The development of a kinetic model to predict iron oxide growth in reheating furnaces

In steel industry, Quality Strip Production plant (QSP®) represents the latest generation of Danieli’s thin slab casting and rolling technology, introducing a new level of quality and flexibility to the market. The main characteristic of QSP® plants is that they work continuously, therefore, after continuous casting, the semi-finished steel product enters directly inside the tunnel furnace to reheat slabs up to rolling temperature. During the reheating operation, hot steel surface reacts with the in-furnace oxidizing atmosphere resulting in the formation of an iron oxide layer, also known as scale. The yield loss due to this phenomenon depends on furnace operating conditions (i.e oxidizing atmosphere, furnace residence time, etc.) and ranges between 0.4 to 1% of reheated slabs. However, scale is also able to remove some surface defects. In this Thesis, the purpose is the development of a kinetic model able to predict, quantitatively, the growth of scale thickness inside tunnel furnace of QSP® plant, for two steel grades denoted as SAE1006-LC and SAE400-MC. The models obtained, one for each steel grade, were developed starting from more than 200 steel oxidation tests from literature, carried out at different process conditions, and from a series of laboratory oxidation tests executed at University of Udine. Furthermore, to study qualitatively scale formed, a surface characterization was performed using SEM, optical microscope and EDX. The research activity was conducted in Danieli & C. Officine Meccaniche SpA in collaboration with the Dipartimento Politecnico di Ingegneria e Architettura (DPIA) of University of Udine. The predictive capability of the two models obtained results to be rather accurate, indicating a promising prospect of application at industrial level to predict scale growth in reheating furnaces.