Abstract
Hot rolling of bars issued from continuous-casting aims at refining the material structure and guaranteeing the central soundness of the metallurgical product. The rolling route must be designed to achieve the complete closure of the shrinkage porosity inherent in the continuous casting process. To predict the void evolution, many models exist that can be implemented in the finite element simulation of the process. Nevertheless, these models need parameter adjustments to be adapted to the forming process, the formed material, and the real geometry of the void. Real scale tests being very expensive in the long product rolling mill, an improved representativeness experimental configuration was designed to reproduce at the laboratory scale the key characteristics of the thermomechanical path driving the void closure phenomenon. This testing consists of successive forming stages with shaped anvils applied to samples containing a shrinkage cavity. The shaped anvils and the forming conditions are calibrated to reproduce the levels of strain and the stress triaxiality of rolling stands, and the alternation of the forming direction of the industrial process. The geometry of the voids before and after the forming paths are measured by tomography. The simulation of the test with an explicit modelling of the void is developed parallel to the experiments. The simulation/experiment comparison allows the validation of the numerical model. The obtained model will be used in future works to perform a more extended design of experiments to characterise void closure during hot rolling of bars.
Highlights
Hot rolling of bars issued from continuous-casting aims at refining the material structure and guaranteeing the central soundness of the metallurgical product
The geometry of the void obtained by tomography and by simulation at its initial state and after the first stage are shown in Fig.6 and Fig.7 (Sample T9)
This protuberance can be due to nearly closed zones of the initial cavity, too thin to be observed by tomography, which reopens during forming
Summary
Hot rolling of bars issued from continuous-casting aims at refining the material structure and guaranteeing the central soundness of the metallurgical product. Shrinkage porosities are mainly concentrated in the centre of the bloom Their geometrical and physical properties are of great importance on their evolution during the forming process and on their final closure and healing. The considered porosities are empty (vacuum) without oxide layer at their internal surfaces During forming, their closure can be split up into two stages as described by Park and Yang [1]. To evaluate the void closure, Tanaka et al [5] proposed a parameter corresponding to the integration of the stress triaxiality according to the Numerical and experimental simulation of shrinkage porosity closure during hot rolling. An experimental and numerical simulations for the study of the void closure during hot rolling of cast bloom are presented. The numerical results and the experimental measurements are compared and discussed
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