Impact of Rolling Conditions on Propagation of a Potential Crack
The paper reveals information about crack behavior during hot rolling of heavy-gauge products. FEM-based mathematical modeling has been used to investigate the impact of crack shape and rolling parameters on the distribution of the principal tensile stress and the Cockroft-Latham fracture criterion value and on the crack closing capacity. The results clearly show that the crack shape has the most powerful influence on the observed quantities followed by the rolling geometry factors. To find a critical value of the LCK for a specific steel grade and an actual rolling process, a laboratory experiment has been conducted, in which problems related to propagation of initial cracks were detected. It consisted in rolling of wedge-shaped specimens with a notch, which was introduced for the purpose of raising the probability of crack occurrence. In order to find the Critical LCK value in the area of the notch, an additional computer simulation was performed. Results of these experiments led to the conclusion that the steel possesses excellent formability. The Critical LCK values were up to 300 MPa, which is, essentially, an order higher than in actual rolling. As the critical value of LCK depends, among others, on the metallurgical characteristics of the metal, the key to the issue is in the steel microstructure. The findings brought the conclusion that in this specific case the rolling itself affects the crack propagation to a small extent only. The heating process poses a much greater challenge, as it is the likely stage involving the steel overheating.
Jitai NIU, Zuyan LIU, Cheng JIN and Guangtao Zhou
R. Fabík et al., "Impact of Rolling Conditions on Propagation of a Potential Crack", Materials Science Forum, Vols. 575-578, pp. 1445-1454, 2008