UNS S32550 · W.Nr. 1.4507 · in ASTM A240: 24.0-27.0% Cr – 4.5-6.5% Ni – 2.90-3.90% Mo – 0.10-0.25% N – 1.50-2.50% Cu – C ≤ 0.04% – balance Fe. THIS IS THE ONLY ONE OF THE FIVE WHOSE COPPER IS BOUND BY THE SPECIFICATION (1.50-2.50%); copper does not appear in the PREN formula and does not raise PREN, its effect being on behaviour in reducing media. It is a ferritic-austenitic (super duplex) stainless steel; it is NOT PRECIPITATION HARDENABLE, NOT AGED, and its only heat treatment is solution annealing followed by a quench. ‘Ferralium 255’ is a TRADE NAME; ‘F255’ is NOT an ASTM class code — see ‘standart_notu’ for the detail.
It is bought for mixed service where a reducing acid is present alongside chlorides: sour production equipment, pump and valve bodies, equipment seeing both seawater and process streams. The copper addition is what separates it from the other super duplex grades.
Forms
Round bar · Flat bar · Plate · Sheet · Pipe and tube · Forgings. All forms are supplied to order.
Standards
THERE IS NO AMS. ASTM: A182 / SA-182 — GRADE F61 (forged flanges and fittings) · A240 / SA-240 (plate, sheet and strip) · A276 / SA-276 (bar and shapes, Condition A) · A479 / SA-479 (bar and shapes) · A789 / SA-789 (tube) · A790 / SA-790 (pipe) · A815 / SA-815 (wrought fittings). EN: 1.4507 · 10088-3. NORSOK MDS D54 and MDS D57 · NACE MR0175 / ISO 15156 · API 6A · ASME Code Case 1883 (Langley Alloys). ASME Section IX welding group P-No 10H (Langley Alloys: ‘ASME IX: Group P10H’). THE NAMING TRAP — THE MOST IMPORTANT ITEM: ‘F255’ IS NOT AN ASTM A182 CLASS CODE. The complete duplex class list of ASTM A182 is: F50 = S31200, F51 = S31803, F52 = S32950, F53 = S32750, F54 = S39274, F55 = S32760, F57 = S39277, F59 = S32520, F60 = S32205, F61…
Advantage
Its minimum tensile strength in ASTM A240 is 760 MPa, above the 750 MPa of S32760 in the same table; its yield minimum of 550 MPa equals that of the other two super duplex grades.
Welding
FILLER METAL: AWS A5.4 E2553 (Langley Alloys gives ‘AWS 5.4 E2553-XX W39553’ for Ferralium 255 SD50 weld wire). The same source states why the filler is over-alloyed: ‘over-alloyed in nickel to ensure correct phase balance is maintained when welding with standard shielding and backing gases.’…
Limits
THE TEMPERATURE CEILING is about 270-300 °C; the reason is 475 °C embrittlement. Industeel gives ‘-50 °C / +270 °C’ for super duplex; IMOA’s duplex family ceilings sit in the 250-315 °C band. NO SINGLE FIGURE IS GIVEN.
Compiled from manufacturer data sheets · confirm against the current specification before ordering
On this page · click to jump
Standards by Product FormPRENWelding, Heat Treatment and MachiningWhat the Copper BuysFrequently Asked Questions
AISI F255 is a super duplex stainless steel, used in applications requiring high temperature capability and corrosion resistance. Like the other super duplex grades it combines ferritic and austenitic phases, and it is generally specified for applications involving welding and machining.
Corrosion resistance: With excellent corrosion resistance, this super duplex stainless grade has good corrosion resistance and mechanical strength even under the most demanding conditions.
Weldability: Just as welding is difficult with all duplex materials, it is difficult with this duplex material, and its use is not recommended where extensive welding is involved.
Machinability: This material is not easy to machine. Not metallurgically well suited to forging, this grade is not the choice where parts are to be produced by forging.
Heat treatment: Because it is used in applications requiring high temperature capability, corrosion resistance and high strength, correct heat treatment is critically important for this type of steel in order to raise the mechanical properties of the material and improve its performance.
Applications: This stainless grade is chosen where very high mechanical values and very high corrosion resistance are required at the same time. It is the choice for shafts in oil refineries and similar industries where ordinary duplex stainless steel (1.4462) is not sufficient and better corrosion resistance is required. Regarded as a step above the 1.4410 and 1.4501 super duplex grades, this grade can be specified in almost every application in which 1.4410 and 1.4501 are used — although there is little difference between the three super duplex materials.
Round bar · Flat bar · Plate · Sheet · Tube · Forgings All forms are supplied to order.
Standards by Product Form
STANDARDS BY PRODUCT FORM
DEFENCE METAL
Product form
Standards
Forgings, flanges and fittings
NO AMS. ASTM A182 / ASME SA-182 — GRADE F61 (S32550). ‘F255’ IS NOT AN A182 CODE. Dimensions to ASME B16.5 / B16.47 / B16.11. Heat treatment per A182: 1050-1125 °C followed by a liquid quench.
