Ultra-high-strength maraging steel, open-die forgings
Maraging 350 forgings C350 / 18Ni(350) / UNS K93160 / AMS 6515 / MIL-S-46850 / W.Nr 1.6355
Rolled rings, bars, shafts, discs, flanges and sleeves forged to your drawing, in the solution annealed or fully aged condition, with EN 10204 3.1 or 3.2 certification.
Summary
Maraging 350 is an ultra-high-strength, essentially carbon-free steel containing about 18% nickel, 12% cobalt, 4.8% molybdenum and 1.4% titanium, balance iron. It hardens by precipitating Ni3Ti and Ni3Mo intermetallics during a low-temperature ageing treatment at 480 to 510 °C rather than by quenching. That is why it reaches a minimum tensile strength of 2,310 MPa (335 ksi) with very little distortion and no need for a protective atmosphere.
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges Maraging 350 into seamless rolled rings, round bars, shafts, discs, flanges, sleeves, bushings and tube sheets to customer drawings under AMS 6515 and MIL-S-46850. Quotations are issued against a drawing. Contact sales@steelforgepieces.com or +86 189 2135 9659.
- UTS, aged
- 2310 MPa min
- 0.2% proof
- 2242 MPa min
- Hardness, aged
- 53 HRC min
- Elongation
- 6 % min
- Density
- 8.02 g/cm³
- Spec
- AMS 6515
What Maraging 350 is
Ordinary high-strength steels get their strength from carbon. You quench them to form hard martensite, then temper back some of the brittleness. Maraging steels work the other way round. Carbon is held below 0.03%, so the martensite that forms on cooling from the solution annealing temperature is soft and tough, around 30 to 35 HRC, and cuts much like a mild steel. Strength comes later, during a low-temperature ageing soak, when nickel-titanium and nickel-molybdenum intermetallic compounds precipitate through the martensitic matrix.
Maraging 350 sits at the top of the 18% nickel family. The grade number is its nominal tensile strength in thousands of pounds per square inch: 350 ksi, or about 2,400 MPa. The extra cobalt and roughly double the titanium of Maraging 300 are what take it there.
Three consequences matter more to a forging shop than the headline number.
- It is machined soft and hardened last. Parts are finish machined at 30 to 35 HRC and then aged, so tool wear and cycle times are those of a mild steel rather than a 55 HRC part.
- Ageing barely moves the metal. Dimensional change is small, uniform and predictable, so close-tolerance features survive hardening. Quenched and tempered steels of similar strength distort, and often need straightening or extra grinding stock.
- No quench, no atmosphere, no carbide problems. Ageing at 480 to 510 °C in air needs no protective gas, and with no carbon there is no decarburisation and no hard, crack-prone heat-affected zone when the material is welded.
Where this grade is filed on this site. This page sits in our nickel alloy section because of the 18% nickel content, but Maraging 350 is an iron-based steel, not a nickel-base alloy and not a stainless steel. Chromium is capped at 0.50%, far below the 10.5% or so needed for passivity, so it will rust without a coating. Corrosion protection options are covered in the FAQ.
Names, designations and specifications
Maraging 350 reaches us under a dozen different names. They all refer to the same alloy.
| Common names | Maraging 350, Maraging C350, C350, C-350, 18Ni(350), 18Ni-350, MS350 |
|---|---|
| Trade names | Vascomax C350, ATI C-350, AlMar 350 |
| UNS | K93160 |
| Aerospace spec | AMS 6515 (bar, forgings, tubing) |
| Military spec | MIL-S-46850 |
| Werkstoff / DIN | 1.6355 |
| Nominal composition | 18Ni, 12Co, 4.8Mo, 1.4Ti, balance Fe |
| Delivery conditions | Solution annealed (30 to 35 HRC), or solution annealed and aged (53 HRC min) |
If your specification uses a designation not listed here, send it with the enquiry and we will confirm equivalence before quoting.
