What 1.6359 is
1.6359 is the European material number for X2NiCoMo18-8-5, an 18% nickel maraging steel sold commercially as Maraging 250 or C250 and listed in the United States as UNS K92890. The alloy is based on iron, nickel, cobalt and molybdenum with a carbon content of 0.03% maximum. After aging at 480 °C it reaches a minimum 0.2% proof stress of 1,700 MPa and a hardness of 48 to 52 HRC. No quench is involved, so distortion during heat treatment is small.
1.6359 is not a stainless steel and it is not a nickel-base superalloy. It is a precipitation-hardening structural steel, used for parts that must combine very high strength with good toughness and hold their dimensions through heat treatment.
Conventional high-strength steels such as 4340 and 300M develop strength from carbon-rich martensite formed on quenching, which brings distortion and quench cracking risk with it. 1.6359 works in a different way. Solution annealing produces a soft, low-carbon martensite at 28 to 35 HRC that machines easily. Strength is then developed by precipitating intermetallic phases, mainly Ni3Mo and Ni3Ti, during a low-temperature age. The result is a high strength-to-weight ratio together with good fracture toughness and good weldability.
Jiangyin Jiangnan Metal Co., Ltd. supplies 1.6359 as open-die forgings produced to the customer drawing rather than as stock bar. Forms include seamless rolled rings, discs, shafts, flanges, sleeves, bushings, blocks, tube sheets and forged round bar. Parts are shipped either in the solution-annealed condition for the customer to machine and age, or fully aged and machined to finished dimensions.
- Material class
- 18Ni maraging steel
- Standard designation
- X2NiCoMo18-8-5
- Strength grade
- 250 ksi class
- Melting route
- VIM + VAR (double vacuum)
- Supplied condition
- Solution annealed or aged
- Corrosion resistance
- Low, protective coating required
1.6359 designations and equivalents
1.6359 carries a different designation in each specification system. The table below lists the designations that refer to the same 250 ksi grade of 18% nickel maraging steel.
| System | Designation | Scope |
|---|---|---|
| Werkstoff-Nr. (SEL) | 1.6359 | German and European material number |
| EN / DIN name | X2NiCoMo18-8-5 | Chemical designation |
| UNS | K92890 | Unified numbering system, USA |
| AMS | 6512 | Bar, forgings and forging stock, VIM+VAR |
| AMS | 6520 | Sheet, strip and plate |
| ASTM | A538/A538M Gr. B | Pressure-vessel plate, 250 ksi class |
| MIL | MIL-S-46850 Gr. 250 | US military specification |
| BS | S162 | British aerospace specification |
| DTD | 5212 | British aerospace specification |
| Common names | Maraging 250, C250, 18Ni(250) | Industry usage |
| Trade names | Vascomax C250, Böhler V250, Udimar 250, NiMark 250 | Producer brands |
Note: 1.6359 is Maraging 250. 1.6358 (X2NiCoMo18-9-5) is Maraging 300 and 1.6356 (X2NiCoMoTi18-12-4) is Maraging 350. One digit separates three different strength levels, so state the full designation on the purchase order.
Chemical composition of 1.6359
The composition limits below follow AMS 6512 and EN practice for X2NiCoMo18-8-5. The typical column gives the aim analysis of a representative heat.
| Element | Min | Max | Typical heat | Function |
|---|---|---|---|---|
| Nickel, Ni | 17.00 | 19.00 | 18.50 | Forms the soft Fe-Ni martensite matrix |
| Cobalt, Co | 7.00 | 8.50 | 7.50 | Raises Mo activity, drives precipitation |
| Molybdenum, Mo | 4.60 | 5.20 | 4.80 | Forms the Ni₃Mo strengthening phase |
| Titanium, Ti | 0.30 | 0.50 | 0.40 | Forms Ni₃Ti, adds strength |
| Aluminum, Al | 0.05 | 0.15 | 0.10 | Deoxidizer, minor hardening |
| Carbon, C | - | 0.03 | 0.008 | Held low, carbides reduce toughness |
| Silicon, Si | - | 0.10 | 0.05 | Residual |
| Manganese, Mn | - | 0.10 | 0.04 | Residual |
| Phosphorus, P | - | 0.010 | 0.005 | Residual, restricted |
| Sulfur, S | - | 0.010 | 0.004 | Residual, restricted |
| Chromium, Cr | - | 0.25 | 0.10 | Residual |
| Boron, B | - | 0.010 | 0.004 | Restrains grain growth |
| Zirconium, Zr | - | 0.020 | 0.010 | Grain refinement |
| Iron, Fe | Balance | Matrix | ||
Some aerospace purchase specifications restrict carbon to 0.010% maximum and widen titanium to 0.30 to 0.60%. State the governing specification and revision on the enquiry so that the heat can be selected against it.
