UNS S32205 · W.Nr. 1.4462 · X2CrNiMoN22-5-3 · in ASTM A240: 22.0-23.0% Cr – 4.5-6.5% Ni – 3.00-3.50% Mo – 0.14-0.20% N – C ≤ 0.03% – balance Fe. A SECOND UNS NUMBER CARRIES THE SAME W.Nr.: S31803, whose band is wider (21.0-23.0% Cr – 2.50-3.50% Mo – 0.08-0.20% N) and which is NOT EQUIVALENT to S32205. It is a ferritic-austenitic (duplex) stainless steel; in the annealed condition the structure is roughly half ferrite and half austenite (Outokumpu: ‘a phase balance of approximately 50% ferrite and 50% austenite’; Rolled Alloys gives 40-50% ferrite in the annealed condition for 2205). It is NOT PRECIPITATION HARDENABLE, it is NOT AGED and it does not transform to martensite on cooling; its only heat treatment is solution annealing followed by a rapid quench.
It is bought where 316 and 316L cannot be used in chloride service because of stress corrosion cracking: chemical and petrochemical process equipment, structures and piping near seawater, pressure vessels, heat exchangers, flue gas desulphurisation plant.
Forms
Round bar · Flat bar · Plate · Sheet · Pipe and tube · Forgings. All forms are supplied to order.
Standards
THERE IS NO AMS — no AMS number could be confirmed for this alloy; see ‘standart_notu’ for the detail. ASTM: A240 / SA-240 (plate, sheet and strip — S32205 and S31803) · A276 / SA-276 (bar and shapes — S31803) · A479 / SA-479 (bar and shapes) · A182 / SA-182 (forged flanges and fittings — F60 for S32205, F51 for S31803) · A789 / SA-789 (seamless and welded tube) · A790 / SA-790 (seamless and welded pipe) · A815 / SA-815 (wrought fittings) · A923 (acceptance test for detecting detrimental intermetallic phase). EN: 1.4462 · 10088-2 · 10088-3. NORSOK MDS D45 (Langley Alloys). ASME Section IX welding group P-No 10H (Rolled Alloys, Langley Alloys). S32205 AND S31803 ARE NOT EQUIVALENT, even though they carry the same W.Nr. (1.4462). IMOA states the difference: ‘The composition range that was originally set for 2205 (UNS S31803) was too broad.
Advantage
More than twice the yield strength of 316 in the same ASTM A240 table: 450 MPa against 205 MPa, and 655 MPa against 515 MPa in tension. Alongside that its PREN floor is 34.1 (formula %Cr + 3.3×%Mo + 16×%N, calculated from the bottom of the A240 composition band) against roughly 24 for 316.
Welding
FILLER METAL: AWS E2209 / ER2209 (Rolled Alloys: ‘2205 is welded with E2209 or ER2209 fillers’). The filler is enriched in nickel to hold the austenite balance; Industeel states the requirement as ‘Chemical composition has to be adapted to stabilize austenite’.
Limits
THE TEMPERATURE CEILING is about 300 °C and the reason is 475 °C embrittlement. IMOA: ‘The upper temperature limit for duplex stainless steel service is controlled by alpha prime formation.’ The ceilings, each with its source: the ASME limit IMOA gives for 2205 is 315 °C both unwelded and welded, the TÜV limit 280 °C unwelded and 250 °C…
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormS31803 or S32205?Welding, Heat Treatment and MachiningService Limits and ComparisonFrequently Asked Questions
Corrosion resistance: AISI 318 is characterised by an excellent combination of corrosion resistance comparable with that of austenitic grade 1.4404, together with a yield strength approximately 150% higher than that austenitic grade. The use of duplex stainless steels, and of 1.4462 in particular, is gaining in popularity because of the unique combination of excellent corrosion resistance, resistance to stress corrosion cracking and high tensile and yield strength.
Weldability: As with all duplex stainless steels, care must be taken when welding 1.4462. The window of optimal welding parameters is narrow, so deviations outside those optimal limits can lead to poor welds. Within the prescribed welding parameters, weldability is good. It is preferable to use somewhat higher heat inputs (1-3 kJ/mm) during welding.
Machinability: Care must be taken when forging 1.4462, as it is susceptible to problems. Gradual heating to 1200 °C is recommended, with forging then carried out at temperatures between 1200 °C and 900 °C. Air cooling should follow the forging operation.
Heat treatment: Like the austenitic stainless steels, AISI 318 is generally regarded as a material that does not harden under heat treatment and can be formed.
Applications: The application areas of 1.4462 are the construction sector, the chemical industry, the petrochemical industry, electronic equipment, the food and beverage industries, mechanical engineering, offshore structures and shipbuilding.
Chemical Composition
DEFENCE METAL
C
Max. 0.03
Mn
Max. 2.00
Si
Max. 1.00
P
Max. 0.03
S
Max. 0.02
Cr
Min. 21.00 · Max. 23.00
Ni
Min. 4.50 · Max. 6.50
N
Min. 0.10 · Max. 0.22
Mo
Min. 2.50 · Max. 3.50
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
700-900
Proof Stress (MPa)
460-500
Elongation A50 mm
20
Hardness Brinell
– Max HB
Density
7.805 g/cm3
Melting Point
– °C
Modulus of Elasticity
200 Gpa
Electrical Resistivity
0.85 x10^-6 Ω .m
Thermal Conductivity
19.0 W/m.K
Thermal Expansion
13.7 x10^-6 /K
Standards and Equivalents · AISI 318
DEFENCE METAL
Trade name
AISI 318
UNS
S31803 · S32205
W.Nr (DIN/EN)
1.4462
ASTM
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
Plate
NO AMS. ASTM A240 / ASME SA-240 (S32205 and S31803) · EN 10088-2 · 1.4462
Sheet and strip
NO AMS. ASTM A240 / ASME SA-240 · EN 10088-2
ASTM A182 / ASME SA-182 (F60 / F51) — forged flanges, fittings and valve parts · dimensions to ASME B16.5 / B16.47
Fitting
ASTM A815 / ASME SA-815 — wrought duplex fittings; post-weld heat treatment is mandatory (1020-1100 °C + water quench)
Seamless and welded pipe
ASTM A790 / ASME SA-790 (S32205 and S31803)
Seamless and welded tube
ASTM A789 / ASME SA-789 (S32205 and S31803)
Testing and acceptance (independent of product form)
ASTM A923 — test methods for detecting detrimental intermetallic phase in duplex stainless steels. Rolled Alloys lists A923 separately in its 2205 specification list.
DEFENCE METAL
Additional information
AMS note
No AMS number could be confirmed for this alloy. The AMS-mapped stainless list of Rolled Alloys gives AMS numbers for austenitic, martensitic and precipitation-hardening grades but carries none on the duplex rows. Since the four independent source threshold was not met, no AMS number has been put on the card.
No AMS number is written on any row because none could be confirmed. Orders should be written against the UNS number: ‘F51’ permits S31803, ‘F60’ permits S32205.
AISI 318 / 2205 (EN 1.4462) is the reference duplex stainless steel. The most valuable information on this page comes down to one distinction: UNS S31803 and S32205 are not the same thing. Both are sold as “2205”, but their nitrogen floors differ — and that difference shows up directly in weld quality.
Standards by Product Form · AISI 318 / 2205 (S31803 · S32205 / 1.4462)
DEFENCE METAL
Sheet · Plate · Strip
ASTM / ASME A240 / SA-240 — S31803 and S32205 appear as separate line items in the same standard
Bar
ASTM / ASME A276 · A479 / SA-479
Forgings · flanges · fittings
ASTM / ASME A182 / SA-182, Grade F51
Seamless pipe · tube
A790 / SA-790 (pipe) · A789 / SA-789 (tube)
Welded pipe · tube
A789 and A790 cover both seamless and welded product — their titles say so explicitly
Fittings
— (ASTM A815 could not be confirmed by number in the mill sources reviewed; forged fittings fall under A182 F51)
Wire
— (no verifiable wire standard was found for S31803/S32205)
Welding wire
AWS A5.9 ER2209 (bare wire, GTAW/GMAW) — filler metal number S39209
The grade-letter trap: F51 is the single most misquoted designation in duplex catalogues. It is not exclusive to S31803: current mill literature lists dual-certified S31803/S32205 material as F51. Some distributor pages cite a separate grade letter for S32205; that claim could not be independently verified and is therefore not printed here. The practical rule: order by UNS number, not by grade letter.
S31803 or S32205? — the Most Important Section on This Page
S32205 is the tightened-chemistry version of S31803. The reason is metallurgical: S31803’s original nitrogen floor (0.08%) was too low, and heats near that floor could develop excess ferrite and chromium-nitride precipitation in the weld HAZ, losing toughness and corrosion resistance. Industry experience showed that a 0.14% minimum nitrogen is necessary for 2205 welded fabrication, and S32205 was created to fix exactly that.
