UNS S32750 · W.Nr. 1.4410 · X2CrNiMoN25-7-4 · in ASTM A240: 24.0-26.0% Cr – 6.0-8.0% Ni – 3.00-5.00% Mo – 0.24-0.32% N – Cu ≤ 0.50% – C ≤ 0.03% – balance Fe. ITS NITROGEN BAND IS THE HIGHEST OF THE FIVE (0.24-0.32%) and its molybdenum band the widest (3.00-5.00%); that is what gives it the highest calculated PREN ceiling of the five (47.6). 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 rapid quench.
It is bought for seawater and hot chloride service where the highest-strength super duplex is required: seawater piping systems, desalination plant, chemical process equipment, flue gas scrubbers, offshore production equipment, heat exchangers.
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 F53 (forged flanges and fittings) · A240 / SA-240 (plate, sheet and strip) · A479 / SA-479 (bar and shapes) · A789 / SA-789 (tube) · A790 / SA-790 (pipe) · A815 / SA-815 (wrought fittings) · A276 / SA-276 (cited in the Rolled Alloys specification list). EN: 1.4410 · 10088-2 · 10088-3. NORSOK MDS D57 · NORSOK M-650 · NACE MR0175 / ISO 15156 · API 6A (Langley Alloys). ASME Section IX welding group P-No 10H (Rolled Alloys, Langley Alloys). ‘F53’ 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
Of the five grades this one carries the highest ASTM A240 tensile minimum: 795 MPa (116 ksi). In the same table S32550 is 760 MPa, S32760 750 MPa, S32205 655 MPa and S32900 620 MPa. Its yield minimum of 550 MPa equals that of the other two super duplex grades.
Welding
FILLER METAL: AWS E2594 / ER2594 (Rolled Alloys: ‘2507 is welded using E2594 or ER2594 filler metal’). Sandmeyer and Penn Stainless describe the same job as ‘2507/P100 filler metal is suggested when welding 2507 because it will produce the appropriate duplex weld structure’.
Limits
THE TEMPERATURE CEILING is about 270-315 °C; the reason is 475 °C embrittlement. Each with its source: Sandmeyer ‘not recommended for applications which require long exposures to temperatures above 570 °F because of the risk of a reduction in toughness’ (299 °C) · Rolled Alloys ‘2507 should be limited to applications below 600 °F’ (316…
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormWeldingHeat Treatment, Machining and FormingService Limits and ComparisonFrequently Asked Questions
AISI F53 is an alloy in the duplex stainless steel class. Duplex steels combine ferritic and austenitic structures and so offer the properties of both phases together. This type of steel is notable in particular for its high corrosion resistance, high mechanical strength and excellent weldability.
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 super duplex material, and its use is not recommended where extensive welding is involved.
Machinability: This material is not easy to machine. Although European material machines better than comparable grades, machining this material is nevertheless quite difficult. Not metallurgically well suited to forging, this grade is not the choice where parts are to be produced by forging.
Heat treatment: Post-weld heat treatment is not required. The maximum service temperature is 280 °C (536 °F) for long exposure times and 300 °C (572 °F) for short exposure times.
Applications: This stainless grade is chosen where very high mechanical values and very high corrosion resistance are required at the same time. It is very frequently used where ordinary duplex stainless steels (such as 1.4362 or 1.4462) are not sufficient, in places such as oil refineries where better corrosion resistance is needed. It is very frequently used on oil platforms, in chemical production plants, in heat exchangers, in high corrosion and wear environments, in power generation plants, and in bolting requiring very high corrosion resistance. This grade is the most widely used super duplex material, and 1.4410 can be specified in almost any application where a super duplex material is required.
