Automotive

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

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Typical Parts and Material Selection

Part	Grade	Surface / Thickness	Watch Out For
Exhaust manifold / downpipe	409 / 441	2B / 1D, 1.2–2.0 mm	High-temperature oxidation, thermal fatigue
Muffler / tailpipe	409 / 436L	8–1.5 mm	Condensate corrosion
Trim / bright molding	304 / 430	BA / 8K, 0.3–0.8 mm	Surface grade, no cracking at bends
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 common 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 Bottlenecks in This Industry

In exhaust, "the more expensive the better" does not apply

409 is titanium-stabilized, cheaper and sufficient; 441 adds Nb+Ti for higher heat. Both mistakes are common: 304 in exhaust cracks at the weld due to thermal expansion, and 409 in the hot section scales up.

Deep drawing depends on r-value, not hardness

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

Electrode life sets your takt time

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