An in situ Study of the Formation of Rare Earth Inclusions in Arsenic High Carbon Steels

Abstract

The application of rare earths is an effective way to stabilize residual elements in steel, such as As and P, so as to improve the performances of steel products. In situ methods were used to investigate the formation of inclusions and their stability at high temperatures in arsenic high carbon steels with additions of lanthanum. The results show that La₂O₃ and La₂O₂S started generating in molten steel and had significant difference of appearances and growth behaviors. La₂O₃ started with triangular particles and rapidly grew up like crystals; by contrast, La₂O₂S particles were always spherical or near-spherical and didn’t significantly grow up. Arsenic existed as LaAsO₄ that turned out to be unstable under high temperatures. LaAsO₄ decomposed and As dissolved into the matrix when the temperature was higher than 1200°C. The formation of LaAsO₄ during solidification and the dissolution of As into the matrix during heat treatment can effectively avoid the local enrichment of As. Therefore, it is possible to control As distributed uniformly in steel by appropriate heat treatment process.