S31254 Stainless Steel vs. S32205 Stainless Steel

1. Indledning

Corrosion-resistant alloys underpin critical infrastructure—from offshore platforms to chemical-processing plants.

As service environments grow more aggressive, selecting the right stainless grade proves vital.

In particular, duplex 2205 (UNS S32205) and super-austenitic 254 SMO (UNS S31254) occupy leading roles where chloride, acid or sour-gas attack threatens asset integrity.

Følgelig, this article delivers a professional, data-driven comparison of stainless steel S32205 vs S31254,

structured to guide engineers and specifiers through chemistry, microstructure, Mekanisk ydeevne, corrosion behavior, fabrication, Varmebehandling, applikationer, and relevant standards.

2. Chemical Composition & Microstructure

Element	S32205 (2205)	S31254 (254 SMO)
Cr	22.0–23.0 wt%	20.0–22.0 wt%
I	4.5–6.5 wt%	17.0–19.0 wt%
Mo	2.5–3.5 wt%	6.0–7.0 wt%
N	0.08–0.20 wt%	0.24–0.32 wt%
Cu	0.50 max	—
Mn	2.00 max	2.00 max
Og	1.00 max	1.00 max
C	0.03 max	0.02 max

Desuden, S32205 exhibits a roughly 50/50 ferrite–austenite duplex microstructure, which confers high strength and good toughness.

I modsætning hertil, S31254 forms a fully austenitic matrix stabilized by its high nickel (≈18 wt%) and nitrogen (up to 0.32 wt%).

Som et resultat, grain sizes in S31254 tend to remain uniform under heat, while 2205’s dual phases resist localized deformation.

Desuden, S31254’s elevated molybdenum and nitrogen boost inclusion control and suppress sigma-phase formation, enhancing long-term corrosion resistance.

3. Mechanical Properties Comparison

Property	S32205	S31254
Yield Strength (Rp0.2)	~450 MPa	~300 MPa
Trækstyrke (Rm)	~650 MPa	~650 MPa
Elongation (A%)	≥25 %	≥40 %
Reduction of Area (Z%)	≥50 %	≥60 %
Impact Toughness (Charpy V)	≥150 J @–40 °C	≥100 J @–20 °C
Creep Resistance	Up to 300 °C service	Up to 350 °C service

At room temperature, S32205 delivers superior yield strength—approximately 450 MPa versus S31254’s 300 MPa—thanks to its duplex phase hardening.

Nevertheless, both alloys reach similar tensile strengths (~650 MPa). In addition, S31254 boasts higher ductility (40 % elongation) and reduction of area (60 %), which facilitate deep drawing and complex forming.

When operating at elevated temperatures, S31254 maintains creep resistance up to 350 °C, while S32205 typically limits service to around 300 °C.

Finally, fatigue tests in chloride environments reveal comparable S–N curves, although S31254 shows a slight edge in high-cycle fatigue due to its homogeneous austenitic matrix.

4. Corrosion Resistance of S32205 vs. S31254

Corrosion Mode	S32205 (PREN ≈ 35)	S31254 (PREN ≈ 49)
Pitting	Chloride threshold ~0.8 wt% NaCl	~3.5 wt% NaCl
Crevice	Moderate	Excellent
Chloride SCC	50–60 °C	70–80 °C
General Acidic Corrosion (H₂SO₄)	~10 mm/year @ 20 °C	~2 mm/year @ 20 °C
Oxidizing Acids (HNO₃)	Good	Superior
Sulfide SCC (SSC)	Risk at H₂S > 1 bar	Minimal up to 5 bar H₂S

Because PREN (Pitting Resistance Equivalent Number = Cr + 3.3 Mo + 16 N) correlates with localized‐corrosion resistance, S31254 (PREN ≈ 49) outperforms S32205 (PREN ≈ 35).

Følgelig, S31254 tolerates chloride levels up to 3.5 wt% at ambient temperature without pitting, whereas 2205 caps out around 0.8 wt%.

Desuden, S31254 resists chloride stress-corrosion cracking (SCC) up to 80 °C, compared to 60 °C for S32205.

In addition, aggressive reducing acids (F.eks., 10 wt% H₂SO₄) corrode S32205 at ~10 mm/year, but only ~2 mm/year attacks S31254 under the same conditions.

Finally, sour-gas tests reveal S31254’s superior performance in H₂S service up to 5 bar, while S32205 shows SSC susceptibility above 1 bar.

5. Fabrication & Weldability of S32205 vs. S31254

Aspect	S32205	S31254
Cold Work	Up to 30% thickness reduction	Up to 50%
Min. Bend Radius	3 × thickness (duplex constraints)	2 × thickness
Weld Heat Input	0.5–1.5 kJ/mm; risk of sigma phase if >2	1.0–2.5 kJ/mm; maintained austenite resists cracking
Post-Weld Annealing	1020 °C × 30 min	1100 °C × 15 min
Bearbejdningsevne	40 – 50 % of 304 SS; tool wear moderate	30 – 40 % of 304 SS; tool wear higher

I praksis, S31254 tolerates more severe cold working—up to 50 % area reduction—due to its austenitic ductility, while S32205 work-hardens faster, limiting reduction to 30 %.

During bending, engineers maintain a minimum radius of 3 × thickness for 2205 to avoid ferrite cracking; in contrast, S31254 allows tighter bends at 2 × thickness.

Welding 2205 requires heat inputs between 0.5 og 1.5 kJ/mm to preserve the duplex balance; excessive heat (>2 kJ/mm) risks sigma-phase formation.

Meanwhile, 254 SMO’s fully austenitic structure tolerates up to 2.5 kJ/mm without cracking.

After welding, 2205 benefits from solution annealing at 1020 °C for 30 minutes, whereas S31254 calls for 1100 °C for 15 minutes to redissolve nitrides.

Finally, machinability tests rank S32205 at 40–50% of 304 SS’s material-removal rate, while S31254 runs slightly slower (30–40%) and accelerates tool wear due to its high Mo content.

6. Comparison of Heat Treatment Methods

Treatment	S32205	S31254
Solution Annealing	1020 °C × 15–30 min → water quench	1100 °C × 10–20 min → water or air quench
Stress Relief	600–650 °C × 1 h	650–700 °C × 1 h
Aging	Avoid above 300 °C (σ-phase risk)	Stable up to 400 °C; limited aging

To restore the optimal duplex balance in S32205 after forming or welding, metallurgists perform solution annealing at 1020 °C for 15–30 minutes, followed by a water quench.

I modsætning hertil, S31254 requires a higher solution-anneal temperature of 1100 °C for 10–20 minutes, with either water or air quenching to retain its austenitic structure.

When stress relief proves necessary (F.eks., after heavy fabrication), 2205 demands 600–650 °C for one hour, while S31254 tolerates 650–700 °C without adverse phase changes.

Finally, aging studies show that S32205 may form harmful sigma phase if held above 300 °C for prolonged periods, whereas S31254 remains stable up to 400 °C, reducing the need for low-temperature stress-relief cycles.

7. Industry Applications of S32205 vs. S31254

Petrochemical & Offshore Platforms:

Engineers specify S32205 for jackets and topsides when moderate chloride exposure and high strength matter.

Imidlertid, platforms facing severe splash-zone salinity lean on S31254’s superior pitting and SCC resistance.

Desalination Plants & Seawater Handling:

In reverse-osmosis membranes and piping, S31254’s PREN (~49) withstands continuous contact with seawater (3.5 wt% NaCl), whereas S32205 (PREN ~35) functions best in feedwater stages with lower salinity.

Chemical-Processing Equipment:

Heat exchangers handling hot H₂SO₄ (10–20 wt%) favor S31254 for its low corrosion rates (~2 mm/year).

Conversely, S32205 suits less aggressive services—such as brine coolers—where its higher strength reduces wall thickness.

Real-World Performance:

A North Sea platform retrofit replaced aged 2205 risers with 254 SMO, cutting pitting repairs by 80%.

Meanwhile, a petrochemical plant reports five years of trouble-free service in 3 % HCl with duplex 2205 condensers.

8. Reference Standards

• ASTM A240/A240M: “Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications”
• ASTM A182/A182M: “Standard Specification for Forged or Rolled Alloy- and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service”
• UNS Designations: S32205 (duplex 2205), S31254 (254 SMO)
• NACE MR0175/ISO 15156: “Materials for Use in H₂S-Containing Environments in Oil and Gas Production”

9. Equivalent Grades

Below is a compiled list of common international equivalents for UNS S32205 (Duplex 2205) and UNS S31254 (254 SMO), facilitating cross‐reference between major standards bodies.

