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What is the difference between 409 and 304 stainless?

Posted by Heidi Harbridge on

With the introduction of most suppliers moving from mild steel exhaust to a 409 grade stainless, one of the most common questions we get asked is "what is the difference between the two?".  

There are lots of myths around stainless steel products and how to use them, even to the very experienced.  Both have excellent mechanical properties and high-temperature corrosion resistance, however, they have very different applications.


Grade 409 Stainless Steel is a Ferritic steel that offers good mechanical properties and high-temperature corrosion resistance.  It is commonly considered as a chromium stainless steel, with applications in exhaust systems of automobiles and applications that demand weldability.

Grade 409 stainless steel has excellent resistance to exhaust gas and atmospheric corrosion.  

This being said, the grade of 409 is liable to mild corrosion, which limits the usage of this steel for decorative purposes.


One of the most versatile and commonly used stainless steels on the market.  Grade 304 stainless is the most standard used alloy of this type.  

304s chromium content promotes the material's considerable resistance to the effects of corrosion and oxidation.  The stainless steel alloy resists most oxidising acids and will withstands ordinary rusting, though this does not mean that the steel will not tarnish over time.  

304 Grade stainless is more expensive than 409 but common in custom exhaust systems as its aesthetically pleasing to the eye and easier to clean.




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