Why is the mechanical properties of nodular cast iron higher than that of gray cast iron and malleable cast iron?
Organizational differences lead to significant differences in performance:
Gray cast iron is a kind of flake graphite split matrix, which is easy to cause stress concentration, brittleness and good vibration reduction performance. It is mainly used to produce all kinds of high strength cabinets/bases that do not need to bear compressive stress.
Ductile iron is a spherical graphite matrix. The splitting between grains is minimal and the stress concentration is minimal. Therefore, it has high strength and is equivalent to medium carbon steel. It can give full play to the performance of the matrix and has certain plasticity. Good toughness. It is usually used to manufacture parts with high toughness and complex shape, such as crankshaft/chain of internal combustion engine. Ductile iron can also be heat treated for strengthening, whereas gray iron is not heat treated for increasing strength (the effect of flaky graphite).
Malleable cast iron is a ferrite (F) + aggregated graphite (G) matrix, which can be used to generate impact or vibration and torsional loads. It is usually used to manufacture rear axles, spring brackets, low pressure valves, pipe fittings, tool wrenches.