Chemical Composition
DEFENCE METAL
C
Max. 0.030
Mn
Max. 1.20
Si
Max. 0.80
P
Max. 0.035
S
Max. 0.015
Cr
Min. 24.00 · Max. 26.00
Ni
Min. 6.00 · Max. 8.00
N
Max. 0.30
Mo
Min. 3.00 · Max. 5.00
Cu
Max. 0.5
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
750-930
Proof Stress (MPa)
–
Elongation A50 mm
25
Hardness Brinell
260 Max HB
Density
7.75 g/cm3
Melting Point
1396-1450 °C
Modulus of Elasticity
210 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 F53
DEFENCE METAL
Trade name
AISI F53
UNS
S32750
W.Nr (DIN/EN)
1.4410
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 F53 (S32750). Dimensions to ASME B16.5 / B16.47 / B16.11. Heat treatment per A182: 1025 °C followed by a liquid quench.
Plate
NO AMS. ASTM A240 / ASME SA-240 · EN 10088-2 · 1.4410
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 (SEPARATE minimums above and below 50 mm) · ASTM A276 / ASME SA-276 · EN 10088-3 · NORSOK MDS D57 · NORSOK M-650 · NACE MR0175 / ISO 15156 · API 6A
Seamless and welded pipe
ASTM A790 / ASME SA-790 (1025-1125 °C + rapid cooling)
Seamless and welded tube
ASTM A789 / ASME SA-789 (1025-1125 °C + rapid cooling)
Wrought fitting
ASTM A815 / ASME SA-815 — post-weld heat treatment is mandatory: 1025-1125 °C + water quench
Weld wire and electrode
AWS E2594 / ER2594 (Rolled Alloys) · 2507/P100 (Sandmeyer, Penn Stainless) · ASME IX Group P10H
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. ‘F53’ is NOT an AMS number but an ASTM A182 forging class code, and it is valid only on the forging row.
‘F53’ is valid only on an ASTM A182 forging order; on plate, bar, pipe and tube the relevant specification and UNS S32750 must be written. ASTM A479 makes a diameter distinction; the ordered diameter changes the mechanical acceptance criteria.
F53 / SAF 2507 (UNS S32750 / EN 1.4410) is the reference super duplex grade: PREN ~42, with a yield strength more than three times that of 316L. In exchange, the grade is unforgiving — the welding and heat-treatment sections below are the most important part of this page.
Standards by Product Form · F53 / 2507 (S32750 / 1.4410)
ASTM A580 / A580M is the general stainless wire standard; S32750’s presence in its grade table could not be independently confirmed
Welding wire
AWS A5.9 ER2594 (bare wire)
Welding electrode
AWS A5.4 E2594 (covered electrode) — the “25Cr-10Ni-4Mo-N” family
Offshore purchasing
NORSOK M-630 (current edition M-630:2020, Edition 7), titled “Material data sheets and element data sheets for piping”
Why NORSOK is cited separately: M-630 does not replace ASTM; it is layered on top of it. Where ASTM defines minimum chemistry, mechanical properties and heat treatment, NORSOK MDS sheets add project-level requirements: tighter ferrite-content windows, mandatory ASTM G48-type pitting and crevice corrosion testing, low-temperature Charpy impact testing, and formal welding-procedure qualification tied to the specific MDS number. No numeric NORSOK thresholds are published on this page, because the standard’s clause text is licensed and could not be independently verified — confirm them against the project MDS.
Composition: C ≤0.030% · Cr 24.0–26.0% · Ni 6.0–8.0% · Mo 3.0–5.0% · N 0.24–0.32% · Mn ≤1.20% · Si ≤0.80% · P ≤0.035% · S ≤0.020% · Cu ≤0.50%. PREN = %Cr + 3.3×%Mo + 16×%N; at mid-range values (Cr 25, Mo 4, N 0.28) that gives ≈42.7. Published figures range from 41 to 42 and all comfortably clear the conventional PREN ≥ 40 super duplex threshold.
2507’s yield strength is roughly 22% higher than 2205’s and more than three times 316L’s. Down-gauging is the grade’s principal commercial justification
Welding — the Central Risk for This Grade
Super duplex is welded in a narrow window, and there is a way to get it wrong in both directions. Cooling too fast (too low a heat input) leaves no time for ferrite to transform back to austenite; excess ferrite remains at the fusion line and in the HAZ, and toughness and corrosion resistance both fall. Cooling too slowly (too high a heat input) precipitates sigma and chi phases in the 700–1000 °C window and degrades the same two properties by a different route.
