Effect of phosphorus and carbon mass fractions on microstructure and properties of PM high manganese non-magnetic steels

Fe–Mn–P–C non-magnetic steel balance block parts were prepared by pressing-sintering method by adding Fe₃P powders and graphite powders in different mass fraction to the high manganese steel alloy powders. The effects of phosphorus and carbon content on the microstructure and properties of high manganese non-magnetic steels were studied, and the properties of Fe–Mn–P–C high manganese steels and Fe–Mn–Cu–C high manganese steels were compared. The results show that, the non-magnetic high manganese steels with the uniform structure can be prepared by adding Fe₃P powders to the high manganese steel powders. The density and hardness of the sintered parts increase with the increase of Fe₃P content. When the Fe₃P mass fraction exceeds 2%, the density of sintered parts remains basically unchanged. The hardness of sintered parts with 3% Fe₃P is the highest, reaching about HRB 95. When the Fe₃P mass fraction is less than 1%, the sintered part shows no magnetic characteristics; when the Fe₃P mass fraction is 2%, the sintered part shows the weak magnetic characteristics; when the Fe₃P mass fraction is 3%, the sintered part shows the strong magnetic characteristics. The density and hardness of sintered parts increase with the increase of graphite content. When 0.30% graphite is added, the density of sintered parts exceeds 7.30 g∙cm⁻³. When the graphite mass fraction is less than 0.30%, the sintered part shows no magnetic characteristics; when the graphite mass fraction is 0.60%, the sintered part shows the weak magnetic characteristics; when the graphite mass fraction is 0.75%, the sintered part shows the strong magnetic characteristics. Compared with the Fe–Mn–Cu–C high manganese steels, the density of Fe–Mn–P–C high manganese steels is relatively low, and the hardness and magnetism are equivalent, but the mechanical properties are better than that of the Fe–Mn–Cu–C high manganese steels.