Lot of really nasty stuff in house fire smoke, evidently at least some of it is quite corrosive.
Personally, I'd BOIL it in a baking soda solution for about 1/2 hour, then let the hottest tap water your house can provide wash over it for 10 min, shake it off, let it dry, and use a good penetrating oil while it is still hot.
Personally, I'd BOIL it in a baking soda solution for about 1/2 hour, then let the hottest tap water your house can provide wash over it for 10 min, shake it off, let it dry, and use a good penetrating oil while it is still hot.