Chengchang Industry Park, Jiangyin, Jiangsu, China
Written by the engineering team at Jiangsu Liangyi Co., Limited — an ISO 9001:2015 certified open-die forging manufacturer established in 1997, located in Jiangyin, Jiangsu, China. We manufacture Alloy 24 (UNS S34565) forged rings, bars, flanges, and custom forgings for oil & gas, chemical, and marine industries worldwide. All technical data in this article is sourced from publicly available standards including ASTM A182 and EN 10222-5. Learn more on our custom Alloy 24 (UNS S34565) open die forgings and seamless rolled rings.
1. Overview & Designations
Alloy 24 is a nitrogen- and molybdenum-alloyed superaustenitic stainless steel engineered for corrosion-critical environments where conventional 316L or duplex stainless steels cannot perform. Originally developed for the demanding conditions of seawater desalination, flue gas desulfurization (FGD), and offshore oil and gas, Alloy 24 delivers an exceptional combination of mechanical strength, crevice corrosion resistance, and weldability at a significantly lower cost than higher-nickel equivalents such as Alloy 31 or Hastelloy C-276.
The alloy's high manganese content (5–7%) enables very high nitrogen solubility in the austenite matrix. This nitrogen — at 0.40–0.60%, among the highest of any standard wrought stainless steel — simultaneously raises the Pitting Resistance Equivalent Number (PREN) above 45 and strengthens the alloy through solid-solution hardening, while the material remains fully austenitic from −196°C to +400°C.
Engineers and procurement teams will encounter this alloy under the following equivalent international designations — all referring to the same material:
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Table 1 — Equivalent international designations for Alloy 24 (UNS S34565)
Standard / Body
Designation
Product Scope
Region
UNS (Unified Numbering System)
S34565
All wrought product forms
USA / Global
EN / DIN (European Norm)
1.4565
Pressure vessels, forgings
Europe
ASTM A182 (Forgings)
F49
Pipe flanges, fittings, valves
USA / Global
ISO / EN Chemical Name
X2CrNiMnMoN25-18-6-5
Chemical composition descriptor
International
Trade Name
Alloy 24 / Alloy24
All product forms
Industry-wide
Specification Tip
Always use UNS S34565 or ASTM A182-F49 on purchase orders and inspection documents. "Alloy 24" is a trade name and may be interpreted differently across suppliers and certification bodies.
2. Chemical Composition
The defining feature of Alloy 24 (UNS S34565) is its carefully balanced, high-alloy chemistry. Elevated manganese and nitrogen contents replace some of the nickel typically used to stabilize austenite, while the high chromium and molybdenum levels together with nitrogen create an outstanding passive film against chloride attack. All values below are per ASTM A182-F49 and EN 10222-5.
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Table 2 — Chemical composition requirements for Alloy 24 (UNS S34565 / 1.4565) per ASTM A182-F49
Element
Symbol
Min (%)
Max (%)
Function in the Alloy
Carbon
C
—
0.030
Ultra-low C prevents weld sensitization and intergranular corrosion
Silicon
Si
—
1.00
Deoxidizer; limited to avoid embrittlement
Manganese
Mn
5.00
7.00
Stabilizes austenite; enables very high nitrogen solubility in the melt
Phosphorus
P
—
0.030
Controlled impurity
Sulfur
S
—
0.010
Low S improves corrosion resistance and weldability
Chromium
Cr
23.0
25.0
Primary passive film former; critical PREN contributor
Nickel
Ni
17.0
19.0
Austenite stabilizer; improves general corrosion resistance
Molybdenum
Mo
4.00
5.00
Dramatically boosts pitting and crevice corrosion resistance (PREN factor: 3.3×)
Nitrogen
N
0.40
0.60
Raises PREN by 16× per percent; provides solid-solution strengthening
Copper
Cu
—
1.00
Improves resistance to reducing acids such as dilute H₂SO₄
Why Nitrogen Is Alloy 24's Key Differentiator
At 0.40–0.60% N, Alloy 24 carries one of the highest intentional nitrogen additions of any commercial wrought stainless steel. The high manganese content is what makes this possible — Mn dramatically increases nitrogen's solubility in liquid steel. This enables PREN values above 45 while providing 30–40% higher yield strength than conventional 316L through solid-solution hardening — without any loss of ductility or toughness.
