What 1.3974 is
1.3974 (X2CrNiMnMoNNb23-17-6-3) is a nitrogen-alloyed, manganese-bearing austenitic steel, supplied as a non-magnetizable steel to SEW 390 : 1991-11 and to the WL 1.3974 material sheets. Manganese at 4.50 to 6.50 % and nitrogen at 0.30 to 0.50 %, with 21.0 to 24.5 % chromium and 15.5 to 18.0 % nickel, hold the structure fully austenitic. Relative magnetic permeability stays at or below 1.01, the limit SEW 390 uses to define a non-magnetizable steel. The nitrogen also lifts strength well above a 316-type austenitic. German mills sell the grade under the name U-Boot-Stahl, submarine steel, which is a fair description of what it is for.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We forge 1.3974 to customer drawings: rings, seamless rolled rings, discs, tube sheets, shafts, flanges, sleeves, bushings, blocks and bars. Send enquiries to sales@steelforgepieces.com or call +86 189 2135 9659.
1.3974 at a glance
- Material number
- 1.3974
- EN / DIN name
- X2CrNiMnMoNNb23-17-6-3
- Standards
- SEW 390 : 1991-11, WL 1.3974
- Trade name
- U-Boot-Stahl (submarine steel)
- Structure
- Austenitic, non-magnetizable
- Permeability
- 1.01 or lower
- Density at 20 °C
- 7.90 kg/dm³
- Max. service temp.
- 400 °C
- Solution anneal
- approx. 1020 to 1120 °C, water
- Welding filler
- 1.3984
- Melting route
- EAF + VOD + ESR
- Certification
- EN 10204 3.1 / 3.2
Designations, standards and near-equivalents
Published data on this grade carries a common error, so the table below separates what is exact from what is only close. 1.3974 has no exact UNS equivalent. Mill material databases list ASTM A182 F49 and UNS S34565 against it, both with the qualifier "similar" attached. The "UNS S33228" that appears on a number of trading-company pages is wrong: S33228 is a cerium-bearing heat-resisting alloy, EN 1.4877, with roughly 27 % chromium and 32 % nickel and no molybdenum at all.
| Designation | Value | Status |
|---|---|---|
| Material number | 1.3974 | Exact |
| EN / DIN name | X2CrNiMnMoNNb23-17-6-3 | Exact |
| Standard | SEW 390 : 1991-11, Nichtmagnetisierbare Stähle, Technische Lieferbedingungen | Exact |
| Defence material sheet | WL 1.3974 series, for example WL 1.3974-1 for plates | Exact |
| Trade name | U-Boot-Stahl, submarine steel | Mill trade name |
| ASTM A182 F49 / UNS S34565 / EN 1.4565 | X2CrNiMnMoN25-18-6-5, with Cr 24 to 26, Ni 16 to 19, Mn 5.0 to 7.0, Mo 4.0 to 5.0, N 0.3 to 0.6 | Similar only. About 1.5 % more molybdenum, so noticeably better in chlorides. Not interchangeable without approval. |
| 1.3964 / X2CrNiMnMoNNb21-16-5-3 | The leaner non-magnetizable steel in the same SEW 390 family | Related grade, see the comparison below |
| UNS S33228 | Cr 26 to 28, Ni 31 to 33, Nb 0.6 to 1.0, Ce 0.05 to 0.1, no Mo. This is EN 1.4877. | Not an equivalent. Widely mis-listed, disregard it. |
If your drawing calls out F49 or 1.4565 and a supplier offers 1.3974 against it, or the other way round, treat that as a substitution and get it approved. The molybdenum difference is real.
