Nicolas Repetto uploaded a set of free materials that you can use for personal and commercial projects.
The set features four Substance Designer files: Rubber, Painted Metal, Steel and Epoxy Paint PBR calibrated materials. Their albedos are said to be in a mid grey value ready to export to UE4 and use color blending.
You can use these for free for both personal and commercial (please credit and notify Nicolas by email).
Author: Artyom Sergeev