3. Mechanical Properties
In the solution-annealed and water-quenched condition, Alloy 24 (UNS S34565) significantly outperforms standard 316L in yield and tensile strength while retaining excellent ductility down to cryogenic temperatures. The values below represent minimum guaranteed properties per ASTM A182-F49 for forged product forms.
Tensile Strength (min)
650
MPa / 94 ksi
0.2% Proof Stress (min)
320
MPa / 46 ksi
Elongation A5 (min)
35%
Gauge length 5d
Hardness (max)
250
HBW
Charpy Impact (min)
≥100
J at −196°C
Max. Service Temp.
400
°C (per EN 10222-5)
Cryogenic Performance Down to −196°C
Alloy 24 retains its fully austenitic, non-magnetic microstructure down to −196°C with no martensitic transformation. Impact energy remains ≥100 J at liquid nitrogen temperature, making it suitable for LNG and cryogenic storage applications per EN 10222-5 without special additional impact testing qualifications.
4. Corrosion Resistance & PREN
The dominant reason engineers specify Alloy 24 (UNS S34565) over conventional stainless steels is its outstanding resistance to chloride-induced corrosion. This resistance is quantified using the Pitting Resistance Equivalent Number (PREN) — a calculated index that combines the contributions of chromium, molybdenum, and nitrogen to passive film stability.
Table 3 — Corrosion resistance summary for Alloy 24 (UNS S34565) by mechanism
Corrosion Mechanism
Performance
Typical Environments
Pitting Corrosion
Excellent
Seawater, chlorinated process water, brine, FGD slurry
Crevice Corrosion
Excellent
Flanged joints, tube sheets, heat exchangers
Stress Corrosion Cracking (SCC)
Excellent
Hot chloride solutions where 304/316 fail
Intergranular Corrosion
Excellent
Post-weld zones; low C prevents carbide precipitation
Sour Gas (H₂S + Cl⁻)
Excellent
Oil & gas wellheads, subsea service
Reducing Acids (H₂SO₄, HCl)
Good
Dilute concentrations; verify per specific service conditions
Oxidizing Acids (HNO₃)
Good
Moderate concentrations; test above 60% concentration
Alkaline / Caustic
Excellent
NaOH, bleach solutions in pulp & paper
5. Forging Process & Heat Treatment
Producing premium-quality Alloy 24 (UNS S34565) forged parts requires careful control of temperature, press capacity, and post-forge heat treatment at every stage. The high nitrogen content makes the alloy approximately 20–30% stiffer than conventional 304 or 316 grades under forging conditions, requiring greater press tonnage — but the resulting fine-grained microstructure delivers mechanical and corrosion properties that are consistently superior to cast equivalents.
01
Ingot Preparation & Melting Route
Standard Alloy 24 ingots are produced via EAF + AOD (Electric Arc Furnace + Argon Oxygen Decarburization), with nitrogen precisely controlled during the AOD step to reach 0.40–0.60%. For critical pressure service applications, VIM + ESR (Vacuum Induction Melting + Electroslag Remelting) may be specified to minimize segregation and achieve tighter nitrogen control. The melting route should be declared on the material test certificate.
02
Heating & Soaking (1150°C – 950°C)
Billets are heated uniformly to the upper forging temperature range (start: 1150°C). Soaking time should be sufficient based on the section thickness to ensure complete temperature homogeneity through the billet before forging begins, preventing cold spots that would cause cracking during pressing.
03
Forging Operations
Alloy 24 is open-die or closed-die forged using hydraulic presses or forging hammers. Seamless ring rolling machines are used for ring products. All forging must be completed above 950°C — working below this temperature risks precipitation of sigma or chi phase in the microstructure, which reduces toughness and corrosion resistance. A minimum forge ratio of 3:1 for round bars is recommended to ensure adequate grain refinement.
04
Solution Annealing (1050°C – 1150°C) — Mandatory
After forging, all Alloy 24 components must undergo solution annealing at 1050–1150°C for sufficient time to fully dissolve sigma phase, carbides, and any intermetallic precipitates formed during the forging sequence. This step is non-negotiable — omitting or under-running solution annealing will degrade the corrosion resistance of the finished part.
