A belt sander may be a good idea to remove most of the deep scratches, but used lightly....it is too easy to get 'carried away' and remove too much metal. Once the worse scratches are removed, I would recommend coarse 'wet and dry' abrasive paper used with light mineral oil or WD40, progressively using finer grades.
It may be a good idea to give the blade an 'etch' before you reach the final 'sanding ' to see if you have an interesting pattern in the blade

From there you could decide whether to polish or smooth the blade a little more and then re-etch. my 0.02 cents worth.