Automotive Industry
Stainless steel in vehicles falls into two groups: heat-resistant (exhaust systems) and decorative. Their grade systems and acceptance criteria differ, and mixing them up costs you money or causes failures.
Typical Parts and Material Selection
| Part | Grade | Surface / Thickness | 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 molding | 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 welding |
| Seat frame | 301 / 304 | High-strength sheet 0.5–1.2 mm | Yield strength ratio, fatigue |
Three Practical Constraints in This Industry
The "more expensive is better" myth for exhaust gas
409 is titanium-stabilized, inexpensive, and sufficient; 441 adds Nb+Ti for higher heat. Both mistakes are common: 304 in exhaust gas cracks at weld seams due to thermal expansion, and 409 in hot sections scales.
Deep drawing depends on r-value, not hardness
Decorative 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 out fast. Plan electrode changes by weld count and control incoming oil film and roughness.
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