Technical guide · 2026-08-03
Duplex Stainless Steel
Duplex stainless steels are chromium-nickel grades engineered to contain substantial ferritic and austenitic phases after correct processing. They combine higher strength than common annealed austenitic grades with useful resistance to localized corrosion and chloride stress-corrosion cracking in suitable environments.
01
Definition and boundary
“Duplex” is a family, not one performance level: lean duplex, standard 2205 and super duplex 2507 differ in alloy content, corrosion resistance, fabrication window and cost.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Balanced ferrite/austenite phases combine complementary strength, toughness and corrosion behavior.
Chromium, molybdenum and nitrogen raise localized-corrosion resistance in higher-alloy grades.
Excessive or insufficient thermal exposure can shift phase balance or form harmful intermetallic phases.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| Lean-duplex choices for strength and moderate corrosion requirements. | Verify the ordered product specification, condition and dimensions before substitution. | |
| Widely used standard duplex grade for process, water and structural service. | Verify the ordered product specification, condition and dimensions before substitution. | |
| Super-duplex option for more severe chloride and localized-corrosion exposure. | Verify the ordered product specification, condition and dimensions before substitution. |
04
Properties and trade-offs
Higher yield strength can reduce section thickness only after code and stability checks.
Localized-corrosion resistance varies strongly with grade chemistry and surface condition.
Toughness and phase stability impose temperature and fabrication limits.
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Desalination, water treatment and seawater systems
- Chemical process, pulp and paper, tanks and heat exchangers
- Offshore, energy and corrosion-resistant structural components
Properties and trade-offs
- Quantify chloride, temperature, acidity, deposits and crevice geometry.
- Use lean, standard or super duplex only after corrosion and fabrication requirements are both satisfied.
- Check design-code allowables, toughness and temperature limits before using strength advantage.
07
Fabrication, durability and inspection
Use qualified welding procedures that control heat input, interpass temperature and filler selection.
Avoid prolonged exposure in harmful temperature ranges during forming, heat treatment and repair.
Restore clean, oxide-free surfaces and verify phase/intermetallic requirements when specified.
08
Procurement checklist
- State exact UNS/EN grade, product standard and solution-annealed condition.
- Specify corrosion tests, ferrite/phase checks, impact tests and NDE where required.
- Control weld consumables, repair procedure, PMI, traceability and surface acceptance.
09
Standards, sources and review
Standards and designation context
- ASTM A240/A240M for applicable duplex plate, sheet and strip
- ASTM/ASME product standards specific to pipe, fittings, forgings and pressure service
- Project corrosion and welding specifications may add ASTM G48 or phase-related acceptance
Authoritative research sources
worldstainless · Technical overview, accessed 2026
Nickel Institute · Technical Guide 9014, 2020
ASTM International · A240/A240M-26 scope page