Plate
NO AMS. ASTM A240 / ASME SA-240 · EN 1.4507
Sheet and strip
NO AMS. ASTM A240 / ASME SA-240
Round bar and flat bar
NO AMS. ASTM A479 / ASME SA-479 · ASTM A276 / ASME SA-276 (Condition A) · EN 10088-3 · NORSOK MDS D54 and D57 · NACE MR0175 / ISO 15156 · API 6A · ASME Code Case 1883
Seamless and welded pipe
ASTM A790 / ASME SA-790 (1040 °C min. + rapid cooling)
Seamless and welded tube
ASTM A789 / ASME SA-789 (1040 °C min. + rapid cooling)
Wrought fitting
ASTM A815 / ASME SA-815 — post-weld heat treatment is mandatory: 1065-1080 °C + water quench
Weld wire and electrode
AWS A5.4 E2553 (Langley Alloys: ‘AWS 5.4 E2553-XX W39553’) · BS EN ISO 15614-1 Group 10.1 · ASME IX Group P10H
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Additional information
AMS note
No AMS number could be confirmed for this alloy; since the four independent source threshold was not met, no AMS number has been put on the card. FURTHERMORE: ‘F255’ is neither an AMS number nor an ASTM A182 class code; in ASTM A182 the counterpart of S32550 is F61.
‘F255’ is not a specification code; a forging order should be written as ‘ASTM A182 F61, UNS S32550’. The number 1.4507 does not distinguish S32520 from S32550; in ASTM A182, S32520 = F59 and S32550 = F61.
F255 / Ferralium 255 (UNS S32550 / EN 1.4507) is the only common super duplex grade with a deliberate copper addition. Two things matter most on this page: what the copper actually buys, and two separate naming traps — both the ASTM grade code and the EN number are very easy to get wrong on this grade.
Standards by Product Form · F255 / Ferralium 255 (S32550 / 1.4507)
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Sheet · Plate · Strip
ASTM / ASME A240 / SA-240 · ASME BPVC Section VIII (Code Case 1883)
Bar
ASTM A276 (Condition A) · A479 / SA-479
Forgings · flanges
ASTM A182 · ASTM A473 — see the warning below about the grade code
Seamless pipe
ASTM A790 / SA-790
Seamless tube
ASTM A789 / SA-789
Welded pipe · tube
A789 and A790 cover both seamless and welded product
Fittings
Forged fittings and flanges: A182 · Wrought fittings: A815
Wire (mill product)
— (not verified; do not publish a standard for this form)
Welding wire
AWS A5.9 ER2553 (bare wire, GTAW/GMAW) — filler metal number W39553
Welding electrode
AWS A5.4 E2553-XX (covered electrode, the “25-9-4 / 2553” family)
WARNING — two separate naming traps. (1) There is no such code as “ASTM A182 Grade F255”. “255” and “F255” are shorthand for the Ferralium 255 trade name; the grade code used for S32550 in ASTM A182 is F61. That finding rests on a single primary source and should be confirmed against the current A182 edition before ordering — but in any case, ordering by UNS number (S32550) is the right practice. (2) EN 1.4507 does not map to a single UNS number: the duplex industry guide’s own cross-reference table assigns the same Werkstoff number to both S32550 and S32520, two distinct alloys with different copper and nitrogen ranges and different PREN bands. An offer citing only “1.4507” is ambiguous.
Composition (S32550): C ≤0.04% · 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% · Mn ≤1.50% · Si ≤1.00% · P ≤0.04% · S ≤0.030%. The producer typically ships to a tighter window than this (Cr 24.5–26.5% · Ni 5.5–6.5% · Mo 3.1–3.8% · Cu 1.5–2.0% · N 0.20–0.25% · C ≤0.025% · S ≤0.005%) — that is the mill’s internal practice, not the ASTM minimum.
PREN — the Honest Number
PREN = %Cr + 3.3×%Mo + 16×%N. The published figures for this grade diverge, and the page should be straight about it:
F255 / S32550 · The PREN Reality
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Industry guide (independent)
A band of 38–41 for S32550
Independent service-centre calculation
For a representative heat (Cr 25.5 / Mo 3.4 / N 0.175): 39.5
Producer marketing
“PREN over 40” — true for heats at the top of the alloying range, but not a guaranteed minimum
Conclusion
State the PREN as “38–41 typical” or “up to 40+”; a flat “>40” claim is over-optimistic. It does not clearly clear the conventional PREN ≥ 40 super duplex threshold — it straddles it
How S32520 differs
The closely related UNS S32520 carries higher nitrogen and lower copper; its PREN band is 40–43, making it the unambiguous “true” super duplex on PREN
1 · SOLUTION ANNEAL + QUENCH — this is the only valid heat treatment
Step
1 · SOLUTION ANNEAL + QUENCH — this is the only valid heat treatment
Summary
It takes intermetallic phases back into solid solution and sets the ferrite-austenite balance. IT DOES NOT RAISE STRENGTH. This is the delivery condition.
Temperature
Sources differ, EACH WITH ITS SOURCE: ASTM A182 F61 1050-1125 °C [1920-2060 °F] · ASTM A815 1065-1080 °C [1950-1975 °F] · ASTM A479 1040 °C [1900 °F] min. · ASTM A790 and A789 1040 °C [1900 °F] min. · IMOA 1040 °C [1900 °F] min. · Industeel (UR 2507Cu) 1080-1120 °C. NO SINGLE FIGURE IS GIVEN AND NO AVERAGE IS TAKEN. Practical envelope: about 1040-1125 °C. The binding one is the specification of the product form ordered: on forgings the A182 F61 band of 1050-1125 °C applies, on wrought fittings the A815 band of 1065-1080 °C.
Time
Until the whole section is at temperature. No numerical time was found in four independent sources, so none is given.
Cooling
QUENCHING IS MANDATORY. ASTM A182 says ‘solution treat and quench’ for F61 and requires cooling in a liquid medium down to 260 °C [500 °F]; ASTM A815 says ‘Water quench’; ASTM A790 and A789 say ‘rapid cooling in air or water’; ASTM A479 requires a quench or rapid cooling; Langley Alloys states ‘solution-treated, water-quenched and ultrasonically tested as standard’.
Resulting hardness
ASTM A240 ceiling 302 HBW · ASTM A276 ceiling 302 HBW · ASTM A479 ceiling 297 HB. This is the second highest hardness ceiling of the five (S32750 has 310 HBW).
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2 · AFTER WELDING — AN INTERMEDIATE-TEMPERATURE STRESS RELIEF IS FORBIDDEN
Step
2 · AFTER WELDING — AN INTERMEDIATE-TEMPERATURE STRESS RELIEF IS FORBIDDEN
Summary
Where a heat treatment is required, a full solution anneal and quench is performed.
Temperature
ASTM A815 states the requirement for wrought fittings explicitly: ‘heat treatment shall be performed after welding and in accordance with the requirements of Table 1’ — for S32550 that is 1065-1080 °C followed by a water quench.
Time
Until the whole section is at temperature; no separate numerical time could be confirmed.
Cooling
Water quench.
Resulting hardness
The hardness of the solution annealed condition.
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3 · A PRODUCER ADDITION: ULTRASONIC EXAMINATION
Step
3 · A PRODUCER ADDITION: ULTRASONIC EXAMINATION
Summary
Langley Alloys describes the delivery condition as ‘solution-treated, water-quenched and ultrasonically tested as standard’. This is not a heat treatment stage; it is the examination that checks the result of the heat treatment, and it was found in a single source.
Temperature
—
Time
—
Cooling
—
Resulting hardness
ASTM A923 methods are used to detect intermetallic precipitation in the product form; IMOA cites AWS A4.29 and EN ISO 8249 for ferrite measurement.
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4 · PRECIPITATION HARDENING — THERE IS NONE
Step
4 · PRECIPITATION HARDENING — THERE IS NONE
Summary
This alloy has NO ageing stage such as H900 / H1025 / H1075 / H1150 and cannot be hardened by ageing.
Temperature
—
Time
—
Cooling
—
Resulting hardness
IMOA: ‘Duplex stainless steels will not form martensite during cooling. High strength and hardness in a duplex stainless steel are the result of high nitrogen content, the duplex structure itself, and work hardening.’ The only way to raise strength is cold work, and cold work leaves residual stress.
DEFENCE METAL
TWO SEPARATE FORBIDDEN BANDS — (1) sigma and intermetallic precipitation, (2) 475 °C embrittlement
Step
TWO SEPARATE FORBIDDEN BANDS — (1) sigma and intermetallic precipitation, (2) 475 °C embrittlement
What happens
BAND 1 — SIGMA AND INTERMETALLIC PHASES (about 600-1000 °C): sigma, chi and similar intermetallics precipitate from the ferrite. IMOA: ‘The presence of sigma phase decreases the pitting resistance of duplex stainless steels, due to the depletion of chromium and molybdenum in surrounding areas’ and ‘Toughness and ductility are also sharply reduced when intermetallic phase precipitation occurs.’ IMOA also states ‘Detrimental phases can form in a matter of minutes at the critical temperature’ — this band is measured in minutes, not hours. BAND 2 — 475 °C EMBRITTLEMENT (about 300-525 °C): alpha prime (α’) precipitates inside the ferrite, the material hardens and loses toughness. IMOA: ‘Alpha prime can form in the ferrite phase of duplex stainless steels below about 525 °C.’ This band sets the SERVICE TEMPERATURE CEILING of duplex steels; IMOA: ‘The upper temperature limit for duplex stainless steel service is controlled by alpha prime formation.’
As named in the source
SIGMA / INTERMETALLIC BAND, every figure with its source: IMOA 700-1000 °C (‘Sigma phase and other intermetallic phases such as chi can precipitate from the ferrite … on cooling too slowly through the temperature range of 700-1000 °C’), and 700-950 °C for the 2205 sigma field · Outokumpu 600-1000 °C (‘Intermetallic phases such as sigma phase occurs in the temperature range 600-1000 °C’) · Industeel 1000-600 °C (‘At high temperature: 1000-600 °C (1830-1110 °F), the α phase may transform in α, χ,… intermetallic phases’) · Rolled Alloys 1300-1800 °F, i.e. 704-982 °C (‘Sigma phase will precipitate upon exposure to temperatures within the 1300-1800 °F range’) · Sandmeyer 1300-1800 °F, i.e. 704-982 °C. PRACTICAL ENVELOPE: about 600-1000 °C. NO SINGLE FIGURE IS GIVEN AND NO AVERAGE IS TAKEN. 475 °C EMBRITTLEMENT BAND, every figure with its source: IMOA 300-525 °C · Rolled Alloys 650-980 °F, i.e. 343-527 °C (‘Exposure to temperatures in the 650-980 °F range causes the precipitation of alpha prime in the ferritic portion of the material. This phenomenon is also referred to as 885 °F embrittlement’) · Outokumpu 350-500 °C (‘decomposition of ferrite occurs in the range 350-500 °C (475 °C embrittlement)’) · Industeel 300-500 °C (‘At lower temperature (300-500 °C) the α phase transforms in α′ resulting in a hardening’). PRACTICAL ENVELOPE: about 300-525 °C.
