I lived in Yuma Ariz. when I was a kid, I had a tire on my bicycle explode cause of the sun, {I may have overinflated it just a bit too} I had rode it to the service station {about a mile} filled it up and rode it back home,{another mile} parked in the driveway, went in the house, about an hour later BOOM!!!!
Worked in an auto salvage yard when I was 17. Lotsa tires laying around there, on cars, off cars, on the ground, on the hoods of cars, in the {very Hot} trunks of cars. Never seen one melt or explode there. Seen a real huge tire fire though {caused by a careless worker with an Oxy/Acetylene cutting torch}{NOT ME EITHER!} The fire department had a hard time extinguishing it too!
Never seen Metal melt one either. I suppose a crushed in fender rubbing it for miles and miles might melt it a bit though.