§01
What 1.4439 is, and when it is the right grade
1.4439 is a 17 % chromium, 13 % nickel, 4.5 % molybdenum austenitic stainless steel with a deliberate nitrogen addition of 0.12 to 0.22 %. It sits between 317L and the 6 % molybdenum super austenitics. The molybdenum buys resistance to chloride pitting and crevice attack; the nitrogen does three jobs at once. It stabilises austenite so the nickel content can stay moderate, it raises proof strength by roughly 80 MPa over 316L, and it contributes to pitting resistance at 16 times the weight of chromium in the PREN formula.
The carbon ceiling of 0.030 % is what makes 1.4439 usable as welded or as forged and welded without a sensitisation problem: there is not enough carbon to form a continuous chromium carbide network at the grain boundaries in the heat-affected zone.
Choose 1.4439 when
- 316L or 317L has pitted, and the failure analysis points at chlorides rather than reducing acid.
- The design needs a higher proof strength than 316L can offer without going duplex.
- Full austenitic ductility and impact toughness down to cryogenic temperature are required. 1.4439 has no ductile-to-brittle transition, and EN 10222-5 carries an impact requirement at −196 °C.
- The service temperature is above about 300 °C, where duplex grades are ruled out by 475 °C embrittlement.
- Non-magnetic behaviour matters; solution annealed 1.4439 is fully austenitic.
Choose something else when
- Sulphuric or phosphoric acid dominates. 904L, with its copper addition, is usually the better answer.
- Seawater at ambient temperature in a crevice-forming joint. Step up to ASTM A182 F44 / 254 SMO or AL-6XN at PREN above 40.
- Strength is the governing constraint and the temperature stays below 250 °C. A182 F51 / 2205 duplex gives more than double the proof strength at a similar PREN.
- Chloride stress corrosion cracking is the named risk. 1.4439 is more resistant than 304 or 316 but, like all standard austenitics, is not immune. Duplex or a nickel alloy is the safer route.
§02
Designations and governing standards for 1.4439
| System | Designation | Scope |
|---|---|---|
| EN steel number | 1.4439 | European numeric designation |
| EN steel name | X2CrNiMoN17-13-5 | European chemical designation |
| UNS | S31726 | Unified Numbering System, USA |
| AISI / trade | 317LMN | Common industry name |
| EN 10088-3 | 1.4439 | Bars, rods, sections and semi-finished products. The normal reference for forged bar |
| EN 10222-5 | 1.4439 | Steel forgings for pressure purposes, stainless steels (German national annex NB) |
| EN 10088-2 | 1.4439 | Sheet, plate and strip |
| ASTM A182 / A182M | F48 | Forged flanges, fittings, valves and parts for high-temperature service |
| ASTM A240 / A479 | S31726 | Plate and bar |
| Close relative | UNS S31725 (317LM, ASTM A182 F47) | Same Mo level without the nitrogen addition. Lower strength, lower PREN, not interchangeable |
ASTM A182 grade F48 covers UNS S31726; grade F47 covers UNS S31725. The two are one digit apart in the specification and easy to confuse on a purchase order.
§03
Chemical composition of 1.4439
EN 10088-3 and ASTM A182 do not specify the same chemistry for this alloy. The EN window for 1.4439 is narrower on chromium and nickel and slightly higher on nitrogen than the ASTM window for UNS S31726. A single heat satisfies both certificates only if it is aimed at the overlap.
| Element | EN 10088-3 · 1.4439 | ASTM A182 F48 · S31726 | Dual-certification aim |
|---|---|---|---|
| C | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Si | ≤ 1.00 | ≤ 0.75 | ≤ 0.75 |
| Mn | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| P | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S | ≤ 0.015 | ≤ 0.030 | ≤ 0.015 |
| Cr | 16.5 – 18.5 | 17.0 – 20.0 | 17.0 – 18.5 |
| Ni | 12.5 – 14.5 | 13.5 – 17.5 | 13.5 – 14.5 |
| Mo | 4.0 – 5.0 | 4.0 – 5.0 | 4.0 – 5.0 |
| N | 0.12 – 0.22 | 0.10 – 0.20 | 0.12 – 0.20 |
| Fe | Balance | Balance | Balance |
Why this matters on a purchase order. The dual-certification window above is roughly 1.5 points wide on chromium and 1.0 point wide on nickel. That is a tight melt aim, and it has to be set before the heat is tapped, and it cannot be recovered afterwards. If a 1.4439 forging needs both an EN and an ASTM stamp, say so on the enquiry, not on the order acknowledgement.
