Fundamental Study On The Control Of Inclusions By Rare Earth In Sulfur-Free-Cutting Steel

At present,sulfur-free-cutting steel commonly have problems such as unstable cutting performance and difficulties in continuous casting process.This is directly related to the control of the inclusions in the steel.In order to achieve effective control of inclusions in sulfur-free-cutting steel,the paper attempts to use rare earth treatment in it.Through high-temperature simulation experiments combined with thermodynamic analysis,the rare earth treatment of sulfur-free-cutting steels under different deoxidation process conditions was investigated.The influence law of the evolution of non-metallic inclusions in the research work has important theoretical significance for the improvement of the quality of sulfur-free-cutting steel products and the solution of process problems.The study found that under the experimental conditions,Ce was added to the aluminum deoxidized sulfur-free-cutting molten steel,and there was a process of Ce modified Al2O3 inclusions,and Al2O3 inclusions gradually transformed into Ce-Al-O inclusions.With the increase of Ce addition,the Ce/Al value of Ce-Al-O inclusions increases.The local enrichment of Ce can lead to the formation of an unstable inclusion phase of Ce-S.With the uniform diffusion of Ce,Ce-S inclusions will dissolve and disappear.When the Ce content is 0.05%,the Ce-S inclusions gradually change to Ce2O2S.When the Ce content is 0.01%,the stable inclusion phase in the molten steel is Ce-Al-O.When the Ce content is 0.05%,the stable inclusion phases in the molten steel are Ce2O2S and Ce-Al-O system.Under this experimental condition,Ce was added to silico-manganese deoxidized in sulfur-free-cutting molten steel.The process of inclusion of Ce-modifying Si-Mn-Al-o inclusions was gradually observed.The Si-Mn-Al-o inclusions gradually changed to Ce-Si-Al-O inclusions.When the Ce content is 0.1%,the Si-Mn-Al-0 inclusions are transformed into Ce2O2S inclusions.The local enrichment of Ce can lead to the formation of unstable inclusion phases such as Ce-S and Ce2O2S.With the uniform diffusion of Ce,the unstable inclusion phase will dissolve or disappear into a stable phase.When the Ce content is 0.01%,the stable inclusion phase in the molten steel is Ce-Si-Al-O.When the Ce content is 0.05%,the stable inclusion phase in the molten steel is Ce2O2S and Ce-Si-AI-O system;When the Ce content is 0.10%,the stable inclusion phases in the molten steel are Ce-S and Ce2O2S.The results show that Ce-Al-O,Ce-S and Ce2O2S inclusions in sulfur-free-cutting molten steel can provide nucleation for the precipitation of MnS in the solidification process,which is beneficial to control the morphology of MnS inclusions.