UNS S32760 · W.Nr. 1.4501 · X2CrNiMoCuWN25-7-4 · in ASTM A240: 24.0-26.0% Cr – 6.0-8.0% Ni – 3.00-4.00% Mo – 0.20-0.30% N – 0.50-1.00% Cu – 0.50-1.00% W – C ≤ 0.03% – balance Fe. THIS IS THE ONLY SUPER DUPLEX OF THE FIVE THAT CONTAINS TUNGSTEN, and the W band is binding in the specification. ASTM A240 places a further ACCEPTANCE CRITERION on this row: ‘Cr + 3.3 Mo + 16 N = 40 min.’ — so PREN ≥ 40 is not a calculated result here but a specification requirement. 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.
It is bought for seawater and hot chloride service where the PREN has to be guaranteed by the specification: seawater piping systems, offshore production equipment, pump and valve bodies, heat exchangers, sour service equipment.
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 F55 (forged flanges and fittings) · A240 / SA-240 (plate, sheet and strip) · A276 / SA-276 (bar and shapes) · A479 / SA-479 (bar and shapes) · A789 / SA-789 (tube) · A790 / SA-790 (pipe) · A815 / SA-815 (wrought fittings) · A314 (billets and bars for forging) · A473 (forging stock). Rolled Alloys additionally lists A890, A928, A988 and A995. EN: 1.4501 · 10088-2 · 10088-3. NORSOK MDS D57 · NACE MR0175 / ISO 15156 · API 6A (Langley Alloys). ASME Section IX welding group P-No 10H (Rolled Alloys, Langley Alloys). ‘F55’ IS a genuine ASTM A182 forging class code, not an alloy name. 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 =…
Advantage
It is the only one of the five whose PREN IS GUARANTEED BY THE SPECIFICATION: ASTM A240 places the footnote ‘Cr + 3.3 Mo + 16 N = 40 min.’ on the S32760 row. In the other four grades PREN is a result calculated from the composition and the specification does not make it an acceptance criterion;
Welding
FILLER METAL: for Zeron 100 the producer specifies its own over-alloyed filler — Rolled Alloys states ‘ZERON 100 is welded using ZERON 100X filler metal’ and ‘ZERON 100X overalloyed weld filler for welding of ZERON 100 to itself and other stainless steels’.
Limits
THE TEMPERATURE CEILING is about 300 °C; the reason is 475 °C embrittlement. Rolled Alloys gives two different figures in two documents: in the data book ‘not recommended for uses which involve extended exposure to temperatures greater than 572 °F (300 °C)’, and in the data sheet ‘greater than 600 °F as this causes a substantial…
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormPREN / PREWWelding, Heat Treatment and MachiningService Limits and an Honest Comparison with F53Frequently Asked Questions
AISI F55 (UNS S32760) is an alloy in the super duplex stainless steel class. Steels of this type are used in applications requiring high corrosion resistance and high strength in particular. AISI F55 has a super duplex structure combining ferritic and austenitic phases, and its composition and microstructure give excellent durability in demanding environments.
Corrosion resistance: UNS S32760 is a duplex stainless steel designed specifically for service in aggressive chloride-bearing environments, and carries tungsten and copper additions compared with UNS S32750. Together with high mechanical strength it has very good resistance to localised corrosion and to stress corrosion cracking.
High resistance to stress corrosion cracking in halide-bearing environments. High resistance to pitting and crevice corrosion. High resistance to general corrosion. High mechanical strength. High resistance to erosion corrosion and corrosion fatigue.
Machinability: Because it has a super duplex structure, its machinability is generally similar to that of duplex steels. It is more difficult than other steels, however, because its high hardness, high strength and duplex phase structure all make the material harder to machine.
Heat treatment: Heat treatment consists of solution annealing at 1100 °C followed by quenching. For super duplex stainless steels such as AISI F55, heat treatment is carried out in order to improve the mechanical properties of the steel and to stabilise the phase structure. Heat treating duplex steels must be done carefully, however, because the phase structure can be degraded at high temperature.
Applications: 1.4501 is widely used in oil and natural gas, hydroelectric power, pressure vessels, pulp and paper, structural components and chemical tankers.
