stainless 409 rusts?-never seen a cafeteria counter-top rust --thats what they are made of. 304 is a common architectural grade, 409 as well as other grades stainless can get a rust stain put on them, but they wont rust by themselves.
Look @ factory exhaust systems nowadays, 409 stainless & they rust. Not saying they rust through & rot fast, but they do rust, Look @ what materials are in it.
Grade 409 resists atmospheric and exhaust gas corrosion. A light surface rust will form in most atmospheres; this rust retards further corrosion but makes the surface undesirable for decorative applications. The corrosion resistance is about the same as that of 3CR12 and the 12% chromium martensitic grades such as 410, and inferior to the 17% chromium grade 430.
The price difference between 304 & 409 should give you a hint on what is better material/rust resistant.
If a magnet can stick to 409 stainless, which it does, that means it's gonna rust, no?
