Is there any Superman references?

Irons has a Superman tattoo.

At one point his uncle says 'you're not Superman'.

They say 'the man of steel' a lot as well.

The other guy noted all of the Superman references I can remember. Additionally, there are a few Batman references. One of the cops jokingly suggests that Steel is going to the Batcave and his younger brother compares himself to Robin when speculating about being Steel's sidekick.

"I'm the RA, and as the RA, I'm supposed to be the fun-sucker. I *beep* the sun."
-Abe Christiansen

I think in this universe Superman only exists in the comics.

Like Matrix, I fight for love.

There's a song playing in the factory where Shaq's character works that repeats the lyric "I'm Superman" a few times.