Rust or iron oxide forms on surfaces when iron in water comes in contact with the air or "oxidizes." Stainless steel, as the name indicates, "stains less." This does not mean, however, that it is immune to rust. Marks can form on the surface of stainless steel from rusting iron particles. For stainless sinks, stains and marks form when non-stainless cookware is placed in the sink. Treating rust on stainless steel requires a specialised removal product.
Purchase a rust-removal product such as CLR, Bar Keeper's Friend, Ajax, Lime-A-Way or Citrisurf 77 Plus. You can also purchase oxalic acid crystals from by various suppliers. Oxalic acid is the active ingredient in Bar Keeper's Friend and works well to remove rust marks and stains.
Put on gloves to protect your skin.
Apply the rust-remover to the rust marks using a sponge or brush. For powered forms of Ajax and Bar Keeper's Friend, you may need to mix them with water.
Rub the rust marks. Apply stronger or lighter pressure and add more product as necessary.
Rinse the stainless steel with water.
Look for any remaining rust marks. Reapply the rust-remover as needed.
Dry the stainless steel with a clean cloth.
CLR and Citrisoft 77 Plus can be sprayed on or applied with a sponge. No scrubbing or rubbing is necessary.