Industrial realisation of the production of thin strip in a casting rolling line

The aim of the project was the substitution of cold rolled and annealed strip for deep drawing applications by hot strip thinner than 2 mm. The hot strips were produced on a casting rolling line by low-temperature ferritic rolling. Based on ELC steel grades, two production routes were used: 1. high finishing and coiling temperatures to get a soft and ductile thin gauge hot strip for direct application, 2. low finishing and coiling temperatures to get a strained thin hot strip for direct annealing, particularly well-suited to a hot dip galvanising treatment just after pickling. The first mill trial was carried out in 2003 with a Ti-concept. Strips with low coiling temperatures were produced. Selected strained thin hot strips were hot dip galvanised. The requirements for drawing quality could not be achieved in the first test. For comparison, the mill trial was repeated at the pilot line at TU BA Freiberg. The results of the mill trial were confirmed. In a next step the chemical composition was optimised in Freiberg. Alloying concepts with Ti, Nb and B were tested. Meanwhile, the lubrication system of the casting rolling line was modified and optimised. The tested boron concept showed promising results and new production trials were performed. The results of the mill trials showed a clear improvement, but in most cases the desired properties were not achieved. New pilot trials were performed in Freiberg. The target was the understanding of the differences between pilot and mill trials. Additionally the influence of a higher B level was studied. The results of all additional tests in Freiberg demonstrated no clear solution for further mill trials. The expected mechanical properties, low yield strength in combination with high r-values, could not be reached with an ELC steel. These results confirmed the conclusion that a safe and successful industrial production on the casting rolling line could not be guaranteed.