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Material: F51, F53, F55, F60
Type: Round bar,Square bar,Hex bar,Flat bar
Tolerance: H7 H9 H10 H11
Surface: Black or Bright or Pickling white
Diameter: 5~500mm
Length: ≦12M or As Per Client's Requirements.
Duplex round bar is a solid cylindrical product with a circular cross-section, produced by hot rolling, forging, or cold drawing. Round bars are the starting stock for machining fasteners, shafts, valve stems, pump components, flange bolting, and a wide range of subsea and chemical process equipment.
The duplex round bar is the most common semi-finished shape for duplex alloys, serving as the starting point for pump shafts, valve stems, fasteners, and pressure-retaining components.
Type | Round Bar Square Bar Hexagon Bar Flat Bar | ||
Surface | Black or Bright or Pickling white | ||
Standard | SUS, AISI, DIN | ||
Manufacture Technique | Hot Rolling, Cold-drawing | ||
Diameter | 5~500mm | ||
Length | ≦12M or As Per Client's Requirements. | ||
Diameter Tolerance | H7 H9 H10 H11 | ||
Material Grade | Stainless Steel | ASTM/ASME SA 276 /479 | F51/S31803/2205, F53/S32750/2507, F55/S32760, F60/S32205 |
Duplex 2205 offers a minimum yield strength of 450 MPa. This means a smaller cross-section can carry the same load, reducing material weight by up to 30–40% in structural designs. (Source: ASTM A276/A276M-24a; Outokumpu Duplex Data Sheet)
Duplex round bars are available in the same five principal surface conditions as austenitic bars, but with additional processing considerations due to their higher strength and dual-phase microstructure.
Hot-Rolled Duplex Round Bars
Hot-rolled duplex bars are the baseline product and the most widely stocked form. After rolling, they must undergo solution annealing (typically at 1,020–1,100 °C depending on grade) followed by rapid water quenching. This step is critical: without it, the ferrite/austenite phase balance deviates from the target 50/50 ratio, and brittle secondary phases (sigma, chi) can precipitate, degrading both corrosion resistance and toughness.
Cold-Drawn Duplex Round Bars
Cold drawing duplex bars requires significantly higher drawing forces than austenitic bars due to their elevated base yield strength. The increased work-hardening rate means that fewer drawing passes are possible before intermediate annealing is required. However, the resulting bars offer excellent dimensional consistency and surface finish, making them ideal for CNC machining blanks and precision fasteners.
Centerless-Ground Duplex Round Bars
Centerless-ground duplex bars achieve the tightest tolerances and smoothest surfaces, specified for hydraulic cylinder rods, subsea pump shafts, and linear motion components. A key processing note: grinding generates localized heat that can transform the surface microstructure if not properly controlled. Coolant flow and feed rates must be optimized to prevent surface phase transformation, which would create a thin martensitic layer that acts as a corrosion initiation site.
Forged Duplex Round Bars
Forging is essential for large-diameter duplex bars (typically >150 mm) that cannot be economically hot-rolled. Forged duplex bars offer superior grain-flow alignment, which improves fatigue resistance and impact toughness — critical for offshore connector components, subsea manifold flanges, and high-pressure valve bodies. Forging temperatures must stay within the 1,000–1,200 °C window; overheating promotes sigma-phase formation, while underheating risks ferrite dominance and cracking.
The production of duplex and super duplex round bars follows a similar sequence to austenitic bars.
Duplex stainless steels are melted in Electric Arc Furnaces (EAF) and refined in Argon Oxygen Decarburization (AOD) or Vacuum Oxygen Decarburization (VOD) vessels. Nitrogen control is the most critical metallurgical parameter — nitrogen is both an austenite stabilizer (ensuring the target 50% austenite fraction) and a potent pitting-resistance enhancer (16× weighting in the PREN formula). Typical nitrogen targets: 0.14–0.20% for standard duplex, 0.24–0.32% for super duplex. After refining, the melt is continuously cast into billets or round blooms for rolling.
Solution annealing is the single most important heat treatment for duplex round bars. The bar is heated to 1,020–1,100 °C (grade-dependent), held long enough for complete dissolution of any sigma, chi, or carbide phases, then rapidly water-quenched. This restores the optimal ≈50/50 austenite-ferrite balance and maximizes corrosion resistance.
Failure to solution-anneal, or slow cooling (air cooling instead of water quench), allows sigma phase to precipitate in the 600–900 °C range. Sigma phase is brittle and chromium-rich, depleting the surrounding matrix of chromium and drastically reducing both toughness and pitting resistance. A duplex bar that has not been properly annealed may pass dimensional inspection but will fail catastrophically in service — this is a well-documented failure mode in offshore applications.