Product analysis tolerances to the relevant standard apply in addition to the cast analysis limits shown.
§04
Mechanical properties of 1.4439 forgings
All values below are for the solution annealed and quenched condition, which is the only delivery condition in which 1.4439 has the corrosion resistance the grade is bought for. Properties fall with increasing ruling section, the row that applies is set by the governing dimension of the forging, not by the finished part dimension.
EN 10088-3: bars, rods and sections
| Ruling section | Rp0.2 min | Rp1.0 min | Rm | A min | KV min | Hardness |
|---|---|---|---|---|---|---|
| ≤ 160 mm | 280 MPa | 315 MPa | 580 – 800 MPa | 35 % | 100 J | ≤ 250 HBW |
| 160 – 250 mm | 280 MPa | 315 MPa | 580 – 800 MPa | 30 % | 60 J | ≤ 250 HBW |
EN 10222-5: forgings for pressure purposes
| Property | Requirement |
|---|---|
| 0.2 % proof strength Rp0.2 | ≥ 285 MPa |
| 1.0 % proof strength Rp1.0 | ≥ 315 MPa |
| Tensile strength Rm | 580 – 800 MPa |
| Elongation A | ≥ 40 % |
| Impact energy KV at +20 °C | ≥ 100 J |
| Impact energy KV at −196 °C | ≥ 60 J |
| Solution treatment | 1060 – 1140 °C, water or air |
ASTM A182 grade F48 (UNS S31726)
| Property | Requirement |
|---|---|
| Tensile strength | ≥ 550 MPa (80 ksi) |
| Yield strength, 0.2 % offset | ≥ 240 MPa (35 ksi) |
| Elongation in 50 mm | ≥ 40 % |
| Reduction of area | ≥ 50 % |
| Heat treatment | ≥ 1040 °C (1900 °F), liquid quench to below 260 °C (500 °F) |
Note the direction of the difference: EN sets the higher proof-strength floor, ASTM the higher ductility floor. A forging released to EN 10088-3 alone will not automatically satisfy the A182 elongation requirement, and vice versa.
Physical properties at 20 °C
| Property | Value |
|---|---|
| Density | 8.0 g/cm³ (8,000 kg/m³) |
| Modulus of elasticity | 200 GPa |
| Thermal conductivity | 14 W·m⁻¹·K⁻¹ |
| Specific heat capacity | 500 J·kg⁻¹·K⁻¹ |
| Electrical resistivity | ≈ 0.85 Ω·mm²/m (published 0.75–0.85) |
| Coefficient of thermal expansion, 20–100 °C | ≈ 16 × 10⁻⁶ K⁻¹ |
| Magnetic response | Non-magnetic in the solution annealed condition |
Thermal conductivity is roughly a third that of carbon steel and the expansion coefficient is about 40 % higher, which is why 1.4439 tube sheets and heavy flanges need slower heating rates and more generous expansion allowance than a carbon steel equivalent of the same size.
§05
Corrosion resistance and PREN of 1.4439
The pitting resistance equivalent number for 1.4439 is calculated as PREN = %Cr + 3.3 × %Mo + 16 × %N, which gives 31.6 at the bottom of the EN composition window, 38.5 at the top, and about 35 for a mid-range heat. That places 1.4439 alongside 904L and 2205 duplex, comfortably above 316L, and below the 6 % molybdenum super austenitics.
| Grade | EN / UNS | Mo, % | N, % | PREN ≈ |
|---|---|---|---|---|
| 316L | 1.4404 / S31603 | 2.1 | 0.05 | 25 |
| 317L | 1.4438 / S31703 | 3.1 | 0.05 | 29 |
| 1.4439 | 1.4439 / S31726 | 4.5 | 0.17 | 35 |
| 904L | 1.4539 / N08904 | 4.3 | 0.06 | 35 |
| 2205 duplex | 1.4462 / S32205 | 3.1 | 0.16 | 35 |
| 254 SMO | 1.4547 / S31254 | 6.1 | 0.20 | 43 |
PREN values for the comparison grades are calculated from nominal compositions and published figures vary by a point either way. A 30 × %N variant of the formula is also in use, mainly for duplex grades, and gives higher numbers. PREN is a ranking index, not a qualification. It says nothing about reducing acids, stress corrosion cracking or crevice geometry, and a weld or a poorly quenched section will pit at a PREN the parent metal would survive.
