Automotive
Vehicles split into two stainless families: heat-resistant (exhaust) and decorative. Their grade systems and acceptance criteria differ, and mixing them either costs you money or causes failure.
Common Parts and Material Selection
| Part | Grade | Surface / Size | Avoid |
|---|---|---|---|
| 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 class, no cracking on bending |
| 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 |
Three real constraints in this industry
In exhaust, "the more expensive the better" is not true
409 is titanium-stabilized, inexpensive and sufficient; 441 adds Nb+Ti for higher heat. Both mistakes are common: 304 in exhaust cracks at welds due to thermal expansion, and 409 in hot sections forms scale.
Deep drawing depends on r-value, not hardness
Trim parts require high r and low Δr. The same grade behaves completely differently under different rolling schedules — always run a drawing trial before the batch, don't just read the mill certificate.
Electrode life determines takt time
Stainless has higher resistance and lower conductivity, so spot welding electrodes wear quickly. Plan electrode changes by weld count, and control incoming oil film and roughness.
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