Ask AI: What are the chief impurities in cast iron

Cast iron, an alloy of iron that contains 2% to 4% carbon, typically has several impurities. The chief impurities include: 1. Carbon: Although it's not an impurity, excess carbon can be seen as one. Apart from the desired 2% to 4%, any additional carbon may exist in forms of graphite and hard cementite, affecting the properties of cast iron. 2. Silicon: Silicon is not exactly an impurity and plays a key role in cast iron production. However, if present in larger quantities (over 3%), it fosters the formation of graphite, resulting in a softer type of cast iron known as "gray iron". 3. Sulphur: While it helps in making the cast iron more pliable, too much sulphur can lead to 'hot shortness', which causes the cast iron to become brittle and crack when it is heated. 4. Phosphorus: Excess phosphorus (over 1%) makes the iron too fluid when molten, resulting in 'cold shortness', which can make it brittle when cold. 5. Manganese: Manganese helps to counteract the harmful effects of sulfur, but excessive manganese can make the cast iron brittle. 6. Other impurities: Other impurities in smaller amounts may include elements like oxygen, hydrogen, nitrogen, and trace metals. These can affect the ductility, hardness, and toughness of the cast iron.