The cast iron when heated to red heat with powdered red haematite in an oven for increasing its toughness, is converted to A. Grey cast iron B. White cast iron C. Mottled cast iron D. Toughed cast iron

The correct answer is D. Toughed cast iron.

When cast iron is heated to red heat with powdered red haematite in an oven for increasing its toughness, it is converted to toughed cast iron. This is because the red haematite reacts with the carbon in the cast iron to form iron carbide, which makes the cast iron harder and more resistant to wear.

Grey cast iron is a type of cast iron that is composed of graphite flakes in a matrix of iron. It is the most common type of cast iron and is used for a variety of applications, including machine tools, engine blocks, and stove parts.

White cast iron is a type of cast iron that is composed of cementite (iron carbide) in a matrix of iron. It is very hard and brittle, and is used for applications where strength is more important than toughness, such as machine tool dies and molds.

Mottled cast iron is a type of cast iron that is composed of a mixture of grey cast iron and white cast iron. It is less hard than white cast iron, but more tough than grey cast iron. It is used for applications where both strength and toughness are important, such as crankshafts and connecting rods.