Iron is the Universe is the final book in The Iron Three trilogy following The Iron Universe and The Sun of the Iron Universe.
It is a wide-ranging collection of the Universe's life-cycle short stories meant to hammer home the aspects of Iron's role in the Primordial, Galactic, Stellar and Solar Universes
The sub-title of Iron is the Universe describes Iron in a nutshell: THE ETERNAL ELEMENT.
Yes, Iron, the most stable element, has been around for an eternity and will be around for many more eternities.