Chemical composition of 1.3974
The figures below are the SEW 390 specification for X2CrNiMnMoNNb23-17-6-3. Every heat we forge is analysed, and the ladle analysis is printed on the EN 10204 certificate that ships with the parts.
| C | Si | Mn | P | S | Cr | Ni | Mo | N | Nb | Fe |
|---|---|---|---|---|---|---|---|---|---|---|
| max. 0.03 | max. 1.00 | 4.50 to 6.50 | max. 0.025 | max. 0.010 | 21.0 to 24.5 | 15.5 to 18.0 | 2.80 to 3.40 | 0.30 to 0.50 | 0.10 to 0.30 | Balance |
Carbon is held at 0.03 % maximum and niobium is added as a stabiliser. That combination stops chromium carbides forming at the grain boundaries during welding, which is what keeps 1.3974 resistant to intergranular corrosion in the as-welded condition.
Mechanical properties by delivery condition
1.3974 is ordered in one of two conditions, and the suffix on the material number says which. 1.3974.9 is solution annealed. 1.3974.7 is warm work-hardened. Proof strength roughly doubles between them, so name the condition on your enquiry. Most ordering mistakes on this grade come from leaving it out.
| Property | 1.3974.9, solution annealed | 1.3974.7, warm work-hardened |
|---|---|---|
| 0.2 % proof strength Rp0.2 | min. 450 MPa | min. 940 MPa |
| Tensile strength Rm | 700 to 900 MPa | max. 1040 MPa |
| Elongation A5 | min. 25 % | min. 15 % |
| Impact energy, ISO-V | min. 100 J | min. 50 J |
| Hardness | max. 280 HB | Higher than annealed |
| Relative permeability | 1.01 or lower | 1.01 or lower |
Read this before you specify. Datasheets for 1.3974 do not all agree. The figures above come from sources that state which delivery condition they apply to. Other published datasheets, including mill material databases, give the solution-annealed condition as Rm 800 to 1050 MPa with hardness up to 341 HBW. That band is higher, and it does not reconcile with its own ceiling, because 341 HBW converts to roughly 1070 to 1100 MPa. We have not been able to settle the difference from public sources, so treat every figure on this page as indicative for the grade. Agree the acceptance values for your order in writing. What binds us is the test result from the piece taken off your forging, recorded on the EN 10204 3.1 or 3.2 certificate.
Physical properties
| Property | Value | Condition |
|---|---|---|
| Density | 7.90 kg/dm³ | at 20 °C |
| Electrical resistivity | 0.70 Ω·mm²/m | at 20 °C |
| Thermal conductivity | 13.5 W/(m·K) | at 20 °C |
| Coefficient of thermal expansion | 15.5 × 10-6 K-1 | 20 to 100 °C |
| Coefficient of thermal expansion | 17.3 × 10-6 K-1 | 20 to 400 °C |
| Relative magnetic permeability | 1.01 or lower | SEW 390, at about 8 000 A/m |
| Maximum application temperature | 400 °C | Structural use |
| Solution annealing | approx. 1020 to 1120 °C | water quench |
| Microstructure | Austenitic | All conditions |
Why 1.3974 is non-magnetic
Under SEW 390 a steel counts as non-magnetizable when its relative magnetic permeability does not exceed 1.01, normally verified at a field strength of about 8 000 A/m. Ordinary austenitic grades such as 304 or 316 start out close to that figure, but they form strain-induced martensite when they are cold worked or machined hard, and permeability climbs.
1.3974 avoids that because manganese and nitrogen make its austenite thermodynamically stable rather than merely metastable. Nitrogen at 0.30 to 0.50 % is a strong austenite former and a solid-solution strengthener. Manganese at 4.50 to 6.50 % raises nitrogen solubility, so that much nitrogen can be held without porosity. The result is a steel that keeps its permeability through forging, machining and service. The sister grade 1.3964 is documented as staying non-magnetizable after roughly 80 % cold deformation. That stability is why the grade gets specified where a steel part sits inside or next to a magnetic field: submarine and mine countermeasure vessel construction, generator and motor components, instrument and sensor housings, and tools that must not disturb magnetic survey readings.
Put the permeability limit in the order. The 1.01 figure is the SEW 390 definition of a non-magnetizable steel, not an automatic guarantee on every delivery. Published mill data for this family occasionally quotes values slightly above it. If your specification carries a permeability limit, name it on the enquiry. We will include the measurement in the test scope and report the measured value on the certificate alongside the tensile and impact data, or tell you up front if we cannot commit to it.
