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Production of ductile iron has been linked to the use of Mg and Mg-alloys since its invention. In the early history of ductile iron production, pure or high Mg containing alloys were needed due to the higher S level in the base iron. With the introduction of basic slag cupolas and low S base iron, the high Mg containing alloys were replaced with materials with lower Mg-content providing a calmer reaction with less slag generation and more predictable results and tighter control of the final Mg level. MgFeSi was recognized early as an excellent material to introduce Mg into the cast iron melt. MgFeSi offered the possibility to design both chemical composition and sizing to accommodate needs such as reaction control for different treatment processes, trace element control, packing density, and boosting of Mg-level. One of the main goals with MgFeSi treatments is to minimize the overall addition of Mg to tight reproducible low levels to reduce the shrinkage tendency observed with high final Mg levels. This can be achieved through a combination of optimization of the MgFeSi composition as well as improvement of the treatment process. A well designed MgFeSi-treatment can reduce fume and flare, slag generation, and the need for subsequent inoculation. The history and evolution of MgFeSi treatment along with relevant recent case studies will be presented in this paper. Examples of how the MgFeSi material can be optimized will be presented both in terms of theory and case studies. Focus of case studies will be on the recent evolutions focusing on maximizing Mg-yield through delayed and calm reaction.

During the 1960s and 70s research was aimed at developing a material withstanding the ever higher temperatures in a combustion engine. This work resulted in what have later been named SiMo and D5S. SiMo is a nodular cast iron typically containing 4–6 % Si and 0.5–2 % Mo and can be used in temperatures up to 850–860 °C. D5S is a nickel base material. High silicon and silicon–molybdenum content improves the dimensional stability of ductile iron. Silicon increases the transformation temperature where austenite transforms to ferrite. Molybdenum partly segregates and freezes in intercellular regions, promoting carbides while during the solid state transformation molybdenum particles precipitate around grain boundaries. The solidified material shows a range of interesting structures and phases which will be presented.

The structural characteristics of inoculated grey irons were studied. As a general rule, the beneficial influence of the three inoculating elements is in the order Ba⩽Ca

Specific investigations concerning La-contributions in graphite nucleation process in Ca,Al,La-FeSi inoculated grey cast irons were performed by using a scanning electron microscopy (SEM, EDS). It was re-confirmed that complex (Mn,X)S compounds act as major nucleation sites for graphite flakes. La was mainly concentrated in the first formed oxide-based micro-inclusions (similarly to Al), but also at an important level in the shell of (Mn,X)S compounds (accompanying Ca). It is assumed that La forms micro-inclusions later than Al, as La-reached phase surrounded Al-reached phase. Complex Al-La small micro-inclusions, as possible better nucleation sites for (Mn,X)S compounds and La-Ca presence in the shell/body of these sulphides, possible better nucleation sites for flake graphite, appear to be the peculiar effects of ferrosilicon based inoculants, which include these active elements, promoting type-A graphite, inclusively in low S-grey iron.

Two main chemistry systems of micro-inclusions can be identified in ductile iron: Ca-S-X and Mg-Si-O-X with the majority of the inclusions regardless of treatment type and location being of the second type, silicates. Laboratory investigations have shown that simple silicates were present in the matrix, while more complex silicates were present in conjunction with graphite, probably acting as graphite nucleation sites. In these more complex silicates, elevated levels of Al, Ca, Ce and La were typical. Comparing micro-particles embedded in iron matrix and graphite nodules of iron treated with pure Mg-metal and iron treated with MgFeSi alloy showed a higher amount of complex silicates with elevated Al-levels in the iron treated with MgFeSi. Further laboratory investigation was undertaken to explore which source of Al and which range of residual Al would have a favorable impact on the graphite nucleation in ductile iron. The work showed that a residual aluminum of 0.005 to 0.020 wt.% appears to be beneficial for improving ductile iron solidification characteristics without the incidence of pinholes. Greatest benefits were achieved when introducing the Al into the iron via an inoculant late during processing or via a pre-conditioner to the base iron. Al added via the MgFeSi provided less benefit. Some case studies illustrating the effect of Al in ductile iron are also presented, as Al-containing pre-conditioner or/and Al-bearing, FeSi inoculant application.