This specification covers castings made of silicon-molybdenum ferritic iron, commonly known as SiMo, with spheroidal graphite (SG), compacted graphite (CG), and mixed graphite (MG) microstructure, respectively, and intended for high temperature service in automotive and allied industries.
Among ASTM standards of iron castings, there are two standards (A518 and A861) specifying very high-silicon content of 14% for corrosion-resistant irons. But the rest of iron casting standards specify silicon content less than 3.0% (austenitic iron castings are not in the scope of this discussion). Advantage of silicon is evident in solution strengthening and heat resisting for ferritic iron castings. It is noticed that ASTM specifications are lacking for high-silicon iron castings for use at elevated-temperatures in which silicon content ranges from 3.5 to 4.8%. ASTM standards are available for spheroidal graphite (SG) iron specifying minimum 90% graphite nodularity percentage (e.g., A395), and for compacted graphite (CG) iron specifying maximum 20% nodularity percentage (A842). It was found that mixed graphite (MG) iron having graphite nodularity between CG and SG exhibits improved materials properties and manufacturability. However, no standard specification for MG iron castings has been created yet.
KeywordsHigh-Silicon Ferritic Iron; Silicon-molybdenum (SiMo) Iron; Spheroidal Graphite (SG); Mixed Graphite (MG); Compacted Graphite (CG); High Temperature Applications.
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
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