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 a failure.
Typical parts and material selection
| Part | Grade | Surface / size | Watch out 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 profile | 304 / 430 | BA / 8K, 0.3–0.8 mm | Surface class, 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 real constraints in this industry
The answer is not "the more expensive, the better"
409 is titanium-stabilized, economical and adequate; 441 adds Nb+Ti for higher temperature. Both mistakes are common: 304 in the exhaust cracks at the welds due to thermal expansion, 409 in a hot section oxidizes and scales.
Deep drawing depends on the r value, not hardness
Finish parts need a high r value and a low Δr. The same grade with different rolling schedules behaves very differently: always run a drawing trial before the batch, don't just read the mill certificate.
Electrode life defines cycle time
Stainless steel has high strength and low conductivity, so spot welding electrodes wear fast. Plan electrode changes by weld count and control the oil film and incoming roughness.
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