Stainless Steel 255-SD50
Grade
AISI/SAE 255 · UNS S32550 · EN 1.4507, X2CrNiMoCuN25-6-3 · also Ferralium 255
SD50 = ferralium 255-SD50
Proprietary high-nitrogen variant used when 80 ksi (550 MPa) minimum yield must be guaranteed in heavy sections and forgings, with PREN at the top of the S32550 range.
Values for the SD50 condition
Other 255 tempers and conditions
255 is listed in 5 conditions; see the grade overview at 255.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Cast + Solution Annealed | Cast counterpart of 255 for seawater pump casings and impellers; lower strength and ductility than wrought product but same alloy chemistry family. | 550 | 760 | 20 | 23 HRC | 2.2 % IACS |
Forged + Solution Annealed | Condition for valve bodies, flanges and heavy forged components; heavy sections give slightly lower typical strength and toughness than thin plate. | 580 | 800 | 25 | 26 HRC | 2.2 % IACS |
Solution AnnealedDefault 1040–1120 °C, water quenched | Standard stocked condition for plate, hot-finished bar, forgings, pipe and fittings; balanced 50/50 ferrite–austenite with best corrosion resistance and toughness. | 610 | 830 | 28 | 27 HRC | — |
SD50This page Ferralium 255-SD50 | Proprietary high-nitrogen variant used when 80 ksi (550 MPa) minimum yield must be guaranteed in heavy sections and forgings, with PREN at the top of the S32550 range. | 660 | 880 | 25 | 29 HRC | 2.2 % IACS |
Solution Annealed + Cold Worked | Pick for small-diameter bar, shafting and fasteners needing higher strength and tighter tolerance; ductility and toughness are reduced. | 760 | 950 | 20 | 32 HRC | — |
What is 255-SD50?
255-SD50 is 255 in the SD50 grade — proprietary high-nitrogen variant used when 80 ksi (550 MPa) minimum yield must be guaranteed in heavy sections and forgings, with PREN at the top of the S32550 range. 255-SD50 has a yield strength of 660 MPa (95.7 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi). 255-SD50 has a density of 7.81 g/cm³ (0.282 lb/in³), heavier than 57% of stainless steel grades. It melts at 1,400°C (2,552 °F). Solution Annealed is the default condition FabDigit quotes; SD50 is available on request or by drawing note.
Advantages
- Good corrosion resistance — 88/100, better than 97% of stainless steel grades
- High strength — 660 MPa (95.7 ksi), better than 91% of stainless steel grades
Limitations
- Difficult to machine — 22/100, worse than 95% of stainless steel grades
- Limited service temperature — 300°C (572 °F), worse than 90% of stainless steel grades
- High embodied carbon — 5.6 kg CO₂/kg, worse than 83% of stainless steel grades
255-SD50 properties
Typical room-temperature values for 255-SD50; 22 are specific to this condition. Other listed values are 255 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
255-SD50 has a density of 7.81 g/cm³ (0.282 lb/in³), heavier than 57% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
255-SD50 has a yield strength of 660 MPa (95.7 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal5
255-SD50 is rated for continuous service to 300°C (572 °F). It conducts heat at 13.5 W/m·K (7.8 BTU/hr·ft·°F), worse than 83% of stainless steel grades. Thermal expansion is 13 µm/m·K (7.22 µin/in·°F).
Electrical3
255-SD50 conducts electricity at 2.2 % IACS, worse than 61% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is excellent (88/100), better than 97% of stainless steel grades.
Sustainability4
Producing a kilogram of 255-SD50 takes about 85 MJ of energy and emits 5.6 kg of CO₂ — more than 92% of stainless steel grades. Typical recycled content is 50%.
Manufacturability8
255-SD50's machinability is poor (22/100, worse than 95% of stainless steel grades); weldability good (68/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 255-SD50
Is 255 easy to machine?
Machine like a super duplex: rigid setup, 30–50 % of 316 cutting speed, heavy positive feed to cut under the work-hardened layer, sharp coated carbide and flood coolant.
Can 255 be welded?