Chemical composition of Maraging 350
Jiangyin Jiangnan Metal Co., Ltd. supplies Maraging 350 to the AMS 6515 chemistry below, verified by ladle analysis and reported on every EN 10204 mill certificate. Product analysis is available on request.
| Element | Min | Max | Role in the alloy |
|---|---|---|---|
| Ni, Nickel | 18.00 | 19.00 | Forms the soft, tough lath martensite matrix |
| Co, Cobalt | 11.50 | 12.50 | Lowers molybdenum solubility, driving precipitation |
| Mo, Molybdenum | 4.60 | 5.20 | Forms Ni3Mo strengthening precipitates |
| Ti, Titanium | 1.30 | 1.60 | Forms Ni3Ti, the main strengthener in C350 |
| Al, Aluminium | 0.05 | 0.15 | Deoxidiser, minor precipitation contribution |
| C, Carbon | – | 0.03 | Held low, since carbides would embrittle the alloy |
| Si, Silicon | – | 0.10 | Residual |
| Mn, Manganese | – | 0.10 | Residual |
| P, Phosphorus | – | 0.010 | Impurity, restricted for toughness |
| S, Sulphur | – | 0.010 | Impurity, restricted for toughness |
| Cr, Chromium | – | 0.50 | Residual, too low for stainless behaviour |
| Cu, Copper | – | 0.50 | Residual |
| Fe, Iron | Balance | Base metal | |
Phosphorus and sulphur are held to 0.010% max because maraging steels rely on clean, inclusion-free steel for their toughness. That is why the grade is double melted rather than air melted. See how we forge it.
Mechanical properties of Maraging 350
The table gives the guaranteed minimums we certify to in the aged condition, alongside the values our test pieces usually reach and the properties of the material as delivered before ageing.
| Property | Solution annealed (as supplied) | Aged (AMS 6515 min) | Aged (typical) |
|---|---|---|---|
| Tensile strength | 1030 MPa approx. | 2310 MPa / 335 ksi | 2380 to 2450 MPa |
| 0.2% proof stress | 830 MPa approx. | 2242 MPa / 325 ksi | 2280 to 2350 MPa |
| Elongation (4D) | 17 % approx. | 6 % min | 7 to 9 % |
| Reduction of area | 70 % approx. | 25 % min | 30 to 40 % |
| Hardness | 30 to 35 HRC | 53 HRC min | 55 to 58 HRC |
| Fracture toughness KIc | – | not specified | 30 to 50 MPa·m0.5 |
| Charpy V-notch | high | by agreement | 15 to 25 J |
Typical and annealed values are indicative figures for orientation, not design allowables. Certified values are the AMS 6515 minimums, and the mill test certificate issued with your forging governs. Fracture toughness in particular is sensitive to melt practice, section size and test orientation, so request lot-specific testing if the part is fracture-critical.
Read the toughness row before specifying this grade. Maraging 350 buys its extra 400 MPa over Maraging 300 with a large loss of fracture toughness. For fracture-critical, pressure-retaining or fatigue-driven parts, Maraging 300 is very often the better engineering answer. We would rather quote the right grade. See when Maraging 350 is the wrong choice.
Ageing response, where the strength comes from
Maraging 350 gains roughly 25 HRC and more than 1,300 MPa of tensile strength during a single 480 °C soak, without a quench. The curve below shows the shape of that response. Almost all of the hardening happens in the first three hours. Beyond about six hours the alloy begins to over-age as precipitates coarsen and reverted austenite forms.
| Ageing time at 480 °C | Hardness |
|---|---|
| 0 h, solution annealed | 32 HRC |
| 1 h | 48.5 HRC |
| 2 h | 54 HRC |
| 3 h | 56 HRC |
| 6 h | 57.5 HRC |
Physical properties
| Property | Value | Note |
|---|---|---|
| Density | 8.02 g/cm³ (0.290 lb/in³) | Higher than plain carbon steel, due to Ni, Co and Mo |
| Modulus of elasticity | 180 to 190 GPa | Slightly below carbon steel, so check stiffness-driven designs |
| Coefficient of thermal expansion | 10.1 × 10-6 /K (20 to 300 °C) | Low, which helps dimensional stability in tooling |
| Maximum service temperature | 450 °C approx. | Strength is retained to about this point |
| Low-temperature toughness | good to −50 °C and below | No sharp ductile to brittle transition in this range |
| Magnetic | Ferromagnetic | Martensitic matrix, so not suitable where non-magnetic is required |
| Nitriding | Yes | Surface above 60 HRC for wear faces, done during or after ageing |
Typical values for guidance. Where a physical property drives your design, modulus in particular, request the specific value for your heat.
