Wiktionary
melt down
vb. To melt a metal, especially so that it can be remade into something else.
WordNet
Usage examples of "melt down".
It is officially certain that in thirteen days nine hours from now, the Niccola will be so close to the sun that her hull will melt down.
We melt down the armor and the swords and use the steel to make coins.
So that they could melt down an asteroid, and make the whole smelter dirty again.
Coins are ready to spend, but we'd have to melt down the sand, and I've never been very good at that.
I drank slowly, hugging the hot cup to my chest, watching the second lot of snow melt down in the pan.