Notes on Equivalents

• DIN Designation—for example, “1.4462” for 2205—appears alongside the steel’s chemical symbol (X2crminnan22-5-3), where “22-5-3” denotes nominal Cr-Ni-Mo-N levels.
• AFNOR (French) grades use a Z-prefix: “Z3CN22-05-03” mirrors 2205’s 22 % Cr, 5 % I, 3 % Mo.
• JIS (Japanese) og GOST (Russian) designations reflect national numbering systems; the appended “L” in SUS329J4L indicates low-temperature impact toughness requirements.
• Chinese grades—0Cr22Ni5Mo3N and 0Cr25Ni20Mo3CuN—align closely with the UNS compositions, specifying carbon (0), Krom, nikkel, molybdenum and nitrogen content.

10. Comprehensive Comparison of S32205 vs. S31254

To bring all key differences into sharp relief, the table below summarizes chemistry, performance, fabrication and cost metrics for UNS S32205 (Duplex 2205) and UNS S31254 (254 SMO).

Criterion	S32205 (Duplex 2205)	S31254 (254 SMO)
Phase Structure	~50 % ferrite / 50 % austenite	100 % austenitic
Cr–Ni–Mo–N Chemistry	22 % Cr, 5 % I, 3 % Mo, 0.14 % N	20 % Cr, 18 % I, 6.5 % Mo, 0.28 % N
PREN	≈ 35	≈ 49
Yield Strength	450 MPA	300 MPA
Trækstyrke	650 MPA	650 MPA
Elongation	25 %	40 %
Charpy Toughness	≥ 150 J @ –40 °C	≥ 100 J @ –20 °C
Pitting Threshold	~ 0.8 % NaCl	~ 3.5 % NaCl
SCC Resistance	≤ 60 °C	≤ 80 °C
Creep Service Limit	≤ 300 °C	≤ 350 °C
Cold-Work Limit	30 % thickness reduction	50 % thickness reduction
Weld Heat Input	0.5–1.5 kJ/mm (avoid > 2.0)	1.0–2.5 kJ/mm
Solution Anneal	1 020 °C × 15–30 min → water quench	1 100 °C × 10–20 min → water or air quench
Cost Index	1.0 (base)	~ 1.4 (≈ 40 % premium)

Key Takeaways:

1. Strength vs. Korrosion: S32205 delivers higher yield strength (≈ 450 MPA) and excellent toughness, making it ideal for load-bearing parts.
   Imidlertid, its pitting resistance (PREN ≈ 35) limits chloride service to ~ 0.8 % NaCl.
2. Superior Corrosion Resistance: S31254’s elevated Mo and N boost PREN to ≈ 49, tolerating seawater (3.5 % NaCl) and resisting SCC to 80 °C, albeit at a 40 % higher material cost.
3. Fabrication Ease: The fully austenitic S31254 supports deeper cold working (50 % reduction) and wider welding windows (up to 2.5 kJ/mm),
   whereas the duplex grade requires more precise heat input to maintain its phase balance.
4. Thermal Stability: You can run S31254 at moderately higher temperatures (up to 350 °C) without aging risks, while S32205 remains stable up to about 300 °C.

11. Conclusions

S32205 and S31254 each deliver distinct advantages. By understanding their chemistry, microstructure, Mekanisk opførsel, corrosion performance, fabrication nuances, and heat-treatment windows, engineers can make informed, authoritative decisions.

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FAQS

What primary factors govern the choice between S32205 vs S31254?

I praksis, engineers weigh strength versus corrosion resistance. S32205 delivers higher yield strength (~450 MPa) at a lower cost,

while S31254 offers superior pitting resistance (PREN ≈ 49) and chloride-SCC resistance to 80 °C.

Can I cold-form S31254 more aggressively than S32205?

Ja. The fully austenitic structure of S31254 supports up to 50% thickness reduction, whereas S32205 work-hardens faster and typically limits cold reduction to 30% to avoid cracking.

What welding precautions apply to these grades?

For S32205, maintain heat input between 0.5–1.5 kJ/mm and perform solution annealing at 1 020 °C to restore duplex balance.

I modsætning hertil, S31254 tolerates 1.0–2.5 kJ/mm and calls for a 1 100 °C solution‐anneal to redissolve nitrides.

Which alloy performs better in sour‐gas environments?

In H₂S service, S31254 resists sulfide stress-cracking up to about 5 bar, while S32205 shows SSC susceptibility above 1 bar.

Therefore, 254 SMO often becomes the preferred choice for sour-gas applications.