Kinetik uyarisi
KINETICS NOTE — SUPER DUPLEX: S32550 is a super duplex and its sigma kinetics are FASTER than those of standard duplex 2205. IMOA states the rule: ‘Precipitates tend to form quicker with increasing alloy content as shown in Figure 4 where the start curve for 2507 is to the left (shorter time) of the one for 2205.’ The chromium band of S32550 (24.0-27.0%) is the widest of the five and has the highest ceiling; its molybdenum sits above that of 2205. Industeel puts the same point as ’25 Cr super duplex grades are subject to intermetallic phase precipitations (σ…)’, noting that it manages that sensitivity on the production side with batch furnace heat treatment. THE NITROGEN BAND IS WIDE (0.10-0.25%) and that changes the kinetics from heat to heat: IMOA states ‘The addition of nitrogen significantly delays formation of these phases’, and a heat at the bottom of the band benefits less from that retardant. The bottom of the band also takes PREN below 40.
En sik hata
THE MOST COMMON MISTAKE: cooling slowly after solution annealing, or leaving the part in the furnace to cool on its own. Rolled Alloys puts the measure plainly: ‘It is important to cool to below 700 °F as quickly as possible. If the cooling rate is too slow, it will lead to decreased corrosion resistance and lowered impact strength.’ IMOA says the same: ‘Allowing a plate or a fitting to cool into the 700-980 °C range prior to quenching may lead to the formation of intermetallic phases.’ THE SECOND MISTAKE: applying an intermediate-temperature stress-relief anneal as one would on an austenitic stainless — on a duplex steel that anneal lands inside the sigma band.
The diagram is schematic; the time axis is NOT to scale. No published TTT/CCT curve was used, so no curve is drawn. THIS ALLOY IS A DUPLEX (ferritic-austenitic) STAINLESS STEEL: it is NOT PRECIPITATION HARDENABLE, it is NOT AGED, and it does not transform to martensite on cooling. There is NO ageing step such as H900 / H1025 / H1075 / H1150 and no ageing diagram is drawn. IMOA states: ‘Duplex stainless steels will not form martensite during cooling. High strength and hardness in a duplex stainless steel are the result of high nitrogen content, the duplex structure itself, and work hardening.’ The only valid heat treatment is SOLUTION ANNEALING FOLLOWED BY RAPID QUENCHING; strength comes from the composition, the two-phase structure and cold work. The diagram is schematic; the time axis is not to scale. No published TTT/CCT curve was used, so no curve is drawn. The stages are NOT ageing stages; this alloy is not precipitation hardenable.
Welding
GTAW, GMAW and SMAW are all usable. Filler: AWS A5.9 ER2553 (W39553) bare wire; guaranteed weld-metal minimums are tensile ≥ 750 N/mm², yield ≥ 550 N/mm², elongation ≥ 20%, impact at −46 °C ≥ 45 J, hardness ≤ 300 HV. Shielding gas: argon, DC. No preheat is required — confirmed by two independent sources; what matters is careful cleaning of the surfaces to be joined. Maximum interpass temperature 100 °C (producer data). Post-weld heat treatment is not mandatory, but is preferred on heavy sections to fully restore corrosion resistance — two independent sources state this in almost identical words. No verified kJ/mm heat-input range was found; it must be set by welding-procedure qualification.
Heat treatment
Solution annealing: 1060–1120 °C followed by an immediate water quench. An independent service centre gives a point value of 1066 °C inside that range. Quenching is mandatory: slow cooling re-precipitates chromium- and molybdenum-rich intermetallics in the precipitation window and depletes the adjacent matrix of chromium, destroying both pitting resistance and low-temperature toughness. Sigma / intermetallic band: from about 1000 °C down to about 550 °C. There is a critical practical point here: super duplex grades precipitate sigma markedly faster than 2205, because the driving force for sigma formation increases with chromium and molybdenum content. Heat-treatment instructions copied from a generic duplex page understate this risk. 475 °C embrittlement: 300–525 °C. A stress relief at 357 °C is cited as permitted for heavily machined components; since that sits at the low end of the embrittlement band, time and temperature need tight control. Standard delivery: solution annealed and water quenched.
Machining and forming
Because sulphur is deliberately kept low for corrosion resistance, duplex grades are harder to machine than austenitics: chip breaking is poor and the chips are tough and abrasive. The work-hardening rate is at least comparable to the austenitics. Coarse-toothed blades, slow-to-moderate cutting speeds, heavy feeds and generous coolant (ideally a synthetic emulsion) are recommended. Hot-working range: 982–1149 °C. A grade-specific minimum finishing temperature for S32550 could not be verified; general super duplex practice is not to work down to the bottom of the band. (No numeric machinability index against 316L or 2205 could be verified — do not publish a percentage.)
