Influence of the rare-earth elements on the morphology of non-metallic inclusions in microalloyed steels

Purpose: The modification of the chemical composition of non-metallic inclusions by rare-earth elements in the new-developed microalloyed steels was discussed in the paper. The investigated steels are assigned to production of forged elements by thermo-mechanical treatment. Design/methodology/approach: The modification of the chemical composition of non-metallic inclusions by rare-earth elements in the new-developed microalloyed steels was discussed in the paper. The investigated steels are assigned to production of forged elements by thermo-mechanical treatment. Findings: The high metallurgical purity is confirmed by a small fraction of non-metallic inclusions averaging 0.075%. A large majority of non-metallic inclusions are fine, globular oxide-sulfide or sulfide particles with a mean area 17 μm2. The chemical composition and morphology of non-metallic inclusions was modified by Ce, La and Nd, what results in a small deformability of non-metallic inclusions during hot-working. Research limitations/implications: Transmission electron microscopy investigations of non-metallic inclusions after initial hot-plastic working is predicted. Practical implications: Introduction of mischmetal in the amount of 2 g per 1 kg of steel causes total modification of chemical composition of non-metallic inclusions. Originality/value: The presence of dispersive, complex modified oxysulfide-type non-metallic inclusions can have advantageous influence on a decrease of grain growth of austenite during hot working similarly as MX interstitial phases. The factors mentioned above should favour the production of forgings with high strength and ductility.