Mechanical properties of 1.6359
The values below apply to material solution annealed at 815 to 830 °C and aged at 480 °C, tested at room temperature. Longitudinal and transverse values are listed separately because grain flow in forged rings and discs makes test direction significant.
| Direction | 0.2% proof stress MPa, min |
Tensile strength MPa |
Elongation %, min |
Reduction of area %, min |
Impact, Izod ft·lbf, min |
|---|---|---|---|---|---|
| Longitudinal | 1,700 | 1,800-2,000 | 8 | 40 | 18 |
| Transverse | 1,700 | 1,800-2,000 | 5 | 25 | 8 |
| Condition | Hardness | Tensile strength | Notes |
|---|---|---|---|
| Solution annealed | 28-35 HRC | approx. 1,000 MPa | Machining and forming condition |
| Aged 480 °C / 3-6 h | 48-52 HRC | 1,800-2,000 MPa | Standard service condition |
| Aged 525-540 °C / 6 h | 44-48 HRC | approx. 1,650 MPa | Die-casting cycle, longer thermal fatigue life |
Plane-strain fracture toughness KIc for aged 1.6359 is normally reported between 80 and 110 MPa·m0.5, roughly twice the value of 4340 steel heat treated to the same strength level. These are typical published values and not guaranteed minimums. Where KIc is a design requirement, specify it on the order so that it can be tested and reported.
Physical properties of 1.6359
| Property | Value | Unit |
|---|---|---|
| Density | 8.0 | g/cm³ (0.289 lb/in³) |
| Modulus of elasticity, aged | approx. 186 | GPa |
| Modulus of elasticity, annealed | approx. 179 | GPa |
| Coefficient of thermal expansion, 20-100 °C | approx. 10.1 | 10⁻⁶/K, aged |
| Thermal conductivity | approx. 20 | W/(m·K) |
| Specific heat capacity | approx. 450 | J/(kg·K) |
| Electrical resistivity, annealed | approx. 0.60 | µΩ·m |
| Melting range | approx. 1,413 | °C |
| Magnetic response | Ferromagnetic | - |
| Linear contraction during aging | 0.04-0.06 | %, allow for it before finish machining |
A ring of 1,000 mm diameter contracts about 0.4 to 0.6 mm on diameter during aging. Allow for this in the machining stock, or finish machine after aging.
Forging and heat treatment of 1.6359
1.6359 is heat treated without quenching. The alloy contains almost no carbon, so annealing and aging are carried out in air with no protective atmosphere and no decarburization, and the dimensional change during aging is small.
Forging
- Heat uniformly to 1,150 to 1,200 °C and soak, allowing approximately one hour per 100 mm of section.
- Do not forge below 900 °C. Reheat instead, since finishing too cold can cause cracking.
- Air cool after forging. No quench is used at any stage.
- Ring rolling, upsetting, drawing and punching are all suitable. The alloy is ductile hot.
Solution annealing
- 815 to 830 °C, hold one hour per 25 mm of section with a one hour minimum, then air cool to room temperature.
- Hardness after annealing is 28 to 35 HRC. This is the condition in which the part is machined, drilled, threaded and welded.
- Peak aged strength follows a solution anneal in the 800 to 815 °C band. Annealing above 830 °C coarsens the grain and reduces strength.
Age hardening
- 480 ± 5 °C for 3 to 6 hours, then air cool. Heavy sections take the longer time.
- Hardness rises to 48 to 52 HRC and tensile strength to 1,800 to 2,000 MPa.
- For die-casting and hot-work tooling, aging at 525 to 540 °C for 6 hours trades some hardness for better thermal fatigue resistance.
- Aging is reversible. Parts can be re-annealed and re-aged if rework is required.
