Effect of Ca-Mg and MgFeSi Graphite Nodularizers on the Nodular Graphite Characteristics of Ductile Cast Irons

The study investigated the effect of a series of Ca-Mg and a commercial grade MgFeSi graphite nodularizers, Fe75Si, and NiFeSi inoculants on the nodular characteristics (particle size, excursion ratio, degree of sphroidization, nodule count, and shape factor/nodularity) of ductile cast irons produced using a 100 kg diesel fired rotary furnace. This was with a view to controlling the volatile and fading effects of magnesium as a graphite nodularizer in the cast iron melt. Heats of the rotary furnace melts were pre-desulphurized with a pre-determined amount of CaC2:Fe45%Si in ratio 3:1. Subsequently, each melt was treated with different ratios of Ca-Mg based master alloys and the cast irons produced were compared with a commercial grade MgFeSi treated cast iron produced under the same conditions. Post-treatment inoculation in each case was carried out using Fe-75-Si. Microstructural characterization was carried out to determine the graphite nodularity and distribution characteristics. The results showed that the cast iron treated with 1:4 ratio of Ca:Mg combination master alloy yielded the optimum graphite nodularity with ASTM type 1 graphite nodule features, which are comparable to cast irons produced using the commercial grade MgFeSi nodularizer.