It can be seen from the experiment that in terms of mechanical properties, the mechanical properties of experimental gray cast iron sample D inoculated with silicon zirconium manganese inoculant are better than those of experimental gray cast iron samples a, B and C inoculated with other inoculants. There are two main reasons why ideal results can be obtained by inoculating experimental gray cast iron with Si Zr Mn inoculant:
First, in addition to the fact that silicon can promote graphitization, zirconium can also form zirconium carbide in molten iron. As the core of graphite nucleation, zirconium can promote the formation of fine and uniform graphite and improve graphite structure. Moreover, silicon zirconium inoculants can also reduce the tendency of white mouth and have strong anti-aging ability.
Second, based on the fact that sulfides and oxides are the nucleation matrix of graphite, the silicon zirconium manganese inoculant contains the alloy element Mn, Mn will form MNS with s in molten iron as the graphite nucleation matrix to promote graphitization and improve the inoculation effect.
In addition, the existence of manganese will also reduce the austenite transformation temperature, hinder the precipitation of ferrite and promote the formation of pearlite. Moreover, manganese dissolved into austenite as an alloy element will prevent the diffusion and precipitation of carbon atoms in the solid solution phase, inhibit the Eutectic Transformation and reduce the temperature of Eutectic Transformation. Therefore, the austenite phase area is expanded. The primary austenite can grow in the liquid phase at a lower temperature, squeezing the growth space of eutectic phase and limiting the growth space of graphite structure in eutectic phase, The graphite structure becomes more curved and fine, which will improve the tensile strength of gray cast iron.
Another reason for the improvement of tensile strength is that the experimental gray cast iron has formed primary austenite with equiaxed network framework structure, and the more complex the network framework structure of austenite, the smaller the dendrite spacing, and the more refined and developed the secondary dendrite. When it is transformed into pearlite, the finer the pearlite layer is, the more complex the pearlite cluster network framework structure is. When subjected to external tension, The more the complex network skeleton structure inhibits crack propagation.