1.4439 stainless steel (EN: X2CrNiMoN17-13-5, UNS: S31726, ASTM: 317LMN) is a nitrogen-enhanced, high-molybdenum austenitic stainless steel containing 16.5–18.5% Cr, 13.0–15.0% Ni, 4.0–5.0% Mo and 0.10–0.20% N. Its PREN (Pitting Resistance Equivalent Number) is typically above 40. It is solution annealed at 1,060–1,140°C with water quenching, achieves a minimum Rp0.2 of 270 MPa per EN 10222-5, and retains excellent impact toughness down to –196°C. Primary applications include chemical processing, desalination, offshore oil & gas, pulp & paper, pharmaceutical equipment, and flue-gas desulphurisation. Custom 1.4439 forgings are manufactured by Jiangsu Liangyi Co., Limited — ISO 9001:2015 certified, based in Jiangyin, Jiangsu, China — supplied from 30 kg to 30,000 kg per piece with EN 10204 inspection documents.
Why engineers specify 1.4439 — and why many discover it too late
If you are specifying stainless steel forgings for environments where standard 316L does not hold up — chloride-rich process streams, dilute sulphuric acid duty, seawater cooling circuits, or pulp bleaching plants — 1.4439 (X2CrNiMoN17-13-5) is the grade that consistently emerges in engineering discussions. Many engineers encounter it for the first time only after a failure investigation has identified 316L as under-specified for the service conditions.
This guide was prepared by Jiangsu Liangyi Co., Limited — an ISO 9001:2015 certified open-die forging manufacturer based in Jiangyin, Jiangsu, China — to provide a clear, technically grounded reference for engineers evaluating this material for forging applications. The data and process descriptions reflect published standard requirements (EN 10088-1, EN 10222-5) and general industry practice; they are informational in nature and should be verified against applicable project specifications and standards. If you are sourcing rather than researching, you can go directly to our 1.4439 stainless steel forging parts page for product specifications, available shapes, and to request a quotation.
EN numeric: 1.4439 · EN chemical: X2CrNiMoN17-13-5 · UNS: S31726 · ASTM: 317LMN · AFNOR: Z3CND18-14-05Az · Standard: EN 10088-1 / EN 10028-7 / ASME SA-240
What exactly is 1.4439 (X2CrNiMoN17-13-5) stainless steel?
1.4439 is a nitrogen-enhanced, high-molybdenum austenitic stainless steel standardised under EN 10088-1 and covered for pressure-vessel applications by EN 10028-7 and ASME SA-240 (as UNS S31726). It belongs to the same austenitic 300-series family as 316L (1.4404), but with two deliberate upgrades: a significantly higher molybdenum content — 4.0 to 5.0 wt% versus 316L's 2.0–2.5 wt% — and a mandatory nitrogen addition of 0.10–0.20 wt%.
That combination of elevated Mo and N is the reason 1.4439 achieves a PREN (Pitting Resistance Equivalent Number) typically above 40, placing it substantially ahead of 316L (PREN ≈ 24) and the higher-Mo grade 317L (PREN ≈ 32). A PREN above 40 is widely used in engineering practice as the threshold for highly pitting-resistant grades in seawater and aggressive chloride environments.
The chemical designation X2CrNiMoN17-13-5 is a compact technical summary: X = stainless steel; 2 = maximum carbon 0.02%; Cr17 = 16.5–18.5% chromium; Ni13 = 13.0–15.0% nickel; Mo = molybdenum present; N = nitrogen present; 5 = target molybdenum level around 5%.