Chemical Composition
DEFENCE METAL
C
Max. 0.030
Mn
Max. 1.00
Si
Max. 1.00
P
Max. 0.030
S
Max. 0.010
Cr
Min. 24.00 · Max. 26.00
Ni
Min. 6.00 · Max. 8.00
N
Min. 0.20 · Max. 0.30
Mo
Min. 3.00 · Max. 4.00
Cu
Min. 0.50 · Max. 1.00
W
Min. 0.50 · Max. 1.00
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
860
Proof Stress (MPa)
–
Elongation A50 mm
16
Hardness Brinell
270 Max HB
Density
7.90 g/cm3
Melting Point
– °C
Modulus of Elasticity
200 Gpa
Electrical Resistivity
2.2 x10^-6 Ω .m
Thermal Conductivity
15.0 W/m.K
Thermal Expansion
13.0 x10^-6 /K
Standards and Equivalents · AISI F55
DEFENCE METAL
Trade name
AISI F55
UNS
S32760 · S32750
W.Nr (DIN/EN)
1.4501
ASTM
A182 · A276 · A479
Available forms
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 F55 (S32760). Dimensions to ASME B16.5 / B16.47 / B16.11. Heat treatment per A182: 1100-1140 °C followed by a liquid quench.
Plate
NO AMS. ASTM A240 / ASME SA-240 — PREN footnote: Cr + 3.3 Mo + 16 N = 40 min. · EN 10088-2 · 1.4501
Sheet and strip
NO AMS. ASTM A240 / ASME SA-240 · EN 10088-2
Round bar and flat bar
NO AMS. ASTM A479 / ASME SA-479 · ASTM A276 / ASME SA-276 (Conditions A and S) · EN 10088-3 · NORSOK MDS D57 · NACE MR0175 / ISO 15156 · API 6A
Forging stock, billets and bars
ASTM A314 (billets and bars) · ASTM A473 (forging stock) — Rolled Alloys lists both in its specification list.
Seamless and welded pipe
ASTM A790 / ASME SA-790 (1070-1140 °C + rapid cooling) · ASTM A928 (welded with filler metal)
Seamless and welded tube
ASTM A789 / ASME SA-789 (1070-1140 °C + rapid cooling)
Wrought fitting
ASTM A815 / ASME SA-815 — post-weld heat treatment is mandatory: 1100-1140 °C + water quench
Castings (for information; outside the scope of this card)
Rolled Alloys lists ASTM A890 and A995; the cast counterpart carries its own UNS number and is not subject to the same acceptance criteria as wrought S32760.
DEFENCE METAL
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. ‘F55’ is NOT an AMS number but an ASTM A182 forging class code, and it is valid only on the forging row.
‘F55’ is valid only on an ASTM A182 forging order; on plate, bar, pipe and tube the relevant specification and UNS S32760 must be written. A314, A473, A890, A928, A988 and A995 are taken from the Rolled Alloys specification list; those rows rest on a single source and are for information.
F55 / Zeron 100 (UNS S32760 / EN 1.4501) is the only super duplex grade carrying both tungsten and copper. The most commercially valuable fact on this page, however, is this: a base ASTM A182 F55 certificate does not by itself prove pitting resistance — the G48 corrosion test and the ferrite check are not performed unless they are separately called out on the order.
Standards by Product Form · F55 / Zeron 100 (S32760 / 1.4501)
AWS A5.9 / SFA-5.9 ER2594 — an over-alloyed (nickel-rich) filler
Welding electrode
AWS A5.4 / SFA-5.4 E2594-15
Offshore
NORSOK M-630, MDS D57
WARNING — the most important commercial point on this grade. ASTM A182’s own text states plainly: “Supplementary requirements are provided for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the order.” So the base F55 table (like the A240 / A276 / A479 / A789 / A790 / A815 tables) sets only chemistry and tensile, yield, elongation and hardness minimums; it does not by itself impose a G48 pitting or crevice test or a numeric ferrite-balance requirement. That is why G48A testing and ferrite certification are marketed by producers as services available on request. Offshore projects invoke them routinely through NORSOK M-630 / M-650; commercial buyers often forget to. If your order does not explicitly call out G48 — with practice, temperature and acceptance criteria — the mill certificate you hold most likely proves only chemistry and mechanical properties.
Composition (S32760): Cr 24.0–26.0% · Ni 6.0–8.0% · Mo 3.0–4.0% · N 0.20–0.30% · W 0.50–1.00% · Cu 0.50–1.00% · C ≤0.025–0.03% · Mn ≤1.00% · Si ≤0.80–1.00% · P ≤0.025–0.03% · S ≤0.005–0.01%. (Minor differences in the C/P/S/Si maxima are normal: different standards in the same family — A182/A240 versus A276/A479 — carry slightly different limits.)
