Automotive

Automotive stainless steel falls into two families: heat-resistant (exhaust) and decorative. They use different grade systems and acceptance criteria, and mixing them leads to cost overruns or rejects.

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General Parts & Material Selection

Part	Grade	Surface / Size	Notes
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 molding	304 / 430	BA / 8K, 0.3–0.8 mm	Surface grade, no cracking on bending
Fuel tank / bracket	304 / 441	0–2.0 mm	Formability, spot weldability
Panel frame	301 / 304	High-strength sheet 0.5–1.2 mm	Yield ratio, fatigue

This is a general configuration.Actual selection depends on medium, temperature and welding method— The same part can move from 304 to 316L or 2205. Describing the service conditions is more useful than specifying a grade.

Three practical constraints in this industry

For exhaust systems, more expensive is not better

409 is a titanium-stabilized steel — inexpensive and sufficient; 441 adds Nb+Ti for higher heat resistance. Two mistakes are common: using 304 in exhaust systems causes cracking at welds due to thermal expansion, and using 409 in high-temperature sections leads to scaling.

Deep drawing depends on r-value, not hardness

Trim parts need high r and low Δr. The same grade behaves very differently depending on the rolling schedule — always run a drawing trial before mass production, don't just read the mill certificate.

Electrode life determines 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.