A protective atmosphere is not required, since there is virtually no carbon to oxidize or lose. Vacuum or inert-gas aging gives a cleaner surface on finished parts.
1.6359 forged shapes and size range
All parts are open-die forged to the customer drawing or dimension list. There is no standard catalog. The shapes below are the geometries most often ordered in this grade.
| Form | Size range | Also supplied as |
|---|---|---|
| Seamless rolled rings | OD 200-2,500 mm, height to 800 mm | Rectangular, contoured or stepped section |
| Discs and blanks | Ø 100-1,600 mm, thickness 20-500 mm | Solid or trepanned |
| Shafts and spindles | Ø 80-800 mm, length to 6,000 mm | Straight, stepped, eccentric, flanged |
| Flanges and hubs | OD 150-2,000 mm | Weld-neck, blind, slip-on, custom profile |
| Sleeves, bushings, hollow bars | OD 120-1,200 mm, bore from 60 mm | Bored, or supplied solid for customer boring |
| Blocks, round and square bar | 80-900 mm section | Forged and peeled, or rough turned |
| Maximum single piece | approx. 20 t | Heavier pieces on enquiry |
Delivery condition
- Solution annealed, 28 to 35 HRC. The usual delivery condition. The customer machines the part soft and then ages it at 480 °C.
- Aged, 48 to 52 HRC, rough machined. Ready for grinding to final size.
- Aged and finish machined to drawing, including bores, faces, keyways, threads and grinding.
Surface options are as-forged and shot blasted, rough turned, peeled, ground, or machined to drawing tolerance.
Machining, welding and finishing
Machining
Machine 1.6359 in the solution-annealed condition at 28 to 35 HRC and age afterwards. The alloy cuts slightly tougher than 4140 at the same hardness and work hardens if the tool rubs instead of cutting. Use positive rake carbide tooling, rigid setups, a positive feed rate and ample coolant. Because aging contracts the part by only 0.04 to 0.06%, semi-finishing before aging and grinding afterwards is a reliable route to close tolerances.
Welding
1.6359 welds well. No preheat is required and the low-carbon heat-affected zone does not embrittle. Weld in the solution-annealed condition by GTAW or electron beam with matching maraging filler, keeping heat input low and the joint clean. The assembly is then aged, optionally after a further solution anneal, so that weld metal and parent metal harden together.
Corrosion protection
1.6359 has approximately the corrosion resistance of a low-alloy steel and will rust. Parts are normally nitrided, plated, painted or otherwise coated in service. Where both high strength and corrosion resistance are required, a precipitation-hardening stainless such as 17-4PH, 15-5PH or PH13-8Mo is used instead, at a lower strength level.
Nitriding at approximately 455 °C raises surface hardness to about 65 HRC while the core remains at aged strength. This is used for wear faces on tooling and shafts.
Where 1.6359 forgings are used
1.6359 is specified where a part must carry a high load in a small envelope, resist fatigue and remain dimensionally stable through heat treatment.
- Aerospace structures and mechanisms. Landing-gear components, actuator bodies and rods, slat and flap tracks, drive shafts, high-load fittings.
- Tooling. Die-casting dies and inserts, plastic injection molds, extrusion tooling, cold-forming punches and dies, die holders.
- Motorsport and high-performance drivetrains. Gears, gearbox shafts, half shafts, crank components, suspension pins.
- Oil, gas and subsea equipment. High-strength connectors, load-bearing housings and stems in coated or protected service.
- Heavy industry. Press and machine spindles, couplings, torque tubes, high-load fasteners, springs and flexures.
Orders in this grade are typically single pieces or short runs, for example one ring, a set of six shafts, or a replacement disc for a mold base. Open-die forging requires no dies, so a quantity of one is economic.
