Automotive exhaust systems commonly use ferritic stainless grades selected by temperature and corrosion location:

| Grade | Cr | Characteristics | Typical section | |---|---|---|---| | 409 | about 11% | low cost, good formability | muffler shells, cooler areas | | 439 | about 17% + Ti/Nb | better high-temperature oxidation and condensate corrosion resistance | hot end, near manifold | | 441 | about 18% + Ti/Nb | higher high-temperature strength and corrosion resistance | hot sections, severe areas |

Selection points:

1) For hot ends above ~700°C, prefer 439/441; 409 has limited long-term oxidation margin. 2) For condensate corrosion zones (cold end), Cr content and surface condition still matter. 3) For welds, consider stabilisation and HAZ toughness, and qualify the procedure. 4) Do not downgrade blindly on cost-sensitive projects; validate with bench/road tests first.

Purchasing reminder: exhaust materials are usually thin sheet — check thickness tolerance, flatness and weldability; the certificate should state grade and Cr content.