Zr添加硫黄快削鋼に関する研究

抄録

Effects of zirconium addition on sulphide morphology, mechanical properties and machinability of resulphurized steels have been studied. Zirconium forms zirconium oxide, nitride, carbon-nitrogen sul phide and different types of sulphides in resulphurized steels. Remarkable improvements of sulphide morphology are observed in hot rolled steels containing a certain minimum amount of zirconium or more, which depends on both nitrogen and oxygen contents in steels. X-ray diffraction and electron diffraction analyses show that this non-deformable sulphide during hot rolling is MnS-Zr₃S₄ eutectic.
The formation of oval sulphide by zirconium addition has beneficial effects on the tensile ductility for the transverse specimens and the cold forgiability evaluated by the upset test, while little effect is observed for the properties of the longitudinal specimens.
Effects of zirconium addition on the machinability have also been investigated. In turning with high speed steel tool, the tool life, cutting force and cutting ratio are not apparently influenced by zirconium addition. Oval sulphides in zirconium contained steels, however, promote the void formation at the sulphide/matrix interface in the primary shear zone during chip formation.