Until #21, the Metal Men appeared to be the only super-heroes, none of the DC heroes showing up to help fight the menaces or even referred to.
The Metal Men then reappeared during the Infinite Crisis storyline (Infinite Crisis #1-7, December 2005 - June 2006, Villains United #1-6, July-December 2005), battling the O.M.A.C.S cyborgs and acting as part of a superhero strike force assembled to protect the city of Metropolis from the Secret Society of Supervillains.