# UNS S32550 Super Duplex Forgings (ASTM A182 Grade F61)

**UNS S32550 is a copper-bearing super duplex stainless steel with a ferritic-austenitic structure. Forged products are specified under ASTM A182 Grade F61; the European equivalent is EN 1.4507, X2CrNiMoCuN25-6-3. Composition runs 24.0 to 27.0 % Cr, 4.5 to 6.5 % Ni, 2.9 to 3.9 % Mo, 1.50 to 2.50 % Cu and 0.10 to 0.25 % N, giving a PREN of about 40.**

Supplier: Jiangyin Jiangnan Metal Co., Ltd., an integrated steel melting works and open-die forge in Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 1997 with 460 staff. The plant melts, forges, heat treats, machines and certifies this grade on one site, so the certificate traces back to the melt number.

Source page: https://www.steelforgepieces.com/Stainless-Steel/UNS-S32550.html

| Field | Detail |
|---|---|
| UNS | S32550 |
| ASTM / ASME forging grade | A182 F61 / SA182 F61 |
| EN designation | 1.4507, X2CrNiMoCuN25-6-3 |
| Structure | Super duplex, ferrite plus austenite |
| PREN | About 40 |
| Tensile strength, min | 109 ksi, 750 MPa |
| Yield strength, min | 80 ksi, 550 MPa |
| Elongation, min | 25 % |
| Reduction of area, min | 50 % |
| Solution treatment | 1920 to 2060 F, 1050 to 1125 C, liquid quench below 500 F, 260 C |
| Melting route | EF, LF, VOD. ESR on request |
| Certification | EN 10204 3.1 or third-party 3.2 |
| Press capacity | 6,300 tonne open-die press |
| Ring mill | 6 metre radial-axial |
| Maximum single-piece weight | 30 tonnes |
| Approvals | CCS, BV, DNV, LR, NK |
| Telephone | +86 189 2135 9659 |
| Email | sales@steelforgepieces.com |

## Grade overview

Duplex stainless steels hold roughly equal fractions of ferrite and austenite, which gives about double the yield strength of a standard austenitic grade along with strong resistance to chloride stress-corrosion cracking. UNS S32550 sits in the super duplex band, carrying 25 to 26 % chromium in practice plus a deliberate copper addition of 1.50 to 2.50 %.

Langley Alloys maps ASTM A182 F61 to UNS S32550 and identifies the grade as an approximation of Ferralium 255, the first super duplex stainless steel, invented by Langley Alloys and launched in 1969. Ferralium is a registered trademark of Langley Alloys Ltd; Jiangyin Jiangnan Metal supplies to the UNS S32550 and ASTM A182 F61 specifications, not the trademarked product.

Some supplier listings describe A182 S32550 as a 13 % chromium 410-type martensitic material. That is incorrect. S32550 is ferritic-austenitic.

## Equivalent designations

| System | Designation | Note |
|---|---|---|
| UNS | S32550 | Primary designation |
| ASTM / ASME | A182 F61, SA182 F61 | Forged flanges, fittings, valves, parts |
| EN / Werkstoff | 1.4507, X2CrNiMoCuN25-6-3 | European equivalent, chemistry differs slightly |
| Generic trade names | Alloy 255, Grade 255, Super Duplex 255, SD50 | Ferralium 255 is a Langley Alloys trademark |
| Related ASTM grade | A182 F59, UNS S32520 | Separate grade, same family |
| Related JIS grade | SUS 329J4L | Listed alongside S32550 in reference tables |
| Other listings | 52N+, UR52N, X3CrNiMoCuN26-6-3-2 | Proprietary and national variants |

Cross-reference tables show similar grades, not interchangeable ones. EN 1.4507 calls for 6.0 to 8.0 % Ni and 0.20 to 0.30 % N, while UNS S32550 allows 4.5 to 6.5 % Ni and 0.10 to 0.25 % N.

## Chemical composition, ASTM A182 Grade F61

| Element | Min | Max |
|---|---|---|
| C | – | 0.040 |
| Mn | – | 1.50 |
| Si | – | 1.00 |
| P | – | 0.040 |
| S | – | 0.030 |
| Cr | 24.0 | 27.0 |
| Ni | 4.5 | 6.5 |
| Mo | 2.9 | 3.9 |
| Cu | 1.50 | 2.50 |
| N | 0.10 | 0.25 |
| Fe | Balance | Balance |

