Which material is known for having good ductility?

Ductility refers to a material's ability to deform under tensile stress, which means it can be stretched into a wire or bent without breaking. Among the materials listed, steel is widely recognized for its good ductility, especially when alloyed with certain elements and properly processed.

Steel's ductility makes it a versatile material in engineering and construction applications, where it is often subjected to bending, stretching, and other forms of deformation during use. It retains considerable strength while allowing for some degree of elastic and plastic deformation, which enhances its ability to absorb energy.

Copper is also known for its excellent ductility, allowing it to be drawn into thin wires easily. Aluminum, while not as ductile as copper, still possesses good ductility and can be formed into various shapes. Cast iron, on the other hand, is known for its brittleness, particularly when compared to the other materials, which limits its ability to deform without breaking.

The understanding of ductility in these materials helps to guide engineers in selecting the appropriate material for a given application based on the expected stresses and deformations. In this context, steel's combination of strength and ductility makes it the most recognized choice among the options provided.