Material data sheet · Maraging steel
UNS K93120 (Maraging 300) Forgings Rolled rings · shafts · flanges · discs · sleeves · tube sheets · bars
Grade UNS K93120 · W.Nr. 1.6358 · AMS 6514 · ASTM A538 Gr C | Updated
Quick answer
UNS K93120 is the UNS designation for 18% nickel maraging steel grade 300, also called Maraging 300, C300, 18Ni(300) or Vascomax C300. It is an ultra-low-carbon iron–nickel alloy strengthened by cobalt, molybdenum and titanium. In the solution-annealed condition the alloy machines at about 30–35 HRC. A single low-temperature age at roughly 480 °C then raises it to 1,900–2,050 MPa (275–297 ksi) tensile strength and 50–54 HRC, with very little distortion.
Jiangyin Jiangnan Metal Co., Ltd. forges UNS K93120 to AMS 6514 and ASTM A538 Grade C at its open-die plant in Jiangyin, Jiangsu, China. Product forms include rolled rings, shafts, flanges, discs, sleeves and tube sheets up to about 2,500 mm OD, supplied with EN 10204 3.1 or 3.2 certification. Enquiries: sales@steelforgepieces.com · +86-189-2135-9659.
- UNS number
- K93120
- Common names
- Maraging 300, C300, 18Ni(300), Vascomax C300
- Werkstoff Nr.
- 1.6358 (X2NiCoMo18-9-5)
- Key specifications
- AMS 6514 · ASTM A538 Gr C · ASTM A579 · MIL-S-46850
- Melt route
- VIM + VAR (aerospace) · VIM + ESR (industrial)
- Aged strength
- 1,900–2,050 MPa UTS · 50–54 HRC
- Forged size range
- 20 – 2,500 mm OD · up to ~8 t per piece
- Delivery condition
- Solution annealed, or annealed + aged
§ 01
What UNS K93120 is
UNS K93120 is a maraging steel. It hardens through intermetallic compounds that precipitate during a low-temperature age, and carbon plays almost no part in the process.
Ordinary high-strength steels get their hardness from carbon trapped in the lattice after a fast quench. That mechanism carries a penalty. The harder the steel gets, the more brittle it becomes, and the quench pulls the part out of shape. UNS K93120 behaves differently. Carbon is held below 0.03%, and the strength comes from Ni₃Mo and Ni₃Ti precipitates that form when the alloy is held at about 480 °C.
For anyone specifying a forging, that changes three practical things:
- Machine soft, harden later. At 30–35 HRC in the annealed state, UNS K93120 cuts like a medium alloy steel. Complex features can be finished before hardening.
- Almost no distortion. Ageing is an air-cool process with roughly 0.05% uniform contraction, so there is no quench crack risk and no straightening operation.
- Toughness at very high strength. At around 1,950 MPa, UNS K93120 still holds fracture toughness in the region of 70–90 MPa·√m, well above what a carbon-hardened steel manages at the same strength.
UNS K93120 is not a stainless steel. Several supplier data sheets describe Maraging 300 as an "iron–nickel stainless steel". No chromium is added to this grade, so it will rust. Plating, phosphating, nitriding, passivation or paint is normal for parts in humid or wet service.
§ 02
Designations, standards and equivalents
| UNS | K93120 |
|---|---|
| Trade & common names | Maraging 300, Maraging C300, 18Ni(300), Type 300, Vascomax C300 |
| Werkstoff / DIN | 1.6358 (X2NiCoMo18-9-5); 1.6354 also cited |
| Aerospace (bar, forging stock, rings) | AMS 6514 |
| ASTM (plate and pressure) | ASTM A538 Grade C |
| ASTM (superstrength forgings) | ASTM A579 (Grade 73 covers the 18Ni-300 type) |
| Military | MIL-S-46850, MIL-S-13881 |
| Sheet, strip and plate (18Ni family) | AMS 6521 |
| GB / JIS / EN structural | No exact equivalent; order against AMS 6514 or ASTM A538 Gr C |
The three UNS numbers are easy to mix up. Maraging 250 is UNS K92890, Maraging 300 is UNS K93120 and Maraging 350 is UNS K93160. Cobalt, molybdenum and titanium levels differ between them, so they cannot be substituted for one another. The comparison table below sets them side by side.
