A simple material which demonstrates how you can setup a material for surfaces which have it's edges scratched off, much like can be seen on old well used machinery, spaceships, old weapons and much much more. This example is a base for you to experiment further on..

Try for example to duplicate the occlusion layers from the Metal layer, drop them under the Red Painted layer and invert them, play with the occlusion distances and variance scale to achieve different results. Also exchange both the redpainted colormaterial and the metal with anything you want and you can also exchange the procedural scratchmap under each groupmask with any bitmap/procedural you prefer. You just have to respect the order of things in the shadertree, maintain that and it will work for you.

Last note, this material is setup for larger objects at around 1 meter in scale, but by adjusting the occlusion distances you can make it work for smaller or bigger sized objects too.

Have fun! :)