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 either money or a failure.
Typical Parts and Material Selection
| Part | Grade | Surface / Size | What to Watch 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 profiles | 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 | Drawability, spot weldability |
| Seat frame | 301 / 304 | High-strength sheet 0.5–1.2 mm | Yield strength ratio, fatigue |
Three Real-World Constraints in This Industry
The exhaust system is not "the more expensive, the better"
409 is titanium-stabilized, inexpensive and sufficient; 441 adds Nb+Ti for higher temperature. Both mistakes are common: 304 in an exhaust system cracks at the welds due to thermal expansion, 409 in the hot section scales.
Deep drawing depends on the r value, not hardness
Trim parts require 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 sets the cycle time
Stainless steel has high resistance and low conductivity, so spot welding electrodes wear quickly. Plan electrode replacement by weld count and control incoming oil film and roughness.
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