§ 03
Chemical composition of UNS K93120
Composition limits below follow AMS 6514 and ASTM A538 Grade C. Every heat we forge is supplied with the mill's ladle analysis, and product analysis can be added on request.
| Element | Specified range | Typical | Role in the alloy |
|---|---|---|---|
| Nickel, Ni | 18.0 – 19.0 | 18.5 | Forms the soft, ductile iron–nickel martensite matrix |
| Cobalt, Co | 8.5 – 9.5 | 9.0 | Lowers Mo solubility so more Ni₃Mo precipitates on ageing |
| Molybdenum, Mo | 4.6 – 5.2 | 4.8 | Primary strengthener, as Ni₃Mo |
| Titanium, Ti | 0.55 – 0.80 | 0.65 | Secondary strengthener, as Ni₃Ti |
| Aluminium, Al | 0.05 – 0.15 | 0.10 | Deoxidiser, small ageing contribution |
| Carbon, C | 0.03 max | ≤ 0.02 | Restricted, since carbides would cut toughness |
| Silicon, Si | 0.10 max | ≤ 0.06 | Restricted for cleanliness |
| Manganese, Mn | 0.10 max | ≤ 0.05 | Restricted for cleanliness |
| Phosphorus, P | 0.010 max | ≤ 0.005 | Embrittles grain boundaries |
| Sulphur, S | 0.010 max | ≤ 0.004 | Embrittles grain boundaries |
| Boron, B | 0.003 max | — | Aerospace cleanliness control (AMS) |
| Zirconium, Zr | 0.02 max | 0.01 | Grain refinement |
| Calcium, Ca | 0.05 max | — | Aerospace cleanliness control (AMS) |
| Iron, Fe | Balance | ~67 | Base |
Chromium is not specified in UNS K93120, so this grade is not corrosion resistant.
Melting route
Because carbon, sulphur and phosphorus must all stay near trace levels, UNS K93120 is vacuum melted. VIM + VAR (vacuum induction melting followed by vacuum arc remelting) is the double-vacuum route required for aerospace-quality material to AMS 6514. VIM + ESR is available where a tooling or general industrial application does not call for the aerospace melt. State the melt route you need on the enquiry, since it affects both price and lead time.
§ 04
Mechanical properties: annealed vs aged
A single 480 °C age roughly doubles the strength of UNS K93120. Both conditions are listed below, because parts are usually bought in one and used in the other.
| Property | Solution annealed | Aged 480 °C |
|---|---|---|
| 0.2% proof / yield strength | 760 – 830 MPa 110 – 120 ksi | 1,860 – 1,960 MPa 270 – 284 ksi |
| Ultimate tensile strength | 965 – 1,035 MPa 140 – 150 ksi | 1,900 – 2,050 MPa 276 – 297 ksi |
| Elongation (4D) | 16 – 19 % | 6 – 10 % |
| Reduction of area | 70 – 75 % | 35 – 55 % |
| Hardness | 30 – 35 HRC | 50 – 54 HRC |
| Fracture toughness KIC | — | ≈ 70 – 90 MPa·√m |
| Charpy V-notch impact | high | ≈ 20 – 27 J |
Values are typical for forged and heat-treated UNS K93120 and are given for design orientation only. Guaranteed minima depend on the ordered specification, section size and test location, and are confirmed on the mill test certificate for each heat.
§ 05
Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.0 g/cm³ | 0.289 lb/in³ |
| Melting range | ≈ 1,413 °C | ≈ 2,575 °F |
| Modulus of elasticity | 190 GPa | 27,600 ksi |
| Shear modulus | 73 GPa | 10,600 ksi |
| Poisson's ratio | 0.30 | 0.30 |
| Thermal conductivity (20 °C) | 25.3 W/m·K | 176 BTU·in/hr·ft²·°F |
| Mean thermal expansion (21–480 °C) | 10.1 µm/m·°C | 5.6 µin/in·°F |
| Magnetic response | Ferromagnetic in both annealed and aged conditions | |
§ 06
Forging and heat treatment of UNS K93120
Forging
We heat UNS K93120 stock to 1,150 – 1,200 °C and finish forging above about 900 °C, then air cool. Reheating is preferred to finishing cold, because working below the recommended finish temperature raises forging loads without refining the structure further. Every forging is solution annealed after the last hot-work operation to reset grain size and dissolve the ageing precipitates.