Behaviour in service
Chloride pitting and crevice corrosion
The reason the grade exists. 1.4439 holds up in brackish water, chloride-bearing process streams and flue gas desulphurisation liquor where 316L pits within months.
Intergranular corrosion
With carbon held to 0.030 % maximum, 1.4439 passes ASTM A262 Practice E and ISO 3651-2 in the solution annealed condition and remains resistant after welding.
Sulphuric and phosphoric acid
Better than 316L across most of the dilute range, but without the copper addition of 904L. For concentrated reducing acid, specify 904L or a nickel alloy.
Chloride stress corrosion cracking
More resistant than 304 or 316 thanks to the higher nickel and molybdenum, but not immune. Above about 60 °C in chlorides under tensile stress, consider duplex.
Sigma and chi phase
At 4–5 % Mo, slow cooling through roughly 550–1000 °C precipitates intermetallics that destroy both toughness and pitting resistance. Rapid quench is mandatory.
Cryogenic service
Fully austenitic with no ductile-to-brittle transition. EN 10222-5 carries a 60 J minimum impact requirement at −196 °C for forgings.
§06
How 1.4439 forgings are made at this works
Most forging suppliers in China buy 1.4439 billet; Jiangyin Jiangnan Metal Co., Ltd. starts one step earlier, at the furnace. That matters for this grade in particular, because the two properties 1.4439 is bought for, the 0.030 % carbon ceiling and the 0.12–0.22 % nitrogen window, are set in the melt shop and not on the press.
Melting and refining
1.4439 runs through the 25 t electric arc furnace, is refined in a 25 t or 50 t ladle furnace, and is decarburised under vacuum in a 30 t or 60 t VOD unit. VOD is the step that makes this grade practical: it drops carbon to below 0.030 % without burning out the chromium, and it is where the nitrogen is trimmed into the narrow 0.12–0.22 % window rather than left wherever the scrap happened to put it. Maximum heat size is 60 tonnes.
Hot working
Mill data sheets give a hot-forming window for 1.4439 of approximately 1120–900 °C; this is a recommendation rather than a requirement of EN 10088-3 or ASTM A182, and the practical range on a heavy ingot is set by the section and the press. The grade work-hardens quickly and is stiffer under the hammer than 316L, so reductions are taken in more passes with more reheats than a standard austenitic of the same section. Forging is carried out on 6,300 t, 4,000 t and 2,000 t hydraulic open-die presses, with 5 t, 3 t, 2 t, 1 t and 750 kg hammers for drawing out and smaller work. Rings are rolled on 6 m, 3 m and 1 m radial-axial mills.
Solution annealing, the step that cannot be shortened
1.4439 is not usable in the as-forged condition. EN 10222-5 requires solution treatment at 1060 to 1140 °C with water or air cooling; ASTM A182 requires a minimum of 1040 °C followed by a liquid quench to below 260 °C. Between roughly 550 and 1000 °C, with the fastest precipitation between about 600 and 900 °C, a 4–5 % molybdenum austenitic forms sigma and chi phases at the grain boundaries, and a heavy section that cools slowly through that band loses both impact toughness and the pitting resistance the alloy was specified for. Section thickness is therefore a real constraint on quench rate, and heavy 1.4439 forgings are quenched in water rather than air. Furnace charts are recorded and issued with the certificate.
Fourteen heat-treatment furnaces are on site, including car-bottom furnaces to 8,000 × 2,000 × 2,000 mm and two 15 m well-type furnaces that allow long 1.4439 shafts to be quenched vertically without the distortion a horizontal quench would put into them.
