Alloy 409 plate is a general purpose, chromium, titanium stabilized, ferritic stainless steel whose primary application is automotive exhaust systems. Alloy 409 plate contains 11% chromium which is the minimum amount for the formation of the passive surface film which gives stainless steels their corrosion resistance. Alloy 409 plate combines good elevated temperature corrosion resistance with medium strength, good formability, and overall cost. Alloy 409 plate resists corrosion strongly compared to carbon steel and is used as an alternative to carbon steel in mildly challenging environments where its high resistance to corrosion and high temperature oxidation gives an advantage. Alloy 409 plate is commonly used in applications where appearance is a secondary quality to mechanical properties and corrosion resistance.

Although Alloy 409 is designed principally for the automotive exhaust industry, it has been successfully used in other industrial applications as well. Some examples of applications that call for Alloy 409 include: