Fracture Mechanisms of Cold-Rolled Light-Weight Steel Plates Containing Different Carbon Content

An investigation was conducted into the effects of kappa-carbides on the cracking phenomenon, which often occurred in cold-rolled light-weight steel plates. Three kinds of steels were fabricated by varying the C content, and their microstructures and tensile properties were investigated. In the two steels that contained a high carbon content, the band structures of ferrites and kappa-carbides that were severely elongated along the rolling direction were well developed, whereas continuous arrays of kappa-carbides were formed in the steel that contained a low carbon content. Detailed microstructural analyses of the deformed region beneath the tensile fracture surface showed that the cracks initiated at arrays of kappa-carbides or kappa-carbides formed interfaces between the band structures, which initiated cleavage fractures in the ferrite bands, while the bands populated with a number of kappa-carbides did not play an important role in propagating the cracks. Thus, the minimization of interfacial kappa-carbides or kappa-carbide arrays by increasing the carbon content was essential for preventing cracking from occurring during cold rolling.