conversion of 3d models from revit projects and families (.rvt, .rfa) in neutral step cad format is not possible in a single step: in the past (<2013) two conversions could be made (I don't know now in current versions).
first saved the model in autodesk revit in the sat format (acis), then converted this file using e.g. free application inventor fusion (including autocad) in a step file (or iges, parasolid/.x_t, inventor/.ipt, catia/.catpart, etc.).
or there is this programme that performs the conversion (to payment).
apart from that there is a revit section and therefore it makes more sense to write there rather than in a generalist section, in This is what discussion a few days ago we read that revit does not export step, but can export a .stl