Hmmm. That sounds a little like Slow burn by :smash86:

Summary: Sam’s idea of heaven shatters Dean’s heart and he realises now he can never confess his true feelings for his brother and he just wants to walk away from it all. But when Sam is taken by Zachariah and sent to Purgatory, they are thrown headlong into a battle against the devil. With the help of Castiel, the brother’s devise a plan to defeat Lucifer but unless they are truly bound to each other…Sam will be lost forever. The secrets they are both keeping might just get them both killed.
AU ending for “Dark Side of the Moon”

Sam is definitely tortured by an angel and Dean definitely goes after him...don't remember the piece of metal though...oh, and it is Wincest.

http://smash86.livejournal.com/24978.html#cutid1 (http://smash86.livejournal.com/24978.html#cutid1)