The best way to clean cast iron grill gates is gently yet effectively. Washing your grill gates in a sink filled with hot soapy water and using a stiff brush or steel wool is one of the best ways to remove any built-up seasoning and remove surface rust.
Once you've removed the rust and seasoning on your grill gates, rinse them thoroughly before allowing them to dry completely to avoid any formation of rust. A great tip is to dry your cast iron barbecue grill in the oven on low heat for a few minutes.
Some people prefer using a vinegar soak, especially for removing the rust. Thereafter, use the same process to rinse and dry.