Chemical composition of 1.4439 — element by element
The composition limits below are those defined by EN 10088-1. Values are for reference; always verify against the applicable standard revision and project specification.
| Element | Symbol | Range (wt%) | Primary metallurgical function |
|---|---|---|---|
| Carbon | C | ≤ 0.030 | Ultra-low to prevent sensitisation — Cr₂₃C₆ precipitation at grain boundaries during welding or slow cooling through 500–850°C |
| Chromium | Cr | 16.5 – 18.5 | Forms passive Cr₂O₃ film; primary corrosion barrier; largest contributor to the PREN formula |
| Nickel | Ni | 13.0 – 15.0 | Stabilises austenite phase; improves low-temperature toughness; raises resistance to reducing acids |
| Molybdenum | Mo | 4.0 – 5.0 | Key pitting and crevice corrosion inhibitor; raises PREN by 3.3×Mo; provides matrix strengthening at elevated temperature |
| Nitrogen | N | 0.10 – 0.20 | Interstitial solid-solution strengthener; raises PREN by 16×N; retards sensitisation; stabilises austenite against delta-ferrite |
| Silicon | Si | ≤ 1.00 | Melt deoxidant; improves high-temperature oxidation resistance |
| Manganese | Mn | ≤ 2.00 | Secondary austenite stabiliser; improves nitrogen solubility in the liquid melt |
| Phosphorus | P | ≤ 0.045 | Controlled tramp element — excessive P causes hot-shortness during forging |
| Sulphur | S | ≤ 0.030 | Controlled tramp element — limits MnS inclusion density and hot ductility loss |
Why nitrogen is the key differentiator between 1.4439 and 317L
Standard 317L contains elevated molybdenum but no mandatory nitrogen. The deliberate N addition in 1.4439 achieves four simultaneous benefits:
Mechanical properties of 1.4439 in the forged and solution-annealed condition
The values below are per EN 10222-5 for solution-annealed open-die forgings. Always verify against the applicable standard revision and project specification. Values are for sections up to 100 mm unless otherwise noted.
| Property | EN 10222-5 Minimum | Typical range | Test condition |
|---|---|---|---|
| 0.2% Proof Strength Rp0.2 | ≥ 270 MPa | 290 – 330 MPa | RT, solution annealed |
| 1.0% Proof Strength Rp1.0 | ≥ 310 MPa | 330 – 370 MPa | RT, solution annealed |
| Tensile Strength Rm | 580 – 800 MPa | 600 – 720 MPa | RT, solution annealed |
| Elongation A (gauge 5d) | ≥ 40% | 45 – 55% | RT |
| Reduction of Area Z | ≥ 50% | 60 – 70% | RT |
| Charpy Impact KV at –196°C | ≥ 100 J (average) | typically >120 J | 3×10×55 mm notched |
| Brinell Hardness | ≤ 215 HBW | 160 – 190 HBW | Solution annealed |
| Rp0.2 at 100°C | ≥ 218 MPa | approx. 230–260 MPa | Elevated temperature |
| Rp0.2 at 200°C | ≥ 186 MPa | approx. 200–225 MPa | Elevated temperature |
| Rp0.2 at 300°C | ≥ 167 MPa | approx. 180–205 MPa | Elevated temperature |
The nitrogen addition gives 1.4439 a room-temperature Rp0.2 appreciably higher than 316L (which typically achieves 220–250 MPa per EN 10222-5). Under EN 13445 or ASME VIII-1 pressure vessel design codes, higher allowable stress can translate to reduced required wall thickness for the same design pressure — partially offsetting the higher alloy cost in some applications. Always confirm allowable stresses with the applicable design code edition.
Corrosion resistance of 1.4439 — PREN and specific environments
The Pitting Resistance Equivalent Number is calculated as: PREN = %Cr + 3.3×%Mo + 16×%N
At mid-range composition (Cr 17.5%, Mo 4.5%, N 0.15%), the PREN calculation gives approximately 34.75 from Cr and Mo, plus 2.40 from N — placing typical production heats in the region of 40–50. This compares favourably with 316L (~24), 317L (~32), duplex 2205 (~34), and super-duplex 2507 (~43). Note that actual PREN values depend on the specific heat analysis and should be calculated from the certified chemical composition on the MTC.
