Grey cast irons
Advantages: low cost, good castability and favorable thermal conductivity
Typical applications: engine blocks, cylinder heads, fly wheels, and brake discs
Effects of molybdenum: retains strength, improves creep resistance
Grey cast iron has limited strength and almost no ductility. Nevertheless, pearlitic grey cast iron is the preferred material for applications such as engine blocks, cylinder heads, fly wheels, and brake discs because of its low cost, good castability and favorable thermal conductivity. Demands for higher thermal efficiency and weight reduction, enabled by reducing component cross-sections, require the development of high-performance grey cast iron with an improved combination of tensile strength and heat conductivity.
The thermal conductivity is nearly independent of graphite flake length and aspect ratio above a threshold length of approximately 100 µm. From an alloying point of view, reducing the level of solute elements appears favorable for improving thermal conductivity in the ferrite matrix. Solutes with small atomic radius like Si significantly increase strength but simultaneously lower heat conductivity.
On the contrary, molybdenum being a carbide stabilizer with good solubility and rather large atomic size is favorable to strength and less harmful to heat conductivity. Every 0.1% addition of Mo increases the tensile strength by approximately 10 MPa. The strengthening effect can be even larger in synergy with other alloying elements. At elevated operating temperatures, Mo-alloyed grey cast iron retains strength better and has improved creep resistance.
Strengthening effect of Mo in grey cast iron
Influence of Mo alloying on thermal conductivity of grey cast iron