Solution annealing
815 – 830 °C, roughly one hour per 25 mm of section, air cool. This produces the soft, fully martensitic condition at 30–35 HRC in which UNS K93120 is machined, welded and formed. After heavy hot work a higher homogenising anneal in the 900–1,050 °C range may be used first, followed by the standard 815–830 °C solution treatment.
Ageing
480 °C (900 °F) for 3 – 6 hours, air cool. There is no quench and no straightening operation afterwards, and most industrial work does not call for a protective atmosphere. Longer ageing gives a small further rise in hardness before the alloy over-ages. Shorter cycles are sometimes used to hold a particular strength and toughness balance.
Plan for shrinkage. Ageing contracts UNS K93120 by roughly 0.05% in every direction, about 0.5 mm per metre. The change is uniform and repeatable, so parts are commonly machined to near-final size in the annealed condition and aged last. Measure a first article before releasing a production batch, particularly on long shafts and large-diameter rings.
Machining and welding
- Machining: no particular difficulty in the annealed condition. Treat it broadly like a 4340-class alloy steel at similar hardness. Rigid setups and sharp tooling matter more once the part is aged.
- Welding: readily welded by TIG, electron beam and laser without preheat, using matching maraging filler. Weld in the annealed condition, then age the assembly so weld and parent metal reach comparable strength.
- Grinding and finishing: normal practice for a 50+ HRC steel. Avoid grinding burn, which can leave residual tensile stress in a high-strength part.
- Surface protection: the grade is not corrosion resistant, so specify plating, nitriding, phosphating or paint for damp service.
§ 07
UNS K93120 forged product forms we supply
Every item below is produced as an open-die forging or a seamless rolled ring, worked to drawing or to a dimensional sketch. Rough-machined, semi-finished and finish-machined states are all available.
- Forged rings & seamless rolled ringsRectangular, contoured and stepped sections; ring rolling gives circumferential grain flow for hoop-loaded parts.
- Forged shafts & spindlesStraight, stepped and flanged shafts, plus eccentric shafts, up-set forged where a large flange is needed.
- Forged flangesBlind, weld-neck-style and special-profile flanges forged from solid, not cut from plate.
- Forged discs & disksSolid and bored discs for turbine, gear and coupling applications; upset forged for radial grain flow.
- Forged sleeves & bushingsBored and mandrel-forged hollows with sound through-wall structure.
- Forged tube sheetsThick circular plates for heat exchangers, drilled to your layout on request.
- Forged bars & blocksRound, square, flat and rectangular sections as feedstock or finished parts.
- Forged tubes & hollow barsTrepanned or expanded hollows where a seamless bore is required.
Also available in this family: nickel alloy forgings such as Inconel, Incoloy, Hastelloy and Monel. See the related grades at the foot of this page.
§ 08
Our UNS K93120 forging capability
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Jiangyin sits in the Yangtze River Delta forging cluster, about 150 km from the Port of Shanghai, so export shipments move quickly.
| Outside diameter | 20 – 2,500 mm |
|---|---|
| Single-piece weight | 0.5 kg – 8,000 kg |
| Length, shafts and bars | up to 6,000 mm |
| Processes | Open-die forging, ring rolling, upsetting, mandrel forging, trepanning |
| Heat treatment | Solution annealing and ageing in-house, with calibrated furnace charts |
| Machining | Rough, semi-finish and finish machining; CNC turning, boring, milling, drilling |
| Typical lead time | 4 – 8 weeks depending on size, melt route and machining scope |
| Minimum order | Single prototype pieces accepted |
The figures above cover the standard envelope for maraging steel work. Send the drawing and we will confirm feasibility, weight and lead time for the specific part.
§ 09
Testing, inspection and certification
Most UNS K93120 parts go into critical duty, so inspection records are usually part of the order. The following are supplied as standard or on request.
