Why does cast iron have high compressive strength but low tensile strength?

Explanation:

Cast iron, a widely used engineering material, has distinct mechanical properties that make it suitable for various applications. One of the notable characteristics of cast iron is its high compressive strength coupled with low tensile strength. This unique combination of properties is primarily due to the presence of graphite flakes within its microstructure.

Graphite Flakes in Cast Iron: The microstructure of cast iron contains graphite flakes, which are essentially small, flat pieces of graphite dispersed throughout the iron matrix. These flakes play a crucial role in determining the mechanical properties of cast iron.

• High Compressive Strength: The presence of graphite flakes does not significantly affect the material's ability to withstand compressive forces. In compression, the graphite flakes are compressed along with the iron matrix, providing substantial resistance to deformation. As a result, cast iron exhibits high compressive strength, making it suitable for applications where the material is subjected to compressive loads, such as in columns, bases, and heavy-duty machine frames.
• Low Tensile Strength: In contrast, the graphite flakes have a more pronounced effect on the tensile properties of cast iron. The flakes act as stress concentrators, creating points of weakness within the material. When tensile forces are applied, these stress concentrators can easily initiate cracks, leading to premature failure. This behavior results in cast iron having relatively low tensile strength compared to its compressive strength. Therefore, cast iron is not typically used in applications where it would be subjected to significant tensile loads.