High Silicon Molybdenum
High silicon molybdenum ductile iron has excellent high temperature strength, thermal fatigue resistance, oxidation resistance, growth and high-temperature creep resistance and other good properties, so it is often made into exhaust pipe, turbine casing and other products as automotive high temperature components. Car exhaust pipes and other products have different models, so high silicon molybdenum ductile iron content requirements also are different. Generally silicon content is between 3.0~5.0% and molybdenum content is between 0.4~1.2%. The following table shows different alloy composition of high silicon molybdenum ductile iron and mechanical properties:
| Alloy Composition （%） | Tensile Strength（MPa） | Yield Strength（MPa） | Ductility （%） | Hardness（HB） |
| Si4.7 Mo0.85 C3.3 | 710 | - | 3 | 266 |
| Si4.6 Mo0.6 C3.3 | 675 | 620 | 9 | 229 |
| Si4.2 Mo0.6 C3.6 | 575 | - | 18 | 229 |
| Si3.5 Mo0.5 C3.6 | 545 | - | 19 | 194 |
From the table we can see high silicon molybdenum content has good tensile strength, but the casting hardness is higher, while the plasticity is lower, which is not conducive to casting process. This is mainly because the molybdenum will lead to matrix pearlite core section to produce rich molybdenum carbide structure, so the matrix will become hard and brittle.
Silicon molybdenum content has some impact on its high temperature properties. If the silicon content is excess, high temperature performance will deteriorate and the casting fragility will increase. On the one hand, silicon as ferrite stabilizing element can make the casting to obtain ferritic matrix. On the other hand, high silicon content can promote cast iron to form dense silica oxide film to prevent oxidation. Further, silicon through solid solution strengthening can improve the strength of the casting. Molybdenum as effective element can use for adjust casting high temperature performance and can refine grains and graphite to improves the yield strength of cast iron, to improve their high temperature performance, which is good for improving castings high temperature creep resistance and creep resistance fracture properties.
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