Type 409 (UNS S40920)
Type 409 is a heat resisting ferritic stainless steel providing good oxidation and corrosion resistance compared to carbon steel. This titanium stabilized grade was developed for automotive exhaust systems but its good formability, weldability, and corrosion resistance has led to its use in other applications. The corrosion resistance of Type 409 is better than coated carbon steel, similar to that of Type 410 stainless steel, and less than that of Type 304/304L stainless steel. Type 409 is not suggested for cosmetic or surface critical applications as light surface rusting can form during exposure to atmospheric conditions.