Heat treatment of Maraging 350 forgings
Hardening happens last, at low temperature, after the metal has been cut. The standard route has four steps.
| Step | Parameters | Result |
|---|---|---|
| 1. Solution anneal | 815 to 830 °C, about 1 h per 25 mm section, air cool | Soft lath martensite, 30 to 35 HRC |
| 2. Machine | Rough and finish machine soft, leave 0.1 to 0.3 mm stock | Cuts like a mild steel |
| 3. Age | 480 to 510 °C, 3 to 6 h, air cool, ±5 °C control | 53 to 58 HRC, 2310 MPa min UTS |
| 4. Finish and inspect | Light finishing, hardness, tensile, UT | Certified to AMS 6515 |
- No protective atmosphere is required. With carbon below 0.03% there is nothing to decarburise, so air furnaces are used for both stages.
- Heavy sections need the longer soak, six hours rather than three, so that the centre reaches temperature and completes precipitation.
- Ageing temperature control is the critical variable. A drift of ±5 °C moves the end point measurably and shows up as scatter in fatigue life.
- Order the delivery condition you want. We supply Maraging 350 forgings solution annealed for customers who machine and age in house, or fully aged and certified.
Maraging 350 forgings we produce
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, not a stockist. Every Maraging 350 piece is forged to the customer's drawing rather than cut from standard stock. The forms below cover most enquiries.
| Item | Capability |
|---|---|
| Diameter range | 100 to 6,000 mm |
| Length range | 100 to 12,000 mm |
| Single-piece weight | 10 kg to 15,000 kg |
| Press and hammers | 4,500 t hydraulic press, plus 1 t, 3 t, 6 t and 9 t forging hammers |
| Ring rolling | 3 m and 6 m radial-axial seamless ring rolling mills |
| Melting routes | VIM and ESR, or VIM, ESR and VAR |
| Product forms | Seamless rolled rings, forged rings, round and square bars, shafts, spindles, eccentric shafts, discs, flanges, sleeves, bushings, tube sheets, blocks, nozzles, valve parts |
| Heat treatment | Solution annealing and ageing in house |
| Machining | Rough or finish machined to drawing |
| Minimum order | Single piece and prototypes accepted |
| Maraging 350 size limit | Confirmed per enquiry. Ingot availability for this grade governs, not press capacity |
The figures above are our general open-die capability across all grades. For Maraging 350 the binding constraint is almost always ingot availability rather than press capacity, so send the dimensions and we will confirm feasibility and lead time before quoting.
How we forge Maraging 350
Jiangyin Jiangnan Metal Co., Ltd. has forged in Jiangyin, Jiangsu since 1997 and employs about 460 people, among them 9 senior engineers, 32 intermediate engineers and 140 technicians. Shop approvals include CCS, BV, DNV, Lloyd's Register and NK.
Maraging steels depend on clean steel, so melting practice matters as much as the forging. Jiangyin Jiangnan Metal Co., Ltd. sources Maraging 350 melted by vacuum induction melting followed by electroslag remelting (VIM and ESR), or by VIM, ESR and vacuum arc remelting where the specification calls for it. Both routes take sulphur, phosphorus and non-metallic inclusions down to the levels the grade's toughness depends on.
1. Ingot inspection
Heat number, ladle analysis and PMI verification before the ingot enters the shop, with traceability carried through to the finished forging.
2. Heating
Soaked to 1,150 to 1,200 °C with controlled ramp rates. Maraging steels are forged in a narrower window than carbon steels and are not worked below about 900 °C.
3. Open-die forging
Upsetting and drawing on hydraulic presses to break down the cast structure and develop grain flow along the part's principal stress direction.
4. Ring rolling
Radial-axial rolling for seamless rings, giving continuous circumferential grain flow that a cut or welded ring cannot match.
5. Solution annealing
815 to 830 °C, air cooled, to reset the structure to soft martensite and remove forging stresses.
6. Machining and ageing
Rough or finish machining in the soft condition, then ageing at 480 to 510 °C where the aged condition is ordered.