PREN comparison — indicative values for common grades (higher = better pitting resistance in chloride environments)
General resistance to specific corrosive environments
Note: The following is general guidance based on published literature. Actual suitability depends on specific concentration, temperature, and flow conditions. Always consult corrosion engineers and verified isocorrosion diagrams for your application.
| Corrosive Environment | General Assessment | Notes |
|---|---|---|
| Seawater (aerated, flowing) | Generally suitable | PREN above 40 provides improved resistance; stagnant crevice conditions require careful joint design |
| Sulphuric acid, dilute (<10%) | Good resistance | Performance improves with higher Ni and Mo content versus 316L; verify at operating temperature |
| Phosphoric acid | Good resistance | Broad concentration range; commonly specified in phosphate processing |
| Organic acids (acetic, formic) | Good resistance | Generally low corrosion rates; verify at operating conditions |
| Pulp bleaching (ClO₂, hypochlorite) | Generally suitable | Improved resistance versus 316L; verify free chlorine concentration and temperature |
| Hydrochloric acid | Limited | Austenitic grades generally not recommended for HCl service above very low concentrations; consult corrosion specialist |
Heat treatment of 1.4439 stainless steel forgings
1.4439 forgings are supplied in the solution-annealed condition. No age hardening, precipitation hardening, tempering, or normalising cycle is applicable. Solution annealing parameters per EN 10222-5 are shown below; always refer to the applicable standard for mandatory requirements.
| Parameter | EN 10222-5 / Industry practice | Notes |
|---|---|---|
| Annealing temperature | 1,060 – 1,140°C | Higher than 316L due to elevated alloy content; ensures dissolution of Mo, N, and carbides |
| Hold time | ≥ 1 min/mm section, min 30 min | Soak time typically measured from when the forging thermocouple reaches set point |
| Cooling method | Rapid water quench | Air cooling is insufficient for sections above a few mm — sigma phase can re-precipitate |
| Furnace atmosphere | Neutral or slightly oxidising | Avoid sulphurous atmospheres; nitrogen/argon atmospheres acceptable |
Slow cooling through the 700–900°C range can allow sigma phase — a Cr- and Mo-rich intermetallic — to precipitate at grain boundaries, significantly reducing toughness and locally depleting the corrosion-resistant elements from the surrounding matrix. Rapid water quenching is required to avoid this. The specific quench delay acceptable depends on section size and furnace configuration; follow the requirements of EN 10222-5 and your applicable project specification.
Manufacturing 1.4439 forgings: 7-step process overview
1.4439 is more demanding to forge than standard 316L due to its elevated nitrogen and molybdenum content, which narrows the safe forging temperature window and increases forging load requirements. The following describes the general manufacturing approach used by Jiangsu Liangyi Co., Limited.
Melting and refining — EAF + LF + VOD
Steel is melted in an Electric Arc Furnace and refined through Ladle Furnace and Vacuum Oxygen Decarburisation to achieve the required ultra-low carbon and controlled nitrogen content. Electroslag Remelting (ESR) is available for orders requiring enhanced internal cleanliness and reduced macro-segregation in heavy sections.
Ingot homogenisation
Ingots are soaked at elevated temperature to homogenise alloy element segregation before forging. The forging temperature window for 1.4439 is narrower than for standard austenitic grades; working below approximately 950°C risks surface cracking, while excessively high start temperatures can cause localised melting of alloy-rich regions.
Open-die forging on hydraulic press
Jiangsu Liangyi Co., Limited operates hydraulic presses capable of producing 1.4439 forgings from 30 kg to 30,000 kg per piece. Sufficient forging reduction is maintained to break the cast dendritic structure and achieve mechanical property uniformity throughout the section.
Seamless ring rolling (for ring-type forgings)
Ring forgings are produced on CNC ring rolling mills. Controlling ring geometry and wall thickness uniformity in this high-alloy grade requires careful process monitoring throughout the rolling cycle.
Solution annealing and water quench
Performed per EN 10222-5 parameters: 1,060–1,140°C, minimum 1 min/mm section, followed by rapid water quench. Heat treatment records are maintained for traceability.
Non-destructive testing and dimensional inspection
Standard NDT includes Ultrasonic Testing (UT) per EN 10228-3 or ASTM A388, and Dye Penetrant Testing (PT) per EN 10228-2. Hardness testing is performed on all forgings. Additional testing such as radiographic testing or intergranular corrosion testing is available on request.
