Why this happens
201 grade steel (lower nickel content, less corrosion-resistant) costs meaningfully less than 304, and it's visually near-identical when new — some suppliers substitute 201 while billing it as 304, and the difference only becomes obvious months later when 201 starts showing surface rust that 304 wouldn't.
Practical checks that don't need a lab
- Ask for the Mill Test Certificate (see our MTC guide) — a legitimate supplier can produce this; a request that's dodged is itself a signal
- Magnet test — genuine 304 is only weakly magnetic; 201 tends to be more strongly magnetic. This isn't foolproof (cold-working can affect it) but a strongly magnetic "304" piece is worth questioning further
- Price sanity check — if a quote is meaningfully below the going rate covered in our pricing guide, ask specifically how
Why a GST-registered, established supplier matters here
See our GST registration guide — a supplier with a real registered business and a track record has more to lose from grade substitution than an unregistered trader does.
What to do if you suspect substitution
Ask directly and request the MTC before proceeding. A confident, prompt answer with documentation is what you want to see — hesitation or excuses are the signal to walk away.