§ 01 / 304

304 vs 316 — when moly matters

The critical difference: 316 contains 2–3% molybdenum, which gives it pitting resistance in chloride environments.

Environment304 suitable?316 suitable?
Indoor dry✓ Yes✓ Overkill
Outdoor clean air✓ Yes✓ Yes
Coastal / marine⚠ Pits over time✓ Yes
Saltwater immersion✗ Pits quickly✓ Yes (service, not severe)
Food contact✓ Yes (standard)✓ Yes (pharmaceutical grade)
Medical implants✗ No⚠ Limited — 316L preferred
Chemical processing (acid)⚠ Grade-dependent✓ Better; evaluate vs Hastelloy

316 costs roughly 30% more than 304 per kg. Use 316 only when corrosion environment justifies it; otherwise 304 is the default.

§ 02 / POST-WELD

Post-weld passivation

Welding stainless creates two problems: (1) heat-affected zone loses some corrosion resistance due to chromium carbide precipitation; (2) weld spatter and surface iron contamination can initiate rust.

Passivation fixes both:

  • Citric acid passivation — standard, RoHS-compliant, 20–30 minute bath
  • Nitric acid passivation — stronger, ASTM A967-compliant, for aerospace/medical
  • Electropolishing — removes a thin layer + polishes; for cosmetic/pharma applications

We include passivation on all welded stainless assemblies unless customer opts out.

READY WHEN YOU ARE

Stainless sheet metal — 304 or 316.

Upload DXF. Specify 304 or 316 and desired finish (2B / brushed / mirror). Passivation included on welded parts.

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