The Corona Converter is installed by default with Corona and can be opened using:
- The dedicated Corona Toolbar icon
- The quad menu after right-clicking in any viewport
Note #1: in order for Corona Converter to convert scenes created with other renderers and 3rd party plugins, those render engines and plugins must be installed in the 3D application, so they are recognized and properly converted, even without an active license for them.
Note #2: If you are converting scenes from V-Ray to Corona, you need V-Ray version 3 or newer. Older versions are currently not supported.
The new Corona Converter, introduced in Corona Renderer 7, uses the CoronaPhysicalMtl as the new conversion default. It is not possible to convert other materials to the CoronaLegacyMtl (previously called CoronaMtl) anymore, and any Corona Legacy Materials existing in the scene will be also converted to the Corona Physical Material.
Please note that while the converter was developed based on many user scenes and materials and it generally tries to match the appearance of the converted materials as closely as possible to the originals, the conversion results may be sometimes imperfect. This means that when using the Corona Converter, you may need to make some minor manual adjustments to the converted materials. This is especially true in case of unphysical ("fake") materials and when setting up various material properties using extreme values. Some examples of incorrectly set up materials are presented in the "Examples" section below.

If you ever encounter a material that was converted incorrectly, please feel free to report it to us and we will do our best to improve our converter.
See also: Corona Physical Material
Conversion examples
Note: Incorrectly set up materials are for showcasing the possible conversion differences. When the material has a physically correct model, the conversion is correct. When there are "fakes" and non-physical settings, the converted material may look different than the original.
Incorrectly set up materials:
Refraction is used with Translucency, which is incorrect. The converted CoronaPhysicalMtl looks different than the original.
Before conversion:

After conversion:

Note: As you can see, the Corona Converter tries to keep all the information of the original material (Diffuse, Translucency, Reflection and also their multiplications) in the newly created nodes, also naming them accordingly. This gives you a better view of the settings used and lets you modify them easily.
Correctly set up materials:
Refraction is NOT used for a translucent material in this case (correct model for grass, leaves, paper etc.). The converted CoronaPhysicalMtl looks identical to original material. Also note that Thin shell (no inside) option is enabled for CoronaPhysicalMtl, as "Enable Thin shell if translucent" option is checked in Corona Converter options.
Before conversion:

After conversion:

Note #1: Again, Corona Converter kept all the settings in the nodes for better view and easy tweaking.
Note #2: There is no Reflection color parameter in PhysicalMtl. CoronaPhysicalMtl's reflectivity is controlled with Base IOR or Specular (for non metals). For this, the original CoronaColor for Reflection color is mixed with other parameters of CoronaLegacyMaterial's reflectivity through CoronaMix and plugged to Base IOR for CoronaPhysicalMtl.
CoronaLegacyMtl to CoronaPhysicalMtl
Before conversion:

After conversion:

Before conversion:

After conversion:

VrayMtl to CoronaPhysicalMtl
Example 1:
Before conversion:

After conversion:

Example 2:
Before conversion:

After conversion:

Example 3:
Before conversion:

After conversion:

Note: Corona Converter again tried to keep as many of the original settings as possible in newly created nodes. For Refractive, Translucent, and Volumetric materials sometimes there will be more nodes than in the original material. Nevertheless, the Converted materials will look and render just fine.
If you ever encounter a material that was converted incorrectly, please feel free to report it to us and we will do our best to improve our converter.