During a fight with Whiplash, Iron Man’s face plate gets cracked and the press gets a shot of Tony’s face.
It’s so hard to figure out when the world knows Tony is Iron Man and when it doesn’t. Marvel seems, at least to me, to go back and forth pretty often on that.
Then it turns out to be a dream(!?), but his armor was actually damaged and Jocasta realizes that his armor has gained self-awareness.
And it is pissed at Whiplash for damaging it, so, during a rematch with Whiplash, the armor takes over and kills the villain.
GET PIC OF IRON MAN KILING WHIPLASH #28
Yes, he’s dead. Actually dead. Not coming back later. Really dead.
At this point, Tony has to put on an older suit and go to war with his living armor.
While that’s going on, we take a detour through New Warriors #9, where the sentient armor attacks that team and nearly kills them.
In the big conclusion, Iron Man #30, Tony lures the armor into a trap and has a massive heart attack–the armor, loving Tony more than itself, saves him by killing itself.
We do not learn how it became sentient during this story.