Inspection document issuance
Forgings are supplied with EN 10204 Type 3.1 inspection documents as standard, covering chemical analysis, mechanical test results, heat treatment records, and NDT results. EN 10204 Type 3.2 documents (with independent third-party inspector countersignature) are available upon request for projects where this is required by the applicable specification or purchasing authority.
Typical applications for 1.4439 stainless steel forgings
1.4439 is typically selected in applications where the combination of high PREN, low carbon, and reasonable yield strength advantage over standard austenitic grades provides clear benefit, and where the higher alloy cost is justified by the service conditions.
Chemical Processing
Pump casings, valve bodies, flange forgings, and agitator components for chloride-contaminated process streams, dilute sulphuric acid, and phosphoric acid service.
Desalination
High-pressure pump and valve forgings for SWRO and MED desalination plants, where seawater chloride concentrations and operating temperatures demand high PREN grades.
Oil & Gas / Offshore
Components for subsea and topside applications where chloride corrosion resistance and compliance with NACE MR0175 / ISO 15156 are specified requirements.
Pulp & Paper
Bleach plant equipment exposed to chlorine dioxide, hypochlorite, and hot acidic washwater in kraft pulping processes.
Pharmaceutical / Biotech
Process equipment and reactor components where CIP chemical resistance and low contamination risk are requirements alongside quality system compliance.
Flue Gas Desulphurisation
Absorber and scrubber components handling hot dilute sulphuric acid with entrained chlorides in FGD systems.
1.4439 vs. competing grades — selection matrix
The table below compares 1.4439 against grades most commonly evaluated alongside it. Values shown are indicative ranges based on published standards; verify all properties against applicable standard and heat-specific MTC data. Jiangsu Liangyi Co., Limited forges all grades listed below — see the linked product pages for individual specifications.
| Property | 316L / 1.4404 | 317L / 1.4438 | 1.4439 — This Grade | 2205 Duplex | 2507 S-Duplex |
|---|---|---|---|---|---|
| Mo content (%) | 2.0–2.5 | 3.0–4.0 | 4.0–5.0 | 3.0–3.5 | 3.5–4.5 |
| N content (%) | — | — | 0.10–0.20 | 0.10–0.22 | 0.24–0.32 |
| PREN (indicative) | ~24 | ~32 | ~40–50 | ~34 | ~43 |
| Rp0.2 at RT (min.) | ≥220 MPa | ≥230 MPa | ≥270 MPa | ≥450 MPa | ≥550 MPa |
| Toughness –196°C | Excellent | Excellent | Excellent | Limited | Limited |
| Weldability | Excellent | Good | Good | Good (controlled) | Moderate |
| Relative alloy cost | Reference | Higher | Significantly higher | Higher | Much higher |
General selection guidance
- Consider 1.4439 when the application requires both high PREN (above 40) and excellent cryogenic toughness — a combination that duplex grades do not satisfy.
- Consider 1.4439 over 317L when the nitrogen addition provides meaningful benefit for the specific application, particularly for yield strength and sensitisation resistance in welded construction.
- Consider duplex 2205 when high strength is the primary driver and service temperatures remain above –50°C.
- Consider 316L when chloride content and temperature are within the normal range for that grade, and the higher alloy cost of 1.4439 is not justified by the service conditions.
See also: 1.4439 vs. 1.4432 vs. 1.4404 — Choosing the Right Molybdenum-Grade Stainless Steel →
Welding 1.4439 stainless steel forgings
1.4439 is weldable by TIG (GTAW), MIG (GMAW), and MMA (SMAW). The following guidance is general; always develop and qualify welding procedures in accordance with EN ISO 15614-1 or ASME IX as applicable to your project, and engage a qualified welding engineer.
- Filler metal: AWS ER317LMN / EN 19 12 5 NL — matching or overmatching the Mo and N content of the base metal. 316L filler should not be used as it significantly under-matches the corrosion performance in the weld fusion zone.
- Pre-heat: Generally not required for solution-annealed sections in the normal thickness range. Verify with the applicable welding procedure and WPS.
- Interpass temperature: Keep below 150°C to limit sigma phase risk in multi-pass welds.
