409 is a low cost ferritic stainless steel. Its dominant use is in vehicle exhaust systems, so much so that it is often referred to as “muffler” grade.
Approximate Composition – 11% Cr plus Ti (titanium). (Exact composition ranges vary between EN and ASTM standards).
This grade combines the following characteristics:
- Basic corrosion and oxidation resistance
- Composition balanced for optimum formability
- Weldable only in thin sections due to fully ferritic structure
- Low cost and limited cost variation due to low alloy content
Automotive exhaust systems have to withstand aggressive conditions from high temperatures at the manifold end, sulphuric acid condensate and de-icing salt. Given the severity of these conditions, it can seem surprising that the 11% Cr 409 grade has met the challenge for many years. Exhaust components are also required to be bent, expanded and pressed into all sorts of convoluted shapes. The ability of a ferritic steel to meet these formability requirements is little short of amazing.
Other applications include:
Heat exchangers, gas boilers, fuel filters.