Automotive Industry
Stainless steel in vehicles splits into two families: heat-resistant (exhaust systems) and decorative. Their quality systems and acceptance criteria differ, and mixing them up costs you either money or a failure.
Typical Parts and Material Selection
| Part | Grade | Surface / Size | Watch Out For |
|---|---|---|---|
| Exhaust pipe / 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 trim | 304 / 430 | BA / 8K, 0.3–0.8 mm | Surface class, no cracking during 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 strength ratio, fatigue |
Three Real 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 heat. Both mistakes are common: 304 in an exhaust system cracks at welds due to thermal expansion, 409 in a hot section flakes.
Deep drawing depends on 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 tensile test before the batch, don't just read the mill certificate.
Electrode life determines cycle time
Stainless steel has high resistance and low conductivity, so spot welding electrodes wear quickly. Plan electrode changes by weld count, and check incoming oil film and surface roughness.
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