1.6359 compared with the other maraging grades
The 18Ni maraging grades are separated mainly by cobalt and titanium content. Higher levels of both give higher strength and lower toughness. 1.6359 is the toughest of the group.
| Grade | EN name | W.-Nr. | Proof stress, min | Tensile | Hardness | Selected for |
|---|---|---|---|---|---|---|
| Maraging 250 | X2NiCoMo18-8-5 | 1.6359 | 1,700 MPa | 1,800-2,000 MPa | 48-52 HRC | Best toughness and weldability of the group |
| Maraging 300 | X2NiCoMo18-9-5 | 1.6358 | 1,930 MPa | 2,000-2,150 MPa | 52-56 HRC | Higher strength, slightly lower toughness |
| Maraging 350 | X2NiCoMoTi18-12-4 | 1.6356 | 2,350 MPa | 2,400-2,500 MPa | 56-59 HRC | Maximum strength, lowest toughness |
| Tool grade | X3NiCoMoTi18-9-5 | 1.2709 | approx. 1,900 MPa | 1,950-2,100 MPa | 50-54 HRC | Mold and die stock, also used as AM powder |
1.6359 or a quenched and tempered steel
Compared with 4340, 300M or 4330V at similar strength, 1.6359 costs several times more per kilogram. It is selected when distortion control, weld repair or crack tolerance govern the design, for example a large mold base that must not move in heat treatment, a welded assembly required to reach 1,800 MPa, or a fatigue-critical shaft. For a heavily loaded part without those constraints, a quenched and tempered alloy steel forging is usually the more economic choice.
Testing, inspection and certificates
| Test | Standard | Scope |
|---|---|---|
| Chemical analysis | Spectrometer, combustion for C and S | Every heat, ladle and product analysis |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Volumetric, acceptance class to order |
| Magnetic particle testing | EN 10228-1, ASTM E709 | Surface, on request |
| Tensile test | ISO 6892-1, ASTM A370 | Longitudinal and transverse |
| Impact test | ISO 148-1, ASTM E23 | Charpy or Izod, temperature to order |
| Hardness | ISO 6508, ASTM E18 | Before and after aging |
| Grain size and microstructure | ASTM E112 | On request |
| Dimensional report | Customer drawing | Every piece, with heat number traceability |
Documentation
- EN 10204 type 3.1 mill test certificate as standard, issued against the heat number stamped on the piece.
- EN 10204 type 3.2 with third-party witness, by TÜV, SGS, BV, Lloyd's or the customer's own inspector.
- Ultrasonic and NDT reports, heat-treatment charts, dimensional reports and material traceability from ingot to shipped part.
If the order is governed by a specific specification such as AMS 6512, ASTM A538, a customer standard or an aerospace approval, state it on the enquiry so that the melt route, testing and documentation are set up correctly from the start.
How to order 1.6359 forgings
Send a drawing, a sketch or the dimensions. A price and delivery date are issued within 24 hours on working days.
Include as much of the following as is available:
- Shape and finished dimensions, or a drawing in PDF, DWG or STEP
- Quantity. One piece is acceptable, as open-die work carries no die cost
- Governing specification, if any: AMS 6512, ASTM A538 or a customer standard
- Delivery condition: solution annealed, aged, rough machined or finish machined
- Certificate type: EN 10204 3.1 or 3.2, and any third-party witness required
- Testing beyond the standard scope: UT class, impact temperature, KIc, grain size
Questions about 1.6359
What is 1.6359 material?
1.6359 is the European material number for X2NiCoMo18-8-5, an 18% nickel maraging steel also called Maraging 250, C250 or UNS K92890. It contains 17 to 19% nickel, 7 to 8.5% cobalt, 4.6 to 5.2% molybdenum and a maximum of 0.03% carbon. Aging at 480 °C takes it to 1,800 to 2,000 MPa tensile strength and 48 to 52 HRC.
Is 1.6359 a stainless steel?
No. 1.6359 contains at most 0.25% chromium, far below the roughly 10.5% needed for stainless behaviour, so it corrodes much like a low-alloy steel. Parts in 1.6359 are normally nitrided, plated, painted or otherwise coated. Where a part needs high strength and corrosion resistance together, a precipitation-hardening stainless such as 17-4PH, 15-5PH or PH13-8Mo is the better choice.
What is 1.6359 equivalent to?
1.6359 corresponds to X2NiCoMo18-8-5 in the EN system, UNS K92890 in the United States, AMS 6512 for bar and forgings, AMS 6520 for sheet and plate, ASTM A538 Grade B, MIL-S-46850 Grade 250, and BS S162 or DTD 5212 in the United Kingdom. Producer trade names for the same grade include Vascomax C250, Böhler V250, Udimar 250 and NiMark 250.
What is the tensile strength of 1.6359?
