Is a special heat-resistant alloy used for high-temperature applications. In these so-called SiMo alloys, the addition of silicon increases heat-resistance by forming a protective layer on the surface.

The main application for SiMo is in Automotive Exhaust and Turbocharger Systems, but it is suitable for any high temperature application where both strength and ductility are required.

Ductile irons of the type of Si-Mo are characterized by increased resistance to long-term influence of high temperatures and cyclic temperature changes. They are mainly used in castings of combustion engine exhaust piping and other castings utilized at temperatures of up to 850°C.

Cast iron materials intended for high-temperature applications must possess both the necessary thermal stability as well as sufficient resistance to scale formation and changes in volume.

To obtain these properties, SiMo-cast iron (alloyed, ferritic SG cast iron) was developed. The carbon contained in the material is overwhelmingly present as nodular graphite chunks; this material is then alloyed with silicon (for the formation of a protective oxidation coating) and with molybdenum (to improve the mechanical properties at higher temperatures).

The improved resistance to scale formation provided by the silicon is based on the formation of a silicon-oxide-rich coating, which initially hinders and eventually stops further oxidation.

The element that is most helpful for improving high-temperature tensile strength, yield strength, and above all the fatigue properties at high temperatures, is molybdenum; the effects are best with a proportion of 0.5% to 3% (although this may be higher in special cases).