*Iron Man* is a children's book written and illustrated by Ted Hughes' wife, Sylvia Plath, and published in 1964. It is one of her most well-known works and a beloved children's classic.
It's possible you are thinking of a different book or confusing the author. Perhaps you were thinking of a story featuring a character who could be interpreted as "iron" or "metallic", as Hughes did write some poems that explored themes of transformation and human-animal interactions, but he did not write the *Iron Man*.