Corrosion resistance
- Seawater. Published datasheets state resistance in seawater up to approximately 60 °C. Read that as indicative rather than as a design limit, for the reasons set out below.
- Stress corrosion cracking. Resistant. The high nickel content is what buys this, and it is a common reason for choosing 1.3974 over a leaner manganese austenitic.
- Intergranular corrosion. Resistant, thanks to the 0.03 % carbon cap and the niobium stabilisation. Testing to ASTM A262 practice E or EN ISO 3651-2 can be added to the order.
- Pitting and crevice corrosion. Datasheets for the grade describe it as resistant to pitting. Read the note below before relying on that in a chloride application.
Where we would be careful. On the nominal composition the pitting resistance equivalent number, Cr + 3.3 Mo + 16 N, works out at about 39 to 40. Across the full specification range a heat can land anywhere between roughly 35 and 44. The usual rule of thumb for warm seawater service is a PREN above 40, so this grade sits on that line rather than above it. A purpose-built seawater grade such as 1.4565 / F49 is around 46.
There is a second effect. In this family of steels, high manganese contents are reported to lower pitting resistance compared with an equivalently alloyed low-manganese steel, because manganese sulphide inclusions act as pit initiation sites. The mechanism scales with sulphur, and 1.3974 is specified at 0.010 % S maximum, which limits it considerably. The mill datasheet for the sister grade 1.3964 states the effect directly.
1.3974 is a non-magnetizable structural steel with good corrosion resistance. It is not a corrosion-service grade that happens to be non-magnetic. If your duty is warm, stagnant or crevice-prone chloride service, tell us and we will say so rather than sell you the wrong steel.
1.3974 forged products we make
Everything below is forged to your drawing, or to a machining allowance you specify. We do not hold 1.3974 as standard stock, because non-magnetic grades are almost always ordered to a specific size.
Forged rings
Open-die forged and mandrel-expanded rings for housings, spacers and retaining components.
Seamless rolled rings
Ring-rolled sections with circumferential grain flow, for the best strength around the ring.
Discs and tube sheets
Upset-forged solid discs and drilled tube sheets, rough or finish machined.
Shafts and stepped shafts
Straight, stepped and flanged shafts, including long slender sections with straightening after heat treatment.
Forged flanges
Weld-neck, slip-on, blind and special flanges to drawing.
Blocks, bars and billets
Round, square and rectangular forged sections, saw cut to length.
Hollow bars and cylinders
Bored and trepanned forged cylinders and sleeves.
Valve and wellhead parts
Bodies, bonnets, seat rings, stems and blocks in non-magnetic grades.
How we make a 1.3974 forging
Melting, EAF + VOD + ESR
Electric arc furnace melt, then vacuum oxygen decarburisation to reach the 0.03 % carbon level while holding nitrogen, then electroslag remelting for a clean ingot with little segregation. Clean steel matters on this grade, because a nitrogen-alloyed austenitic is unforgiving of inclusions.
Open-die forging
The ingot is upset and drawn under the press so that grain flow follows the finished contour. Forging reduction and finishing temperature are controlled to keep the structure fully recrystallised.
Solution annealing and quenching
Parts are solution annealed at approximately 1020 to 1120 °C and water quenched, which takes carbides and nitrides back into solution and locks in the austenitic, non-magnetizable structure. The exact cycle is agreed at order stage and recorded on the certificate.
Machining
Rough turned, pre-machined or finish machined to drawing. 1.3974 work-hardens quickly, so we run reduced cutting speeds, heavier positive-rake carbide tooling and rigid setups.
Testing and certification
Ultrasonic examination, mechanical testing, chemical analysis, and on request permeability and corrosion testing, released with the certificate.
