Magnesium treatment method for cast iron melts developed by International Meehanite-Metal Co. Ltd., Reigate (England).
In this process, the magnesium treatment is performed directly in the casting mold in contrast to other common methods. The magnesium master alloy required for treatment is a granular powder or raw mold which contains magnesium along with calcium and silicon and therefore not only induces the formation of nodular graphite but also acts as an inoculum for mold inoculation. Thus, separate inoculation treatment is not necessary.
The treatment alloy is inserted into a treatment chamber formed in the runner section between the downsprue and gate. The relevant dosing quantity depends on parameters such as the casting weight, casting time, solution factor of the used treatment alloy and the required residual magnesium content in the casting.
This treatment process only requires small amounts of magnesium (residual magnesium content > 0.035%) and uses untreated iron up to casting; there is no fading effect and virtually no environmental impact due to magnesium fumes.
Disadvantages of this method include that a uniform distribution of the incorporated quantity of nodulizing agents must be ensured and that the generated reaction products, especially MgS, must be removed carefully and completely. However, the most severe disadvantage is that the successful Mg treatment must be verified for all castings. This is the reason why this process is rarely used today.
Nodular graphite cast iron
Structure formation of cast iron
Metal matrix of cast iron