Guides
2026-03-27 · 10 min read
201 and 304 look alike but differ sharply in corrosion resistance (nickel) and price. Using 201 in wet sites rusts fast. Here are four practical checks — spark, test solution, and spectrometer — plus where 201 must never go.
304 is the gold standard; 201 is a lower-cost manganese-heavy substitute. After brushing or coloring they look alike while priced thousands apart per ton. Bad actors hide 201 in substrates or recesses. Humidity or acidic cleaners then rust the wall within months.
Chromium gives baseline protection; nickel boosts corrosion resistance and ductility. - 201: ~3.5–5.5% Ni (some junk near 0.2%). Grades J1–J5 differ; J4 is stretchier; J2 is common, hard, poor for grooving/bending; J5 is worst for brittleness. - 304: ~8–10.5% Ni — strong in most weak acids; often 3–4 years clean outdoors without care. - 316: ~10–14% Ni plus Mo for marine / chloride exposure.
- 201 may be acceptable in very dry northern interiors, benign mall zones, and low-duty furniture frames. - Never use 201 for: 1. Kitchens and baths — steam and cleaners rust it fast. 2. Basements — damp; use 304. 3. Coastal / outdoor chloride air — consider 316; 304 marginal; 201 no. 4. Aggressive industrial or acid-rain environments.
Four checks: 1) Raw 2B color — 201 often duller; 304 brighter — useless after heavy PVD/brush. 2) Test drops — faster/deeper red means lower nickel (201 risk); fake reagents exist. 3) Grinder sparks — 201: big, branched; 304: smaller, cleaner streaks (skilled operator). 4) Portable spectrometer — authoritative; 304 Ni often ~7.9–8.3%+; junk 201 may read ~0.2% Ni.
- Absurdly cheap “304” is usually fake grade or severe under-gauge (e.g. labeled 1.0 mm, mic’d 0.6 mm). - Even real 201: avoid worst J5 — low Cu, high C, brittle breaks on bend or groove.
- Myth: 304 never rusts. Truth: it resists rust, not immune. Strong acids/alkalis break the passive film. Field killers: bleach-like cleaners, acidic tile cleaners (“cement removers”), or acidic sealant left on the surface — even top 304 can spot-rust in days.
Greateson spectrometers incoming and outgoing stock: if drawings say 304, delivered Ni meets national minimums. We helped a five-star hotel expose mixed 201 from a prior supplier — seconds on the gun, avoiding bathroom maintenance disaster.
You get what you pay for in stainless. Keep 201 out of wet zones. For critical acceptance, do not trust words alone — use test solution or demand spectrometer video proof.
Q1: If a magnet sticks, is it fake 201; if not, 304?
A1: Wrong — widespread myth. 304 is austenitic and normally non-magnetic but cold work can add weak magnetism; 400-series chrome steel is strongly magnetic. Magnets cannot separate 201 from 304 reliably.
Q2: What grade for kitchen cabinets?
A2: Use 304 — kitchens have moisture, salt, and condiments; 201 will rust over time.
Q3: Same weight for 201 and 304?
A3: Same density ~7.93 g/cm³ — weighing does not distinguish them.
Q4: Why does some 201 crack when bent and some not?
A4: 201 has J1–J5 families — J4 is stretchier for deep draws; J2 is common for simple 90° bends only; J5 is brittle and cracks on bend or groove.
Q5: Acidic tile cleaner caused rust — can I fix it?
A5: Light surface rust: stainless rust paste then protective oil. Deep pits through substrate or ruined PVD/mirror usually means replace the panel.
Share your application scenario and expected finish, and we can provide a practical material recommendation.