PREN / PREW — the Tungsten Trap
For tungsten-bearing grades the correct formula is different, and this is the calculation catalogues most often get wrong:
S32760 · Calculating PREN
DEFENCE METAL
The correct formula
PREN = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N — the tungsten term is halved before being added to Mo
Representative calculation
Cr 25.0 · Mo 3.6 · W 0.7 · N 0.22 → PREN ≈ 41.5
Guaranteed minimum
PREN ≥ 40 (producer)
Common error 1
Treating %W as 1:1 equivalent to %Mo
Common error 2
Dropping the tungsten term altogether and applying the ordinary (Cr + 3.3Mo + 16N) 2205/2507 formula — this understates S32760’s real corrosion resistance by roughly 1–2 PREN points
Mechanical minimums (solution annealed): 0.2% yield ≥ 550 MPa (80 ksi) · tensile ≥ 750 MPa (109 ksi) · elongation ≥ 25% · hardness ≤ 270 HB (≈28 HRC max) · reduction of area ≥ 45% · Charpy V 80 J at room temperature and 60 J average / 45 J minimum at −46 °C.
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
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, sets the ferrite-austenite balance and delivers the corrosion resistance the specification demands. IT DOES NOT RAISE STRENGTH. This is the delivery condition.
Temperature
There is a narrow spread between sources, EACH WITH ITS SOURCE: ASTM A182 F55 1100-1140 °C [2010-2085 °F] · ASTM A815 1100-1140 °C · Rolled Alloys 1100-1140 °C (‘ZERON 100 should be solution annealed in the temperature range 2012-2084 °F (1100-1140 °C) followed by water quenching’) · ASTM A479 1100 °C [2010 °F] · IMOA 1100 °C [2010 °F] min. · ASTM A790 and A789 1070-1140 °C [1960-2085 °F] · Outokumpu (Forta SDX 100) 1040-1120 °C. NO SINGLE FIGURE IS GIVEN. Practical envelope: about 1070-1140 °C, with most sources taking 1100 °C as the floor. THIS IS THE HIGHEST ANNEALING TEMPERATURE OF THE FIVE GRADES.
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. Rolled Alloys says ‘followed by water quenching’; ASTM A182 says ‘solution treat and quench’ for F55 and requires cooling in a liquid medium down to 260 °C [500 °F]; ASTM A815 says ‘Water quench or rapidly cooled’; ASTM A790 and A789 say ‘rapid cooling in air or water’; Langley Alloys states ‘solution annealed and water quenched as standard’.
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 S32760 that is 1100-1140 °C.
Time
Until the whole section is at temperature; no separate numerical time could be confirmed.
Cooling
Water quench or rapid cooling by other means.
Resulting hardness
The hardness of the solution annealed condition.
DEFENCE METAL
3 · COLD-WORKED CONDITION (ASTM A276 Condition S) — this is NOT a heat treatment
Step
3 · COLD-WORKED CONDITION (ASTM A276 Condition S) — this is NOT a heat treatment
Summary
The only way to raise strength is cold work. ASTM A276 defines a separate condition for it; this is NOT an ageing or hardening heat treatment.
Temperature
—
Time
—
Cooling
—
Resulting hardness
ASTM A276 Condition S (cold finished): tensile minimum 860 MPa (125 ksi), yield minimum 720 MPa (105 ksi), elongation minimum 16%, hardness ceiling 335 HBW. These must not be confused with the Condition A (hot or cold finished, annealed) values.
DEFENCE METAL
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: S32760 is a super duplex and its sigma kinetics are MARKEDLY 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, molybdenum and nitrogen of S32760 all sit above those of 2205, so its curve moves further to the left. The practical consequence: a cooling delay that 2205 tolerates is not tolerated here. IMOA also states ‘Detrimental phases can form in a matter of minutes at the critical temperature.’ This grade also has the highest annealing temperature (A182 F55: 1100-1140 °C), so the temperature range the part has to cross through the forbidden band is wider and the quench arrangement has to be correspondingly faster.
