Hi @Sergey_Dukman ,
The .iam file you attached is missing its .ipt files. They need to be all in the same folder (then create a .zip of the folder to upload here). Otherwise we can't open it.
I tested a weld created in the assembly environment, and indeed I could not idealize it in Nastran (select the object and assign a material). You would need to model the weld separately and then insert it into the assembly, so you can then assign the solid elements and material to it. You could also export the assembly as a .STEP file and then re-import the model to inventor (which will make the welds separate solid parts):
https://knowledge.autodesk.com/support/inventor-nastran/learn-explore/caas/sfdcarticles/sfdcarticles...
This forum also has other posts regarding welding simulations and common problems (which may help you):
https://forums.autodesk.com/t5/inventor-nastran-forum/weld-sizing/m-p/10181005
https://forums.autodesk.com/t5/inventor-nastran-forum/idealization-solid-weld/m-p/7397893
https://forums.autodesk.com/t5/inventor-nastran-forum/how-add-weld-on-shell/m-p/9508540
Best regards
