Like I stated, 409 stainless rusts.
"A light surface rust will form in most atmospheres"
304 stainless does not surface rust & a magnet does not stick to it, no carbon steel.

409 stainless is a low grade stainless. 304, 316 much, much better.
Its applications(409) are those where appearance is a secondary consideration to mechanical properties and corrosion resistance.
tells you there in black & white, secondary consideration for appearance, hence, it rusts.

Need to look @ exhaust systems on most all cars, surface rust all over. Does not stay rust free like 304 or 316 does.

MBHD


12 port SDS EFI