05
Water Quenching
Immediately after solution annealing, components are water-quenched to freeze the fully austenitic microstructure and prevent sigma-phase re-precipitation during cooling. Air cooling is only acceptable for very thin sections. For heavy sections, confirm that the cooling rate through the 900–700°C range is sufficient to prevent sigma precipitation.
06
Final Inspection & Documentation
Finished forgings undergo dimensional inspection, visual and surface examination, non-destructive examination (NDE) as specified in your purchase order, chemical composition verification, and mechanical testing. Material test certificates (MTC) are issued in accordance with your contractual requirements.
About Jiangsu Liangyi Co., Limited
Established in 1997 and ISO 9001:2015 certified, we operate from an 80,000 m² production facility in Jiangyin, Jiangsu, China, equipped with advanced hydraulic presses and ring rolling machines. We produce open-die forgings and seamless rolled rings in Alloy 24 (UNS S34565) and many other specialty alloys, from 30 kg to 30,000 kg, with annual capacity of 120,000 tons. View our full range of Alloy 24 forged rings, round bars, flanges, and custom shapes for dimensional specifications and available product forms.
6. Applicable Standards & Certifications
Alloy 24 (UNS S34565) forged parts are manufactured and inspected to recognized international standards. The following are the key standards buyers should specify in their purchase orders. Note that Jiangsu Liangyi Co., Limited holds ISO 9001:2015 quality management system certification. Any additional third-party product certification (such as EN 10204-3.2, PED, or NACE compliance) should be confirmed with us at the inquiry stage, as it depends on the specific order and customer requirements.
ASTM A182 / A182M — Grade F49: The primary product standard for Alloy 24 forged pipe flanges, fittings, valves, and other pressure components. Specifies composition, heat treatment, mechanical testing, and inspection requirements. Reference this on all purchase orders for forged Alloy 24.
EN 10222-5:2017: European standard covering steel forgings for pressure purposes — austenitic and duplex stainless steels. Covers grade 1.4565 (Alloy 24) for service from −196°C to +400°C. Required for CE-marked pressure equipment in the EU.
ASTM A388 / EN 10228-3 (Ultrasonic Testing): Ultrasonic examination standards for forged steel. The specific acceptance class should be specified in your purchase order. Always request the full UT scan record, not just a conformance statement. Availability of in-house or third-party UT should be confirmed with the supplier at inquiry stage.
EN 10204 — Material Test Certificates: Type 3.1 = test results certified by the manufacturer's own authorised inspector. Type 3.2 = additionally certified by an independent third-party inspector. Specify which type you require in your purchase order, and confirm availability with the supplier before ordering.
NACE MR0175 / ISO 15156 (Sour Service): International standard for materials in sour (H₂S-containing) oil and gas environments. Alloy 24 (UNS S34565) may be applicable subject to compliance with hardness limits and heat treatment requirements specified in the standard. Buyers should verify applicability for their specific service conditions.
ASME BPVC Section II, Part D: Lists allowable stress values for pressure vessel design. Confirm the applicable S-values for UNS S34565 at your design temperature from the current edition of ASME BPVC.
ASTM G48 (Corrosion Testing): Standard method for evaluating pitting and crevice corrosion resistance. Specify G48 Method A or E when incoming corrosion testing is required. Confirm test availability at inquiry stage.
7. Industry Applications of Alloy 24 Forged Parts
Alloy 24 (UNS S34565) is the deliberate choice for service environments where corrosion-related failure is unacceptable. The following sectors represent the primary demand for Alloy 24 forged components worldwide:
Oil & Gas
Subsea connectors, wellhead flanges, sour gas valves, pump shafts, and pipeline fittings in chloride-rich or H₂S environments.
Seawater Desalination
Heat exchanger tube sheets, pump impellers, and valve bodies in SWRO and MSF plants exposed to concentrated hot brine.
Flue Gas Desulfurization
Absorber tower internals, spray nozzles, and agitator shafts handling hot SO₂-laden gases and chloride-rich slurries in power plants.
Chemical Processing
Reactor vessels, heat exchangers, pump casings, and piping flanges in HCl, H₂SO₄, and mixed acid service at elevated temperatures.