In the aged condition 1.6359 has a tensile strength of 1,800 to 2,000 MPa and a minimum 0.2% proof stress of 1,700 MPa, with minimum elongation of 8% longitudinal and 5% transverse. Hardness is 48 to 52 HRC. In the solution-annealed condition, before aging, tensile strength is about 1,000 MPa at 28 to 35 HRC, which is why machining is done at that stage.
How is 1.6359 heat treated?
1.6359 is solution annealed at 815 to 830 °C for one hour per 25 mm of section and air cooled, giving 28 to 35 HRC. After machining it is aged at 480 ± 5 °C for 3 to 6 hours and air cooled, reaching 48 to 52 HRC. There is no quench and no protective atmosphere is needed, since the alloy is essentially carbon free. The part contracts only about 0.04 to 0.06% during aging.
Can 1.6359 be welded?
Yes. 1.6359 is one of the more weldable ultra-high-strength steels. Carbon content below 0.03% means the heat-affected zone does not form brittle martensite, so no preheat is required. Weld in the solution-annealed condition by GTAW or electron beam with matching maraging filler, then age the assembly at 480 °C so that weld and parent metal harden together.
Is 1.6359 difficult to machine?
No, provided it is machined in the solution-annealed condition at 28 to 35 HRC rather than after aging. Use sharp positive rake carbide tooling, rigid setups, a positive feed rate and plenty of coolant, since the alloy work hardens if the tool rubs. As aging shrinks the part by only 0.04 to 0.06%, semi-finishing before aging and grinding afterwards gives close tolerances reliably.
What is the difference between 1.6359 and 1.6358?
1.6359 (X2NiCoMo18-8-5) is Maraging 250, with 7 to 8.5% cobalt and a minimum proof stress of 1,700 MPa. 1.6358 (X2NiCoMo18-9-5) is Maraging 300, with higher cobalt and titanium, a minimum proof stress near 1,930 MPa and 52 to 56 HRC. 1.6358 is stronger and 1.6359 is tougher and more forgiving to weld. Confirm which number appears on the drawing before ordering.
Who supplies 1.6359 forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging works in Jiangyin, Jiangsu Province, China that manufactures 1.6359 (X2NiCoMo18-8-5 / Maraging 250) forgings to customer drawings, including rolled rings, discs, shafts, flanges, sleeves, blocks and bars. Contact: sales@steelforgepieces.com, +86 189 2135 9659, No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China.
What certificates come with 1.6359 forgings?
Every 1.6359 forging is supplied with an EN 10204 type 3.1 mill test certificate covering chemical analysis, mechanical properties, hardness, heat treatment record and heat number traceability. EN 10204 type 3.2 certificates witnessed by TÜV, SGS, BV or Lloyd's are available on request, together with ultrasonic reports to EN 10228-3, SEP 1921 or ASTM A388.
What is the minimum order quantity and lead time?
The minimum order for 1.6359 open-die forgings is one piece, since open-die forging needs no dies and there is no tooling charge to spread over a batch. Typical lead time is four to eight weeks depending on size, delivery condition and heat availability, as 1.6359 is a vacuum-melted grade that is often ordered against a specific melt.
Supplier and document data
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging manufacturer based in Jiangyin, Jiangsu Province, China. The works produces forged rings, discs, shafts, flanges, sleeves, blocks and bars to customer drawings in carbon steel, alloy steel, tool steel, stainless steel, nickel alloys and maraging steels such as 1.6359, supplied with EN 10204 3.1 or 3.2 certification and shipped worldwide.
- Company
- Jiangyin Jiangnan Metal Co., Ltd.
- Works address
- No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Telephone
- +86 189 2135 9659
- Website
- www.steelforgepieces.com
- Capability
- Open-die forging, ring rolling, heat treatment, machining
Data sources
Technical data on this page is taken from the published specifications for X2NiCoMo18-8-5 and Maraging 250, including AMS 6512, ASTM A538, EN documents and producer datasheets, together with test records from heats processed at this works. Values marked typical are typical and are not guaranteed minimums.
Jiangyin Jiangnan Metal Co., Ltd., "1.6359 / X2NiCoMo18-8-5 Technical Datasheet", rev. 7 August 2026, www.steelforgepieces.com/Nickel-Alloy/1.6359.html