Abstract: Industrial experimental research was carried out on the effect of adding rare earths at different times in the production process of “BOF→LF→VD→CC” for heavy rail steel. The rare earth content, inclusion size, number density and morphology in billet were analyzed. The results show that the yield of rare earth in the billet produced by adding rare earth after VD is 11.73 %, which is higher than that in the billet produced by adding rare earth after LF, which is 2.83 %. Combined with the analysis results of the oxygen content in the whole process, it shows that the rare earth participates in the deoxidation reaction after being added to the steel, and the reaction product floats up and removes. The addition of rare earth can effectively reduce the size of inclusions in the steel. Compared with the heavy rail steel without rare earth, in the heavy rail steel billet samples produced by adding rare earth after LF and after VD, the average length of inclusions decreases from 9.28 μm to 7.91 μm and 1.42 μm, respectively, and the average width decreases from 5.71 μm to 4.81 μm and 2.27 μm, respectively. The inclusion rating can be reduced, and the effect of reducing the inclusion rating of A, B, and D inclusions is obvious, and the inclusion rating of the heavy rail steel billet samples produced by adding rare earth after VD is better. By comparing the experiments of adding rare earths in different time, it is found that the process of adding rare earths after VD can improve the ability of heavy rail steel inclusions to modify. SEM and EDS analysis results show that rare earth mainly exists in Si-Ca-Mg-Al inclusions, which makes Si-Ca-Mg-Al inclusions change from water droplets to spherical, and the surface is enriched with sulfur. The analysis results of manganese sulfide inclusions show that, the process of adding rare earth after VD can make manganese sulfide and Si-Ca-Mg-Al inclusions coexist in steel, reducing the harm caused by manganese sulfide to steel.

Key words: rare earth, heavy rail steel, inclusions, adding time, manganese sulfide