Non-destructive testing
- Ultrasonic testing to EN 10228-3, SEP 1921, ASTM A388 or your own acceptance class
- Magnetic particle inspection to ASTM E1444 / EN 10228-1 for surface indications
- Dye penetrant inspection to ASTM E165 where surface condition suits it
Mechanical and metallurgical testing
- Tensile, hardness, Charpy impact, and grain size to the ordered specification
- Chemical analysis: ladle analysis as standard, product analysis on request
- Macro and micro examination; intergranular and inclusion rating where specified
- Dimensional and roughness report against the drawing
Certification
Material test certificates are issued to EN 10204 3.1, or to EN 10204 3.2 with third-party endorsement by TÜV, SGS, BV, DNV, Lloyd's Register or your own nominated inspector. Traceability is by heat number, marked on the forging and carried through every document.
Export documentation. High-strength maraging steels are subject to export-control rules in several jurisdictions. Orders are supplied with the documentation required for lawful export, and an end-use statement may be requested before shipment. Tell us the destination country and end application at enquiry stage so the paperwork is prepared in advance.
§ 10
Where UNS K93120 forgings are used
UNS K93120 gets specified when a part has to carry a very high load in a small envelope and still hold its dimensions through hardening.
Tooling and die work
Extrusion dies and stems, die-casting inserts, cold-forming and coining tooling, punches and mandrels. The near-zero distortion on ageing lets a complex cavity be cut soft and hardened afterwards.
Aerospace and defence structures
Landing gear components, actuator bodies, structural fittings and high-load pins, ordered to AMS 6514 with VIM+VAR melt and full traceability.
Power transmission
High-torque drive shafts, gear blanks, couplings, torsion members, machine-tool spindles and clutch components, where torque capacity per unit of section is worth more than the saving on material.
Motorsport and high-performance automotive
Gearbox shafts, driveshafts, differential components and connecting hardware, where the strength-to-weight gain justifies the material cost.
Energy, process and heavy industry
Valve stems and blocks, wellhead and completion components, pump shafts, press tooling, and rolls and mandrels for metal-forming lines.
If a part is currently made in 4340, 300M, 17-4PH or a case-hardened alloy steel and the section is running out, UNS K93120 is often the next step up. Send the drawing and the duty and we will say whether the change is worth making.
§ 11
UNS K93120 compared with Maraging 250 and 350
The three 18% nickel maraging grades differ mainly in cobalt and titanium content, which sets how much precipitate forms during ageing. The higher the grade number, the higher the strength and the lower the ductility.
| Property | Maraging 250 UNS K92890 |
Maraging 300 UNS K93120 |
Maraging 350 UNS K93160 |
|---|---|---|---|
| Nickel, % | 17.0 – 19.0 | 18.0 – 19.0 | 18.0 – 19.0 |
| Cobalt, % | 7.0 – 8.5 | 8.5 – 9.5 | 11.5 – 12.5 |
| Molybdenum, % | 4.6 – 5.2 | 4.6 – 5.2 | 4.6 – 5.2 |
| Titanium, % | 0.30 – 0.50 | 0.55 – 0.80 | 1.30 – 1.60 |
| Tensile strength, aged | 1,725 – 1,800 MPa 250 – 261 ksi | 1,900 – 2,050 MPa 276 – 297 ksi | 2,340 – 2,450 MPa 339 – 355 ksi |
| Hardness, aged | 48 – 50 HRC | 50 – 54 HRC | 56 – 58 HRC |
| Elongation, aged | 8 – 12 % | 6 – 10 % | 5 – 8 % |
| Bar / forging spec | AMS 6512 | AMS 6514 | AMS 6515 |
| Best suited to | Toughness-led parts, larger sections, weldments | The general-purpose balance of strength and toughness | Maximum strength where ductility can be traded away |
All three are processed the same way: solution anneal, machine soft, then age at about 480 °C. Maraging 350 usually needs a longer age than UNS K93120.
