Effect of Surfactant Tellurium on the Microstructure and Mechanical Properties of M42 High-Speed Steel

The microstructure and mechanical properties of high-speed steels are sensitive to some surface-active additives. In this work, four M42 high-speed steel ingots containing tellurium (Te) in concentrations ranging from 0 to 500 ppm were prepared with a vacuum induction furnace, and their microstructure and mechanical properties were systematically investigated. Te combines with Mn and possibly forms MnTe phase located in the interdendritic regions together with eutectic carbides. Te obviously refines the primary dendrite stem and decreases the secondary dendrite arm spacing of as-cast M42 steel. Te hardly affects the fraction of eutectic mixtures, but greatly refines the size of eutectic mixtures. The presence of 163 ppm Te strongly promotes the formation of M6C eutectic carbides. This trend, however, is reversed at higher Te contents. 163 ppm Te increases the red hardness of M42 steel from 58.51 HRC to 60.8 HRC by suppressing the dissolution of secondary carbides. Further increasing Te content has no significant effect on the red hardness. Moreover, Te slightly deteriorates the tensile strength of as-cast M42 steel, while substantially improves the compressive and bending strength of tempered M42 steel. The reasons why Te affects the formation tendency of M6C eutectic carbides as well as the mechanical properties of M42 steel were discussed.