Automotive
Stainless steel in vehicles falls into two groups: heat-resistant (exhaust) and decorative. Their steel grades and acceptance criteria differ — mixing them up will cost you money or cause failures.
Typical parts and material selection
| Part | Steel grade | Surface / size | Notes |
|---|---|---|---|
| Exhaust manifold / downpipe | 409 / 441 | 2B / 1D, 1.2–2.0 mm | High-temperature oxidation, thermal fatigue |
| Exhaust pipe / tailpipe | 409 / 436L | 0.8–1.5 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 | 1.0–2.0 mm | Formability, spot weldability |
| Seat frame | 301 / 304 | High-strength sheet 0.5–1.2 mm | Yield ratio, fatigue |
Three practical constraints in this industry
Exhaust is not "the more expensive, the better"
409 is titanium-stabilized, inexpensive and sufficient; 441 adds Nb+Ti for higher temperatures. Both failure modes are very common: 304 in exhaust cracks at welds due to thermal expansion, 409 scales in high-temperature zones.
Draw depth depends on r-value, not hardness
Decorative parts need high r and low Δr. The same steel grade from different rolling schedules behaves very differently — always run a trial draw before mass production, don't just read the mill certificate.
Electrode life determines takt time
Stainless steel has high resistivity and low conductivity, so spot-welding electrodes wear quickly. Plan electrode changes by weld count, and control incoming oil film and roughness.
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