Maraging Steel · 18% Nickel, Cobalt-Molybdenum Strengthened

Maraging 300 / C300 / UNS K93120 / AMS 6514 Forging Parts

• 🇺🇸 USAUNS K93120
  AMS 6514
• 🇺🇸 ASTMA538 Gr. B
  A579 Gr. 72
• 🇺🇸 MilitaryMIL-S-46850D
  Type III Gr. 300
• 🇪🇺 Europe1.6354 · 1.6358
  X2NiCoMo18-9-5
• 🇨🇳 China18Ni(300)
  00Ni18Co9Mo5TiAl
• 📜 Trade namesVascomax® C300
  NiMark® 300

Published: 18 May 2016  |  Last updated: 20 August 2026  |  Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

UNS

K93120

Werkstoff

1.6354

Spec

AMS
6514

Nickel

18wt %

Cobalt

9wt %

UTS aged

2000MPa (290 ksi)

Hardness aged

52–54HRC

Aging temp

480°C (900 °F)

Density

8.0g/cm³

Eight free Maraging 300 engineering tools

These calculators are built specifically for this grade and run entirely in your browser. Nothing is uploaded and nothing is stored. They exist because the three questions we are asked most about Maraging 300 are all arithmetic: what will the aging cycle give me, how much will the part shrink, and what does the forging weigh.

What is Maraging 300 (UNS K93120)?

Maraging 300 is an iron-nickel martensitic steel that reaches roughly 2,000 MPa tensile strength without carbon. Ordinary ultra-high-strength steels such as 4340 and 300M get their strength from carbon trapped in a distorted martensite lattice, and they pay for it in quench distortion, cracking risk, poor weldability and severe notch sensitivity. Maraging steel takes a different route. Carbon is deliberately held below 0.03 %, so the martensite that forms on cooling is soft, tough and dislocation-rich rather than hard and brittle. All the strength is then added afterwards, at low temperature, by precipitating nanometre-scale intermetallic compounds, principally Ni₃Mo, Ni₃Ti and Fe₂Mo, inside that martensite. The name is a contraction of martensite and aging.

Three things follow from that mechanism, and between them they explain almost everything about how the grade is used.

• Hardening happens at 480 °C, not 850 °C, and there is no quench. The part is machined soft at 30–35 HRC, then aged in air. Nothing is quenched into water or oil, so there is no thermal shock, no distortion from differential cooling and no quench cracking. A finished die or a 3-metre shaft comes out of the aging furnace essentially the shape it went in.
• The transformation is diffusionless and section-independent. Maraging 300 hardens fully through the section whether it is 20 mm or 400 mm thick, because there is no cooling-rate-dependent transformation to miss. Heavy forgings therefore have the same properties at the core as at the surface — the single biggest advantage over 4340 in thick sections.
• Cobalt does not precipitate; it makes molybdenum work harder. The 9 % cobalt in Maraging 300 forms no precipitate of its own. It lowers the solubility of molybdenum in the martensite, which drives far more Ni₃Mo and Fe₂Mo out of solution during aging. Remove the cobalt and the same nickel and molybdenum give a much weaker steel — which is precisely why cobalt-free maraging variants exist and why they top out lower.

The trade-off is corrosion resistance. With essentially no chromium, Maraging 300 rusts like a plain low-alloy steel and must be plated, painted, oiled or otherwise protected in service. It is also, at 2 GPa, in the strength band where hydrogen embrittlement and stress-corrosion cracking become real design constraints rather than theoretical ones; see corrosion and hydrogen embrittlement below.

Maraging 300 forgings: supplier quick facts

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging and ring-rolling factory in Jiangyin, Jiangsu Province, China, producing Maraging 300 (UNS K93120 / AMS 6514 / W.Nr. 1.6354) forged rings, seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets and bars to customer drawings.

⚠ Melting route, supplied condition and lead time depend on the order. The figures above describe our normal practice for this grade and are confirmed in writing on every quotation.

What forged products are available in Maraging 300?

Jiangyin Jiangnan Metal produces Maraging 300 through three routes, chosen by geometry and quantity. Open-die forging covers long shafts, blocks, tool bodies and large discs, and is used wherever single-piece size matters more than repeatability. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter with continuous circumferential grain flow. Near-net-shape forging is used where a die profile can remove 30–50 % of the rough machining, which is worth more on this grade than on most, because Maraging 300 is expensive per kilogram and slow to machine once aged.