Testing, inspection and certificates
| Test | Standard | Notes |
|---|---|---|
| Ultrasonic examination | EN 10228-3, SEP 1921, ASTM A388 | Acceptance class per your specification, stated on the enquiry. |
| Chemical analysis | Ladle and, on request, product analysis | Reported on the certificate. |
| Tensile and impact testing | Room temperature or low temperature | Test location and orientation to your drawing. |
| Hardness | HB or HBW | Reference figure for the annealed condition is 280 HB maximum. |
| Magnetic permeability | SEW 390, at about 8 000 A/m | Add to the test scope where a permeability limit applies. |
| Intergranular corrosion | ASTM A262 practice E, EN ISO 3651-2 | On request. |
| Surface and dimensional | Liquid penetrant, dimensional report | On request. |
| Certification | EN 10204 3.1 or 3.2 | 3.2 witnessed by the inspection body named in your order. |
Machining and welding 1.3974
Machining
1.3974 is hard to machine. The high alloy content, nitrogen above all, gives a tough austenite with a very high work-hardening rate. In practice: cut at reduced surface speed, keep the feed high enough that the tool stays under the hardened layer instead of rubbing on it, use sharp positive-rake carbide inserts, flood coolant generously, and never let the tool dwell. Rigidity of the setup matters more here than on a standard austenitic. Allow more machining time and tooling cost in your own quotation than you would for 316.
Welding
The grade welds well. The recommended filler metal is 1.3984, and the mill datasheet for the sister grade 1.3964 names 1.3954 as a second option. Because carbon is capped at 0.03 % and niobium stabilises the steel, chromium carbide precipitation does not occur during normal welding, so no post-weld heat treatment is needed to restore intergranular corrosion resistance. Where heavy cold deformation or a very thick section makes post-weld heat treatment unavoidable, it has to be a full solution anneal and quench. A stress-relief hold in the sensitisation range is the wrong treatment for this steel.
One point is easy to miss. A filler recommendation protects corrosion resistance, but it does not by itself guarantee that the weld metal and heat-affected zone stay inside your permeability limit. If non-magnetizability across the joint is part of the specification, say so, and have it measured on a procedure qualification rather than assumed.
Where 1.3974 is used
1.3974 exists for one reason: a component that has to be strong and corrosion resistant while staying magnetically invisible. Its trade name, U-Boot-Stahl, says where it came from. The established application areas are:
- Naval and defence construction. The home ground for this grade. Submarines and mine countermeasure vessels, where the hull and its equipment have to hold a low magnetic signature. It is also why the grade carries its own WL defence material sheets alongside SEW 390.
- Shipbuilding and seawater technology. Shafting, fittings and equipment exposed to seawater on surface vessels.
- Electrical engineering. Components in and around large electrical machines, where a magnetisable part would distort the field or heat up in it.
- Mechanical and plant engineering. Machine components that need high proof strength together with non-magnetic behaviour.
- Energy engineering and high-strength fasteners. Non-magnetic bolting and structural parts.
- Aerospace and instrumentation. Structural parts next to sensitive magnetic instruments.
Outside those areas, engineers reach for this family of steels whenever a magnetic survey, sensor or measurement must not be disturbed by the structure carrying it. Downhole measurement housings, non-magnetic tooling and test fixtures are typical. If your application is an unusual one, send us the specification and we will tell you whether 1.3974 is the right grade or whether another non-magnetic steel suits it better.
1.3974 compared with 1.3964
The question we get asked most often is how 1.3974 differs from 1.3964, the other widely used SEW 390 non-magnetizable steel. Both are Cr-Ni-Mn-Mo-N austenitics stabilised with niobium. 1.3974 is the more highly alloyed of the two.