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
Processes: GTAW, GMAW, SMAW and SAW. Heat input is specified separately for root and fill passes and by wall thickness: GTAW root ~1.2 kJ/in, second pass ~0.8 kJ/in, fill ~1.5 kJ/in; SAW 23–30 kJ/in; GMAW 25–38 kJ/in in 1G and 15–20 kJ/in in 5G/6G; manual arc root passes scale from 10–15 kJ/in on thin wall (2.9 mm) to 38–46 kJ/in on thick wall (17.8 mm). Maximum interpass temperature: below 149 °C (300 °F) throughout welding. Preheat is normally not required; it is used up to 100 °C when the material is wet or below 5 °C, or for heavily restrained thick sections. Filler: ER2594 / E2594-15 — an over-alloyed (nickel-enriched) type, and that distinction is critical (see below). Shielding gas: root pass — commercial-purity argon with ~0.5% O₂ monitored, or argon + 2% N₂; fill passes — pure argon or argon + 2% N₂; GMAW — 100% Ar or Ar + 35% He + 2% CO₂. GTAW gas purity 99.995% at 17–25 ft³/hr. Root protection: a continuous argon back-purge (20–30 ft³/hr) maintained until at least 12.7 mm of weld has been deposited.
Post-weld heat treatment — it depends on the filler
This is a verified distinction with a direct cost consequence for the buyer: when the over-alloyed filler (ER2594 type) is used, no post-weld heat treatment is necessary. If a matching-composition filler is chosen instead for cost reasons, the joint does require a post-weld solution anneal plus water quench. So the “matching filler is cheaper” calculation should never be made without adding the post-weld heat-treatment cost.
Heat treatment
Delivery condition: solution annealed and water quenched (standard). A grade-specific solution annealing temperature for S32760 is not stated in the mill datasheets reviewed; representative ranges for the duplex family are a minimum of 1040 °C for 2205 and 1025–1125 °C for 2507 — confirm the grade-specific value against a mill datasheet; none is invented here. Why the quench is mandatory: cooling slowly through the 700–1000 °C intermetallic window risks sigma and chi precipitation within minutes, which severely degrades both corrosion resistance and toughness; water quenching is the only practical way to cross that window fast enough. 475 °C embrittlement: 300–525 °C (alpha-prime formation in the ferrite phase). Ferrite acceptance range: no S32760-specific numeric range was found in the mill datasheets; general duplex guidance gives 30–70% in the base metal and 25–75% (FN 30–90) in weld metal. Treat any single fixed figure quoted elsewhere (for example “35–65%”) as unverified for this grade.
Machining and hot forming
Cutting speeds: roughly 98–213 ft/min in rough turning, with ISO P45 carbide inserts and a dedicated cutting oil recommended. For close-tolerance work the producer recommends this sequence: rough machine to about a 2 mm envelope on final size, stabilise for at least 12 hours at room temperature, then finish machine to size — residual stress relief between roughing and finishing passes is expected. No numeric machinability comparison against 316L or 2205, work-hardening rate or power requirement is given in the sources reviewed; do not publish a percentage. Hot-working range: 1100–1280 °C. Minimum finishing temperature and cold-forming notes could not be verified.
Service Limits and an Honest Comparison with F53
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%
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%
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.
Zeron 100 / F55 · Properties
DEFENCE METAL
Service temperature
The producer suggests use between −73 °C and 315 °C (−100 °F to 600 °F); extended exposure above 315 °C causes substantial toughness loss from intermetallic precipitation. That is metallurgically consistent with the independently reported ~300 °C onset of embrittlement. The minimum figure is single-sourced
CPT (pitting)
Above 50 °C (122 °F) by ASTM G48 Method A — confirmed in two independent sources
CCT (crevice)
— (no verified numeric CCT value was found). What is verified: the base metal resists crevice corrosion up to 55 °C, but weld pitting performance is the limiting factor, at about 40 °C
Seawater
Corrosion rate below 0.01 mm/year, with outstanding pitting and crevice resistance. No specific chlorination (ppm) approval level could be verified — commonly quoted but unconfirmed figures are not printed here
Sour service
Listed under NACE MR0175 / ISO 15156 Part 3, with hardness controlled to ≤28 HRC; suitable up to an H₂S partial pressure of 0.2 bar
Acid resistance
Superior resistance to sulphuric acid; the tungsten and copper additions give a marked advantage in reducing-acid environments over W/Cu-free duplex grades
Magnetic
Ferromagnetic; room-temperature relative magnetic permeability is given as ~29–33 across sources
Typical applications
Oil and gas process, seawater, firewater and subsea pipework, risers, manifolds, pressure vessels, valves, heat exchangers; also pollution control, pulp and paper, power generation and desalination
F55 (Zeron 100) and F53 (2507) · Verified Comparison
Zeron 100: 50 °C · 2507: 40 °C (typically per ASTM A923 Practice C)
What the W and Cu actually change
The two grades have near-identical bulk PREN (2507’s extra Mo and N roughly offset the half-coefficient contribution of Zeron 100’s tungsten) — so pitting and crevice performance in plain seawater is broadly comparable. The differences are two: (a) Zeron 100’s copper improves resistance specifically in reducing (sulphuric-type) acid service, where 2507 has no equivalent benefit; and (b) Zeron 100 is typically sold qualified at a higher G48A test temperature (50 °C against 40 °C)
Frequently Asked Questions
We have an F53 (2507) purchase spec — can we substitute F55 (Zeron 100), or vice versa?