What the Copper Buys
F255 · Distinguishing Properties and Comparison
DEFENCE METAL
Copper addition (1.5–2.5%)
Two independent producers describe the same mechanism: copper redeposits at active pit sites (a “self-healing” effect), slowing pit propagation. This is a concrete advantage in sulphuric and phosphoric acid service
Acid resistance
Superior performance in sulphuric, nitric and phosphoric acids — verified in two independent sources and the grade’s real selling point
Chlorides / seawater
CPT above 50 °C and a seawater corrosion rate below 0.01 mm/year (producer data). For pure chloride pitting, 2507 / F53 has the higher PREN
NACE MR0175 / ISO 15156
Listed for sour service, with hardness capped at ≤28 HRC
Service temperature
260 °C (500 °F) under ASME BPVC Section VIII. That is a 475 °C embrittlement margin; talk of “good high-temperature strength” does not mean the grade can run continuously anywhere near 475 °C
Minimum temperature
— (no grade-specific lower limit could be verified for S32550. The duplex family generally retains good toughness to around −40 °C, but that is not a rating for this grade)
Magnetic
Ferromagnetic, owing to its part-ferritic structure
Typical applications
Oil and gas pumps, valves, wellhead and subsea equipment; marine propellers, shafts and seals; desalination and water/wastewater treatment; offshore structural and process equipment; flue-gas desulphurisation; fasteners
W ~0.7% plus Cu ~0.7% · PREN ~41.5 — the only tungsten-bearing grade
Frequently Asked Questions
What does the copper addition actually buy?
F255 / S32550 is the only common super duplex grade with a deliberate, substantial copper addition (1.5–2.5%; 2507 has none, Zeron 100 only about 0.5–1.0%). Two independent producer and distributor sources describe the same mechanism: copper redeposits at active pit sites in reducing acid media and slows pit growth — a kind of self-healing effect. The verified practical payoff is markedly better resistance to sulphuric and phosphoric acid than the copper-free super duplex grades; both producers cite exactly this as the reason to specify F255 rather than 2507 for those acid duties. It does not meaningfully change chloride pitting performance — in pure seawater and chloride service the higher-PREN 2507 stays ahead. The copper’s value is acid-specific, not a general corrosion upgrade.
Does F255 genuinely count as a “super duplex”?
By the numbers it is genuinely borderline, and it is worth being precise about that. The PREN ≥ 40 threshold used to define super duplex sits right at the edge of S32550’s verified composition range: the independent industry guide gives it a band of 38–41, and an independent service centre’s calculation for a representative heat comes out at 39.5 — below or at 40, not comfortably above it. Producer marketing states “PREN over 40”, which is true for compositions at the top of the alloying range but is not the guaranteed minimum. By strength (minimum yield 550–586 MPa, well above 2205’s 450 MPa) and by conventional trade classification it is universally sold and treated as super duplex; by strict PREN chemistry it is borderline. If PREN headroom specifically is the buying criterion, the closely related UNS S32520 (PREN 40–43) is the unambiguous “true” super duplex.
How does F255 compare with F53 and F55 for seawater service?
For pure chloride and seawater pitting resistance, 2507 has the edge: independent PREN figures put 2507 at 41.9–43, Zeron 100 at 41.5 and F255 at 39.5–41 — the highest-molybdenum, highest-nitrogen grade generally wins on chloride pitting. Zeron 100 adds tungsten alongside its copper and has a long-established record specifically in seawater service. F255’s particular edge over both is in acid-contaminated or mixed chloride/acid streams — a desalination intake cleaned with sulphuric-based chemicals, say, or produced water carrying acid gas. For a straightforward clean-seawater pumping or piping duty with no acid exposure, 2507 or Zeron 100 are the more conservative choices on PREN; F255 comes into its own where copper’s acid benefit genuinely applies, or where its higher guaranteed yield strength (586 MPa) is worth having for section reduction.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip
302 HBW max.
550
760
15%
ASTM A479 / ASME SA-479 · bar and shapes
297 HB max.
550
760
15%
ASTM A276 / ASME SA-276 · bar and shapes, Condition A
ASTM A790 / SA-790 (pipe) and A789 / SA-789 (tube)
—
550
760
15%
Producer specification · Langley Alloys Ferralium 255, bar ≤ 100 mm diameter
—
586
790
25%
EVERY ROW IS A SPECIFICATION MINIMUM for room temperature; these are NOT typical values, and a typical value never goes into a calculation. BECAUSE THIS ALLOY IS NOT PRECIPITATION HARDENABLE, the rows are split by SPECIFICATION and PRODUCT FORM, not by ageing condition; there is NO condition column such as H900 or H1075. Different specifications can give different minimums for the same UNS number; that is a difference of test-piece geometry and acceptance criteria, not of the material. COLD-WORKED TEMPERS are NOT in this table unless stated otherwise. Every ASTM row is a specification minimum, not a typical value. The A182 F61 row DIFFERS from the others: tensile 750 MPa (not 760) and elongation 25% (not 15%). That is a difference of acceptance criteria for the forging product form, not of the material. The Langley Alloys row is a PRODUCER minimum and sits above the ASTM floor; calculations use the ASTM floor.
THE FIVE DUPLEX / SUPER DUPLEX GRADES COMPARED BY PREN
PITTING RESISTANCE EQUIVALENT NUMBER (PREN). This is the quantity that ranks these grades; yield or tensile strength does not.
A · PREN — calculated from the ASTM A240 composition band (SAME FORMULA, SAME TABLE)
ASTM A240 / ASME SA-240 composition table. All five UNS numbers are in it. The figures are calculated, not measured.
