You can find several CAD / 3D modeling translation tools that will allow you to convert .iv files (SGI Inventor 3D format) to standard ISO STEP format (.stp, .step). Such iv to step conversion is probably used by users that try to convert their old .iv format to some exchange format supported in modern programs.
Open IV file Open STEP file3D viewer and converter with huge file type support
A CAD viewer program with conversion capabilities