| Item | 1.3974 | 1.3964 |
|---|---|---|
| EN / DIN name | X2CrNiMnMoNNb23-17-6-3 | X2CrNiMnMoNNb21-16-5-3 |
| Chromium | 21.0 to 24.5 % | 20.00 to 21.50 % |
| Nickel | 15.5 to 18.0 % | 15.00 to 17.00 % |
| Manganese | 4.50 to 6.50 % | 4.00 to 6.00 % |
| Molybdenum | 2.80 to 3.40 % | 3.00 to 3.50 % |
| Nitrogen | 0.30 to 0.50 % | 0.20 to 0.35 % |
| Niobium | 0.10 to 0.30 % | max. 0.25 % |
| Carbon | max. 0.03 % | max. 0.03 % |
| Standard | SEW 390 | SEW 390 |
| Permeability limit | 1.01 or lower | 1.01 or lower |
In short, 1.3974 carries more chromium, nickel and nitrogen. 1.3964 is the longer-established and more commonly stocked of the pair, and it is the grade most often named for mine countermeasure vessel and submarine work. Both are forged on the same equipment here, so if your drawing permits either, ask us which gives the better lead time for your size.
1.3974 questions we get asked
Is 1.3974 magnetic?
No. 1.3974 is a non-magnetizable austenitic steel. SEW 390 classifies a steel as non-magnetizable when its relative magnetic permeability does not exceed 1.01, normally measured at a field strength of about 8 000 A/m, and 1.3974 is supplied to that limit. Because manganese and nitrogen make the austenite stable rather than metastable, it does not turn magnetic after cold work or machining the way 304 and 316 can.
What is 1.3974 equivalent to? Is it UNS S33228?
No, 1.3974 is not UNS S33228, and it has no exact UNS equivalent. S33228 is a cerium-bearing heat-resisting alloy, EN 1.4877, with about 27 % chromium and 32 % nickel and no molybdenum. It is a different material, and the pairing you see on several trading-company datasheets is a copy-paste error. Mill datasheets for 1.3974 list ASTM A182 F49 / UNS S34565 / EN 1.4565 as a similar grade, with the qualifier attached. That steel runs 4.0 to 5.0 % molybdenum against 2.80 to 3.40 % here, so it is not interchangeable without approval. The closest genuine relative is 1.3964, X2CrNiMnMoNNb21-16-5-3, the leaner non-magnetizable steel in the same SEW 390 family.
Which standard covers 1.3974?
SEW 390 : 1991-11, Nichtmagnetisierbare Stähle, Technische Lieferbedingungen, which sets the delivery conditions for this grade including the 1.01 permeability requirement. The grade also has its own WL 1.3974 defence material sheets, for example WL 1.3974-1 for plates, so check which document your drawing actually invokes.
What is the chemical composition of 1.3974?
In mass %: C max. 0.03, Si max. 1.00, Mn 4.50 to 6.50, P max. 0.025, S max. 0.010, Cr 21.0 to 24.5, Ni 15.5 to 18.0, Mo 2.80 to 3.40, N 0.30 to 0.50, Nb 0.10 to 0.30, balance iron.
Is 1.3974 resistant to seawater?
Published datasheets state resistance in seawater up to approximately 60 °C, together with resistance to stress corrosion cracking and intergranular corrosion. Treat the 60 °C as indicative rather than as a design limit. It traces back to supplier literature rather than to a mill or standards source, and on the nominal composition the PREN, Cr + 3.3 Mo + 16 N, is only about 39 to 40, right on the conventional threshold for warm seawater service rather than safely above it. A second, documented effect in this family is that high manganese lowers pitting resistance compared with an equivalently alloyed low-manganese steel, because manganese sulphide inclusions act as pit initiators. The 0.010 % sulphur limit here mitigates that but does not remove it. For warm, stagnant or crevice-prone chloride duty, verify the grade against your own service experience or specify a 4.5 to 6 Mo alternative.
Can 1.3974 be welded, and which filler is used?
Yes. The recommended welding filler material is 1.3984, with 1.3954 named as a second option on the mill datasheet for the sister grade. The 0.03 % carbon cap and the niobium addition prevent chromium carbide precipitation, so normal welding does not sensitise the steel and no post-weld heat treatment is needed to restore intergranular corrosion resistance. If post-weld heat treatment is unavoidable, use a full solution anneal and quench. Note that the filler choice protects corrosion resistance but does not by itself guarantee the weld metal stays inside a permeability limit, so qualify that separately if it matters.