### Compared with EN 1.4507

| Element | UNS S32550 (A182 F61) | EN 1.4507 |
|---|---|---|
| C | 0.040 max | under 0.03 |
| Mn | 1.50 max | under 2.0 |
| Si | 1.00 max | under 0.7 |
| P | 0.040 max | under 0.035 |
| S | 0.030 max | under 0.015 |
| Cr | 24.0–27.0 | 24.0–26.0 |
| Ni | 4.5–6.5 | 6.0–8.0 |
| Mo | 2.9–3.9 | 3.0–4.0 |
| Cu | 1.50–2.50 | 1.0–2.5 |
| N | 0.10–0.25 | 0.20–0.30 |

## Mechanical properties

Specified minimums, ASTM A182 Grade F61:

| Property | Imperial | Metric |
|---|---|---|
| Tensile strength, min | 109 ksi | 750 MPa |
| Yield strength, 0.2 % offset, min | 80 ksi | 550 MPa |
| Elongation in 2 in. or 4D, min | 25 % | 25 % |
| Reduction of area, min | 50 % | 50 % |

Typical achieved values for this chemistry: bar up to 12 in. gives around 114.5 ksi, 789 MPa, ultimate tensile with 85 ksi, 586 MPa, yield and 25 % elongation; bar 12 in. and over gives around 110 ksi, 758 MPa, with 83 ksi, 573 MPa, yield. Hardness is generally reported between about 220 and 270 HBW. General data for 1.4507 gives 700 to 900 MPa tensile, yield above 500 MPa and hardness below 270 HB.

### Physical and elevated-temperature data for 1.4507 and S32550

| Property | Value |
|---|---|
| Modulus of elasticity at 20 C | 200 GPa |
| Modulus at 100 / 200 / 300 C | 194 / 186 / 180 GPa |
| Yield Rp0.2 at 100 / 200 / 250 C | over 450 / 400 / 380 MPa |
| Thermal conductivity | 15 W/m·K |
| Specific heat capacity | 500 J/kg·K |
| Linear expansion, 20 to 100 C | 13.0 x 10⁻⁶ /K |
| Electrical resistivity | 0.8 µΩ·m |

The alloy has been evaluated for maximum continuous operation at 500 F, 260 C, under the ASME Boiler and Pressure Vessel Code.

## Corrosion performance

PREN = %Cr + 3.3 x (%Mo + 0.5 x %W) + 16 x %N

| UNS | Common name | PREN |
|---|---|---|
| S31803 | Duplex 2205 | 36 |
| S32550 | Super duplex, 255 type, A182 F61 | about 40 |
| S32750 | Super duplex, A182 F53 | super duplex class |
| S32760 | Super duplex with tungsten, A182 F55 | 41 |

A PREN of 32 to 35 is widely treated as the practical floor for seawater service. The grade is noted for superior sulfuric acid resistance and performs in sour service, phosphoric and nitric acid duty, and organic acids such as acetic and formic. Strongly reducing media remain the limiting case for any stainless steel. Confirm selection against your own process conditions and against NACE MR0175 / ISO 15156 or NACE MR0103 where sour service applies.

## Forging and heat treatment

Rolling and forging of 1.4507 and S32550 runs between roughly 1200 and 900 C. Finishing too cold risks cracking in the ferrite; soaking too hot coarsens the grain and shifts the phase balance toward ferrite.

ASTM A182 requires Grade F61 to be solution treated and quenched, not annealed and air cooled. The range is 1920 to 2060 F, 1050 to 1125 C, with a liquid quench taking the part below 500 F, 260 C. General data for 1.4507 gives a comparable supersaturation range of 1020 to 1100 C. Rapid cooling is required because sigma phase, a hard chromium-rich intermetallic, forms between roughly 600 and 1000 C and cuts both toughness and corrosion resistance. Heat-treatment practice for duplex products aims to hold ferrite between about 40 and 60 %.

Welding: maximum interpass temperature is reported as 100 C for super duplex, against 150 C for 2205. Matching consumables are covered by UNS W39553 and AWS A5.4 E2553-XX, ASME IX group P10H.

Machining: conventional methods at satisfactory rates, but the alloy work-hardens quickly and runs hot. Use a rigid overpowered machine, rigid workholding with minimal tool overhang, sharp positive-rake carbide tooling changed on schedule, heavy constant feeds so the tool never dwells, and soluble-oil lubrication.

