Steel is more ductile than iron. Ductility refers to a material's ability to deform under tensile stress without fracturing. This property is crucial in applications where materials are subjected to bending, stretching, or other forms of stress. While both steel and iron are metals, steel's higher ductility is primarily due to the presence of alloying elements, such as carbon, manganese, and silicon, which enhance its mechanical properties.

The ductility of steel is significantly influenced by its carbon content. High-carbon steel, for instance, has a higher ductility compared to low-carbon steel. This is because the carbon atoms in the steel lattice hinder the movement of dislocations, which are the defects that allow metals to deform plastically. However, the presence of alloying elements can further improve ductility by refining the grain structure and reducing the number of dislocations.

According to data from the American Iron and Steel Institute (AISI), the average elongation (a measure of ductility) for high-carbon steel is around 10-15%, whereas for wrought iron, it is typically less than 5%. This difference in ductility is evident when comparing the tensile strength and yield strength of both materials. High-carbon steel can exhibit tensile strengths ranging from 600 to 1000 MPa, with yield strengths around 300 to 500 MPa. In contrast, wrought iron has tensile strengths of approximately 300 to 500 MPa and yield strengths of around 150 to 300 MPa.

The higher ductility of steel is also attributed to its microstructure. Steel can be heat-treated to achieve various microstructures, such as ferrite, pearlite, and martensite, which can significantly affect its ductility. For example, pearlitic steel has a higher ductility compared to ferritic steel due to its layered structure, which allows for better plastic deformation.

In conclusion, steel is more ductile than iron due to its higher carbon content, alloying elements, and microstructure. These factors contribute to steel's ability to deform under stress without fracturing, making it a preferred material in various engineering applications.