Oxidation processes, which are unavoidable in continuous casting and further hot processing of steel may have a negative impact on the surface quality. In view of the changes in the mix of input materials associated with the decarbonization of steel production, understanding the mechanisms behind high-temperature oxidation is of great importance: The interaction between external oxidation and internal oxidation, decarburization and liquid metal infiltration of grain boundaries will become essential for the retention of product quality under new operating conditions. These effects are influenced by parameters such as oxidation time, temperature, atmosphere and the chemical composition of the steel. Due to higher recycling rates of steel and the associated downscaling of scrap qualities, the issue of rising levels of tramp elements in steel is becoming a key topic, as elements such as Cu, Sn and Ni do not oxidize but accumulate at the bulk/scale interface or along grain boundaries which may lead to additional quality problems.
To address these newly arising research questions a lab test setup was established: Utilizing Simultaneous-Thermal-Analysis in combination with various gas atmospheres (CO2, up to 100 vol.% H2O, N2, O2, Ar) a precise simulation of surface oxidation in a wide variety of metallurgical processes became possible. The present paper addresses results on the behavior of different carbon steel grades with varying content of tramp elements (Cu, Sn, Ni) under the conditions of slab casting (CC), thin slab casting and direct rolling (TSCR) in batch and endless mode as well as the reheating in pusher type and tunnel furnaces. Combustion atmospheres of natural gas and hydrogen were tested.
The results provide a view on the potential quality problems arising with the forthcoming dynamic changes of steel composition and the need for an adoption of process routes and process conditions.