Don't think I can add anything more than it's in the title. Except texturing software may be Photoshop or Mari. By "hard surface" I mean objects like weapons.
I made a mini tut showing how I approach integrating micro texture into hard surface props: https://www.artstation.com/artwork/sculpting-micro-texture-tutorial
There should be no hard/split edes . The displacement goes in direction of vertex normals usually . You need a bevel on hard edges and face weighted normals