Weldable by GTAW/GMAW/SMAW with 25.10.4.L or Ferralium 255 matching filler; keep interpass below ~150 °C, heat input roughly 0.5–1.5 kJ/mm, Ar+2 %N₂ backing, and no post-weld stress relief below 1040 °C.
Can 255 be formed, bent or molded?
Cold forming needs ~2× the press force of 304 with generous bend radii and springback allowance; hot working at 1000–1150 °C followed by full solution anneal and quench.
What surface finishes work on 255?
Pickle and passivate or electropolish after welding to restore the passive film; not anodizable, and grinding must avoid embedding carbon-steel contamination.
255 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | ≤ 0.04 | 0.03 |
| Si | ≤ 1 | 0.5 |
| Mn | ≤ 1.5 | 0.8 |
| P | ≤ 0.04 | — |
| S | ≤ 0.03 | — |
| Cr | 24 – 27 | 25.5 |
| Ni | 4.5 – 6.5 | 5.7 |
| Mo | 2.9 – 3.9 | 3.4 |
| Cuimproves resistance in reducing acids | 1.5 – 2.5 | 2 |
| Nupper end for SD50 high-strength variant | 0.1 – 0.25 | 0.2 |
| Fe | balance | — |
255-SD50 — frequently asked
What is 255-SD50 used for?
255-SD50 is typically used for subsea oil and gas manifolds, FPSO seawater pipework, valve bodies and stems, pump casings and impellers, marine propeller and pump shafts and offshore flanges and fasteners. In short: premium duplex stainless plate.
What is the yield strength of 255-SD50?
255-SD50 has a typical yield strength of 660 MPa (95.7 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is 255-SD50 easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% of stainless steel grades). Machine like a super duplex: rigid setup, 30–50 % of 316 cutting speed, heavy positive feed to cut under the work-hardened layer, sharp coated carbide and flood coolant.
Can 255-SD50 be welded?
Yes — weldability is rated good (68/100). Weldable by GTAW/GMAW/SMAW with 25.10.4.L or Ferralium 255 matching filler; keep interpass below ~150 °C, heat input roughly 0.5–1.5 kJ/mm, Ar+2 %N₂ backing, and no post-weld stress relief below 1040 °C.
What surface finishes work on 255-SD50?
Pickle and passivate or electropolish after welding to restore the passive film; not anodizable, and grinding must avoid embedding carbon-steel contamination.
Can 255-SD50 be formed, bent or molded?
Cold forming needs ~2× the press force of 304 with generous bend radii and springback allowance; hot working at 1000–1150 °C followed by full solution anneal and quench.
What is the maximum service temperature of 255-SD50?
255-SD50 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 255 Solution Annealed and 255-SD50?
Solution Annealed is the default condition — standard stocked condition for plate, hot-finished bar, forgings, pipe and fittings; balanced 50/50 ferrite–austenite with best corrosion resistance and toughness. SD50: proprietary high-nitrogen variant used when 80 ksi (550 MPa) minimum yield must be guaranteed in heavy sections and forgings, with PREN at the top of the S32550 range. Yield strength is 610 MPa in Solution Annealed versus 660 MPa in SD50.
Can FabDigit make parts in 255-SD50?
Yes — 255-SD50 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A240/A240M — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet and Strip (S32550) — ASTM International (2023)
- ASTM A479/A479M — Stainless Steel Bars and Shapes for Boilers and Pressure Vessels — ASTM International (2021)
- ASTM A182/A182M — Forged or Rolled Alloy and Stainless Steel Pipe Flanges and Fittings (F61) — ASTM International (2022)
- ASTM A890/A995 — Castings, Iron-Chromium-Nickel-Molybdenum (Grade 1B, CD4MCuN) — ASTM International (2020)
- EN 10088-2/-3 — Stainless steels, grade 1.4507 (X2CrNiMoCuN25-6-3) — CEN (2014)
- Ferralium alloy 255 / 255-SD50 technical datasheet — Langley Alloys / Meighs (2022)
- ASM Handbook Vol.13B — Corrosion: Materials (duplex stainless steels) — ASM International (2005)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.