7. NDT
Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus MPI or dye penetrant on machined surfaces where specified.
8. Certification and packing
EN 10204 3.1 or 3.2 certificate, dimensional report, oiling and VCI wrapping, seaworthy crating.
Maraging 350 vs Maraging 300 vs Maraging 250
The three common 18% nickel grades differ mainly in cobalt and titanium. More titanium means more Ni3Ti precipitate, which means more strength and less toughness.
| Property | Maraging 250 C250 | Maraging 300 C300 | Maraging 350 C350 |
|---|---|---|---|
| UNS | K92890 | K93120 | K93160 |
| AMS spec | 6512 | 6514 | 6515 |
| Nickel | 18 % | 18 % | 18 % |
| Cobalt | 7.5 to 8.5 % | 8.5 to 9.5 % | 11.5 to 12.5 % |
| Titanium | 0.30 to 0.50 % | 0.60 to 0.80 % | 1.30 to 1.60 % |
| Tensile strength, aged | 1,720 MPa approx. | 1,930 to 2,000 MPa | 2,310 to 2,400 MPa |
| Elongation | 8 to 10 % | 7 to 8 % | 6 to 8 % |
| Hardness, aged | 48 to 50 HRC | 50 to 54 HRC | 53 to 58 HRC |
| Fracture toughness KIc | 100 to 150 MPa·m0.5 | 70 to 110 MPa·m0.5 | 30 to 50 MPa·m0.5 |
| Best suited to | Tooling and structural parts where toughness leads | The general-purpose choice: aerospace structure, shafts, dies | Strength-limited parts where toughness is not critical |
Nominal values collated from published grade data for orientation. Fracture toughness in particular varies widely with melt practice, section size and orientation, and should be verified by test for critical parts. We forge all three grades, Maraging 250, Maraging 300 and Maraging 350, so we have no commercial reason to push you toward the strongest one.
When Maraging 350 is the wrong choice
Specifying the highest number on the datasheet is a common and expensive mistake. Consider a different grade if any of the following apply.
- The part is fracture-critical or holds pressure. At 30 to 50 MPa·m0.5 the critical flaw size in Maraging 350 is small. Maraging 300 gives up roughly 400 MPa and returns roughly double the toughness.
- The design is stiffness-limited rather than strength-limited. Modulus is around 180 to 190 GPa regardless of grade, so a stronger steel buys nothing against deflection.
- Service runs above about 450 °C. The precipitates over-age and strength falls away. Look at Waspaloy, Inconel 625 or Multimet N155 instead.
- The part must resist corrosion without a coating. Maraging 350 is not stainless. PH13-8Mo, 17-4PH or 15-5PH combine high strength with a passive surface.
- Budget is the binding constraint and 1,900 MPa would do. Cobalt and the double-melt route make maraging steels expensive. A quenched and tempered 4340 or 300M forging costs a fraction as much if you can live with the distortion and the quench.
Tell us what the part does and what it has to survive, and we will tell you which of the grades we forge fits, including when that grade is a cheaper one.
Applications for Maraging 350 forgings
Maraging 350 is specified where strength to weight governs and the part can be designed around its toughness. Typical forged applications include the following.
Aerospace structure
Landing gear components, take-off and arrestor gear, high-load fittings and lugs, forged from bar and disc stock and machined before ageing.
Rocket and missile hardware
Motor cases, forged rings and shells, where strength to weight is the design driver.
High-performance shafting
Forged shafts, spindles and eccentric shafts for gearboxes, turbines, compressors and power transmission running at high torque density.
Gears and splines
Forged gear blanks and pinions, often nitrided after ageing for a wear-resistant face above 60 HRC.
Tooling and die inserts
Extrusion and die-casting tooling, punches and cold-forming dies that need dimensional stability through hardening.
Fasteners and studs
High-strength forged bolt blanks and studs for joints that would need an oversized fastener in a conventional steel.
Oil and gas, subsea
Forged valve stems, valve blocks and bodies, sleeves and bushings, where the coating system is designed alongside the part.
Heavy industry
Forged rolls, wheels, manifolds and crankshafts for mills, mixers, marine and heavy machinery.
Related forged shapes in other grades: forged rings, forged valve stems, Waspaloy forging shafts, MP159 forging shafts.
