As above it will have warpped the head and it will be ruined now unfortunately!
Same happened to my dads 1.6 zetec escort, like you couldnt tell it was overheating until he smelt it and saw steam coming from the bonnet, by then it was too late, i towed him 3 miles home, managed to get it started again but sounded like a bag of nails, we dropped a new engine in after all