In the diffuse map the scratches might be dark on the diffuse map and shiny on the specular map.
No need to use or add scratches in the normal map.

For that just colorize the Scratches in black or some other dark color.


Specular might be in white or any other light color.


Branch the specular white scratches into an alpha filter node and adjust its gradient so as to just see the scratches.


Now look at the 3d Preview to view the result.



Cool Tip

You can use this trick for any type of metal. Don't forget that bright colors are shinier.
(use it with a light orange/brown color like "Bronze" in the diffuse map)



Example