One route-selection point is specific to this grade. Because Maraging 300 is bought for fracture toughness at 2 GPa, inclusion cleanliness and grain flow dominate performance. Non-metallic inclusions are the crack-initiation sites that set K_IC, and a forging with grain flow following the principal stress direction will outperform the same part machined from plate by a wide margin in fatigue. For rotating and flight-critical parts, specify the forged route and state the required grain-flow direction on the drawing.

• Seamless rolled rings
• Forged rings
• Forged flanges
• Forged round bars
• Forged flat bars & blocks
• Forged discs & blanks
• Forged shafts & spindles
• Forged sleeves & bushings
• Forged tube sheets
• Forged tubes & hollows
• Forged gear blanks
• Forged die & tool blocks
• Custom near-net-shape parts

Sizes above the envelope shown can often be arranged through our partner mills. Send the drawing and we will confirm feasibility with the quotation.

What are the equivalent designations of Maraging 300?

Engineers reach this grade through at least fifteen different names, depending on the standards body, the producer and the decade the drawing came from. Every designation in the table below refers to the same nominal 18Ni-9Co-5Mo maraging chemistry at the 300 ksi strength level. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them and cross-lists the equivalents on the material certificate.

What is the chemical composition of Maraging 300?

Maraging 300 contains nominally 18–19 % nickel, 8.5–9.5 % cobalt, 4.6–5.2 % molybdenum, 0.5–0.8 % titanium and 0.05–0.15 % aluminium, with carbon held to 0.03 % maximum and iron as the balance. The chemistry looks unusual because every element is there for the aging reaction rather than for hardenability, and the elements normally regarded as useful in steel, carbon above all, are treated here as contaminants.

Limits reflect AMS 6514 practice for consumable-electrode vacuum-melted 18Ni maraging steel at the 300 ksi level. Where your order is placed to ASTM A538 Grade B, ASTM A579 Grade 72 or DIN 1.6354, the limits differ slightly; state the governing specification and revision on the purchase order and the certificate will be issued to it.

Melting practice and why it decides the toughness

Maraging 300 is more sensitive to melting practice than almost any other grade we forge. At 2 GPa the critical flaw size is small, a few hundred microns, so a single titanium-nitride or sulfide inclusion of that size is the crack. This is why AMS 6514 calls for consumable-electrode vacuum melting and why aerospace buyers specify VIM + VAR: vacuum induction melting to control the reactive elements (Ti, Al) and strip dissolved gases, followed by vacuum arc remelting to refine the inclusion population and give a directionally solidified ingot.

Jiangyin Jiangnan Metal Co., Ltd. supplies Maraging 300 forgings from VIM + VAR double-vacuum-melted stock as the default for AMS 6514 and aerospace orders, with an ESR-remelted route available for tooling and general industrial work at lower cost. The two are not equivalent in fracture toughness and should not be swapped silently. State the required melting route in your enquiry; it appears on the EN 10204 certificate along with the heat number and full ladle and product analyses.

How is Maraging 300 heat treated?

Maraging 300 is heat treated in two steps: solution annealing at 815–830 °C (1,500–1,525 °F) followed by air cooling, then aging at 480 °C (900 °F) for 3–6 hours followed by air cooling. There is no quench, no tempering and normally no protective atmosphere requirement, because the alloy is essentially carbon-free, so there is nothing to decarburise.

What happens metallurgically is worth understanding, because it is the reason the cycle is so forgiving. Solution annealing dissolves the precipitates and puts everything back into austenite. On cooling, the austenite transforms to a soft, heavily dislocated iron-nickel martensite. Because the martensite finish temperature is around 100 °C, well above room temperature, the transformation completes in still air regardless of section thickness. Aging at 480 °C then precipitates Ni₃Ti first (fast, within the first hour) and Ni₃Mo and Fe₂Mo more slowly. Hold too long or too hot and the precipitates coarsen and, worse, nickel-rich reverted austenite begins to form on the martensite laths, which softens the steel irreversibly for that cycle.

