Effect of MnS Distribution on Machinability in Low Carbon Free-Cutting Steel

摘要

Conventionally, low carbon free-cutting steels are added lead (Pb) in order to cut the complicated and precise configurations of various parts. However, lead is listed in EU Directives as a harmful element for environments. In these parts, the first priority in developing lead-free free-cutting steel is not only to facilitate high-efficiency cutting but also to provide, without using lead, an extremely smooth finished surface after machining. Usually, to achieve long tool life in steel cutting, sulfur is added and it forms MnS inclusions in the steel. However, the shape and distribution of MnS have great effect on the surface roughness of machined surfaces. Therefore, in this paper, the effect of MnS distribution is studied. As a result, it is clarified that the developed steel with high S content and homogeneous distribution of fine MnS grains has better machinability, especially on the surface roughness, than that of the conventional leaded steel, SAE12L14.