Pulp & Paper
Bleach plant equipment, washing drums, and ClO₂ generator components handling hypochlorite and chlorinated bleach environments.
Marine & Offshore
Deck fittings, sea chest valves, structural brackets, and pipe flanges subjected to seawater immersion or splash zone exposure.
Pharmaceutical
Process vessels and fittings where both corrosion resistance and cleanability are required alongside regulatory compliance.
Tunnel & Civil Construction
Structural fasteners and fittings in aggressive environments such as swimming pools and tunnels with de-icing chloride exposure.
8. Alloy 24 vs. Competing Grades
Material selection for corrosion-critical applications should consider the total lifecycle cost rather than the initial price per kilogram. The comparison below covers the most common alternative materials specified in similar applications:
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Table 4 — Technical comparison: Alloy 24 (UNS S34565) vs. common competing grades. Data sourced from published ASTM/EN standards.
Property
Alloy 24 / S34565
Duplex 2205 / S31803
Alloy 31 / N08031
316L / S31603
254 SMO / S31254
PREN (nominal)
~47
~35
~54
~24
~43
Tensile Strength (min, MPa)
650
620
500
480
650
Chloride SCC Resistance
Excellent
Good (limit ~80°C)
Excellent
Poor
Excellent
Cryogenic (−196°C)
Yes
No
Yes
Yes
Yes
Weldability
Good
Moderate
Good
Excellent
Good
Relative Material Cost
Medium-High
Medium
High
Low
High
When to Choose Alloy 24 Over Duplex 2205
If chloride concentration exceeds approximately 1,000 ppm, operating temperature is above 60°C, or there is a risk of stress corrosion cracking (hot condensates, steam environments), Alloy 24 is generally the more reliable choice. Duplex 2205 can be susceptible to SCC at elevated temperatures in chloride service — Alloy 24's fully austenitic, high-nitrogen microstructure avoids this limitation.
9. Sourcing & Quality Checklist
When sourcing Alloy 24 (UNS S34565) forged parts, thorough documentation and quality controls are essential. Use this checklist as minimum requirements in your RFQ and purchase order. Always confirm each item's availability with your supplier before placing the order — requirements vary by application and by the supplier's scope.
Material Test Certificate (MTC): Verify the reported chemical analysis meets all element limits in S34565. The MTC must explicitly reference your purchase order number, the applicable standard (ASTM A182-F49 or EN 10222-5), and the heat number traceable to the part. Specify whether you require EN 10204-3.1 or 3.2 in your order.
Non-Destructive Examination (NDE) Report: Specify the NDE method (e.g., UT, MT, PT) and the applicable standard and acceptance level in your purchase order. Request the full test record rather than a one-line pass/fail statement.
Heat Treatment Record: Written record of the solution anneal, including furnace identification, actual soak temperature (within ±10°C of target), hold time, and quench method. Water quench is required for sections over 25mm wall thickness.
Mechanical Test Report: Tensile (Rm, Rp0.2, elongation A5%), hardness (HBW), and Charpy impact energy (if specified) from the same heat and heat treatment batch as the delivered forgings. Reports should show actual values, not just pass/fail.
Dimensional Inspection Report: All critical dimensions per drawing or applicable standard tolerances. Include surface roughness (Ra) verification for sealing or hygienic applications where specified.
Forge Ratio Declaration: For bar, ring, and custom-shaped forgings, request the supplier to declare the achieved reduction ratio. Minimum 3:1 for bars is generally recommended to ensure adequate grain refinement.
Melting Route Statement: Confirm whether material was produced by AOD, VIM+ESR, or another route. For high-criticality applications, specify the required melting route in the purchase order.
Positive Material Identification (PMI): For safety-critical applications, specify PMI (XRF or OES) on delivered forgings to confirm alloy identity and detect potential material mix-ups.
Jiangsu Liangyi Co., Limited is an ISO 9001:2015 certified manufacturer. We can produce Alloy 24 forgings to ASTM A182-F49 and EN 10222-5 with material test certificates in accordance with your order requirements. Please visit our Alloy 24 (UNS S34565 / ASTM A182-F49) forged parts product page and contact us to discuss your specific documentation and certification requirements before placing your order.
