When stretched beyond it's elastic limit, a metal rod such as steel

When an elastic material is stretched, depending on the stress, it might reach a point beyond which it will no longer return to its original size and shape. This point is called the elastic limit.

When the material (such as a metal rod (e.g steel, copper)) is stretched beyond its elastic limit, Hooke's law is no longer obeyed. i.e strain is no longer directly proportional to stress.

i would say