Grade | Anneal Temp (°C) | Hold Time (min/mm) | Cooling Method |
2205 (Standard) | 1,020–1,100 | 2–3 | Water quench |
2507 (Super) | 1,025–1,100 | 2–3 | Water quench |
Source: ASTM A276/A276M-24a; Outokumpu Duplex annealing parameters
Unlike austenitic grades that can serve at temperatures up to 816 °C, duplex grades are restricted to lower maximum service temperatures:
• 2205: Maximum 250–325 °C per EN 10028-7 / ASME Section II-D (depending on duration). Above this, 475 °C embrittlement and sigma-phase precipitation accelerate.
• 2507: Maximum 250–300 °C. Even more susceptible to embrittlement at elevated temperature due to higher Cr/Mo content.
Duplex wins in chloride corrosion and strength at ambient-to-moderate temperatures, but austenitic wins at high temperatures. Specifiers must match the grade to the actual operating temperature, not just the corrosive environment.
Standard duplex stainless steels contain approximately 22% chromium, 5% nickel, and 3% molybdenum, with nitrogen additions of 0.10–0.22%. They offer PREN values of 32–36, placing them at or just above the seawater pitting threshold. These grades are the workhorse of the duplex family, widely used in offshore, chemical, and desalination applications.
Grade | UNS | Cr (%) | Ni (%) | Mo (%) | N (%) | PREN |
2205 (most common) | S31803 / S32205 | 21–23 | 4.5–6.5 | 2.5–3.5 | 0.08–0.20 | 33–35 |
2507 (super duplex) | S32750 / S32760 | 24–26 | 6–8 | 3–5 | 0.24–0.32 | 40–43 |
2507Cu (super duplex, Cu-added) | S32760 (Zeron 100) | 24–26 | 6–8 | 3–4 | 0.20–0.30 | 40–43 |
Source: ASTM A276/A276M-22; ASTM A240/A240M-22; EN 10088-2:2023; Outokumpu 'Duplex Stainless Steels Data Sheet' (2023); Sandvik 'Sandvik SAF 2205 / SAF 2507 Product Catalogue' (2022). * S32205 is the 'restricted-composition' variant of S31803 with tighter N range (0.14–0.20%) for improved weldability and corrosion performance; it is the preferred specification for new projects.
Grade (UNS) | Min. UTS (MPa) | Min. YS 0.2% (MPa) | Min. Elongation (%) | Hardness (max HB) | Impact Energy at –40°C (J, typical) |
2205 (S32205) | 620 | 450 | 25 | 290 | ~120 |
2507 (S32750) | 795 | 550 | 15 | 310 | ~80 |
2507Cu (S32760) | 750 | 550 | 25 | 300 | ~80 |
Source: ASTM A276/A276M-22 Table 2; ASTM A479/A479M-22 Table 2; EN 10088-3:2023 Table 6; Outokumpu and Sandvik product data sheets (2022–2023).
Duplex stainless steels over standard austenitic grades is driven by three factors:
(1) higher chromium and molybdenum content, which increases PREN;
(2) the ferrite phase, which resists chloride stress corrosion cracking (SCC) — the dominant failure mode for 304L/316L in hot chloride environments;
(3) nitrogen, which enhances pitting resistance and stabilises the austenite phase.
Corrosion Mode | 304L (S30403) | 316L (S31603) | 2205 (S32205) | 2507 (S32750) | 6% Mo (N08367) |
PREN | 18–20 | 24–26 | 33–35 | 40–43 | 43–45 |
Seawater pitting (CPT, ASTM G48, °C) | 5–10 | 15–20 | 30–35 | > 60 | > 70 |
Seawater crevice (CCT, ASTM G48, °C) | < 0 | 5–10 | 18–22 | > 40 | > 50 |
Chloride SCC resistance | Poor (fails > 60°C) | Poor (fails > 60°C) | Excellent (immune up to 200°C) | Excellent | Excellent |
Sour service (ISO 15156-3) | Not listed (restricted) | Not listed (restricted) | Table C.2 (restricted pH₂S) | Table C.2 (restricted pH₂S) | Table C.3 (qualified) |
CO₂ uniform corrosion (mm/yr, typical) | 0.5–2.0 (uninhibited) | 0.2–1.0 (uninhibited) | < 0.1 | < 0.05 | < 0.05 |
Acid resistance (H₂SO₄, dilute) | Moderate | Good | Good | Very Good | Excellent |
Recommended service limit | Fresh water; indoor; food | Low-Cl⁻ process; < 50°C seawater | Seawater up to 25°C; offshore piping | Hot seawater; subsea; HPHT | Extreme acid; seawater > 35°C |
Source: ASTM G48-11(2020) 'Pitting and Crevice Corrosion Resistance of Stainless Steels'; ISO 15156-3:2015 + Amd 1:2017 Tables C.2, C.3; NACE MR0175; Outokumpu corrosion data sheets; Sandvik SAF corrosion performance reports; JN Alloys internal corrosion test data.
