A New Processing Route for As-Cast Thixotropic Steel
Up to now, no technology exists for producing as-cast thixotropic steel at the industrial or pilot level. The existing processes need to reheat a billet that has been previously cast and wrought on separate equipment. The new processing route, we are developing, will allow producing as-cast steel (or high melting point alloy) with thixotropic properties. CRM has developed and patented a continuous casting technology, which by using a specially designed nozzle (HJN nozzle-hollow jet nozzle), allows to combine powder injection and a low superheat. It has been proven by pilot and industrial trials that the combination of iron powder injection and a low superheat leads to achieve a globular solidification structure in the core of a continuously cast steel billet. Several industrial trials on continuous caster have been carried out both with carbon and stainless steel but also on copper in order to modify the solidification structure of these materials. The application of this HJN technology is being studied in order to achieve a globular structure on as-cast steel with the objective to obtain a thixotropic behaviour of the material after an adequate reheating. Casting trials have been performed on CRM continuous casting pilot-line. Specifically designed equipment has been built for use in a steel foundry. The influence of the solidification rate, the superheat, the amount and the composition of the powder has been studied.
G. Hirt, A. Rassili, A. Bührig-Polaczek
G. Walmag et al., "A New Processing Route for As-Cast Thixotropic Steel", Solid State Phenomena, Vols. 141-143, pp. 415-420, 2008