S31803 and S32205 · Side by Side
DEFENCE METAL
Chromium
S31803: 21.0–23.0% · S32205: 22.0–23.0%
Nickel
Both: 4.5–6.5%
Molybdenum
S31803: 2.5–3.5% · S32205: 3.0–3.5%
Nitrogen
S31803: 0.08–0.20% · S32205: 0.14–0.20% — this is the one critical difference
Others
C ≤0.03% · Mn ≤2.0% · Si ≤1.0% · P ≤0.03% · S ≤0.02% (both)
Standard mill practice today: “2205” is one product stamped S31803/S32205 and made to the tighter S32205 chemistry (which automatically satisfies the S31803 band)
What to write on the order: specify “UNS S32205”, or explicitly “dual certified S31803/S32205” — not S31803 alone. That guarantees the 0.14% nitrogen floor and avoids receiving an old-style low-nitrogen heat that technically meets S31803 but not S32205. It costs nothing extra.
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
1 · HOT WORKING
Step
1 · HOT WORKING
Summary
The lower temperature limit is not a preference; it is a cracking and sigma limit.
Temperature
IMOA gives 1230-950 °C for 2205 and requires a minimum soak at 1040 °C. Being a single source, it is not treated as binding.
Time
No numerical time was found in four independent sources, so none is given.
Cooling
Rolled Alloys: ‘Cool forgings in air and anneal, followed by water quench.’ In other words a SOLUTION ANNEAL AND QUENCH is carried out separately after hot working; hot working alone is not the delivery condition.
Resulting hardness
There is no hardness target at this stage.
Warning
IMOA: ‘If hot-forming takes place at too low a temperature, deformation accumulates in the weaker but less ductile ferrite, which can result in cracking of the ferrite in the deformed region. Additionally, a large amount of sigma phase can be precipitated when the hot-working temperature drops too low.’
DEFENCE METAL
2 · SOLUTION ANNEAL + RAPID QUENCH — this is the only valid heat treatment
Step
2 · SOLUTION ANNEAL + RAPID QUENCH — this is the only valid heat treatment
Summary
It takes intermetallic phases back into solid solution, sets the ferrite-austenite balance and restores corrosion resistance. IT DOES NOT RAISE STRENGTH; strength comes from the composition and the two-phase structure. This is the delivery condition.
Temperature
Sources differ at the ends of the band, EACH WITH ITS SOURCE: ASTM A790 and A789 1020-1100 °C [1870-2010 °F] · ASTM A815 1020-1100 °C · ASTM A479 1040 °C [1900 °F] min. · ASTM A182 1020 °C for F60 and 1020 °C for F51 · IMOA 1040 °C [1900 °F] min. · Outokumpu 1020-1100 °C · DEW (Acidur 4462) 1020-1100 °C · Penn Stainless 1020-1100 °C · Industeel 1040-1080 °C · Langley Alloys 1060-1120 °C · Rolled Alloys 1950 °F (1066 °C) min. · Sandmeyer 1900 °F (1038 °C) min. NO SINGLE FIGURE IS GIVEN AND NO AVERAGE IS TAKEN. Practical envelope: about 1020-1120 °C. THE SPECIFICATION FLOOR IS SEPARATE and it is the binding one.
Time
Rolled Alloys: ‘at least 10 minutes, or 30 minutes per inch of thickness’. Being a single source it is not treated as binding; the time is set by getting the whole section up to temperature. IMOA gives this measure: the holding time should be comparable to the total time the piece spent in the 650-980 °C range since its previous full anneal.
Cooling
QUENCHING IS MANDATORY — not a preference but a metallurgical requirement. ASTM A790 and A789 say ‘rapid cooling in air or water’; ASTM A815 says plainly ‘Water quench’ for S32205; ASTM A182 says ‘solution treat and quench’ and requires cooling in a liquid medium down to 260 °C [500 °F]. Sandmeyer says ‘followed by rapid cooling, ideally by water quenching’, Rolled Alloys ‘followed by a mandatory water quench’, and Industeel and DEW specify water quenching. THE PURPOSE is to pass through the 1000-600 °C band before intermetallic phases can form.
Resulting hardness
The ASTM A240 ceiling is 293 HBW (31 HRC). Langley Alloys gives ≤ 270 HB for bar and DEW ≤ 270 HB.
DEFENCE METAL
3 · AFTER WELDING — AN INTERMEDIATE-TEMPERATURE STRESS RELIEF IS FORBIDDEN
Step
3 · AFTER WELDING — AN INTERMEDIATE-TEMPERATURE STRESS RELIEF IS FORBIDDEN
Summary
The intermediate-temperature anneal that is routine on an austenitic stainless is not applied here; that anneal lands directly inside the sigma band.