Testing, inspection and certification
Every Maraging 350 forging leaves Jiangyin Jiangnan Metal Co., Ltd. with an EN 10204 3.1 mill certificate as standard, and with an EN 10204 3.2 certificate witnessed by a third party, TUV, SGS, BV, Lloyd's Register or DNV, when the order calls for it. The shop also holds CCS, BV, DNV, Lloyd's Register and NK approvals.
| Test | Standard | Scope |
|---|---|---|
| Chemical analysis | AMS 6515 / MIL-S-46850 | Standard, ladle. Product analysis on request |
| Tensile test | ASTM E8 / ISO 6892-1 | Standard, on a representative test piece |
| Hardness | ASTM E18 (HRC) | Standard |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Standard, acceptance class per order |
| Magnetic particle | ASTM E1444 / EN 10228-1 | Optional |
| Dye penetrant | ASTM E1417 / EN 571-1 | Optional |
| Charpy impact | ASTM E23 / ISO 148-1 | Optional, temperature by agreement |
| PMI verification | XRF / OES | Optional |
| Grain size, macro-etch | ASTM E112 / ASTM E381 | Optional |
| Dimensional report | To drawing | Optional |
| Certificate | EN 10204 3.1 / 3.2 | 3.1 standard, 3.2 on request |
Marking and traceability: heat number, part number and specification are hard-stamped or vibro-etched on every piece and cross-referenced to the certificate.
Export control and compliance
Maraging 350 is a controlled dual-use material. Maraging steels capable of tensile strengths above roughly 1,950 to 2,050 MPa are listed on dual-use export control schedules in most jurisdictions, for example ECCN 1C216 in the United States, the corresponding entry in the EU Dual-Use Regulation, and the Nuclear Suppliers Group guidelines. Aged Maraging 350 sits well above that threshold.
Orders therefore require end-use and end-user documentation and, depending on destination, an export licence before shipment. Jiangyin Jiangnan Metal Co., Ltd. supplies the material specification, certification and technical documentation buyers need to support their own compliance filings, and works only with customers who can document a legitimate industrial end use. Please raise the destination country and application at enquiry stage, so that documentation runs in parallel with production rather than after it.
Frequently asked questions about Maraging 350
What is Maraging 350 steel?
Maraging 350 is an ultra-high-strength, essentially carbon-free steel containing about 18% nickel, 12% cobalt, 4.8% molybdenum and 1.4% titanium, with the balance iron. It hardens by precipitating intermetallic compounds during a low-temperature ageing treatment rather than by quenching, which is why it reaches a minimum tensile strength of 2,310 MPa with very little distortion. It is also written C350, 18Ni(350), Vascomax C350, UNS K93160 and W.Nr 1.6355, and is covered by AMS 6515 and MIL-S-46850.
What is the tensile strength of Maraging 350?
After ageing, Maraging 350 has a minimum tensile strength of 2,310 MPa (335 ksi) and a minimum 0.2% proof stress of 2,242 MPa (325 ksi), with 6% minimum elongation, 25% minimum reduction of area and 53 HRC minimum hardness. Typical mill results sit around 2,400 MPa. In the as-supplied solution annealed condition the steel is far softer, around 30 to 35 HRC and roughly 1,030 MPa, which is what makes it easy to machine before ageing.
Is Maraging 350 a stainless steel or a nickel alloy?
Neither. Maraging 350 is an iron-based ultra-high-strength steel. Chromium is limited to 0.50% maximum, far below the 10.5% or so needed for stainless behaviour, so it is not stainless and will rust in humid or marine service unless protected. It is often filed under nickel alloys by suppliers, including on this site, because of its 18% nickel content, but nickel here is an alloying element in a steel, not the base metal.
What is the difference between Maraging 300 and Maraging 350?
Both are 18% nickel maraging steels, but Maraging 350 carries more cobalt (11.5 to 12.5% against 8.5 to 9.5%) and roughly twice the titanium (1.30 to 1.60% against 0.60 to 0.80%). The extra titanium drives more Ni3Ti precipitation, so Maraging 350 ages to about 2,310 to 2,400 MPa against roughly 1,930 to 2,000 MPa for Maraging 300.
