Modification of MnS inclusion with trace tellurium to improve the machinability of medium-carbon low-sulfur steel

Under the industrial process conditions, trace tellurium (13 ppm and 22 ppm) was added to medium-carbon low-sulfur steel to optimize the morphology of MnS inclusion and thereby enhance the machinability of the steel. Voller-Beckermann microsegregation model was used to calculate the precipitation thermodynamics and growth kinetics of MnS inclusion. The morphology of observed MnS inclusion is mainly polygonal (type III), the observed microstructures of the steel are bulk-, acicular-ferrite, and pearlite, the inclusions are mainly present in the bulk-ferrite. The calculation results of inclusion relative plasticity show that 13 ppm Te reduces the relative plasticity of inclusions, while at a Te content of 22 ppm, the relative plasticity of inclusions increases by approximately 70%. Compared with the steel without Te, when containing 22 ppm Te, the material has the best machinability, the average cutting force and average surface roughness of steel are reduced by 3.47% and 38.75%, respectively.