Automotive

Stainless steel in vehicles falls into two families: heat-resistant (exhaust) and decorative. Their grade systems and acceptance criteria differ, and mixing them up costs you money or a failure.

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Typical parts and material selection

Part	Grade	Surface / size	Watch out for
Exhaust manifold / downpipe	409 / 441	2B / 1D, 1.2–2.0 mm	High-temperature oxidation, thermal fatigue
Muffler / exhaust pipe	409 / 436L	8–1.5 mm	Condensate corrosion
Trim / bright trim	304 / 430	BA / 8K, 0.3–0.8 mm	Surface class, no cracking when bending
Fuel tank / bracket	304 / 441	0–2.0 mm	Formability, spot weldability
Seat frame	301 / 304	High-strength sheet 0.5–1.2 mm	Yield ratio, fatigue

These are the usual configurations.Actual selection depends on the medium, temperature and welding method— the same part can move from 304 to 316L or 2205. Describing the service conditions is more useful than naming a grade.

Three real constraints in this industry

Leakage is not "the more expensive, the better"

409 is titanium-stabilized, economical and suitable; 441 adds Nb+Ti for higher temperature. Both mistakes are common: 304 in the exhaust cracks at the welds due to thermal expansion, 409 in a hot section oxidizes flakily.

Deep drawing depends on the r value, not hardness

Finish parts need a high r value and a low Δr. The same grade with different rolling schedules behaves very differently — always run a drawing trial before the batch, don't just read the mill certificate.

Electrode life defines cycle time

Stainless steel has high strength and low conductivity, so spot welding electrodes wear quickly. Plan electrode changes by number of welds, and control incoming oil film and roughness.