§07
1.4439 product forms and size envelope
| Product form | Size limit | Set by |
|---|---|---|
| Seamless rolled rings | OD 50 – 6,000 mm | 6 m radial-axial ring mill; upset-and-punch below ring-mill range |
| Forged flanges | to ASME B16.5, B16.47, API 6A | Weld neck, blind, slip-on, socket weld, lap joint, orifice, long weld neck |
| Forged shafts | to 14,000 mm turned length | C61160 horizontal lathe; 15 m well furnace for vertical quench |
| Discs, tube sheets, covers | to Ø5,000 mm machined | Ø5,000 mm vertical turning lathe |
| Hollow cylinders, sleeves, bushings | to Ø1,600 × 10,000 mm bored | CNC deep-hole drilling machine |
| Bars, blocks and billets | round, flat, square | Feedstock route for machined valve bodies and tooling |
| Valve and wellhead parts | bodies, bonnets, stems, seat rings, spools | API 6A; NACE MR0175 / ISO 15156 where specified |
| Single-piece weight | to 30,000 kg | 60 t heat size; 6,300 t press |
Delivery condition is the customer's choice: as-forged with machining allowance, proof-machined to a surface suitable for ultrasonic examination, or finish-machined to drawing. Machining 1.4439 calls for low speeds, constant positive feed and rigid setups. The grade work-hardens faster than 316L and produces a long, stringy chip, so chip breakers and sharp, well-supported tooling are worth specifying.
§08
Testing, inspection and certification for 1.4439
Because 1.4439 is melted on this site, its chemistry is verified at the furnace rather than taken from a supplier's billet certificate, and the mill certificate traces the forging back to its own melt number. The works holds CCS, BV, DNV, LR and NK classification society approvals and runs its own laboratory.
| Test | Standard | Where performed |
|---|---|---|
| Melt and product chemical analysis | ASTM E415 (OES), ASTM E1019 (C/S) | In-house laboratory |
| Positive material identification | Handheld alloy analyser | In-house |
| Tensile test | ASTM A370 / ISO 6892 | In-house, 600 kN and 300 kN machines |
| Charpy V-notch impact | ASTM A370, to −60 °C | In-house; below −60 °C placed externally |
| Ultrasonic examination | EN 10228-3, ASTM A388, SEP 1921 | In-house |
| Magnetic particle / penetrant | ASTM E709 / ASTM E165 | In-house |
| Grain size, metallography | ASTM E112 | In-house |
| Intergranular corrosion | ASTM A262 Practice E, ISO 3651-2 | Accredited third-party laboratory |
| Pitting corrosion | ASTM G48 | Accredited third-party laboratory |
| Certification | EN 10204 3.1 standard; 3.2 on request | Witnessed by BV, DNV, LR, SGS, TÜV or the customer |
1.4439 is austenitic and therefore non-magnetic in the solution annealed condition, so magnetic particle examination is not applicable to the parent metal, so surface examination is by liquid penetrant. Specify which you require.
§09
Where 1.4439 forgings are used
Flue gas desulphurisation
Scrubber internals, spray header components, absorber flanges and shafts in chloride-concentrating FGD liquor.
Pulp and paper
Bleach plant equipment, digester parts, washer shafts and rolls exposed to chloride dioxide bleaching chemistry.
Chemical and petrochemical
Pressure-vessel flanges, tube sheets, covers, nozzles, pump and valve bodies for dyestuffs, rubber, rayon, ink and bleach production.
Heat exchangers
Solid forged tube sheets, channel covers, hubs and blanks for shell-and-tube exchangers in brackish and chloride-bearing cooling water.
Desalination and seawater
Pump casings, sleeves and flanges in brine handling, where 316L pits and a full 6 % Mo alloy is not justified.
Oil, gas and wellhead
Valve bodies, bonnets, seat rings, spools and manifold blocks, including NACE MR0175 / ISO 15156 sour-service requirements where specified.
Phosphoric and sulphuric acid plant
Agitator shafts, pump parts and vessel flanges in dilute acid duties above the limit of 316L.
Food, textile and dyeing
Process equipment components where chloride-bearing wash and dye liquors attack standard austenitics.
Cryogenic structures
Flanges and rings for low-temperature service, backed by the EN 10222-5 impact requirement at −196 °C.