⚠ Aging response varies between heats. Every Jiangyin Jiangnan Metal order includes coupons from the delivered heat, aged with the parts, and the resulting tensile and hardness results are reported on the certificate. For dimensionally critical work, always run a sample from your own heat before committing production parts.

1. MeltVIM + VAR double vacuum (ESR route on request)
2. ForgeStart 1,150–1,200 °C, finish above 900 °C, ≥ 4:1 reduction
3. Solution anneal815–830 °C, 1 h/25 mm, air cool
4. Rough machineSoft at 30–35 HRC, leave 2–4 mm stock
5. Stress reliefOptional, 425–480 °C where stock removal was heavy
6. Finish machineTo final size plus the aging shrinkage allowance
7. Age480 °C, 3–6 h, air cool — 52–54 HRC
8. Test & certifyTensile, hardness, UT, chemistry — EN 10204 3.1 / 3.2

How much does Maraging 300 shrink when it is aged?

Maraging 300 contracts uniformly during aging, typically by 0.04 % to 0.10 % of each linear dimension, or about 0.0004 to 0.0010 inch per inch. The contraction happens because the intermetallic precipitates occupy less volume than the same atoms did in solid solution. It is uniform in all directions, it is repeatable within a heat, and it is small enough that many parts can be finish-machined before aging and used as-aged.

That last point is the commercial argument for the grade in tooling. A die-casting die in H13 must be machined, quenched, tempered, then re-machined and re-ground to correct the quench distortion. The same die in Maraging 300 is machined complete in the soft condition, aged in air, and comes out to size. On a large die that difference is worth more than the price premium on the steel.

Two cautions apply. First, the contraction rate is a property of the heat, not of the grade. Published figures span a factor of two, and shops that hold tight tolerances on this material run a test coupon from each heat before committing parts. Second, contraction is uniform only if heating is uniform. A part that goes into a cold furnace corner, or a heavy block loaded against a thin one, will age unevenly and move unevenly.

Read the middle column as the planning value and the outer columns as the uncertainty band you are exposed to if you have not run a coupon from the delivered heat. On anything tighter than IT9 at 500 mm, run the coupon.

What are the mechanical properties of Maraging 300?

In the solution-annealed condition Maraging 300 has a tensile strength of roughly 1,000 MPa (145 ksi) at 30–35 HRC. After standard aging at 480 °C it reaches 1,930–2,050 MPa (280–297 ksi) tensile and 1,860–1,965 MPa (270–285 ksi) yield at 52–54 HRC, with 6–10 % elongation. AMS 6514 sets acceptance minima of 1,965 MPa (285 ksi) tensile, 1,895 MPa (275 ksi) yield and 5 % elongation for the aged condition.

Transverse and short-transverse properties in heavy forgings are lower than longitudinal, and the gap widens with inclusion content and with section size. If your design is loaded across the grain flow, specify transverse testing on the purchase order. It is not supplied by default and the difference can be 15–25 % in ductility.

Strength at temperature

Maraging 300 holds useful strength to about 400 °C (750 °F) in continuous service. Above that the aging structure begins to change on the timescale of the exposure. The part is, in effect, being aged further by its own operating temperature, and strength falls. It is not a high-temperature alloy in the sense that Inconel 718 or Waspaloy are; the practical ceiling is set by microstructural stability, not by oxidation.

Indicative values for design screening. Where a component sees sustained temperature, request a stress-rupture or long-time exposure test on the delivered heat rather than relying on short-time tensile data.

What are the physical properties of Maraging 300?

Values marked "typical" or "≈" vary with heat, condition and section, and are given for design screening. Where any physical value is contractually important, state it on the purchase order and Jiangyin Jiangnan Metal Co., Ltd. will report the measured result on the material certificate.

Fracture toughness, fatigue and cryogenic behaviour

Maraging 300 is specified precisely because it holds usable fracture toughness at a strength level where carbon martensitic steels have almost none. Published plane-strain fracture toughness (K_IC) for aged 18Ni(300) spans roughly 50 to 110 MPa·m^0.5, and the spread is not experimental noise: it is inclusion cleanliness. Double-vacuum-melted material sits at the top of the range and air-melted or single-remelt material at the bottom. This is the single strongest argument for specifying the melting route rather than leaving it to the mill.

