To add rounded edges to materials, add a CoronaRoundEdges map, and plug it into the material’s Bump slot:
The CoronaRoundEdges map simulates rounded edges on materials, however this is just a shading effect, and the geometry is not really chamfered. This effect is useful for adding detail to geometric forms such as machine parts, and to add subtle chamfer to walls in interior visualizations.
Example:
See more this tutorials here:
Source: Corona Renderer