## Choosing between duplex forging grades

| Grade | UNS | Type | Position |
|---|---|---|---|
| F51 | S31803 | 22 % Cr duplex | Original 22 % Cr designation |
| F60 | S32205 | 22 % Cr duplex | Tightened composition; S32205 can be dual-certified as S31803, not the reverse; around 80 % of duplex production |
| F53 | S32750 | 25 % Cr super duplex | Higher chromium than F51, higher yield allows thinner sections |
| F55 | S32760 | 25 % Cr super duplex with tungsten | Traces to Zeron 100 development |
| F61 | S32550 | Super duplex with copper | Langley Alloys states F61 gives increased strength and corrosion performance over F53 and F55, with Ferralium 255 minimum yield above 85 ksi where those grades are held to 80 ksi |
| F68 / F71 | S32304 / S32808 | Lean and hyper duplex | Specialist grades, limited availability |

The 85 ksi figure applies to Langley's proprietary Ferralium 255, whose composition is tighter than the generic UNS S32550 band at 24.5 to 26.5 % Cr, 5.50 to 6.50 % Ni, 3.10 to 3.80 % Mo, 1.50 to 2.00 % Cu and 0.20 to 0.25 % N. The generic ASTM A182 F61 minimum yield is 80 ksi.

## Forged shapes available in UNS S32550

Seamless rolled rings, forged rings, gear ring blanks, slewing rings and bearing races. Weld neck, blind, slip-on, socket weld, lap joint, orifice and long weld neck flanges to ASME B16.5, B16.47 and API 6A. Round, flat and square bar. Stepped, pinion and eccentric shafts, spindles and rolls. Solid forged discs, covers and tube sheets, supplied proof-machined for volumetric inspection. Hollow forged cylinders, sleeves, bushings and couplings bored from solid. Valve and wellhead parts including bodies, bonnets, blocks, stems, seat rings, spools, nozzles and manifolds to API 6A and NACE MR0175. Die and mould blocks, wheels, pinions and bespoke open-die profiles.

All parts are made to customer drawing or size list on a 6,300 tonne open-die press and a 6 metre radial-axial ring mill, with a 30 tonne maximum single-piece weight.

## Applications

Published application areas cover waste processing, fertilizer production, seawater and marine environments, sour service, chemical processing, pulp and paper, flue gas desulfurisation, and pumps and valves. Reference data for 1.4507 adds paper, chemical, nitrogen, aviation and power engineering, taking in screws, shafts, sleeves, fittings, pipelines, pump parts, chemical storage tanks, heat exchangers and radiator components.

Forged parts in this grade are most often requested for seawater and firewater systems, subsea and topside oil and gas pipework with risers and manifolds, pressure vessels and heat exchangers, desalination and high-pressure reverse osmosis plant, FGD scrubber equipment, phosphoric and sulfuric acid service, and pump and valve internals.

## Testing and certification

EN 10204 3.1 as standard, or third-party EN 10204 3.2 where independent witness is required. Ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388, acceptance class agreed before manufacture. The works holds CCS, BV, DNV, LR and NK approvals.

ASTM A182 supplementary requirements available on order include S1 macroetch, S2 heat treatment details, S3 material for optimum resistance to stress-corrosion cracking, S4 corrosion tests, S6 hardness and S12 detection of detrimental phases in austenitic-ferritic stainless steels. Project specifications also covered: PED 2014/68/EU, AD 2000-Merkblatt W2, W7 and W10, API 20E BSL 1 and BSL 2, NACE MR0175 / ISO 15156, NACE MR0103.

For super duplex, ferrite content, impact energy at temperature and ASTM A923 type intermetallic screening are usually the clauses that decide acceptance. State them at enquiry stage.

## Questions

**What is UNS S32550?** A copper-bearing super duplex stainless steel with a ferritic-austenitic structure, designated ASTM A182 Grade F61 in forged form and EN 1.4507 in Europe.

**Is UNS S32550 the same as ASTM A182 F61?** F61 is the A182 forging designation for UNS S32550. The F prefix marks forged products; duplex grades are numbered F50 to F71.

**What are the minimum mechanical properties of A182 F61?** 109 ksi, 750 MPa, tensile; 80 ksi, 550 MPa, yield; 25 % elongation; 50 % reduction of area.

**What is the PREN of UNS S32550?** About 40, placing it in the super duplex class.

**How is it heat treated after forging?** Solution treat and quench at 1920 to 2060 F, 1050 to 1125 C, with a liquid quench below 500 F, 260 C.

**How does it compare with 2205?** 2205 is a 22 % chromium duplex with a PREN near 36. S32550 is a 25 to 26 % chromium super duplex with a PREN near 40 and higher strength.

**Who supplies UNS S32550 forgings?** Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Telephone +86 189 2135 9659, email sales@steelforgepieces.com.

---

Ferralium is a registered trademark of Langley Alloys Ltd. Zeron is a registered trademark of its respective owner. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with either company. Figures are published reference data for engineering comparison; confirm against the current edition of the governing standard before ordering.