DEFENCE METAL
Criterion
Criterion
Bilesim a240
Bilesim a240
Pren hesap
Pren hesap
Pren yayimlanan
Pren yayimlanan
Note
Note
AISI 329 · UNS S32900 · 1.4460
AISI 329 · UNS S32900 · 1.4460
Cr 23.0-28.0% · Mo 1.00-2.00% · N NOT specified
Cr 23.0-28.0% · Mo 1.00-2.00% · N NOT specified
26.3 – 34.6
26.3 – 34.6
IMOA typical 30-31
IMOA typical 30-31
THE NITROGEN TERM IS ZERO. ASTM A240 and A789 set no nitrogen requirement for S32900, so the third term of PREN never forms in this grade. This is the lowest PREN of the five.
THE NITROGEN TERM IS ZERO. ASTM A240 and A789 set no nitrogen requirement for S32900, so the third term of PREN never forms in this grade. This is the lowest PREN of the five.
AISI 318 / 2205 · UNS S32205 · 1.4462
AISI 318 / 2205 · UNS S32205 · 1.4462
Cr 22.0-23.0% · Mo 3.00-3.50% · N 0.14-0.20%
Cr 22.0-23.0% · Mo 3.00-3.50% · N 0.14-0.20%
A standard duplex. It is NOT a super duplex; its PREN floor is below 40.
A standard duplex. It is NOT a super duplex; its PREN floor is below 40.
UNS S31803 · 1.4462 (the older, wide-band version of 2205)
UNS S31803 · 1.4462 (the older, wide-band version of 2205)
Cr 21.0-23.0% · Mo 2.50-3.50% · N 0.08-0.20%
Cr 21.0-23.0% · Mo 2.50-3.50% · N 0.08-0.20%
30.5 – 37.8
30.5 – 37.8
IMOA 33-35
IMOA 33-35
THIS IS THE MOST IMPORTANT ROW OF THE COMPARISON: the lower end of the S31803 band falls to PREN 30.5, so a fully COMPLIANT S31803 heat can sit 3.6 points below the S32205 floor of 34.1. The two carry the same W.Nr. (1.4462) but they are NOT equivalent.
THIS IS THE MOST IMPORTANT ROW OF THE COMPARISON: the lower end of the S31803 band falls to PREN 30.5, so a fully COMPLIANT S31803 heat can sit 3.6 points below the S32205 floor of 34.1. The two carry the same W.Nr. (1.4462) but they are NOT equivalent.
F255 / Ferralium 255 · UNS S32550 · 1.4507
F255 / Ferralium 255 · UNS S32550 · 1.4507
Cr 24.0-27.0% · Mo 2.90-3.90% · N 0.10-0.25% · Cu 1.50-2.50%
Cr 24.0-27.0% · Mo 2.90-3.90% · N 0.10-0.25% · Cu 1.50-2.50%
35.2 – 43.9
35.2 – 43.9
IMOA 38-41 · Langley Alloys above 40
IMOA 38-41 · Langley Alloys above 40
THE SPECIFICATION BAND DROPS BELOW 40 (floor 35.2), whereas commercial Ferralium 255 heats hold nitrogen at 0.20-0.25% and lift PREN above 40 (Langley). ASTM A240 sets NO PREN ≥ 40 requirement for S32550 — the only grade it imposes that on is S32760. Copper is NOT in the PREN formula; the copper in S32550 does not raise PREN.
THE SPECIFICATION BAND DROPS BELOW 40 (floor 35.2), whereas commercial Ferralium 255 heats hold nitrogen at 0.20-0.25% and lift PREN above 40 (Langley). ASTM A240 sets NO PREN ≥ 40 requirement for S32550 — the only grade it imposes that on is S32760. Copper is NOT in the PREN formula; the copper in S32550 does not raise PREN.
F55 / Zeron 100 · UNS S32760 · 1.4501
F55 / Zeron 100 · UNS S32760 · 1.4501
Cr 24.0-26.0% · Mo 3.00-4.00% · N 0.20-0.30% · W 0.50-1.00% · Cu 0.50-1.00%
Cr 24.0-26.0% · Mo 3.00-4.00% · N 0.20-0.30% · W 0.50-1.00% · Cu 0.50-1.00%
THIS IS THE ONLY ONE OF THE FIVE WHOSE PREN IS BOUND BY THE SPECIFICATION. ASTM A240 carries the footnote ‘Cr + 3.3 Mo + 16 N = 40 min.’ on the S32760 row; 40 is therefore not a computed result but an ACCEPTANCE CRITERION. With the tungsten formula the same composition gives 37.9-45.7 and Rolled Alloys states it plainly: ‘With this formula ZERON 100 has a PREN > 41.’
THIS IS THE ONLY ONE OF THE FIVE WHOSE PREN IS BOUND BY THE SPECIFICATION. ASTM A240 carries the footnote ‘Cr + 3.3 Mo + 16 N = 40 min.’ on the S32760 row; 40 is therefore not a computed result but an ACCEPTANCE CRITERION. With the tungsten formula the same composition gives 37.9-45.7 and Rolled Alloys states it plainly: ‘With this formula ZERON 100 has a PREN > 41.’
F53 / 2507 · UNS S32750 · 1.4410
F53 / 2507 · UNS S32750 · 1.4410
Cr 24.0-26.0% · Mo 3.00-5.00% · N 0.24-0.32%
Cr 24.0-26.0% · Mo 3.00-5.00% · N 0.24-0.32%
THE TOP OF ITS CALCULATED BAND IS THE HIGHEST OF THE FIVE (47.6), because the molybdenum band runs up to 5.00% and the nitrogen band is the highest of all (0.24-0.32%). But its floor is not bound to 40 as S32760’s is; there is NO PREN footnote on the S32750 row of A240.
