What type of deformation does steel experience when subjected to excessive stress beyond its plastic limit?

When steel is subjected to excessive stress beyond its plastic limit, it experiences plastic deformation. This type of deformation occurs after the material has reached its yield point and is unable to return to its original shape once the stress is removed. In the plastic deformation phase, the steel undergoes permanent changes in its shape and structure due to the applied stresses, which exceed the elastic limits of the material.

Plastic deformation is characterized by a rearrangement of the atomic structure in the steel, allowing for changes such as elongation or distortion. This behavior is critical in engineering and design because it indicates that the material has reached a point where it can no longer sustain loads elastically and is at risk of failure if exposed to further stress.

Elastic deformation, on the other hand, involves temporary changes where the material can return to its original shape upon removal of the stress. Inelastic deformation refers to the range of behavior where some permanent strain occurs but doesn't specifically indicate the plastic zone. The yield point simply defines the transition between elastic and plastic deformation but does not describe the deformation type itself. Therefore, plastic deformation accurately captures the essence of the material behavior under such excessive stress conditions.