Duplex Sheet Plate

Duplex stainless steel is a family of stainless steels whose microstructure consists of approximately 50% austenite (FCC) and 50% ferrite (BCC) phases. This balanced two-phase structure was first developed in Sweden in the 1930s and has since evolved through three generations to become one of the most important families in corrosive-service engineering.

Two phases. One material. Double the performance.

It means: A 3 mm duplex 2205 sheet can often replace a 6 mm 316L sheet while carrying the same load, because 2205 has a yield strength of 450 MPa vs 170 MPa for 316L.

Duplex Steel Sheet Types by Manufacturing Process

Hot-Rolled Sheet & Plate (HR)

Hot rolling reduces an ingot or continuously cast slab to the desired thickness at temperatures above the recrystallization point (≈1,000–1,200°C). The material exits the hot mill with a dark, scaled surface that is subsequently descaled by shot blasting and pickling (No.1 finish). For duplex and super duplex grades, hot rolling parameters — particularly the finishing temperature and cooling rate — are carefully controlled to avoid precipitation of sigma and chi phases.

●Standards: ASTM A240 (plate ≥ 4.76 mm), EN 10088-2, JIS G4304, GB/T 4237

●For duplex: solution-annealed at 1,020–1,100°C, then water-quenched to restore phase balance

●Applications: pressure vessels, structural members, heat exchanger tube sheets, shipbuilding

Cold-Rolled Sheet & Coil (CR)

After hot rolling and pickling, the material is further reduced at room temperature. Cold rolling work-hardens the sheet; a subsequent solution-annealing treatment restores ductility and the correct phase balance. Cold-rolled sheet offers significantly tighter thickness tolerances, superior surface quality, and a broader range of achievable surface finishes.

●Standards: ASTM A240 (< 4.76 mm), EN 10088-2, JIS G4305, GB/T 3280

●Applications: architectural panels, pharmaceutical vessels, kitchen equipment, automotive trim

Special Sheet Forms

Available Duplex Grades Detailed Technical Data

Chemical Composition

Mechanical Properties

Production and Material Standards

Primary International Material Standards for Duplex Sheet

The table below identifies the standards most commonly invoked in purchase orders for duplex sheet material.

Duplex Grade International Equivalents

When procuring duplex sheet internationally, it is essential to verify that the designation on the supplier's certificate matches the equivalent in your project's governing standard:

Frequently Asked Questions

Q1: What is the difference between duplex, super duplex, and lean duplex?

The difference is primarily determined by PREN (Pitting Resistance Equivalent Number): Lean duplex (PREN 24–30) — grades like 2101 and 2304; cost-effective, 2× stronger than 304L, ideal for structural and water treatment. Standard duplex (PREN 30–38) — 2205; the workhorse grade for chemical, oil & gas, and desalination. Super duplex (PREN 38–45) — 2507 and Zeron 100; for seawater, FGD, and offshore where PREN ≥ 40 is mandatory. Hyper duplex (PREN > 45) — 3207; niche extreme-sour applications. The higher the PREN, the more chloride-resistant and more expensive the grade.

Q2: Can duplex steel sheet be welded?

Yes — duplex and super duplex grades are readily weldable by all common arc processes (GTAW/TIG, GMAW/MIG, SMAW, SAW, PAW). However, duplex welding requires three specific precautions not needed for austenitic stainless: (1) Use Ni-overalloyed filler metal (e.g., ER2209 for 2205; ER2594 for 2507) to ensure the weld metal solidifies with a balanced austenite–ferrite microstructure. (2) Control heat input (typically 0.5–2.5 kJ/mm) and interpass temperature (≤ 150°C for 2205; ≤ 100°C for 2507) to prevent excessive ferrite and sigma phase formation. (3) A qualified Welding Procedure Specification (WPS) per ASME Section IX or EN ISO 15614-1 is mandatory. The finished weld should be tested per ASTM A923 to verify freedom from intermetallic phases.

Q3: What is the maximum service temperature for duplex sheet?

The maximum continuous service temperature for all duplex and super duplex grades is 250–280°C, governed by two metallurgical phenomena: (a) 475°C embrittlement — the precipitation of alpha-prime (Cr-rich ferrite) that drastically reduces toughness at temperatures above approximately 280°C, and (b) sigma phase formation in the 600–1,000°C range during fabrication or service. This is the single most important temperature limitation of duplex: it cannot be used in high-temperature applications where austenitic grades (304H, 321H, 310S, 253MA) excel. Conversely, duplex grades are suitable for cryogenic service only to approximately -40°C (2205) or -50°C (2507 Z-grade). For deep cryogenic applications (-196°C LNG), use austenitic grades (304L, 316L).

Q4: Why does duplex steel cost more than 316L — and is it worth it?

Duplex sheet typically costs 2–2.5× (2205) to 3–4× (2507) the purchase price of 316L on a per-kilogram basis. However, three factors offset this premium: (1) Yield strength is 2–3× higher, meaning thinner sheet can often be used — reducing the kilogram requirement by 33–60%. (2) Duplex eliminates SCC replacement cycles — a 316L component in hot chloride service may fail in 2–5 years, whereas duplex lasts 15–30+ years. (3) Lifecycle cost (fabrication + installation + maintenance + downtime + replacement) almost always favors duplex when chloride levels exceed the 316L SCC threshold. The breakeven point is typically 1–3 years for offshore/chemical applications (NACE 2019 Corrosion Cost Study).

Q5: What is the lead time for duplex sheet?

Standard duplex 2205 (S32205) in common gauges (1.5–6 mm, 2B finish) is typically ex-stock or 2–4 weeks from JNAlloy inventory. Super duplex 2507 (S32750) in sheet form generally requires 6–10 weeks from mill — JNAlloy maintains buffer stock of common sizes. Lean duplex (2304, 2101) and specialty grades (Zeron 100, 2906) are mill-order items with 10–16 week lead times. Custom surface finishes (No.4, BA, electropolished) on duplex add 1–3 weeks. MOQ for mill orders is typically 2–5 metric tons per heat.

Q6: Can duplex sheet be used in sour service (H₂S)?

Yes — 2205 (S32205) and 2507 (S32750) are both pre-qualified for sour service under NACE MR0175/ISO 15156-3, subject to specific environmental limits. Key requirements: (1) Hardness: ≤ HRC 28 (2205, solution-annealed) or ≤ HRC 32 (2507). (2) Ferrite content: 35–65% per ASTM A800. (3) ASTM A923 Method A/B/C testing is mandatory. (4) The material must be in the solution-annealed + water-quenched condition — no cold-worked or as-welded duplex is acceptable for sour service without additional qualification. Environmental limits (H₂S partial pressure, pH, Cl⁻, temperature) vary; consult the NACE MR0175 Part 3 tables for the specific grade, condition, and product form.

Q7: What is the minimum thickness of duplex cold-rolled sheet available?

Standard cold-rolled duplex sheet is available from 0.3 mm upward. However, the practical minimum for most industrial applications is 0.5 mm because: (a) Below 0.5 mm, the high yield strength of duplex makes flatness control during rolling and annealing challenging. (b) Thinner gauges require precise temperature control during continuous annealing to avoid variations in phase balance across the coil width. JNAlloy stocks 2205 CR sheet from 0.5 mm; thinner gauges are available on mill order with extended lead time. For foil-gauge applications (< 0.3 mm), precision rerolling from thicker strip can be arranged through our specialty mill partners.