Automotive

Stainless steel in automobiles falls into two groups: heat-resistant (exhaust) and decorative. Their grade systems and acceptance criteria differ, and mixing them up costs you money or causes 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	0.8–1.5 mm	Condensate corrosion
Trim / bright profile	304 / 430	BA / 8K, 0.3–0.8 mm	Surface class, no cracking on bending
Fuel tank / bracket	304 / 441	1.0–2.0 mm	Formability, spot weldability
Seat frame	301 / 304	High-strength sheet 0.5–1.2 mm	Yield strength ratio, fatigue

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

Three real constraints in this field

Exhaust is not "the more expensive, the better"

409 is titanium-stabilized, inexpensive and sufficient; 441 adds Nb+Ti for higher temperatures. Both mistakes are common: 304 in the exhaust cracks at welds due to thermal expansion, and 409 in hot sections scales.

Deep drawing depends on r-value, not hardness

Trim parts require high r and low Δr. The same grade from different rolling schedules behaves very differently — always run a tensile test before the batch, don't just rely on the mill certificate.

Electrode life sets the cycle time

Stainless steel has high resistance and low conductivity, so spot welding electrodes wear out quickly. Plan electrode changes by weld count and control incoming oil film and roughness.