formed along band boundaries worked to initiate the cracking or to facilitate the abrupt crack propagation into ferrites or band boundaries in a cleavage fracture mode, while bands densely populated with fine, lamellar kappa-carbides did not play a critical role in the cracking. Thus, the increase in carbon content effectively minimized the formation of band boundary carbides and reduced their size, thereby resulting in the prevention of cracking during cold rolling and in the simultaneous improvement of ductility and strength.