AISI 409 stainless steel is actually a ferritic stainless steel formulated for Main forming into wrought products. Bottom line, the neatest thing to try and do is avoid the oxidation in the first place, however you can chemically take care of it. On 3xx stainless I'd even suggest polishing. You https://www.madanijayateknik.com/service/detail/as-round-bar-plate-sheet-stainless-steel-409-409l-409m-409cb-409ti