The comparison that matters is against quenched-and-tempered steel at the same strength. At 1,900 MPa yield, 4340 and 300M have K_IC in the region of 40–60 MPa·m^0.5 and are severely notch-sensitive. Maraging 300 at the same yield strength is typically better, and it is far less sensitive to surface defects, machining marks and grinding burn, which is why it survives in service where an equally strong carbon steel would crack from a scratch.

Fracture-toughness figures in the literature vary widely because specimen orientation, section size, aging cycle and cleanliness are all reported inconsistently. Treat the range as a screening band. Where K_IC is a design requirement, specify the test standard (ASTM E399 or ASTM E1820), the orientation (L-T, T-L, S-L) and the acceptance value on the purchase order, and Jiangyin Jiangnan Metal Co., Ltd. will arrange accredited third-party testing on the delivered heat.

Corrosion, stress-corrosion cracking and hydrogen embrittlement

Maraging 300 has essentially no chromium and therefore no meaningful corrosion resistance. It rusts in humid air like a plain low-alloy steel, and it must be protected in service by cadmium or zinc-nickel plating, nickel plating, paint, dry-film lubricant or preservative oil. Unprotected outdoor storage will produce visible surface rust within days in a coastal climate.

Two failure modes need more care than ordinary rusting, and both come from the strength level rather than the chemistry.

Hydrogen embrittlement

At 2 GPa, Maraging 300 is firmly in the strength range where absorbed hydrogen causes delayed brittle fracture. Hydrogen enters during acid pickling, electroplating and cathodic protection, and the crack appears hours or days after the load is applied, long after inspection has passed the part. The controls are standard and non-negotiable on aerospace work:

• Bake after plating. 190–205 °C for a minimum of 4 hours, and preferably 23 hours for highly stressed parts, within 4 hours of plating, per ASTM B850 / AMS 2759/9 practice.
• Avoid acid pickling where possible. Use mechanical descaling, abrasive blast or an alkaline route on aged parts.
• Prefer low-hydrogen-embrittlement coatings. Zinc-nickel, aluminium ion vapour deposition (IVD) and mechanical plating avoid the problem rather than treating it.
• Do not cathodically protect an aged maraging part in seawater without a specific engineering assessment.

Stress-corrosion cracking

Aged maraging steels are susceptible to stress-corrosion cracking in chloride environments, and susceptibility rises with strength. Maraging 300 is more resistant than a carbon martensitic steel at the same yield strength, which is one of the practical reasons it is selected for marine and subsea hardware, but it is not immune, and it is not a substitute for a stainless grade. Where a part combines high sustained tensile stress with a chloride environment, either move to Custom 450, 17-4PH or Inconel 725, or design in a sealed, coated barrier and inspect it.

Nitriding and surface engineering

Maraging 300 takes gas nitriding unusually well, and the reason is a happy coincidence of temperature. Nitriding is normally done at 455–480 °C, the same window as the aging treatment. A single furnace cycle therefore ages the core to full 2 GPa strength and produces a nitrided case, with no separate hardening step and no risk of the nitriding cycle over-tempering the substrate the way it would with a quenched-and-tempered steel.

Jiangyin Jiangnan Metal Co., Ltd. supplies Maraging 300 forgings solution-annealed or aged, with rough or finish machining. Nitriding, plating and peening are arranged through qualified subcontractors when specified on the order; name the process specification and acceptance standard in your enquiry.

How do you machine Maraging 300?

Machine Maraging 300 in the solution-annealed condition wherever possible. At 30–35 HRC it cuts much like annealed AISI 4340 at the same hardness: predictable, chip-forming and not gummy. Its machinability rating is roughly 35–40 % of free-machining AISI 1212, which puts it well ahead of austenitic stainless steel and well behind carbon steel.

Aged material at 52–54 HRC is a different problem entirely. Hardness is only half the problem. It work-hardens rapidly under a rubbing edge and its low thermal conductivity keeps the heat in the tool rather than in the chip. Almost every complaint about machining maraging steel traces back to one of three causes: a dull edge, a tool that dwelled in the cut, or insufficient rigidity.

