To clean metal surfaces of melted on "substances" I use Pig Snot Chrome Cleaner... Yep you read right. This is a wonderful polish I first became familiar when I had an unfortunate incident between a black shopping bag and my hot motorcycle pipes. wound up with an unsightly glob on my chrome.
Went to Bike aftermarket shop and was handed a small "pot" of this magic substance. you just put a small dab on a soft cloth... I use a piece of an old sweatshirt. and VOILA!! it takes that stuff right off.. It's also good for the chrome on you car and will even "correct" rust on chrome with little effort . You can find it online.. just google "Pig Snot."