Temperature
Where a heat treatment is required, a FULL SOLUTION ANNEAL is performed (the temperature of stage 2 above) followed by a rapid quench. ASTM A815 states the requirement for wrought fittings: ‘heat treatment shall be performed after welding and in accordance with the requirements of Table 1’ — for S32205 that is 1020-1100 °C and 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 293 HBW).
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: 2205 is a standard duplex; its sigma kinetics are SLOWER than those of the super duplex grades (S32750, S32760, S32550). IMOA puts the measure this way: ‘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.’ That means 2205 leaves a wider working margin in heavy sections and in welding than a super duplex does; a margin existing is not the same as the prohibition being lifted. Sources differ on where precipitation is fastest inside the sigma band: Rolled Alloys gives 1485 °F (807 °C) and Sandmeyer 1600 °F (871 °C) — NO SINGLE FIGURE IS GIVEN.
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 — heat input has a floor as well as a ceiling
SMAW, GTAW, GMAW, SAW and FCAW are all usable. The most commonly omitted point in duplex welding is this: heat input does damage when it is too low, not only when it is too high. With too little heat input the HAZ cools so fast that the ferrite formed on solidification cannot transform back to austenite, leaving an excessively ferritic zone with chromium-nitride precipitates. Too much heat input, or too slow a cooling rate, precipitates sigma and chi intermetallics instead. Mill sources give a working range of about 0.6–2.5 kJ/mm (15–63.5 kJ/inch) for 2205 and state it plainly: weld 2205 like 304L/316L, not like a nickel alloy — tiny stringer beads are undesirable. The maximum interpass temperature is 150 °C, and this is critical. Preheat is generally not recommended; at most about 100 °C simply to drive off surface moisture. Filler: ER2209 / E2209 — an over-alloyed (nickel-enriched) filler that compensates for the faster cooling of weld metal so enough austenite forms. Shielding gas: welding-grade argon, with up to 2% nitrogen optionally added to support austenite. Target ferrite/austenite balance: roughly 30–70% ferrite, verified by Ferrite Number per AWS A4.2 / EN ISO 8249. Do not stress relieve after welding: there is no safe stress-relief temperature below the solution-annealing temperature for duplex — every intermediate temperature risks sigma precipitation.
Heat treatment
Solution annealing: 1040–1120 °C, typically aiming at 1066–1080 °C, for at least 10 minutes (or about 30 minutes per 25 mm of thickness). Water quenching is mandatory and must follow immediately — if cooling is too slow the corrosion resistance falls markedly, and furnace cooling is definitely not recommended. Sigma / intermetallic precipitation band: about 700–950 °C (mill sources give 704–982 °C), and the cumulative time spent in that band during welding or repair is limited to 5 minutes. 475 °C embrittlement: 300–525 °C. Duplex cannot be hardened by heat treatment; its strength comes from the two-phase structure and from nitrogen. Standard delivery is solution annealed and water quenched.
Machining and forming
With HSS tooling, machinability is close to 316L; with carbide tooling it falls to roughly 65% of 316L. The work-hardening rate is high and, because sulphur is kept low, chip breaking is difficult. Rigid setups, sharp cutting edges and EP-additive cutting fluid are required. Hot forming: heat uniformly to 1120–1150 °C; do not forge below 930 °C; after forging, re-solution-anneal at a minimum of 1070 °C and quench rapidly. Cold forming: austenitic techniques apply, but because elongation is lower (25%) a more generous bend radius is needed — roughly 2 × plate thickness in press braking — with an intermediate anneal recommended after about 25% cold deformation.
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%
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.