Rules that matter for this grade

• Machine soft, age last. Take advantage of the near-zero distortion. Finish-machine in the annealed condition with the shrinkage allowance added, then age. Grinding after aging should be a correction, not the plan.
• Never let the tool dwell. A tool that stops feeding while still in contact glazes and work-hardens a layer the next pass has to cut through. This applies with double force to aged material.
• Sharp, positive-rake carbide; change early. Run inserts to a wear criterion, not to end of shift. A rounded edge on aged maraging generates heat instead of chips.
• Rigid setups, short overhangs, generous flood coolant. Thermal conductivity around 20 W/m·K means the cutting edge carries the heat.
• Heavy positive feed rather than light scraping cuts. Get under the work-hardened layer from the previous pass.
• For aged material, consider ceramic or CBN for continuous turning, and grinding with a soft, friable aluminium-oxide wheel with plenty of coolant for finish work. Watch for grinding burn — at this strength it initiates cracks.

Can Maraging 300 be welded?

Yes. Weldability is one of the main reasons the grade exists. With carbon below 0.03 %, the heat-affected zone does not form hard, crack-prone carbon martensite. No preheat is required, and the alloy can be welded in either the annealed or the aged condition.

The practical procedure is straightforward:

• Weld in the annealed condition where you can. The soft martensite accommodates weld shrinkage without cracking.
• Use matching 18Ni-300 filler, or a deliberately lower-strength maraging filler where the joint is not the critical section and you want more ductility.
• Keep the heat input low. Stringer beads, no weaving, interpass temperature below about 120 °C. High heat input coarsens the structure and forms reverted austenite bands that show up as soft zones after aging.
• Clean scrupulously. Titanium and aluminium in the alloy make it sensitive to oxygen and nitrogen pickup. Full inert gas shielding front and back, and no oil, paint, grease, sulfur or low-melting contamination anywhere near the joint.
• Age after welding. A post-weld age at 480 °C for 3–6 hours brings the weld metal and HAZ up with the parent metal. This is the step that makes a maraging weldment as strong as the base material.
• After weld repair of an aged part, the correct route is a full re-solution anneal plus re-age. A simple re-age recovers most but not all of the properties in the HAZ.

GTAW (TIG), plasma arc, electron beam and laser welding are all used. Electron beam is the aerospace standard for full-penetration joints because the narrow fusion zone minimises the reverted-austenite band. SMAW (stick) is not recommended.

Forging practice for Maraging 300

Maraging 300 is hot-worked from approximately 1,150–1,200 °C with a finishing temperature held above roughly 900 °C. The forging window is narrower than for carbon steel, and two failure modes bracket it.

• Too hot, or soaked too long: the prior-austenite grain coarsens irreversibly and titanium-rich phases begin to liquate at the boundaries. The result is a forging that will never reach its toughness numbers no matter how it is heat treated.
• Finished too cold: below about 900 °C the alloy work-hardens sharply and the risk of surface tearing and internal bursting rises.

A minimum forging reduction of 4:1 from the ingot is used to break down the as-cast structure and disperse the segregation bands that VAR solidification leaves behind. For seamless rolled rings, the pierced blank goes through radial-axial rolling so that grain flow follows the circumference. After the final blow, the piece is cooled in still air. No controlled cooling is required, because the martensite transformation completes above room temperature at any practical section. It is then solution-annealed at 815–830 °C, which is the treatment that establishes the properties the customer will measure.

Furnaces are run neutral to slightly reducing. Sulfur pick-up from fuel or die lubricant causes hot shortness at the grain boundaries in this alloy just as it does in nickel alloys, and the alloy is expensive enough that a lost forging is a real cost.

Maraging 300 vs Maraging 250, 350, 300M, 4340, AerMet 100 and 17-4PH

Ultra-high-strength steel selection comes down to four questions: how much yield strength, how much fracture toughness, does it have to be welded, and does it have to resist corrosion. The table below is the practical selection chart.

The three comparisons that come up most

Maraging 300 against Maraging 250. The 250 grade has less cobalt and titanium, ages to about 1,725 MPa yield, and is noticeably tougher and more forgiving. If your design closes at 250-grade strength, take it. The 300 MPa you give up buys a large margin in K_IC and in tolerance to defects. Move to 300 only when the strength is genuinely needed.

