In the files there are 2 stairs of different configurations.

All objects are made for anti-aliasing. All objects and materials in the scene are logically named and grouped.
Turbosmooth stack included.
Viewport iterations - 0
Render iterations - 2

For Corona render, it is recommended to install a version of at least 1.5, since the glossiness of materials is configured with PBR in mind.
Who works in V-Ray versions lower than 3.1, be careful, in the materials in the BRDF section there is Microfaset GTR ( GGX ), if your version is older than 3.1, then the BRDF field will be empty. Choose Blinn, Phong or Ward - whatever suits you best.