Your best choice for exporting / saving CAD data to NC1 format from Xsteel would be to use Autodesk AutoCAD or similar software that supports it.
Convert IGES 3D exchange format to Xsteel CAD drawing.
We have found 3 software records in our database eligible for .igs to .nc1 file format conversion.
Microsoft Windows software - convert igs to nc1 on Windows
A CAD and Gerber conversion software
Convert from igs file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned igs to nc1. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Leading 2D and 3D CAD development software from Autodesk
Apple macOS / Mac OS X software - convert igs to nc1 on OS X
Mac version of popular Autodesk AutoCAD software