Is 1.3974 difficult to machine?
Yes. The high alloy content, nitrogen in particular, gives a tough austenite with a very high work-hardening rate. Use reduced cutting speeds, a feed high enough to cut beneath the work-hardened layer, sharp positive-rake carbide tooling, generous flood coolant and a rigid setup, and budget more machining time than for 316.
What do the .7 and .9 suffixes mean in 1.3974.7 and 1.3974.9?
They designate the delivery condition, not a different chemistry. 1.3974.9 is solution annealed, with Rp0.2 min. 450 MPa, Rm 700 to 900 MPa, A5 min. 25 %, ISO-V impact min. 100 J and hardness max. 280 HB. 1.3974.7 is warm work-hardened, with Rp0.2 min. 940 MPa, Rm max. 1040 MPa, A5 min. 15 % and ISO-V impact min. 50 J. Proof strength roughly doubles between the two, so name the condition on your drawing and your enquiry.
What is the maximum service temperature of 1.3974?
Approximately 400 °C. Published physical data for the grade is quoted over the 20 to 400 °C range, with a coefficient of thermal expansion of 15.5 x 10-6 K-1 from 20 to 100 °C rising to 17.3 x 10-6 K-1 over 20 to 400 °C. This is a non-magnetizable structural steel, not a heat-resisting grade.
Who supplies 1.3974 open-die forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in China that produces 1.3974 forged rings, seamless rolled rings, discs, tube sheets, shafts, flanges, sleeves, bushings, blocks and bars to customer drawings. Material is melted EAF + VOD + ESR, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and certified to EN 10204 3.1 or 3.2. Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China. Email sales@steelforgepieces.com, telephone +86 189 2135 9659.
Do you hold 1.3974 in stock?
No, 1.3974 is made to order. Non-magnetic grades are almost always specified to a particular size and condition, so standard stock would rarely match what a customer needs. Send the drawing or the finished dimensions with your required delivery condition, and we will quote the forging, the machining allowance and the lead time together.
Request a quotation for 1.3974 forgings
Send a drawing or the finished dimensions and we will come back with a price, a weight and a lead time. It helps if your enquiry states the product form, the finished dimensions and machining allowance, the quantity, the delivery condition (solution annealed 1.3974.9 or warm work-hardened 1.3974.7), the test scope including any permeability limit, and the certificate type you need.
- CompanyJiangyin Jiangnan Metal Co., Ltd.
Open-die forging factory - AddressNo.1 Chengxiqiao Road, Zhouzhuang Town,
Jiangyin City, Jiangsu Province 214423, China - Phone+86 189 2135 9659
- Emailsales@steelforgepieces.com
Sources and how to cite this page
Grade data on this page is drawn from the SEW 390 : 1991-11 specification for non-magnetizable steels, the WL 1.3974 material sheets, and published mill and distributor datasheets for X2CrNiMnMoNNb23-17-6-3. The permeability definition, 1.01 maximum at about 8 000 A/m, follows Merkblatt 827, Magnetische Eigenschaften nichtrostender Stähle, published by Informationsstelle Edelstahl Rostfrei. The designation correction on this page, that 1.3974 is not UNS S33228, follows the mill material databases, which list ASTM F49 and UNS S34565 with an explicit "similar" qualifier, and the published composition of S33228 itself.
Where published sources disagree, this page says so rather than picking the more flattering number. The known conflicts are the two solution-annealed mechanical property datasets, and the seawater and pitting resistance statements. Both are flagged in place above.
Cite this page
Jiangyin Jiangnan Metal Co., Ltd. "1.3974 (X2CrNiMnMoNNb23-17-6-3) Forgings." steelforgepieces.com. Updated . https://www.steelforgepieces.com/Stainless-Steel/1.3974.html
Figures on this page are reference data for the grade, offered in good faith for engineering guidance. They are not a warranty of the properties of any particular delivery. The binding values for your order are the ones recorded on the inspection certificate issued with the goods.