THE TOP OF ITS CALCULATED BAND IS THE HIGHEST OF THE FIVE (47.6), because the molybdenum band runs up to 5.00% and the nitrogen band is the highest of all (0.24-0.32%). But its floor is not bound to 40 as S32760’s is; there is NO PREN footnote on the S32750 row of A240.
B · SOLUTION ANNEALING TEMPERATURE — ASTM A790 and A789 heat treatment table (SAME TABLE)
ASTM A790 (seamless and welded duplex pipe) and ASTM A789 (duplex tube), Table 1. All five UNS numbers are in it.
DEFENCE METAL
Criterion
Criterion
AISI 329 (S32900)
AISI 318 / 2205 (S32205)
F255 (S32550)
F55 (S32760)
F53 (S32750)
F255 (S32550)
Difference
Difference
AISI 329 (S32900)
AISI 318 / 2205 (S32205)
F55 (S32760)
F53 (S32750)
Solution annealing temperature — ASTM A790 and A789 (SAME TABLE, seamless and welded pipe/tube)
Solution annealing temperature — ASTM A790 and A789 (SAME TABLE, seamless and welded pipe/tube)
925-955 °C [1700-1750 °F]
1020-1100 °C [1870-2010 °F]
1040 °C [1900 °F] min.
1070-1140 °C [1960-2085 °F]
1025-1125 °C [1880-2060 °F]
1040 °C [1900 °F] min.
The annealing temperature of 329 is BELOW ALL FOUR of the others, and the top of its band (955 °C) sits inside the sigma band. Modern duplex grades are annealed ABOVE the sigma band; 329 is annealed at its edge. This is the concrete measure of why 329 is regarded as first generation.
The annealing temperature of 329 is BELOW ALL FOUR of the others, and the top of its band (955 °C) sits inside the sigma band. Modern duplex grades are annealed ABOVE the sigma band; 329 is annealed at its edge. This is the concrete measure of why 329 is regarded as first generation.
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Cooling requirement — ASTM A790 and A789
Cooling requirement — ASTM A790 and A789
Rapid cooling in air or water
Rapid cooling in air or water
Rapid cooling in air or water
Rapid cooling in air or water
Rapid cooling in air or water
Rapid cooling in air or water
NO DIFFERENCE — rapid cooling is MANDATORY on all five. On the forging side ASTM A182 states it more tightly: ‘solution treat and quench’, in a liquid medium down to 260 °C [500 °F].
NO DIFFERENCE — rapid cooling is MANDATORY on all five. On the forging side ASTM A182 states it more tightly: ‘solution treat and quench’, in a liquid medium down to 260 °C [500 °F].
ASTM A240 / ASME SA-240 mechanical table. The values are SPECIFICATION MINIMUMS, not typical values.
DEFENCE METAL
Criterion
Criterion
AISI 329 (S32900)
AISI 318 / 2205 (S32205)
F255 (S32550)
F55 (S32760)
F53 (S32750)
Difference
Difference
AISI 329 (S32900)
AISI 318 / 2205 (S32205)
F255 (S32550)
F55 (S32760)
F53 (S32750)
Minimum tensile strength
Minimum tensile strength
620 MPa (90 ksi)
655 MPa (95 ksi)
760 MPa (110 ksi)
750 MPa (108 ksi)
795 MPa (116 ksi)
F53 (S32750) is the highest, 329 the lowest.
F53 (S32750) is the highest, 329 the lowest.
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Minimum yield strength (0.2%)
Minimum yield strength (0.2%)
485 MPa (70 ksi)
450 MPa (65 ksi)
550 MPa (80 ksi)
550 MPa (80 ksi)
550 MPa (80 ksi)
NOTE: on minimum yield, 329 is ABOVE 2205 (485 vs 450 MPa). Yield strength does not rank this family; the quantity that ranks it is PREN. All three super duplex grades are equal at 550 MPa.
NOTE: on minimum yield, 329 is ABOVE 2205 (485 vs 450 MPa). Yield strength does not rank this family; the quantity that ranks it is PREN. All three super duplex grades are equal at 550 MPa.
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Minimum elongation (ASTM A240, plate)
Minimum elongation (ASTM A240, plate)
15%
25%
15%
25%
15%
S32205 and S32760 require 25%; the other three 15%.
S32205 and S32760 require 25%; the other three 15%.
15%
25%
15%
25%
15%
Hardness ceiling (ASTM A240, Brinell)
Hardness ceiling (ASTM A240, Brinell)
269 HBW
293 HBW
302 HBW
270 HBW
310 HBW
The hardness ceiling does not follow the strength order; the ceiling for S32760 is lower than that for S32205.
The hardness ceiling does not follow the strength order; the ceiling for S32760 is lower than that for S32205.
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D · NAMING — ASTM A182 forging class codes (SAME TABLE)
The duplex class list of ASTM A182 / ASME SA-182. This is where market names and specification codes get confused.
