So, this morning over coffee I was reading Joel Hynd's excellent book "The Giants of the Polo Grounds " - much better than his charming but at times sloppy "1957 The Sputnik Season ". Anyhow, it turns out that Iron Man Joe McGinnitty was not nicknamed as such due to his indefatigable pitching arm, but from an interview when he was in Kansas City:

"Contrary to present-day legend, McGinnity did not obtain his nickname of "Iron Man" through the durability of his arm...It was a relic of his minor league days with Kansas City where a writer had asked him what he did in the off-season.

"I work in a foundry," McGinnity hsd replied. "I'm an iron man."

So, long before Robert Downey, Jr. And the MCU, "I am Iron Man" belonged to baseball.