- Post-weld heat treatment: If PWHT is required, only full solution anneal at 1,060–1,100°C followed by rapid water quench is applicable. Sub-critical stress relief in the 650–900°C range is contraindicated and will cause sigma phase and carbide precipitation.
- Shielding gas: Argon or Ar/He mixtures for TIG. Consult the filler wire manufacturer for back-purge gas compatibility with nitrogen-alloyed filler wires.
Common questions about 1.4439 stainless steel
1.4439 (EN chemical designation X2CrNiMoN17-13-5, UNS S31726, ASTM 317LMN) is a nitrogen-enhanced, high-molybdenum austenitic stainless steel per EN 10088-1. It contains 16.5–18.5% Cr, 13.0–15.0% Ni, 4.0–5.0% Mo, and 0.10–0.20% N. Per EN 10222-5, solution-annealed forgings achieve a minimum Rp0.2 of 270 MPa, tensile strength of 580–800 MPa, and Charpy impact toughness at –196°C of at least 100 J average. Its PREN is typically in the range of 40–50 depending on the specific heat analysis.
Yes, they refer to the same alloy family. 317LMN is the ASTM/UNS informal designation; the UNS number is S31726. EN 1.4439 (per EN 10088-1) and ASTM 317LMN are functionally equivalent, though the exact composition limits at the margins differ slightly between the European and American standards. For dual-standard projects, request dual-standard inspection documents to confirm compliance with both specifications rather than assuming automatic equivalence.
PREN = %Cr + 3.3×%Mo + 16×%N. At typical mid-range composition (Cr 17.5%, Mo 4.5%, N 0.15%), the calculated PREN is approximately 17.5 + 14.85 + 2.40 = 34.75 from Cr and Mo alone, with the N contribution bringing the total to approximately 37–50 depending on the actual heat composition. The precise PREN for a specific heat should be calculated from the certified chemical analysis on the MTC.
Yes. The fully austenitic FCC crystal structure means 1.4439 does not exhibit a ductile-to-brittle transition at cryogenic temperatures. EN 10222-5 specifies a minimum Charpy impact value of 100 J average at –196°C for solution-annealed forgings. It is commonly specified for cryogenic pump and valve forgings in LNG and industrial gas service. Verify applicable qualification requirements with the relevant design code (EN 13445, ASME VIII, etc.).
Solution anneal at 1,060–1,140°C for a minimum of 1 minute per mm of section thickness (minimum 30 minutes), followed by rapid water quench. Stress-relief annealing in the 650–900°C range must not be applied — it causes sigma phase and carbide precipitation that degrades both toughness and corrosion resistance. Refer to EN 10222-5 for mandatory heat treatment requirements.
1.4439 austenitic stainless steel is listed in ISO 15156-3 / NACE MR0175. In the solution-annealed condition the hardness is generally well within the standard's limit. Users are responsible for verifying that their specific application conditions (H₂S partial pressure, chloride content, temperature, pH) fall within the limits prescribed in the applicable table of ISO 15156-3, and for confirming compliance with the applicable version of the standard.
The recommended filler wire classification is AWS ER317LMN (GTAW/GMAW) or the equivalent EN 19 12 5 NL classification — matching or overmatching the Mo and N content of the base metal. Using 316L filler (AWS ER316L) produces a weld zone with significantly lower Mo content and PREN, creating a preferential corrosion site in chloride service. Welding procedures should be qualified per EN ISO 15614-1 or ASME IX as applicable.
Yes. Jiangsu Liangyi Co., Limited supplies 1.4439 forgings with EN 10204 Type 3.1 inspection documents as standard. EN 10204 Type 3.2 documents — where the inspection document is countersigned by an independent third-party inspection authority — are available upon request where required by the purchasing specification. Please confirm this requirement at the time of enquiry so that it can be arranged and costed accordingly.
Enquire About 1.4439 Forgings from Jiangsu Liangyi Co., Limited
ISO 9001:2015 certified open-die forging manufacturer based in Jiangyin, Jiangsu, China. Custom 1.4439 forgings from 30 kg to 30,000 kg per piece. EN 10204 3.1 / 3.2 inspection documents. Contact us with your drawing or specification for a quotation.