AISI 318 / 2205 · Properties and Alternatives
DEFENCE METAL
Service temperature — note
The ASME ceiling is 315 °C (600 °F). That is not universal: German TÜV rules give ≤280 °C unwelded and ≤250 °C welded for 2205. The limit comes from 475 °C embrittlement, which develops faster in and near welds. European-code projects may have to work to a lower ceiling
Minimum temperature
Sources vary between −40 °F and −50 °F; low-temperature use is qualified by Charpy impact testing, not by a single blanket figure
Yield strength
450 MPa (65 ksi) — more than double that of 316L (~170 MPa). Down-gauging is the grade’s principal commercial justification
Chloride stress-corrosion cracking
Duplex’s headline advantage over the austenitics: where 304 and 316 are weak in hot chlorides, 2205 is highly resistant
Pitting resistance (CPT)
Sources diverge by test method: one mill gives 35 °C, while the duplex industry guide gives 50–60 °C in 6% FeCl₃ (about 30 °C for 316L). Always quote a CPT figure together with its test method
Thermal expansion
~13.0 ×10⁻⁶/K — markedly below the ~16.4 ×10⁻⁶/K of austenitic 304/316. A real advantage in mixed-material designs and thermal cycling
Magnetic
Ferromagnetic because of its ~50% ferrite. Annealed 316L, by contrast, is essentially non-magnetic
NACE MR0175 / ISO 15156
Recognised for sour service, subject to the applicable hardness and PREN limits
Typical applications
Chemical vessels and heat exchangers, flue-gas desulphurisation, pulp and bleaching equipment, food processing, oilfield piping, offshore pipelines, chemical tankers, structural bridge components
Should I write “S31803” or “S32205” on the purchase order?
Write “UNS S32205” — or explicitly “dual certified S31803/S32205” — not S31803 alone. S31803’s original specification allowed nitrogen as low as 0.08%, and industry experience showed that level can produce an excessively ferritic, chromium-nitride-laden heat-affected zone after welding, with reduced toughness and pitting resistance. S32205 tightened the nitrogen floor to 0.14% specifically to close that gap, and also nudged the chromium and molybdenum minimums up. Every major mill and service centre now makes standard “2205” dual-certified to both specifications and to the tighter S32205 chemistry — so specifying S32205 costs nothing extra and guarantees you are not handed an old heat that satisfies S31803 but not the weld-proven S32205 band.
Can 2205 simply be dropped in to replace 316L?
Not as a drop-in without re-engineering. 2205 offers roughly double 316L’s yield strength (450 MPa against ~170 MPa) and a markedly higher PREN (≈35 against ≈24–25), giving materially better resistance to chloride pitting, crevice attack and stress-corrosion cracking — real advantages that often justify the switch. But 2205 is harder to machine (about 65% of 316L with carbide tooling), work-hardens faster, needs more generous cold-forming radii, is magnetic (annealed 316L is not), and its ASME-recognised service ceiling of 315 °C is below 316L’s practical high-temperature range. Welding procedures, filler metal (over-alloyed 2209-type), heat-input control and post-weld inspection (ferrite balance) also differ substantially from 316L practice. Treat it as a deliberate substitution requiring design and fabrication-procedure review.
What is 2205’s real temperature ceiling, and why?
Mill literature and ASME both recognise 315 °C (600 °F) as the practical maximum continuous service temperature. Above roughly 300–525 °C duplex stainless steels are susceptible to “475 °C embrittlement”, a slow intermetallic precipitation process that reduces toughness over time — less severely than in fully ferritic steels, because the austenite phase retains ductility, but still decisively. Some jurisdictions are stricter: German TÜV rules cap 2205 at 280 °C unwelded and only 250 °C for welded components, because welds are more susceptible to intermetallic formation near this range. Quote 600 °F / 315 °C as the ASME figure, but flag that welded assemblies, or European-code projects, may need to work to a materially lower ceiling — always check the governing code before finalising a design temperature.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip · UNS S32205
293 HBW max. · 31 HRC max.
450
655
25%
ASTM A240 / ASME SA-240 · plate, sheet and strip · UNS S31803
293 HBW max. · 31 HRC max.
450
620
25%
ASTM A479 / ASME SA-479 · bar and shapes · UNS S32205
290 HBW max.
450
655
25%
ASTM A479 / ASME SA-479 · bar and shapes · UNS S31803
290 HBW max.
450
620
25%
ASTM A276 / ASME SA-276 · bar and shapes · UNS S31803 (Condition A)
ASTM A790 / SA-790 (pipe) and A789 / SA-789 (tube) · UNS S32205
—
450
655
25%
ASTM A790 / SA-790 (pipe) and A789 / SA-789 (tube) · UNS S31803
—
450
620
25%
EN 10088 · 1.4462 bar (DEW Acidur 4462, solution annealed)
270 HB max.
450
650-880
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, UNS NUMBER and PRODUCT FORM, not by ageing condition; there is NO condition column such as H900 or H1075. NOTE: the tensile minimum of S32205 and S31803 IS NOT THE SAME (655 against 620 MPa); the yield minimum is 450 MPa for both. That is why the rows are given separately. COLD-WORKED TEMPERS ARE NOT IN THIS TABLE. 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 S32205 and S31803 rows are given separately; the two are not equivalent.
