I’ve been a professional woodworker and CNC operator for years. When we send our blades and bits out to be harpened, the sharpening service first dips them into a strong industrial metal cleaner. It turns out that this  cleaner is chemically identical to Easy- Off oven cleaner (I use the kind in a pump spray bottle). Keep some in a jar for router bits. Drop them in and let them soak for a few hours if they’re really bad. For a sawblade, spray  each side and wrap the blade in heavy plastic. Rinse in clean water, add a little oil to the router-bit bearing, and you’re good as new.