Maraging 300 against 300M and 4340. The quenched-and-tempered steels are five to ten times cheaper per kilogram, and for a solid part with a simple section and no welding they are usually the right answer. Maraging 300 wins where the part is large or complex enough that quench distortion is expensive, where the section is too thick for 4340 to through-harden, where the part must be welded, or where fracture toughness at 2 GPa is the binding requirement. On a big die or a fabricated structure, the machining and rework you avoid pays for the steel.

Maraging 300 against AerMet 100. AerMet 100 is the toughness champion at high strength and is the aerospace choice where damage tolerance governs. It also needs a full quench-plus-cryogenic-plus-temper cycle, does not weld as easily, and costs more. Maraging 300 is chosen when the freedom from distortion and the simple air-age cycle matter more than the last 20 MPa·m^0.5 of toughness.

Where is Maraging 300 used?

Every application below rests on the same combination: about 2 GPa strength, usable fracture toughness at that strength, no distortion when hardened, and the ability to be welded and re-heat-treated.

Maraging 300 production capability at Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. operates an open-die forging and ring-rolling plant in Jiangyin, Jiangsu Province, China, employing approximately 460 people including 9 senior engineers and 32 intermediate engineers. Maraging 300 is produced on the same equipment used for our nickel-alloy and precipitation-hardening stainless range, under the segregation and traceability controls that vacuum-melted aerospace stock requires.

Standards, testing and certification

Maraging 300 orders at Jiangyin Jiangnan Metal Co., Ltd. are produced and certified against the specifications below. The chemistry and property specification is normally AMS 6514; the inspection-document type is normally EN 10204 3.1.

• AMS 6514
• AMS 6521
• UNS K93120
• ASTM A538 Gr. B
• ASTM A579 Gr. 72
• MIL-S-46850D
• MIL-S-13881
• DIN 1.6354 / 1.6358
• EN 10204 3.1
• EN 10204 3.2
• EN 10228-3 (UT)
• SEP 1921 (UT)
• ASTM A388 (UT)
• ASTM E45 (inclusions)
• ASTM E399 / E1820 (K_IC)
• AMS 2750 (pyrometry)
• ASTM B850 (H₂ bake)
• ISO 9001:2015

What appears on the certificate

• Heat number, ingot number and full ladle plus product chemical analysis, including C, S and P reported to the low limits this grade requires
• Melting route stated explicitly: VIM + VAR, or ESR where specified
• Mechanical test results (tensile, 0.2 % yield, elongation, reduction of area, hardness) on coupons cut from the delivered heat and heat-treated with the parts
• Heat-treatment records: solution-anneal temperature, hold time, cooling method; aging temperature, hold time and furnace chart reference
• Ultrasonic examination report to the ordered standard and acceptance class
• Non-metallic inclusion rating to ASTM E45 where specified, the strongest single predictor of fracture toughness in this grade
• Charpy V-notch or K_IC results where ordered
• Dimensional inspection report, and grain-flow macroetch where specified
• Cross-listed equivalent designations (UNS K93120 / AMS 6514 / DIN 1.6354 / 18Ni(300))
• Export-control classification statement and end-use declaration reference

Quality gates and non-conformance handling

Every Maraging 300 order passes seven mandatory hold points at which production cannot continue without QA sign-off: raw-material chemistry and melt-route verification, forging temperature compliance, post-forging ultrasonic examination, solution-anneal chart approval, aging chart and coupon-hardness approval, mechanical test acceptance, and final NDE plus dimensional inspection. Customer-witnessed hold points can be added at no charge. Any out-of-specification finding raises a formal non-conformance report within 24 hours, with root-cause analysis inside five working days and the proposed disposition sent to the customer before any rework is carried out.

How to specify a Maraging 300 forging order

Maraging 300 carries two specification decisions that most grades do not: the melting route, because it sets fracture toughness, and the delivered condition, because whether you or we do the aging changes who owns the shrinkage allowance. Settle both before the enquiry goes out.