§10
How to request a quotation for 1.4439 forgings
Quotations for 1.4439 are prepared from a drawing or a written specification, and sending the six items below in the first email usually gets a price back within two working days. Minimum order is 10 kg with no minimum piece count, and lead time normally runs 20 to 60 days from order confirmation.
| # | Item | Example |
|---|---|---|
| 1 | Grade and governing specification | 1.4439 to EN 10222-5, dual certified to ASTM A182 F48 |
| 2 | Dimensions, or a drawing (PDF, DWG, DXF, STEP) | OD 1,200 × ID 900 × H 260 mm rolled ring |
| 3 | Quantity and expected repeat volume | 12 pcs, about 4 × per year |
| 4 | Delivery condition | Proof-machined for UT, 3 mm allowance on all faces |
| 5 | Heat treatment and testing requirements | Solution annealed 1080 °C water quench; UT to EN 10228-3; ASTM A262 Practice E |
| 6 | Certification and destination port | EN 10204 3.2 witnessed by DNV · Rotterdam |
Two things to flag at enquiry stage for this grade specifically. First, whether a dual EN and ASTM certificate is required, because that constrains the melt aim and cannot be added later. Second, whether intergranular or pitting corrosion testing is required, because those tests go to an outside laboratory and need scheduling into the delivery date rather than added to it.
§11
Frequently asked questions about 1.4439
What is 1.4439 steel?
1.4439 is the EN steel number for X2CrNiMoN17-13-5, a low-carbon, nitrogen-alloyed austenitic stainless steel containing 16.5–18.5 % chromium, 12.5–14.5 % nickel, 4.0–5.0 % molybdenum and 0.12–0.22 % nitrogen. It is the same alloy family as UNS S31726 and AISI 317LMN. The high molybdenum and nitrogen give it a pitting resistance equivalent number (PREN) of roughly 31.6 to 38.5, well above 316L, so it is used where chloride pitting and crevice corrosion defeat ordinary 316L.
Is 1.4439 the same as UNS S31726 and 317LMN?
They are the same alloy family but not identical chemistries. EN 10088-3 limits 1.4439 to 16.5–18.5 % chromium, 12.5–14.5 % nickel and 0.12–0.22 % nitrogen, while ASTM A182 grade F48 for UNS S31726 allows 17.0–20.0 % chromium, 13.5–17.5 % nickel and 0.10–0.20 % nitrogen. A heat can satisfy both only if it falls inside the overlap of the two windows. Jiangyin Jiangnan Metal Co., Ltd. melts to the intersection when a dual EN and ASTM certificate is required, which must be stated at enquiry stage because it constrains the melt aim.
What is the PREN of 1.4439?
Using PREN = %Cr + 3.3 × %Mo + 16 × %N, the EN 10088-3 composition limits for 1.4439 give a PREN between 31.6 and 38.5, with a mid-range composition landing at about 35. For comparison, 316L is typically about 25 and 904L about 35. A PREN above 32 is the usual threshold quoted for seawater-adjacent and chloride process service, although PREN alone does not qualify a material for a specific environment.
What are the mechanical properties of 1.4439 forgings?
In the solution annealed condition to EN 10088-3, for ruling sections up to 160 mm, 1.4439 gives 0.2 % proof strength of 280 MPa minimum, 1.0 % proof strength of 315 MPa minimum, tensile strength of 580 to 800 MPa, elongation of 35 % minimum, impact energy KV of 100 J minimum and hardness of 250 HBW maximum. EN 10222-5 forgings for pressure purposes require 285 MPa minimum proof strength and 40 % elongation in the same section range. ASTM A182 grade F48 requires 550 MPa tensile, 240 MPa yield, 40 % elongation and 50 % reduction of area.
What heat treatment do 1.4439 forgings need?
1.4439 forgings must be solution annealed and rapidly quenched after hot working. EN 10222-5 specifies 1060 to 1140 °C followed by water or air cooling; ASTM A182 requires a minimum of 1040 °C followed by a liquid quench to below 260 °C. Rapid cooling is not optional for this grade: at 5 % molybdenum, slow cooling through roughly 550 to 1000 °C precipitates sigma and chi phases that cut both corrosion resistance and impact toughness. Jiangyin Jiangnan Metal water quenches 1.4439 from the solution temperature and records the furnace chart with the certificate.
