Rust erasers are abrasive all the way through, and they don't scratch. They're very effective and I think they're better suited to cleaning rust off of cast iron.
You don't have to go with Lodge, all rust erasers are pretty equal and the smaller brands can cost a lot less. https://www.amazon.com/gp/product/B001DMX6OG/ref=ppx_yo_dt_b_search_asin_title