Iron Man and the Hulk have fought each other on a handful of occasions. The most brutal battle was during the World War Hulk storyline.
Even with all of his technology and wearing the Hulk Buster suit, Tony is unable to stop the Hulk.
Iron Man dons his "Hulkbuster" Suit, in hopes of defeating Hulk. As the fight rages on, Iron Man, in a monologue, takes full responsibility for the incident, and explains that he knew that this day would come, as soon as he heard news that Hulk had not reached his destination. As they are battling, Iron Man injects nanobots into Hulk's bloodstream. This was supposed to slow him down, but hasn't seemed to take effect yet. After much fighting in the now empty Manhattan, Iron Man seems to have defeated Hulk. But, after a flashback of the death of his wife, Caiera, he only becomes angrier. He bursts from the crater his body had created, and dominates Iron Man.
The one-on-one ends with the Hulk victorious, and Tony's Hulk-Buster armor destroyed. The Hulk goes on to defeat the Fantastic Four, Doctor Strange, and everything and everyone thrown against him.
That red wreckage in those last two panels? That's Tony's Hulk Buster armor. Or... It was.