What sizes of 1.4439 forgings can be produced?
Jiangyin Jiangnan Metal Co., Ltd. rolls 1.4439 seamless rings up to 6,000 mm outside diameter on a 6 m radial-axial ring mill, forges on 6,300 t, 4,000 t and 2,000 t open-die presses, and supplies single pieces up to 30 tonnes. Rings from 50 mm outside diameter are produced by the upset-and-punch route below the ring mill range. Machining reaches 5,000 mm diameter on the vertical lathe, 14,000 mm turned length on the horizontal lathe and Ø1,600 × 10,000 mm on the deep-hole drilling machine. Minimum order is 10 kg.
Can Jiangyin Jiangnan Metal melt 1.4439 in house rather than buying billet?
Yes. 1.4439 is melted on site through the electric arc furnace, refined in a ladle furnace and decarburised under vacuum in 30 t or 60 t VOD units, which is the route that controls both the 0.030 % maximum carbon and the 0.12 to 0.22 % nitrogen window this grade depends on. Because melting is in house, the mill certificate traces the forging back to its melt number instead of stopping at a purchased billet certificate, and the chemistry can be aimed at the forging it will become.
How is 1.4439 tested and certified?
Standard release for 1.4439 forgings covers melt and product chemical analysis by optical emission spectrometry, tensile and Charpy V-notch impact testing, hardness, ultrasonic examination to EN 10228-3 or ASTM A388, magnetic particle or dye penetrant examination as applicable, and dimensional inspection. Intergranular corrosion testing to ASTM A262 Practice E or ISO 3651-2 and pitting testing to ASTM G48 are placed with an accredited third-party laboratory and reported alongside the mill certificate. Certification is EN 10204 3.1 as standard, or EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TÜV or the customer's own inspector on request.
Where is 1.4439 used?
1.4439 is used in flue gas desulphurisation scrubbers, pulp and paper bleach plant equipment, seawater and brackish-water heat exchangers, phosphoric and sulphuric acid process equipment, chemical and petrochemical pressure vessels, offshore and wellhead components, and desalination plant. Typical forged items are tube sheets, heat exchanger covers, weld neck and blind flanges, pump and valve bodies, shafts, seat rings and hollow cylinders.
Should I choose 1.4439 or 904L?
Both land near PREN 35, so the choice usually turns on the acid rather than the chloride. 904L carries 1 to 2 % copper and around 25 % nickel, which makes it the stronger performer in sulphuric acid service, while 1.4439 reaches comparable chloride pitting resistance on a leaner and normally cheaper composition and offers a higher minimum proof strength because of its nitrogen. Where chloride pitting is the governing risk, 1.4439 is generally the lower-cost route; where reducing acid attack dominates, 904L is usually specified. Jiangyin Jiangnan Metal forges both and will quote the two side by side.
What is the lead time and minimum order for 1.4439 forgings?
Minimum order is 10 kg with no minimum piece count, and lead time for 1.4439 normally runs 20 to 60 days from order confirmation. Standard electric arc furnace and VOD melted 1.4439 sits at the lower end of that range. Third-party witnessed inspection to EN 10204 3.2 and corrosion testing placed with an outside laboratory need scheduling, so both should be flagged at enquiry stage rather than after the order is placed.
§13
Data sources and revision
Composition and mechanical property data on this page are taken from the published standards named against each table. Buyers should confirm against the current issue of the governing standard for design purposes; this page is a supply reference, not a substitute for the standard.
- EN 10088-3, Stainless steels, Part 3: Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products. CEN catalogue
- EN 10222-5, Steel forgings for pressure purposes, Part 5: Martensitic, austenitic and austenitic-ferritic stainless steels. CEN catalogue
- ASTM A182 / A182M, Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service (grade F48, UNS S31726). ASTM
- Solution annealing temperature range cross-checked against the Euro Inox / IMOA Tables of Technical Properties & Fabrication Parameters.
Page compiled and technically reviewed by Jiangyin Jiangnan Metal Co., Ltd. · Last reviewed 22 September 2026.