§ 12
How to order UNS K93120 forgings
Send a drawing or a dimensional sketch to sales@steelforgepieces.com. A quotation normally comes back within one working day. Covering the points below in the first email saves a round of questions:
- Shape and dimensions: drawing, or OD × ID × height / length with tolerances
- Quantity and whether repeat orders are expected
- Specification: AMS 6514, ASTM A538 Grade C, ASTM A579, or your own works spec
- Melt route: VIM+VAR or VIM+ESR
- Delivery condition: solution annealed, or annealed and aged to a stated hardness
- Machining state: as forged, rough machined, semi-finished or finish machined
- NDT and acceptance class: for example UT to EN 10228-3 Class 3
- Certification: EN 10204 3.1, or 3.2 with the third party you want to use
- Destination country and end application, for export documentation
§ 13
Frequently asked questions about UNS K93120
What is UNS K93120?
UNS K93120 is the Unified Numbering System designation for 18% nickel maraging steel grade 300, widely known as Maraging 300, C300 or Vascomax C300. It is an ultra-low-carbon iron–nickel alloy strengthened by cobalt, molybdenum and titanium, and it reaches about 1,900 to 2,050 MPa tensile strength after a simple 480 °C ageing treatment.
Is UNS K93120 the same as Maraging 300?
Yes. UNS K93120, Maraging 300, C300, 18Ni(300) and Vascomax C300 all describe the same grade. The related grades carry different UNS numbers, since Maraging 250 is UNS K92890 and Maraging 350 is UNS K93160, so neither one can be substituted for UNS K93120.
Is UNS K93120 a stainless steel?
No. UNS K93120 contains no chromium addition, so it is not stainless and it will rust in humid or wet service. Maraging 300 parts are normally protected by plating, passivation, phosphating, nitriding or paint. Some supplier data sheets describe the grade as stainless, which is incorrect.
What is the chemical composition of UNS K93120?
UNS K93120 contains 18.0 to 19.0% nickel, 8.5 to 9.5% cobalt, 4.6 to 5.2% molybdenum, 0.55 to 0.80% titanium and 0.05 to 0.15% aluminium, with the balance iron. Carbon is held at 0.03% maximum, and silicon, manganese, phosphorus and sulphur are all tightly restricted to protect toughness.
How is UNS K93120 heat treated?
UNS K93120 is solution annealed at 815 to 830 °C for about one hour per 25 mm of section and air cooled, which gives a soft, machinable martensite at roughly 30 to 35 HRC. Parts are then aged at about 480 °C for 3 to 6 hours and air cooled, which raises hardness to 50 to 54 HRC.
How much does UNS K93120 shrink during ageing?
Ageing causes a small, uniform contraction of roughly 0.05% in each direction, about 0.5 mm per metre. Because the change is predictable, UNS K93120 parts are often machined close to final size in the annealed condition and then aged. First-article measurement is recommended before committing a production batch.
Can UNS K93120 be welded?
Yes. The very low carbon content makes UNS K93120 readily weldable by TIG, electron beam and laser processes without preheat, using matching maraging filler. Welds should be made in the annealed condition and the assembly aged afterwards, so that weld and parent metal develop comparable strength.
Which standards cover UNS K93120 forgings?
The main specifications are AMS 6514 for bar, forging stock and rings, ASTM A538 Grade C for maraging plate and pressure applications, ASTM A579 for superstrength alloy steel forgings, and MIL-S-46850. The German material number is 1.6358. There is no exact GB, JIS or EN structural equivalent.
What sizes of UNS K93120 forgings can be supplied?
Jiangyin Jiangnan Metal Co., Ltd. supplies UNS K93120 open-die forgings and seamless rolled rings from roughly 20 mm up to 2,500 mm outside diameter and single-piece weights up to about 8 tonnes, as rings, shafts, flanges, discs, sleeves, bushings, tube sheets, bars and blocks.
Who supplies UNS K93120 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, that forges UNS K93120 maraging 300 rings, shafts, discs and flanges to AMS 6514 and ASTM A538 Grade C. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
Request a quotation
Send your UNS K93120 drawing
Open-die forgings and seamless rolled rings in UNS K93120 (Maraging 300), forged to AMS 6514 and ASTM A538 Grade C, heat treated and machined in house, certified to EN 10204 3.1 or 3.2.
Company Jiangyin Jiangnan Metal Co., Ltd.
Address No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone +86-189-2135-9659
Email sales@steelforgepieces.com