Abstract: The role of rare earth in low carbon manganese (16Mn) steels with ordinary and low sulfur content obtained by ladle injection of SiCa powder has been investigated in industrial scale. It has been shown that elongated MnS inclusion is harmful to the transversal ductility and toughness of the steels. By means of ladle injection of Si-Ca powder or rare earths (RE) additions, its detrimental effect can be alleviated through desulfurization and shape control of sulfides. With the ladle injection of Si-Ca powder, the modification degree of MnS inclusions depends on the ratio of Ca/S in the steel.
It has been found that a small amount of RE addition after ladle injection of Si-Ca powber is available to ensure the complete shape control of sulfide in production practice and the ratio of RE/S required in the steel is much less 3 because of the co-existance of Ca in the steel. It has been suggested that the combination of desulfurization and RE addition is one of the efficient approach to obtain great and stable improvement of ductility and toughness of the steel.