silicon metal casting & Ni-Resist

In addition to all customary steel alloys, CIREX also casts components in SiMo (‘Silicon molybdenum’). This iron composite is chosen for components that will be used in hot environments such as exhaust manifolds, for example. The SiMo alloy is characterised by good heat resistance: components continue to function when exposed to high temperatures.

Silicium Molybdenum metal (SiMo)

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. This protective layer is structured as follows (viewed from the outside)
• Iron oxides (Fe3O4 and Fe2O3)
• Iron and iron silicon oxides (FeO and Fe2SiO4)
• Silicon dioxide (SiO2)

In short, SiMo has good resistance to high-temperature oxidation due to its silicon.

Silicon metall has a ferrite material structure because it consists of 90% pure iron. Pure iron = ferrite. The other elements are either neutral – such as graphite – or ferritising, such as silicon and molybdenum. The alloy element molybdenum (Mo) is added to improve mechanical properties (tensile strength). This forms with silicon carbides. This makes SiMo not only heat-resistant, but also reasonably strong.

SiMo alloys are used in applications with temperatures up to 750/800°C and is an alloy used in turbos, exhaust manifolds and EGR (‘Exhaust Gas Recirculation’), for example. Components made of SiMo start to deform only if they are exposed for an extremely long time to temperatures above the austenite transformation temperature. At temperatures above 750°C, the ferrite gradually transforms into austenite (the higher the temperature, the greater the proportion of austenite), yielding decreased mechanical properties. The deformation begins once the protective layer in the austenite transformation rips open. That is why SiMo is not used in applications in which temperatures exceed 800°C.
SiMo alloys have the following characteristics:
• Iron alloy capable of withstanding high temperatures
• Cheap alloy in comparison with other heat-resistant alloys such as Inconel 625 or 713, for example
• Suitable for mechanical processing
• Low coefficient of expansion

SiMo alloys are included in the DIN EN 16124 standard.

Application

exhaust gas recirculation

Housing for the valve in the exhaust that recirculates exhaust gases in the ‘Exhaust Gas Recirculation’ (EGR) system. This method of reducing NOx emissions is used in internal combustion engines.

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Austenitic cast iron (Ni-Resist)

A stable austenitic basic structure is a characteristic of austenitic types of cast iron. Most types are designated using the trade name ”Ni-Resist“, since the austenitic structure is safeguarded in the first place by a nickel content of more than 20%. Austenitic cast-iron is characterised by the following properties:

• High heat-resistance
• High tensile limits
• Low coefficient of expansion
• High resistance to rust
• Abrasion-resistant material
• Non-magnetic material

Due to these particular properties, austenitic types of cast-iron enjoy a good competitive position compared with non-rusting, heat-resistant nickel alloys. Ni-Resist is much cheaper but has nearly the same mechanical properties as high-value nickel alloys. This makes it an economically interesting alloy for components that will be exposed to high temperatures.

Mechanical properties

CX nr.Mat. No.DesignationHeat treatmentTensile limit Rp0,2Tensile strength (N/mm²)Elasticity (%)HardnessHeat resistance up to*
90-GJS-X SiMo 5-1Ferritic annealing> 550> 650> 3200-270780/820 ℃
91-Ni-Resist D-5SStabilising annealing> 250> 450> 10131-193870/950 ℃

*Guideline for maximum application temperature for cast piece/gas

Benefits of the “lost wax model” casting process:

SiMo and Ni-Resist are cast mainly using sand castings. Parts such as exhaust manifolds often have thick walls and then surface quality and precision dimensioning play less of an important role.

If the application requires components to be precisely dimensioned, thin-walled and/or to have good surface quality, then the limits of sand casting are quickly reached. CIREX has developed a process that allows these properties to be achieved. With our casting process, which is both automated as well as very stable, medium-size to large series of components can be cast in SiMo and Ni-Resist.

Production using the ‘lost wax method’ allows components with very complex forms to be cast. CIREX always tries to optimise a cast piece so that post-processing is minimal or not required. That results in considerable cost savings in both material and in post-processing.

Benefits of the ‘lost wax method’ of casting:

• Capability of building thin walls
• High surface quality
• High degree of dimensioning precision
• Minimal post-processing or no post-processing required
• Significant cost savings on materials