Standard | Scope | Key Details for Duplex Bars |
ASTM A276 | SS bars and shapes — general purpose | Covers duplex grades 2205, 2507, 2304 as bars. Most commonly cited standard for duplex round bars. |
ASTM A479 | SS bars for boilers and pressure vessels | Additional intergranular corrosion and tensile testing. Mandatory for ASME-coded pressure vessel applications. |
ASTM A182 | Forged/rolled SS pipe flanges, fittings, valves | Defines forging grades F51 (2205), F53 (2507), F55 (Zeron 100), F60 (2205 modified). Essential for forged duplex components. |
ASTM A484 | General requirements for SS bars | Umbrella specification for tolerances, quality, and testing. Referenced by A276 and A479. |
Source: ASTM International, 2024–2026 editions
A182 Grade | UNS | Equivalent Bar Grade | PREN | Application Focus |
F51 | S31803/S32205 | 2205 | ≈33–36 | Flanges, valve bodies, fittings for moderate chloride |
F53 | S32750 | 2507 | ≈43 | High-pressure flanges for subsea, seawater, H2S |
F55 | S32760 | Zeron 100 | ≈41–43 | Cu-enhanced super duplex; offshore manifolds, connectors |
F60 | S32205 | 2205 (restricted) | ≈36 | Tight-composition 2205 forgings for critical service |
F61 | S32550 | 255 (Ferralium) | ≈38 | Legacy super duplex; largely superseded by F53/F55 |
Source: ASTM A182/A182M-24; forgings cross-reference table
Standard | Scope | Key Details |
EN 10088-3 | Chemical composition & mechanical properties of SS long products | Defines duplex by EN material number: 1.4462 (2205), 1.4410 (2507), 1.4362 (2304), 1.4162 (2101) |
EN 10278 | Tolerances for bright steel products | Specifies h7–h11 tolerance classes for CD, CG, and polished bars |
EN 10060 | Tolerances for hot-rolled round bars | Diameter, out-of-roundness, straightness for HR bars |
EN 10204 | Inspection documents (MTC) | 3.1 (mill cert) and 3.2 (third-party validated) formats |
Source: CEN — European Committee for Standardization, 2023–2025 editions
Standard | Origin | Scope |
NACE MR0175 / ISO 15156 | International | Sour service (H2S) qualification; defines PREN thresholds for duplex in oil & gas production |
ASME SA-276 / SA-479 | USA | ASME-adopted equivalents of ASTM A276/A479; required for Boiler and Pressure Vessel Code applications |
JIS G 4303 | Japan | Japanese stainless steel bar standard; includes duplex grade designations for Asia-Pacific markets |
GB/T 1220 | China | Chinese SS bar standard; includes domestic duplex grade equivalents for China-market procurement |
Source: NACE/ISO; ASME; JSA; SAC standards
Application | Grade | Bar Type | Key Reason | Alternative |
Offshore topside structural | LDX 2101 / 2304 | HR / CD | High YS + cost savings vs 316L; no immersion | 2205 if splash zone present |
Marine splash zone fasteners | 2205 (S32205) | CD / CG | PREN 36; chloride splash + SCC resistance | 2507 for prolonged wet exposure |
Subsea manifold connectors | 2507 | Forged + CG | PREN 43; seawater immersion + H2S (NACE) | Zeron 100 for Cu-enhanced acid resist. |
Desalination plant shafts | 2507 | CG | Seawater + high-temp brine resistance | 2205 for low-temp brine |
Sour gas wellhead components | 2507 / Zeron 100 | Forged | NACE MR0175 compliant; H2S + chloride | 2707 for extreme sour + acid |
Chemical storage tanks (structural) | 2205 | HR / Peeled | Moderate chloride; 2× YS saves weight | 316L if HAZ welding concerns exist |
Water treatment piping supports | LDX 2404 / 2304 | CD | Cost-effective; PREN 24–30 sufficient | 2205 if higher chloride expected |
Ultra-deep subsea (>3000 m) | 2707 | Forged + CG | PREN ≈50; extreme chloride + pressure | 2507 + Inconel 625 cladding |
Source: NACE MR0175/ISO 15156; DNV-OSS-301; Outokumpu application guides
Q: What is the difference between duplex and super duplex stainless steel?