Not automatically. F53 and F55 are different ASTM grades (S32750 against S32760) with different chemistries: Zeron 100 carries deliberate tungsten (~0.7%) and copper (~0.7%) that 2507 lacks, while 2507 typically runs slightly higher Mo and N and reaches a higher tensile strength (116 ksi against 109 ksi). Bulk PREN is nearly identical (≈41.5 against ≈41.9), so for plain chloride and seawater pitting resistance the two are broadly comparable. But Zeron 100’s copper gives it a real edge in reducing-acid service that 2507 cannot match, and the grades are commonly qualified to different G48/A923 test temperatures (50 °C against 40 °C). A project spec naming one grade by its ASTM designation does not implicitly permit the other: substitution requires a documented engineering deviation or management of change, not just “same PREN”. Where tensile strength governs (high-pressure bolting, say) 2507’s higher UTS may be required and Zeron 100 will not qualify.
Our vendor quoted F55 with a G48 corrosion test certificate — is that always included, or did we pay extra?
It is not automatically included. The base ASTM A182 tables for Grade F55 (and A240 / A276 / A479 / A789 / A790 / A815) define chemistry and tensile and hardness minimums only, and ASTM’s own standard text states that supplementary testing “shall apply only when specified individually by the purchaser in the order”. G48 pitting and crevice testing, and any associated ferrite-content check, is a purchaser-invoked supplementary requirement — commonly bundled in via ASTM A923 Method C acceptance criteria, or mandated wholesale by NORSOK M-630 / M-650 for offshore work. If your purchase order did not explicitly call out G48 with practice, temperature and acceptance criteria, do not assume the mill test report proves pitting resistance; it most likely proves only chemistry and mechanical properties. A separate note: the base-metal CPT does not carry over to the weld — welded joints are typically limited to about 40 °C.
Why does “NORSOK-certified” F55 cost noticeably more than standard mill-certified F55 of the same UNS number?
NORSOK M-630 / MDS D57 compliance is not a chemistry change — it is a testing, documentation and traceability burden layered on top of identical base metal. It typically requires full-lot G48 Method A corrosion testing at the higher 50 °C qualification temperature, demonstrated ferrite-balance verification, third-party witnessed mechanical and impact testing, tighter production-lot traceability, and independent third-party certification (EN 10204 3.2) rather than a mill self-certification (3.1). Each of these adds inspection time, laboratory fees and third-party sign-off cost that a “same grade, standard certificate” order avoids. The steel itself can be identical — what is expensive is the paper trail and the testing regime behind it.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip
270 HBW max.
550
750
25%
ASTM A479 / ASME SA-479 · bar and shapes
300 HBW max.
550
750
25%
ASTM A276 / ASME SA-276 · bar and shapes, Condition A (hot or cold finished, annealed)
290 HBW max.
550
750
25%
ASTM A276 / ASME SA-276 · bar, Condition S (cold finished) — BY COLD WORK, NOT BY HEAT TREATMENT
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. In the chart, a value given as a range is drawn at its lower bound; the full range is in the table. Every row is a specification minimum, not a typical value. The Condition S row is the COLD-WORKED condition; it is not produced by heat treatment and is not compared on the same axis as the other rows. ASTM A182 also sets an UPPER limit on tensile strength for F55 (895 MPa); the other specifications set a lower limit only.
