The use of dilatometry aiming to evaluate the metallurgical aspect of coil slump in a hot-rolled medium carbon steel

The hot coil slump is a recurrent problem in the manufacturing process of medium and high equivalent carbon steel plates. Even with the success of the hot rolling procedure, the posterior coil slump can occur, representing operational disorder and manufacturing cost increase. Some authors point that the coil slump phenomenon can occur due to metallurgical, mechanical and geometric aspects. Preview studies already investigated several possible mechanical and geometric contributions. However, there are few available experimental data about the metallurgical one, that is, the effect of late austenite decomposition during, or after the coiling stage. In this context, this paper presents a study about the application of dilatometry technique aiming to evaluate the influence of late phase transformations as a relevant cause of a medium carbon steel coil slump. Heating cycles that simulated, with good agreement, some possible plate cooling conditions and isothermal coiling procedures were performed in standardized specimens using a quenching dilatometer. Different combinations of cooling rates and coiling temperatures were evaluated. It was possible to conclude that the dilatometry technique application is viable and efficient to evaluate the metallurgical contribution to the coil slump phenomenon. For the studied steel, it was possible to suggest that a decrease of the cooling rate, in association with a slight decrease of coiling temperature, can significantly suppress the metallurgical influence on the coil slump occurrences.