A: Duplex 2205 (PREN ≈36) contains 22% Cr, 3% Mo, and 0.16% N with minimum yield strength 450 MPa. Super duplex 2507 (PREN ≈43) contains 25% Cr, 4% Mo, and 0.28% N with minimum yield strength 550 MPa.
The higher alloy content in 2507 delivers approximately 20% better chloride pitting resistance and 22% higher yield strength, qualifying it for seawater immersion and sour-gas (H2S) service per NACE MR0175/ISO 15156, where 2205 is limited to splash-zone and moderate chloride applications.
Q: Why should I choose duplex 2205 over austenitic 316L for marine applications?
A: Duplex 2205 offers three decisive advantages over 316L:
(1) 2.6× higher yield strength (450 vs. 170 MPa), enabling 30–40% weight reduction;
(2) 40% better chloride pitting resistance (PREN 36 vs. 26);
(3) inherent resistance to stress corrosion cracking, which is the dominant failure mode for 316L in warm chloride environments above 60–80 °C.
The only trade-off is a lower maximum service temperature (250–325 °C for 2205 vs. 816 °C for 316L).
Q: What does PREN mean and how is it calculated for duplex grades?
A: PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3×%Mo + 16×%N. It quantifies resistance to chloride-induced pitting. For duplex grades, nitrogen’s 16× weighting is especially impactful because duplex alloys contain 0.14–0.32% N (vs. 0.06–0.10% in most austenitics). This is why 2205 achieves PREN ≈36 with only 3% Mo, while 316L needs 2.5% Mo but reaches only PREN ≈26 — nitrogen makes the difference. Industry thresholds: PREN < 22 for freshwater only; PREN 30–40 for moderate chloride; PREN 40+ for seawater immersion; PREN 50+ for extreme service.
Q: Can duplex round bars be used in sour gas (H2S) service?
A: Yes, but only specific grades qualify. NACE MR0175/ISO 15156 lists duplex 2205 and super duplex 2507 as acceptable for sour service, with conditions: maximum hardness 22 HRC (2205) or 28 HRC (2507), and the material must be in the solution-annealed condition.
Lean duplex grades (2101, 2304) are NOT qualified for H2S-containing environments. For the most aggressive sour conditions (high H2S + high chloride + elevated temperature), hyper duplex 2707 or nickel alloys (Inconel 625, Hastelloy C276) are recommended.
Q: What is sigma phase and why is it dangerous in duplex stainless steel?
A: Sigma phase is a brittle intermetallic compound (FeCrMo) that precipitates in duplex steels when they are held in the 600–900 °C range — for example, during slow cooling after hot rolling or forging, or during prolonged high-temperature service.
Sigma phase depletes chromium and molybdenum from the surrounding matrix, reducing pitting resistance by up to 50% and dropping impact toughness by 80% or more. Prevention: always water-quench after solution annealing; never air-cool duplex bars; limit service temperature below 325 °C for 2205 and 300 °C for 2507.
Q: Why specify S32205 instead of S31803 for 2205 duplex round bars?
A: UNS S32205 has tighter composition ranges (Cr 22–23%, Mo 3.0–3.5%) than S31803 (Cr 21–23%, Mo 2.5–3.5%). This guarantees PREN ≥35 in every heat, whereas S31803 heats at the low end of the range may have PREN as low as 33 — marginal for marine service.
For any application where corrosion resistance is critical (marine, chemical, offshore), always specify S32205. For general structural applications where PREN margin is not critical, S31803 may be acceptable at a lower cost.
Q: What are the temperature limitations of duplex stainless steel round bars?
A: Duplex grades are restricted to lower maximum service temperatures than austenitic grades due to 475 °C embrittlement and sigma-phase risk: 2205 is limited to 250–325 °C (per EN 10028-7 / ASME II-D), and 2507 is limited to 250–300 °C. Below these limits, duplex performs excellently.
Above them, austenitic grades (304H, 316H, 310S, 321) or nickel alloys should be selected. The 475 °C embrittlement phenomenon affects the ferrite phase and causes progressive toughness loss even during prolonged exposure at 300–475 °C.
Q: What diameter range and tolerances are available for duplex round bars?
A: Standard production ranges: hot-rolled 10–500 mm (h11–h13), cold-drawn 6–100 mm (h9–h11), centerless-ground 6–150 mm (h7–h9), peeled 20–500 mm (h10–h12), forged 50–800 mm (as-forged or machined).
For offshore precision components (pump shafts, hydraulic rods), centerless-ground h7–h8 tolerance (±0.02–0.05 mm) is standard. For structural applications, hot-rolled h11–h13 is sufficient and more economical.
