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 leads to failure.

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Common sections and material selection

Section	Grade	Surface / size	Watch out for
Exhaust manifold / downpipe	409 / 441	2B / 1D, 1.2–2.0 mm	High-temperature oxidation, thermal fatigue
Muffler / tailpipe	409 / 436L	0.8–1.5 mm	Condensate corrosion
Trim / bright moldings	304 / 430	BA / 8K, 0.3–0.8 mm	Surface grade, no cracking on bending
Fuel tank / brackets	304 / 441	1.0–2.0 mm	Formability, spot weldability
Seat frame	301 / 304	High-strength sheet 0.5–1.2 mm	Yield ratio, fatigue

This is a typical configuration.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

Exhaust is not "the more expensive, the better"

409 is titanium-stabilized, inexpensive and adequate; 441 adds Nb+Ti for higher heat. Two common mistakes: 304 on an exhaust cracks at the weld due to thermal expansion, and 409 on hot sections suffers scaling.

Deep drawing depends on the r value, not hardness

Trim parts need high r and low Δr. The same grade from different rolling schedules behaves very differently — always run a drawing trial before the batch, 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 replacement by weld count, and control oil ingress and roughness.