1. Name the grade“Maraging 300 / UNS K93120 / AMS 6514”. Avoid brand names alone
2. State the melt routeVIM + VAR, or ESR. This is not a detail; it sets K_IC
3. State the conditionSolution annealed, or aged to 480 °C. Say who machines after aging
4. Send the drawingDimensions, tolerances, finish, required grain-flow direction
5. Define NDEUT to EN 10228-3, SEP 1921 or ASTM A388, with acceptance class
6. Specify testingTensile and hardness as standard; add Charpy, K_IC, E45 inclusion rating if needed
7. Specify certificationEN 10204 3.1 or 3.2; name the third party for 3.2
8. Export documentsEnd-user statement and end-use certificate, required for this grade

Recommended drawing callout

Note the marking line. Hard stamping an aged Maraging 300 part puts a sharp notch into a 2 GPa material and has caused service failures. Vibro-etch, laser-mark or electro-etch instead.

Top 10 mistakes when ordering Maraging 300 forgings

1. Not specifying the melting route. VIM + VAR and ESR material both meet the AMS 6514 chemistry, but they do not deliver the same fracture toughness. If K_IC matters, name the route on the purchase order.
2. Machining to nominal size and then aging. The part will come out 0.04–0.10 % small in every direction. Add the allowance, or plan to grind.
3. Assuming published shrinkage applies to your heat. The rate varies by a factor of two between heats. Run a coupon before committing production parts.
4. Over-aging by accident. Any hold above about 510 °C permanently softens the part, whether it is a nitriding cycle set too hot, a paint bake gone wrong or a well-meant stress relief. Recovery requires a full re-solution anneal.
5. Treating it as corrosion resistant because it contains nickel. There is no chromium. It rusts. Specify the coating in the same breath as the material.
6. Plating without a hydrogen bake. At 2 GPa this causes delayed fracture days after the part passes inspection. Put the bake on the drawing next to the plating callout.
7. Hard stamping the part. A stamp is a notch in an ultra-high-strength steel. Vibro-etch or laser-mark.
8. Confusing forged AMS 6514 with printed 1.2709. Same nominal chemistry, entirely different anisotropy, porosity and fatigue scatter. They are not interchangeable.
9. Ignoring transverse properties in heavy forgings. If the load runs across the grain flow, specify transverse testing. It is not supplied by default.
10. Sending an enquiry with no end-use information. This grade is export-controlled. An enquiry without an identified end user and application cannot be quoted, and chasing the information afterwards costs a week of lead time.

Glossary

Maraging steel

A family of ultra-low-carbon iron-nickel martensitic steels strengthened by precipitating intermetallic compounds during a low-temperature aging treatment, rather than by carbon in the martensite lattice. The name contracts martensite and aging.

Maraging 300

The 300 ksi strength grade of the 18 % nickel maraging family, containing nominally 18 % Ni, 9 % Co, 5 % Mo and 0.6 % Ti. UNS K93120, AMS 6514, W.Nr. 1.6354.

UNS K93120

The Unified Numbering System designation for Maraging 300. The generic, brand-free name to use on purchase orders.

AMS 6514

SAE Aerospace Material Specification for consumable-electrode vacuum-melted 18 % nickel maraging steel bar, forgings and tubing at the 300 ksi level. The governing specification for most Maraging 300 forging orders.

Aging (mar-aging)

The precipitation-hardening treatment, typically 480 °C for 3–6 hours followed by air cooling, that raises Maraging 300 from 30–35 HRC to 52–54 HRC.

Solution annealing

Heating to 815–830 °C to dissolve precipitates and reset the structure to soft martensite on cooling. The starting point for every heat-treatment cycle in this grade.

Over-aging

Holding too long or too hot during aging, so that precipitates coarsen and reverted austenite forms. Strength falls and is not recovered by further aging; the part must be re-solution-annealed.

Reverted austenite

Nickel-enriched austenite that forms on martensite lath boundaries during over-aging. It is soft, and its appearance marks the upper limit of any thermal exposure.

Ni₃Mo / Ni₃Ti / Fe₂Mo

The nanometre-scale intermetallic precipitates that provide the strength in Maraging 300. Ni₃Ti forms first and fastest; the molybdenum-bearing phases build the peak strength.

VIM + VAR

Vacuum induction melting followed by vacuum arc remelting. The double-vacuum route specified by AMS 6514, used to control reactive elements and to minimise the non-metallic inclusions that set fracture toughness.

