Abstract:
The effects of magnesium (Mg) on the microstructure and properties of 440C stainless bearing steel melted under pressurized conditions were studied. Adding Mg improved the cleanliness of molten steel, modified the inclusions in steel, enhanced the distribution of carbides, and improved the mechanical properties and corrosion resistance of experimental steel. In detail, the contents of TO, S, and N in steel decreased from 0.0013 to 0.0003 wt.%, from 0.0032 to 0.0018 wt.% and from 0.0088 to 0.0049 wt.%, respectively. In addition, the transformation order of oxide inclusions in steel is Al2O3 -> MgO center dot Al2O3 -> MgO, where the content of Mg in steel sharply increased from 0.00 to 29 x 10(-4), 81 x 10(-4), and 160 x 10(-4) wt.%, and the transformation order of S-containing inclusions in steel is MnS -> Mg-S-Mn(-MgO) -> Mg-O-S. Moreover, the number and size of inclusions and the proportion of large-size inclusions in steel decreased rapidly. Furthermore, the network structure of carbides in steel collapsed, the size of carbides was reduced, and the distribution was more uniform. Finally, the tensile strength, impact toughness, and pitting corrosion resistance of the experimental steel were significantly improved.
