What defect is caused by non-uniform cooling, leading to surface ruptures in the metal?

The defect caused by non-uniform cooling that leads to surface ruptures in the metal is known as hot tears. When metal is cast, it transitions from a molten state to a solid state. During this cooling process, if the temperatures are not uniform across the entire piece, certain areas may contract more rapidly than others. This differential contraction can create internal stresses due to the varying levels of thermal expansion and contraction. When these stresses exceed the material's tensile strength, particularly when the metal is still partially molten or transitioning to solid, cracks or ruptures can develop along the surface.

These hot tears are particularly common in thick sections of castings or in regions with complex geometries where cooling rates vary significantly. Proper control of cooling rates during the casting process is essential to mitigate the occurrence of these defects, as they compromise the structural integrity of the metal.