Comparison of results of different roughness settings of Steel Material
Here are the Photoshop CC Default 3D Materials and a sample picture of the material textured on an object.
We have Included the Free additonal Material Textures provided by Adobe. If you don't have these additional materials in your presets you can download them from Adobe or choose "Get More Content" from the 3d menu in Photoshop. Once you have downloaded them and unzipped them, copy them into your presets/materials folder in your Photoshop directory.
You can use this resource panel to quickly find what each material looks like on a 3d object, and materials are available and what group they belong to.