10. Frequently Asked Questions
What is Alloy 24 (UNS S34565) and what makes it a superaustenitic stainless steel?
Alloy 24 (UNS S34565) is a nitrogen- and molybdenum-alloyed austenitic stainless steel classified as "superaustenitic" because its Pitting Resistance Equivalent Number (PREN) exceeds 40 — reaching approximately 46–47. It is distinguished from standard austenitic grades (like 316L, PREN ~24) by its high chromium (23–25%), molybdenum (4–5%), and nitrogen (0.40–0.60%) content. Alloy 24 remains fully face-centred cubic (FCC) austenite at all service temperatures from −196°C to +400°C.
Is Alloy 24 (UNS S34565) the same as 254 SMO or Alloy 31?
No — all three are superaustenitic stainless steels, but with distinct chemistries. 254 SMO (UNS S31254) contains 6% Mo and only 0.20% N, giving a PREN of approximately 43. Alloy 31 (UNS N08031) contains 6.5% Mo and 31% Ni, achieving PREN ~54 at considerably higher cost. Alloy 24 (UNS S34565) uses high manganese (5–7%) to enable very high nitrogen (0.40–0.60%) at moderate nickel (17–19%), achieving PREN ~47 at a competitive price point for most seawater, FGD, and chemical processing applications.
Can Alloy 24 be welded in the field, and does it need post-weld heat treatment?
Yes, Alloy 24 is weldable using TIG (GTAW), MIG (GMAW), or Submerged Arc (SAW) processes with matching or over-alloyed filler metal. The low carbon content (≤0.030%) prevents carbide precipitation and weld sensitization, so post-weld heat treatment is not required for most applications. However, solution annealing of the weld joint is recommended for service in highly aggressive chloride environments above 60°C to fully restore the corrosion resistance of the heat-affected zone.
What is the forging temperature range for Alloy 24, and why does it matter?
Alloy 24 (UNS S34565) must be forged in the temperature range of 950°C to 1150°C. The lower limit (950°C minimum) is critical — below this temperature, sigma phase and other intermetallic precipitates can form in the microstructure during deformation, drastically reducing both toughness and corrosion resistance. After forging, mandatory solution annealing at 1050–1150°C followed by water quenching removes any residual precipitates and restores the specified properties.
What certifications does Jiangsu Liangyi Co., Limited hold?
Jiangsu Liangyi Co., Limited is ISO 9001:2015 certified. We produce material test certificates (MTCs) in accordance with EN 10204-3.1 or EN 10204-3.2 depending on the order requirements. Third-party product certifications (such as PED, NACE, or specific classification society approvals) are available on request depending on the application — please contact us via our product page to discuss your specific certification requirements before placing your order.
Can Alloy 24 replace Hastelloy C-276 in chemical plants?
In many chloride-dominated applications, Alloy 24 can be a cost-effective alternative to Hastelloy C-276 where the primary corrosion mechanism is chloride pitting, crevice corrosion, or stress corrosion cracking. However, Hastelloy C-grades maintain their advantage in strongly oxidizing environments, concentrated HCl at elevated temperatures, and mixed acid service. Always evaluate the specific process chemistry and temperature and conduct corrosion coupon testing or consult published isocorrosion data before substituting materials in any pressure-containing service.
What is the difference between EN 10204-3.1 and EN 10204-3.2 for Alloy 24 forgings?
Both are material test certificate types under EN 10204. Type 3.1 = test results certified by the manufacturer's own authorised inspection representative. Type 3.2 = the same results additionally validated and countersigned by an independent third-party inspector (such as Bureau Veritas, Lloyds Register, or TÜV). For safety-critical applications, specify EN 10204-3.2 in your purchase order. Jiangsu Liangyi can produce both types — please confirm which is required at inquiry stage so we can include the appropriate inspection arrangement and costs in our quotation.
Need Alloy 24 (UNS S34565 / ASTM A182-F49) Forged Parts?
Jiangsu Liangyi Co., Limited — ISO 9001:2015 certified, established 1997, Jiangyin, China. We manufacture rings, round bars, flanges & custom forgings in Alloy 24 (UNS S34565) from 30 kg to 30,000 kg. Contact us to discuss your requirements and certification needs.