Verified parameters
Processes: GTAW (with filler), GMAW, SMAW, PAW, SAW. Heat input: one mill datasheet gives 0.5–2 kJ/mm; that figure is single-sourced and should be treated as indicative — the binding value comes from welding-procedure qualification. Maximum interpass temperature: sources diverge — the duplex industry guide gives 100 °C for super duplex while one mill gives <150 °C, preferably <120 °C. The safer and more commonly cited figure for super duplex is 100 °C, and the divergence itself is worth knowing. Preheat is not recommended (it may be detrimental for duplex). Filler: AWS ER2594 / E2594. Shielding and backing gas: nitrogen additions suppress chromium-nitride precipitation and speed austenite re-formation in the weld — the principle is verified, but no specific %N₂ figure could be. Post-weld solution annealing is normally not done in the field; correct heat-input control is relied on instead. Mill data states “no PWHT required”, though a full solution anneal (1100–1125 °C) may be applied deliberately for heavy-section repairs.
Ferrite/austenite balance
The target balance is quoted in different bands by different sources: 35–60% ferrite for base metal and 30–70% for weld metal in one; another mill gives ~50/50 in the base metal, <70% in the HAZ and 20–60% in the weld metal. Do not publish a single fixed number — the binding figure is set by the project specification, particularly the NORSOK MDS. Measurement is by two routes: a magnetic Ferrite Number meter calibrated to AWS A4.2, and metallographic point count per ASTM E562 (manual) or E1245 (automated). An important caution: a low magnetic ferrite reading may not mean the ferrite content is genuinely low — it can also indicate that ferrite has transformed into intermetallic (sigma) phase.
Heat Treatment, Machining and Forming
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 and sets the ferrite-austenite balance. IT DOES NOT RAISE STRENGTH. This is the delivery condition.
Temperature
Sources differ, EACH WITH ITS SOURCE: ASTM A790 and A789 1025-1125 °C [1880-2060 °F] · ASTM A815 1025-1125 °C · IMOA 1025-1125 °C [1880-2060 °F] · ASTM A182 F53 1025 °C [1880 °F] · Outokumpu (Forta SDX 2507) 1040-1120 °C · Industeel (UR 2507) 1080-1120 °C · Sandmeyer and Penn Stainless 1925 °F (1052 °C) min. NO SINGLE FIGURE IS GIVEN AND NO AVERAGE IS TAKEN. Practical envelope: about 1025-1125 °C.
Time
Until the whole section is at temperature. No numerical time was found in four independent sources, so none is given.
Cooling
RAPID COOLING IS MANDATORY. Sandmeyer and Penn Stainless state ‘Annealing should be followed immediately by a rapid air or water quench’; ASTM A790 and A789 say ‘rapid cooling in air or water’; ASTM A815 says ‘Water quench or rapidly cooled’; ASTM A182 says ‘solution treat and quench’ for F53 and requires cooling in a liquid medium down to 260 °C [500 °F]; Langley Alloys states ‘solution annealed and water quenched’.
Resulting hardness
ASTM A240 ceiling 310 HBW · ASTM A479 ceiling 310 HB · ASTM A182 F53 ceiling 310 HBW · Sandmeyer, Rolled Alloys and Penn Stainless 32 HRC max. THIS IS THE HIGHEST HARDNESS CEILING OF THE FIVE GRADES.
DEFENCE METAL
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 S32750 that is 1025-1125 °C followed by a water quench.
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 (A240 ceiling 310 HBW, 32 HRC).
Warning
INTERPASS TEMPERATURE DURING WELDING: Sandmeyer and Penn Stainless state ‘The interpass weld temperature should not exceed 300 °F’ (about 150 °C). This is not a heat treatment stage but it concerns the same forbidden band.
DEFENCE METAL
3 · DIAMETER DISTINCTION — in ASTM A479 the mechanical minimum CHANGES with section size
Step
3 · DIAMETER DISTINCTION — in ASTM A479 the mechanical minimum CHANGES with section size
Summary
This is not a heat treatment stage; it is the specification’s acknowledgement that the heat treatment does not give the same result in a heavy section.
