Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of duplex stainless. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
The two-phase structure buys high strength plus excellent resistance to chloride stress-corrosion cracking — the failure mode that limits ordinary austenitic grades in warm chloride service.
It is also roughly twice as hard on tooling. The ferrite phase is abrasive and the austenite phase work-hardens, so a tool suffers wear and notching at the same time, from different mechanisms.
Common misuse
Treating duplex as a stronger 316 for machining purposes. It needs different tooling and feeds, and the standard stainless approach will not work.