Nodular cast iron is a high-strength cast iron material whose comprehensive properties are close to steel. Based on its excellent properties, it has been successfully used to cast some parts with complex forces and high requirements for strength, toughness and wear resistance. The performance of ductile iron castings is close to that of carbon steel, but it has good casting performance and is easy to form. Its processing performance is better than cast steel, and it is more heat-resistant, corrosion-resistant and wear-resistant than steel.
The tensile strength, ductility and toughness of ductile iron are lower than that of carbon steel. Although the mechanical properties of ductile iron are inferior to steel, the presence of graphite gives ductile iron many properties that steel can't match. Such as good wear resistance, high vibration damping, low notch sensitivity and excellent cutting performance.
In addition, ductile iron has a high carbon content and its composition is close to the eutectic composition. Therefore, its melting point is low, about 1200 ℃. The molten iron has good fluidity. Due to the volume expansion of graphite during crystallization, the transmission shrinkage rate is small. The performance is better than steel, so the casting method is usually used to make castings.
The anti-corrosion performance of ductile iron parts comes from the galvanized layer on the surface of the product. When the electrochemical reaction between zinc and iron lags behind, a stable protective layer is formed on the surface, which actively protects the product. And when the galvanized layer on the ductile iron is in contact with the soil, the metallic zinc will gradually transform into a dense, adherent and continuous zinc salt layer, which is an insoluble substance.
The purpose of galvanizing ductile iron is to form an automatic repairing protective layer at the damage to ensure the integrity of the workpiece. During the production of ductile iron parts, attention should be paid to the coarse sand and oxide scale on the surface. The risers, vents, fleshy, fins and burrs should be removed.