How to export 3Ds model to STEP?
Nope you can not export it direct from 3D's Max as a .STEP is NURBS and max uses Pollys.....
There is a process you can take it through but most of the time it fails as to the translation through other software's :(
There is a plug in you can buy but I am sure it is very very very pricy.
you need a very powerfull PC and much time to do it and the files are huge
Yes you can, first, you have to export your model as ACIS .SAT fomat, Check the box (export mesh objects) if your model base is mesh, or (Export NURBS) if your model base is NURBS.
Download this software (it's free: http://www.123dapp.com/design)
Open your .SAT file and export it as SAT/STEP file, choose STEP from the drop down menu.
And thats it..
Note: the process will take time according to your mesh complication (but it will be smoother), and for NURBS base will be smoother as it's compatible with the solid formats.