Effect of Mn Content in Steels on the Selective Surface Oxidation Behavior of 1 mass% Si Bearing Low C Steels in Recrystallization Annealing

Abstract

Effect of Mn content and dew point of recrystallization annealing atmosphere were investigated, on the selective surface oxidation and the internal oxidation behavior of 1 mass% Si bearing steels at 800°C, by glow discharged spectroscopy, X-ray photoelectron spectroscopy, secondary electron microscopy, transmission electron microscopy, auger electron spectroscopy, and IR absorption spectroscopy. For the steel of which Mn content was 1 mass% or less, the amount of the selective surface oxides of Si and Mn on the surface after annealing, were increased with the increase in the Mn content in steels, due to suppression of protective SiO₂ formation. For the steel of which Mn content was more than 1 mass%, both the selective surface oxidation and the internal oxidation behavior were remarkably affected by dew point of recrystallization annealing atmosphere. In case the dew point was -40°C, the amount of Si selective surface oxidation was almost constant and the internal oxidation was not occurred regardless of Mn content in steel. While in case the dew point was -30°C, the amount of Si selective surface oxidation was decreased and the amount of internal oxidation was increased with the increase in the Mn content in the steel. Those differences were explained by lowering thermodynamical oxidation potential of Si, Mn bearing steels with increase in the Mn content. At higher dew point, non-protective Si, Mn-oxides were formed at lower dew point of annealing atmosphere, which accelerated internal oxidation of Si, Mn bearing steels.