Effect of MnS distribution on machinability in low-carbon free-cutting steel

The effect of the distribution and size of MnS grains in steels on the machinability, especially on the surface roughness of the machined surface, was analyzed and compared with conventional steels. The workpiece materials used were SAE12L14, SAE1215, coarse MnS steel and fine MnS steel. The developed steel, when 800 parts made of it were machined, showed better machinability than leaded free-cutting steel SAE1215 and equal to or better machinability than leaded free-cutting steel SAE12L14. The comparative steel having the same sulfur content and large coarse MnS was superior to SAE1215 but inferior to SAE12L14. SAE1215 had the largest BUE and SAE12L14 has the second largest one. SAE1215 has the largest number of pieces of BUE and SAE12L14 has the second largest. The roughness of chip surface of the developed steel was fine. The result showed that the fine MnS grains distributed homogeneously inside the workpiece are kept supplied on the deformation zone around the cutting edge as lubricants from the inside of the workpiece along the tool edge position.