ESR

Electroslag remelting. A secondary melting process that refines inclusion content and produces a directionally solidified ingot. Cleaner than air melt, but generally not equivalent to VAR for fracture-critical maraging work.

K_IC

Plane-strain fracture toughness. The material's resistance to the growth of an existing crack under plane-strain conditions, measured to ASTM E399, in units of MPa·m^0.5.

Hydrogen embrittlement

Delayed brittle fracture caused by hydrogen absorbed during pickling, plating or cathodic protection. A first-order design constraint for any steel above roughly 1,200 MPa yield, and therefore always for aged Maraging 300.

Aging contraction

The uniform 0.04–0.10 % linear shrinkage that occurs when Maraging 300 is aged, caused by precipitates occupying less volume than the same atoms in solid solution.

Seamless rolled ring

A ring produced by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow and better fatigue performance than a ring machined from plate.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is a mill certificate issued by the manufacturer's own independent inspection department; 3.2 is countersigned by an independent third party nominated by the purchaser.

ECCN 1C216

The US export control classification number covering maraging steel capable of an ultimate tensile strength of 1,950 MPa or more. Equivalent controls exist in the EU, China and other jurisdictions.

Frequently asked questions: Maraging 300 / UNS K93120

Technical references

Chemistry, mechanical, physical and heat-treatment data on this page are drawn from the published standards and engineering references below. Test results reported on our material certificates are independent and traceable to calibrated laboratory equipment.

1. SAE AMS 6514, Steel, Maraging, Bars, Forgings, Tubing and Rings, 18.5Ni – 9.0Co – 4.9Mo – 0.65Ti – 0.10Al, Consumable Electrode Vacuum Melted, Annealed, SAE International.
2. SAE AMS 6521, Steel, Maraging, Sheet, Strip and Plate, 18Ni Grade 300, SAE International.
3. ASTM A538/A538M, Standard Specification for Pressure Vessel Plates, Alloy Steel, Precipitation Hardening (Maraging), 18 Percent Nickel, ASTM International, West Conshohocken, PA.
4. ASTM A579/A579M, Standard Specification for Superstrength Alloy Steel Forgings, ASTM International.
5. MIL-S-46850D, Steel, Bar, Plate, Sheet, Strip, Forgings and Extrusions, 18 Percent Nickel Alloy, Maraging, 200 ksi, 250 ksi, 300 ksi and 350 ksi, US Department of Defense (withdrawn; retained for legacy drawings).
6. DIN / Werkstoff 1.6354, X2NiCoMo18-9-5, Deutsches Institut für Normung.
7. EN 10204:2004, Metallic products — Types of inspection documents, CEN, Brussels.
8. EN 10228-3, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN.
9. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
10. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
11. ASTM E45, Standard Test Methods for Determining the Inclusion Content of Steel, ASTM International.
12. ASTM E399, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials, ASTM International.
13. ASTM B850, Standard Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement, ASTM International.
14. SAE AMS 2750, Pyrometry, SAE International.
15. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International — section on maraging steels.
16. ASM Handbook, Volume 4: Heat Treating, ASM International — chapter on the heat treatment of maraging steels.
17. Decker, R.F. and Floreen, S., Maraging Steels — The First 30 Years, in Maraging Steels: Recent Developments and Applications, TMS, 1988. The foundational review of the alloy family by its co-developers.
18. Sha, W. and Guo, Z., Maraging Steels: Modelling of Microstructure, Properties and Applications, Woodhead Publishing.
19. Nuclear Suppliers Group, Guidelines for Transfers of Nuclear-Related Dual-Use Equipment, Materials, Software and Related Technology (INFCIRC/254 Part 2), and the Wassenaar Arrangement dual-use list — for the maraging-steel control threshold.

Standards cited are the revisions known to us at the time of the last page review. For procurement, always reference the revision in force at the contract date. All trademarks referenced belong to their respective owners.

Related grades and forged products

• Maraging 250
• Maraging 350
• Custom 450
• 17-4PH
• PH13-8Mo
• A286
• Inconel 718
• Inconel 725
• Waspaloy
• MP35N
• MP159
• Rene 41
• Alloy 42
• Forged & rolled rings
• Forged disks
• Forged tubes
• Forged spindles
• Open die forgings