The trade-off is toughness. Published plane-strain fracture toughness for aged Maraging 350 is typically only about 30 to 50 MPa·m0.5 against roughly 70 to 110 MPa·m0.5 for Maraging 300. For a fracture-critical or pressure-retaining part, Maraging 300 is usually the better engineering choice.
What is the heat treatment for Maraging 350?
Solution anneal at 815 to 830 °C for about one hour per 25 mm of section and air cool, which gives soft martensite at 30 to 35 HRC. Machine the part in that condition, then age at 480 to 510 °C for 3 to 6 hours and air cool, which raises hardness to roughly 53 to 58 HRC. No quench and no protective atmosphere are needed because the steel is essentially carbon-free, and dimensional change during ageing is small and predictable, which is why close-tolerance parts are finish machined before ageing rather than after.
Can Maraging 350 be welded?
Yes. With carbon below 0.03% there is no carbide formation and no hard, crack-prone heat-affected zone, so Maraging 350 welds far more readily than quenched and tempered steels of comparable strength. TIG and electron beam welding are both used, with matching filler, in the solution annealed condition and with clean, oil-free, oxide-free joint preparation. The assembly is aged after welding so that weld and parent metal harden together. Weld metal strength still falls short of parent metal in the highest-strength grades, so joints in Maraging 350 should be placed away from peak stress.
Can Maraging 350 be forged into large seamless rolled rings?
Yes. We run a 4,500 t open-die hydraulic press, forging hammers of 1, 3, 6 and 9 tonnes, and radial-axial seamless ring rolling mills of 3 m and 6 m. Maraging 350 is forged at about 1,150 to 1,200 °C with finishing above roughly 900 °C, then air cooled and solution annealed. For this grade the practical size limit on any given order is usually ingot availability rather than press capacity, so send the ring dimensions and finished weight and the quotation will confirm what is achievable.
Does Maraging 350 rust, and does it need a coating?
Maraging 350 corrodes at roughly the rate of a low-alloy steel and it does rust, because chromium is capped at 0.50%. In service it is normally protected by cadmium or zinc-nickel plating, phosphating, painting, passivation or nitriding, and parts are oiled and VCI-wrapped for shipment. Maraging steels generally resist stress corrosion cracking and hydrogen embrittlement better than quenched and tempered steels at the same strength level, but they are not immune, so any plating process should be followed by a hydrogen bake-out.
What standards and certificates come with Maraging 350 forgings?
Chemistry and properties are supplied to AMS 6515 and MIL-S-46850. Jiangyin Jiangnan Metal Co., Ltd. issues EN 10204 3.1 mill certificates as standard and EN 10204 3.2 certificates witnessed by a third party such as TUV, SGS, BV, Lloyd's Register or DNV on request. Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 to the acceptance class stated on the order, and magnetic particle, dye penetrant, PMI, hardness, tensile and Charpy testing can be added.
What is the minimum order quantity and lead time?
There is no fixed minimum quantity. Single-piece and prototype orders for Maraging 350 are accepted, although small pieces are usually more economical when nested into one forging batch. Lead time depends on ingot availability for this grade, the delivery condition ordered and the ultrasonic and certification scope, and is confirmed with the quotation.
Is Maraging 350 subject to export control?
Yes. Maraging steels capable of tensile strengths above roughly 1,950 to 2,050 MPa, which includes Maraging 350 in the aged condition, appear on dual-use export control lists in most jurisdictions, for example ECCN 1C216 in the United States and the equivalent entries under the EU Dual-Use Regulation and the Nuclear Suppliers Group guidelines. Orders therefore require end-use and end-user documentation and, depending on destination, an export licence before shipment. Jiangyin Jiangnan Metal Co., Ltd. supplies the specification and certification needed to support a buyer's compliance filings.
How do I get a quotation for a Maraging 350 forging?
Email a drawing or dimensioned sketch to sales@steelforgepieces.com, or call +86 189 2135 9659. Include the finished dimensions or rough forging size, the quantity, the specification you work to, the delivery condition (solution annealed or aged), the machining allowance, the ultrasonic acceptance class and the certificate type. With that information Jiangyin Jiangnan Metal Co., Ltd. normally returns a price and lead time within one working day.