Automotive

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

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Typical Parts and Material Selection

Part	Grade	Surface / Size	What to Watch 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 molding	304 / 430	BA / 8K, 0.3–0.8 mm	Surface class, no cracking during 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 common 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 specifying a grade.

Three Real Constraints in This Industry

The Exhaust System 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 system cracks along weld seams due to thermal expansion, while 409 in the hot section scales.

Deep Drawing Depends on r-Value, Not Hardness

Decorative parts need high r and low Δr. The same grade behaves completely differently under different rolling schedules — always run a trial draw before a production batch, and don't rely on the mill certificate alone.

Electrode Life Sets the Cycle Time

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