DEFENCE METAL
Criterion
Criterion
AISI 329 (S32900)
AISI 318 / 2205 (S32205)
F255 (S32550)
F55 (S32760)
F53 (S32750)
AISI 329 (S32900)
F255 (S32550)
Difference
Difference
AISI 318 / 2205 (S32205)
F55 (S32760)
F53 (S32750)
ASTM A182 forging class code
ASTM A182 forging class code
NONE — S32900 is not listed in ASTM A182
F60 (S32205) · F51 (S31803)
F61 — there is NO A182 class called ‘F255’
F55
F53
NONE — S32900 is not listed in ASTM A182
F61 — there is NO A182 class called ‘F255’
The duplex class list of ASTM A182 is: F50 (S31200), F51 (S31803), F52 (S32950), F53 (S32750), F54 (S39274), F55 (S32760), F57 (S39277), F59 (S32520), F60 (S32205), F61 (S32550), F65 (S32906). F255 is NOT on the list.
The duplex class list of ASTM A182 is: F50 (S31200), F51 (S31803), F52 (S32950), F53 (S32750), F54 (S39274), F55 (S32760), F57 (S39277), F59 (S32520), F60 (S32205), F61 (S32550), F65 (S32906). F255 is NOT on the list.
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Origin of the market name
Origin of the market name
An AISI type number (old AISI 300/400 series logic)
‘2205’ comes from the composition: ~22% Cr, ~5% Ni. ‘AISI 318’ is an old type name.
‘255’ comes from the Ferralium 255 TRADE NAME; the letter ‘F’ was attached to it later by the market, not by A182.
‘F55’ IS a genuine ASTM A182 class code. Zeron 100 is the licensed trade name.
‘F53’ IS a genuine ASTM A182 class code. ‘2507’ comes from the composition: ~25% Cr, ~7% Ni.
An AISI type number (old AISI 300/400 series logic)
‘255’ comes from the Ferralium 255 TRADE NAME; the letter ‘F’ was attached to it later by the market, not by A182.
TWO of the three names (F53, F55) are genuine A182 class codes; ONE (F255) is not. Specifying the alloy by its UNS number on the order removes this confusion by itself.
TWO of the three names (F53, F55) are genuine A182 class codes; ONE (F255) is not. Specifying the alloy by its UNS number on the order removes this confusion by itself.
‘2205’ comes from the composition: ~22% Cr, ~5% Ni. ‘AISI 318’ is an old type name.
‘F55’ IS a genuine ASTM A182 class code. Zeron 100 is the licensed trade name.
‘F53’ IS a genuine ASTM A182 class code. ‘2507’ comes from the composition: ~25% Cr, ~7% Ni.
PREN(W) = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N — meaningful only for S32760
Pren formulu tungstenli
PREN(W) = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N — meaningful only for S32760
Ortak sinir
WHAT ALL FIVE SHARE AS A LIMIT: none of them is PRECIPITATION HARDENABLE, and none of them goes into continuous service much above 300 °C. IMOA’s ASME and TÜV ceilings: 2205 unwelded 315 °C (ASME) and 280 °C (TÜV), welded 315 °C (ASME) and 250 °C (TÜV); 2507 seamless tube 315 °C (ASME) and 250 °C (TÜV). Rolled Alloys gives 600 °F (316 °C) for 2205 and 2507 and 300 °C for Zeron 100; Sandmeyer gives 570 °F (299 °C) for 2507; Penn Stainless gives 572 °F (300 °C) for 2205; Industeel gives 280 °C for 2205 and 270 °C for super duplex. The reason is one and the same: 475 °C embrittlement.
Ortak sinir
WHAT ALL FIVE SHARE AS A LIMIT: none of them is PRECIPITATION HARDENABLE, and none of them goes into continuous service much above 300 °C. IMOA’s ASME and TÜV ceilings: 2205 unwelded 315 °C (ASME) and 280 °C (TÜV), welded 315 °C (ASME) and 250 °C (TÜV); 2507 seamless tube 315 °C (ASME) and 250 °C (TÜV). Rolled Alloys gives 600 °F (316 °C) for 2205 and 2507 and 300 °C for Zeron 100; Sandmeyer gives 570 °F (299 °C) for 2507; Penn Stainless gives 572 °F (300 °C) for 2205; Industeel gives 280 °C for 2205 and 270 °C for super duplex. The reason is one and the same: 475 °C embrittlement.
RULE: every block in this diagram is read from ONE TABLE OF ONE SPECIFICATION; different specifications are never compared on the same row. All five UNS numbers fall within the scope of ASTM A240, A789 and A790, so they are listed side by side under the same acceptance criteria (the scope of A182 and A479 is not the same for all five, and that is stated separately). THE PREN COLUMN IS A CALCULATION, NOT A MEASUREMENT: the lower and upper ends of the ASTM A240 composition band were substituted into PREN = %Cr + 3.3×%Mo + 16×%N. Published PREN values are given in a separate column WITH THE NAME OF THE SOURCE; the two columns must not be mixed. THE BLOCKS ARE NOT ADDED TOGETHER AND NOT PLACED ON A COMMON AXIS. The figures in the PREN column are CALCULATED, NOT MEASURED; the ends of the ASTM A240 composition band were substituted into the formula. A calculated PREN band and the PREN of commercial heats are not the same thing: a producer works inside the band and typically aims at its upper half. CPT (critical pitting temperature) and CCT (critical crevice temperature) values have NOT been put on this diagram; the reason is given under ‘atlananlar’. Copper (Cu) does not appear in the PREN formula. The 1.50-2.50% copper of S32550 and the 0.50-1.00% copper of S32760 do not raise PREN; their effect is on behaviour in reducing media and is measured separately. All five grades are supplied SOLUTION ANNEALED AND RAPIDLY QUENCHED; none of them is precipitation hardenable.