Temperature
—
Time
—
Cooling
—
Resulting hardness
ASTM A479: at 50 mm (2 in.) and below, 800 MPa tensile / 550 MPa yield; above 50 mm, 760 MPa tensile / 515 MPa yield. Calculations must be made against the ordered diameter.
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, NAMED DIRECTLY: IMOA’s comparison names this grade explicitly: ‘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 intermetallic start curve of 2507 therefore lies to the LEFT of that of 2205, and precipitation begins sooner at the same temperature. IMOA also states ‘Detrimental phases can form in a matter of minutes at the critical temperature.’ Industeel puts the same point as ’25 Cr super duplex grades are subject to intermetallic phase precipitations (σ…)’. THE PRACTICAL CONSEQUENCE: a quenching delay on a heavy section or a complex geometry is far less tolerated than on 2205, and welding heat input and interpass temperature must be held tight (Sandmeyer and Penn Stainless: the interpass temperature must not exceed 300 °F, about 150 °C).
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.
Heat treatment
Solution annealing: 1025–1125 °C, water quench. Two independent sources confirm this band. The quench must be immediate: the 700–1000 °C sigma/chi window has to be crossed as fast as possible, and the time between leaving the furnace and hitting the water must be minimised, because sigma forms there within minutes. This is the most important practical difference for the grade: 2507’s precipitation curve sits further to the left than 2205’s, because the driving force for sigma formation increases with chromium and molybdenum content — super duplex precipitates sigma markedly faster. The band itself is wider too: 700–1000 °C for 2507 against 700–950 °C for 2205. 475 °C embrittlement: 300–525 °C; the effect is less severe than in fully ferritic steels because about half the structure is austenite, but it is most pronounced in the molybdenum-bearing grades. Duplex cannot be hardened by heat treatment. Standard delivery is solution annealed and water quenched.
Machining
Super duplex requires markedly higher cutting forces than 316L and wears tools faster. Recommended carbide roughing speeds in turning diverge strikingly: 170–240 m/min for lean duplex S32101, 90–120 m/min for 2205, and 50–70 m/min for 2507 — super duplex is machined at roughly half the speed of standard duplex. The work-hardening rate is comparable to the austenitics, but the chip is tough and abrasive, and because sulphur is kept low, chip breaking is difficult too. Powerful, rigid machines, coated carbide inserts with positive chip-breaker geometry, scheduled edge changes (do not run inserts to failure) and generous EP-additive cutting oil or emulsion are required; dry cutting is recommended in face milling to aid chip ejection.
Hot and cold forming
Hot-working range: 1230–1025 °C, with a minimum finishing temperature of 1050 °C. Going below that risks sigma precipitation and ferrite cracking. After hot forming, a full solution anneal plus water quench is mandatory. During annealing the material is soft at solution temperature and prone to warping, so parts need adequate support. Beware shortcuts: a lower temperature, a shorter time, or a stress relief in place of a full anneal all risk leaving harmful intermetallic phases in the structure.
Service Limits and Comparison
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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—
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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.
2507 / F53 · Properties and Alternatives
DEFENCE METAL
Service temperature
315 °C (600 °F) — the ASME maximum design-stress temperature. The limit is set by 475 °C embrittlement and sigma-phase kinetics, not by oxidation. German TÜV rules give a more conservative band (250–480 °C) depending on weld condition
Minimum temperature
Duplex retains good toughness to around −40 °C; unlike the austenitics, however, it shows a ductile-to-brittle transition and is not suitable for cryogenic service
CPT / CCT
Figures diverge by test method and must not be merged: ASTM G48 Method E gives a CPT of ~60–70 °C and Method F a CCT of ~30–40 °C (one mill’s data), while another source quotes a CPT of ~85 °C without stating the method (probably a different, electrochemical protocol). Always quote a corrosion-temperature figure together with its test method
Chloride stress-corrosion cracking
Duplex with ≥30% ferrite is far more resistant than 304 or 316; 2507’s ferrite content is well above that threshold
NACE MR0175 / ISO 15156
Produced for sour service; note that sour-service qualification typically requires tighter controls than the standard mill temper — verify against the relevant NACE part
Magnetic
Ferromagnetic — a two-phase structure with an exceedingly fine austenite/ferrite spacing
Typical applications
Offshore oil and gas (piping, umbilicals, risers), seawater cooling, desalination, flue-gas cleaning, chemical process vessels and piping, chemical tankers, pulp and paper, storage tanks
38–41 — copper-bearing; borderline on the PREN threshold
Frequently Asked Questions
Is F53 the same thing as F55, or just a naming difference?
