It was a story-arc titled Stand-Off. Issue one was Thor #58, Issue two was Iron-Man #64 (review at
http://www.comicsnsuch.com/modules.php?name=News&file=article&sid=24) and issue three was Avengers #63 (review
http://www.comicsnsuch.com/modules.php?name=News&
file=article&sid=58&...)
Iron Man pretty much got stomped... the Thor basher armor didn;t do him so well against the odin-powered Thor, but he showed a certain resiliency and refused to go down for the count. Captain America stepped in and put a stop to the fight before anyone got seriously hurt.
The end result of the story-arc was the breaking up of the friendship between the three central figures of the early Avengers. Tragic.