Yes, steamed vegetables can be frozen to use later. Consider freezing if you plan to cook potatoes and carrots ahead of time to use on busy days. Divide the vegetables into desired portions and place them in a freezer bag, leaving about two inches of headspace as the vegetables expand in the freezer.  Defrost: Remove a portion from the freezer and place it in the fridge overnight.  Reheat: Remove any liquid left after defrosting, place the vegetables in a container and heat in the microwave just until they are hot. Do not heat for a long time, as the vegetables are fully steamed and might disintegrate.  Note: I would suggest freezing plain steamed vegetables and adding seasoning after reheating them rather than freezing the seasoned vegetables.