Intergaph SmartSketch diagramming and technical drawing software supports several CAD formats, including the DWG, in which it can export its own IGR drawing designs. It doesn't look like that any other program supports the IGR format, so it is probably your only choice for IGR to DWG conversion.
Convert SmartSketch drawing design to AutoCAD drawing.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert igr to dwg on Windows
SmartSketch is an innovative product for the technical office, combining world class business diagramming with award winning drawing technology.
Convert from igr file
to dwg file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.