Simple Solutions That Work! Issue 10

S ilicon and magnesium are two of the major elements in ductile iron. Both elements effect the amount and form of graphite and matrix structure and both have a profound effect on the physical properties of the iron. Unlike carbon, which can be adjusted easily to meet specification, controlling silicon and magnesium contents can be difficult. Much of this difficulty arises because in the sequence of making ductile iron, silicon is contributed at almost every stage: The most common method used to produce ductile iron utilizes magnesium ferrosilicon. The silicon level in the untreated, base iron is intentionally kept low so that after the iron is treated with magnesium ferrosilicon and post- inoculated, both the carbon and silicon are within specification. From this point forward, the foundry will have a finite time limit to pour castings (this limit varies but typically will be about 12-15 minutes). The moment ductile iron is treated with magnesium, the clock starts ticking. As time expires, the treated DI should be poured in a “pig mold” as the metal has faded, i.e. magnesium is lost and lower than specification due to oxidation/resulfurization reactions. This paper will primarily focus on magnesium fade in automatic pouring units and how this iron can be rejuvenated back to useable Ductile Iron. The two most common automatic pouring systems are 1.) an un-heated pouring unit with a graphite/refractory stopper rod for indexing the molten metal directly into a highly automated green sand molding line, or 2.) a pressure pour channel induction furnace situated directly over a highly automated green sand molding line. Often, it will be necessary to rejuvenate "dead" or faded ductile iron if there is 1.) a molding line breakdown or 2.) a need to rejuvenate magnesium levels at the beginning of a shift or over a weekend (referred to as Monday morning iron). When confronted with faded treated DI in automatic pouring, unheated pouring units can be drained and refilled with new treated DI with minimal difficulty. DR. ROD NARO AND DAVID WILLIAMS ASI INTERNATIONAL, Inc. ARTICLE TAKEAWAYS: • Controlling silicon and magnesium in ductile iron • Working with faded treated ductile iron in automatic pouring • Ways of boosting magnesium content in faded ductile iron NEW, IMPROVED METHOD TO RESUSCITATE FADED DUCTILE IRON 50 1. Returns, which contain silicon, must be used in the melting furnace charge. 2. Magnesium ferrosilicon alloys, the most widely used additives, typically contain 40 to 50% Si. 3. Most post-inoculants used to promote graphite nucleation may contain up to 75% silicon.