They are related but genuinely distinct alloys, not two trade names for one material. F53 (UNS S32750) and F55 (UNS S32760) are both super duplex grades with PREN comfortably above 40 and broadly 25Cr-7Ni-4Mo chemistry, but F55 carries deliberate copper and tungsten additions that F53 does not. F53, in turn, typically runs slightly higher molybdenum and nitrogen and reaches a higher tensile strength (116 ksi against 109 ksi). Both sit in the ~80 ksi minimum yield class and are used in overlapping offshore and seawater applications, which is why buyers sometimes treat them as equivalent. They are qualified separately under ASTM (different UNS numbers, different grade letters in A182/A240/A789/A790), have different NORSOK MDS numbers, and are not automatically interchangeable on a welding procedure or a corrosion-critical specification. A WPS qualified for F53 is not automatically valid for F55.
Why does NORSOK matter when buying for offshore?
NORSOK M-630 (“Material data sheets and element data sheets for piping”, current edition 7, 2020) is the Norwegian offshore industry’s own materials-qualification framework, and it does not replace the ASTM specifications — it layers on top of them. Where ASTM defines minimum chemistry, mechanical properties and heat treatment, NORSOK MDS sheets add project-level requirements: spec-defined, tighter ferrite-content windows, mandatory ASTM G48-type pitting and crevice testing at defined temperatures, low-temperature Charpy testing, and formal welding-procedure qualification records tied to the specific MDS number rather than a generic ASTM callout. Buying “ASTM A182 F53” material for a NORSOK-governed offshore project without also confirming NORSOK MDS compliance and documentation is a common and costly mistake: the mill certificate must show the relevant MDS reference, not just the ASTM grade, or the material will be rejected at project QA/QC.
Why does super duplex fabrication cost more?
The premium comes not mainly from the raw material but from the process control the grade demands at every fabrication step. Weld heat input has to be controlled tightly enough to be fast enough to avoid sigma and chi phase (which forms far faster in 2507 than in 2205, because higher chromium and molybdenum increase the driving force for precipitation) while staying slow enough to let ferrite transform back to austenite in the weld and HAZ. Interpass temperature is capped (commonly around 100 °C for super duplex, more relaxed for standard duplex). The filler is a specific 25Cr-10Ni-4Mo-N alloy (AWS ER2594 / E2594), not a generic stainless filler. And production welds typically need ferrite-content verification (magnetic and/or metallographic) plus corrosion and impact testing on the qualifying procedure. Each of those needs its own qualified welding procedure specification, tighter-than-usual NDT, and often destructive testing of production coupons — that procedural burden, more than alloy cost, is what drives the higher fabricated cost.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip
310 HBW max. · 32 HRC max.
550
795
15%
ASTM A479 / ASME SA-479 · bar and shapes, diameter ≤ 50 mm (2 in.)
310 HB max.
550
800
15%
ASTM A479 / ASME SA-479 · bar and shapes, diameter > 50 mm (2 in.)
310 HB max.
515
760
15%
ASTM A182 / ASME SA-182 · forgings · GRADE F53
310 HBW max.
550
800
15%
ASTM A790 / SA-790 (pipe) and A789 / SA-789 (tube)
—
550
800
15%
Producer specification · Sandmeyer and Penn Stainless, plate
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. ASTM A479 makes a diameter distinction: above 50 mm the minimums drop. Calculations are made against the ordered diameter. The producer rows do not replace the ASTM floor; the 25% elongation requirement of Langley Alloys is above the 15% of ASTM and is producer-specific.
