18Ni250 Maraging Steel (UNS K92890) – Ultra-High-Strength Alloy Supplier of Round Bars, Forgings & Plates | Shanghai Hangbo Alloy Group
Date: 2026年7月25日 Categories: News Views: 351
By Shanghai Hangbo Alloy Group Co., Ltd. — China Supplier | ISO 9001:2015 Certified | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp: +86 13611656360
Quick Answer: What Is 18Ni250 Maraging Steel?
18Ni250 (Maraging 250 / UNS K92890) is a low-carbon, 18% nickel maraging steel that achieves ultra-high tensile strength (≥1725 MPa / 250 ksi) through a simple low-temperature aging treatment — without the distortion, quench cracking, or decarburization that plague conventional quench-and-temper steels. It is the reference material for aerospace landing gear, rocket motor cases, high-performance tooling, and structural components where maximum strength-per-kg is the primary design criterion. Shanghai Hangbo Alloy Group supplies 18Ni250 as round bars, forgings, and plates with full AMS 6512/6514 certification.
Industry Pain Point: Landing gear manufacturers face an impossible triangle with conventional high-strength steels (e.g., 4340, 300M): to achieve 1800+ MPa strength requires oil quenching from 845°C, which produces distortion that adds 40–80 hours of straightening and machining to every component. 18Ni250 solves this: it is solution-annealed at a modest 815°C (producing a soft, machinable martensite of ~30 HRC), machined to near-net shape, then aged at only 480°C — well below the austenite transformation temperature — to achieve full strength. The aging contraction is <0.1% and is uniform in all directions, eliminating post-heat-treat straightening entirely.
Key Properties at a Glance
| Property | Value |
|---|---|
| UNS Number | K92890 |
| Alloy Family | 18Ni Maraging Steel (Grade 250) |
| Density | 8.00 g/cm³ (0.289 lb/in³) |
| Solidus Temperature | ~1430°C |
| Max Service Temp. | ~400°C (~750°F) — limited by over-aging |
| Tensile Strength (Aged) | ≥ 1725 MPa (≥ 250 ksi) |
| Yield Strength 0.2% (Aged) | ≥ 1655 MPa (≥ 240 ksi) |
| Elongation (Aged) | ≥ 6% |
| Hardness (Aged) | 48–52 HRC |
| Fracture Toughness KIC | ≥ 80 MPa√m |
| Key Standards | AMS 6512, AMS 6514, ASTM A579 |
Product Overview
18Ni250 belongs to the 18Ni-Co-Mo family of maraging steels — "maraging" being a portmanteau of martensite + aging. The alloy's metallurgical genius lies in its simplicity: a low-carbon (≤0.03%) Fe-18Ni matrix that forms a soft, tough lath martensite on air cooling from the solution-annealing temperature (815°C), followed by precipitation of nanometer-scale Ni₃Mo and Ni₃Ti intermetallic particles during aging at 480–500°C. The precipitated particles are only 5–20 nm in diameter, uniformly distributed through the martensitic matrix, and increase the yield strength by approximately 800–900 MPa over the solution-annealed condition.
This mechanism produces five decisive advantages over conventional quench-and-temper steels (4340, 300M, D6AC):
- No quench distortion: The martensitic transformation occurs on air cooling from 815°C — no oil or water quench, no thermal shock, no distortion. Components can be machined in the soft (30 HRC) solution-annealed condition, then aged with dimensional change <0.1%.
- No decarburization: Aging at 480°C is far below the temperature at which carbon diffusion and surface decarburization occur (~700°C+). The finished component surface retains its as-machined chemistry and properties.
- Weldable in the solution-annealed condition: The low carbon content eliminates the heat-affected-zone hardening and hydrogen-induced cracking that make 4340 and 300M essentially unweldable. Post-weld aging restores full strength to the weld zone.
- Superior fracture toughness: At 1725 MPa tensile, 18Ni250 delivers KIC ≥ 80 MPa√m — approximately 30–50% higher than 300M at equivalent strength, translating to larger critical flaw sizes and more forgiving inspection intervals.
- Excellent dimensional stability: The aging contraction (<0.1%) is isotropic — uniform in all directions — making 18Ni250 the standard for precision tooling, gage blocks, and die-casting dies where post-heat-treatment grinding would compromise dimensional accuracy.
Shanghai Hangbo Alloy Group supplies 18Ni250 in the solution-annealed condition for customer aging after machining, or fully aged with certified mechanical properties per AMS 6512.
Executive Standards
| Product Form | Primary Standard | Supplementary | Notes |
|---|---|---|---|
| Bar & Forging Stock | AMS 6512 (VIM/VAR) | ASTM A579 Gr.73 | Solution-annealed or aged |
| Forgings | AMS 6514 | AMS 6512 | Discs, rings, blocks |
| Plate & Sheet | ASTM A579 / AMS 6512 | — | Thickness 5–100 mm |
| Welding Filler | AMS 6512 matching (18Ni250 wire) | — | GTAW, post-weld aging at 480°C |
Chemical Composition (wt.% per AMS 6512 – 100% OES Verified)
| Element | Min | Max | Role in 18Ni250 |
|---|---|---|---|
| Nickel (Ni) | 18.0 | 19.0 | Martensite former — ensures lath martensite on air cooling; lowers Ac₁ to suppress re-austenitization during aging |
| Cobalt (Co) | 7.0 | 8.5 | Raises the martensite start (Ms) temperature; increases the volume fraction of strengthening precipitates |
| Molybdenum (Mo) | 4.6 | 5.2 | Primary strengthening element — forms Ni₃Mo precipitates during aging |
| Titanium (Ti) | 0.30 | 0.50 | Secondary precipitate former — Ni₃Ti provides additional strengthening |
| Aluminum (Al) | 0.05 | 0.15 | Grain refiner; deoxidizer |
| Carbon (C) | — | 0.03 | Must be ultra-low — carbon forms brittle Fe₃C that embrittles the martensitic matrix |
| Manganese (Mn) | — | 0.10 | Kept low — Mn stabilizes retained austenite |
| Silicon (Si) | — | 0.10 | Kept low — Si raises the austenite reversion temperature |
| Phosphorus (P) | — | 0.010 | Impurity — controlled for toughness |
| Sulfur (S) | — | 0.010 | Impurity — minimized for fatigue life |
| Iron (Fe) | Balance | — | Martensitic matrix |
Melting route: VIM (Vacuum Induction Melting) followed by VAR (Vacuum Arc Remelting) is mandatory per AMS 6512. The VIM step controls the ultra-low carbon and tight titanium/aluminum ranges; the VAR step eliminates centerline segregation and ensures micro-cleanliness for the fracture-toughness-critical applications that define 18Ni250's market.
Mechanical & Physical Properties
Room-Temperature Properties (Solution-Annealed 815°C/1h/AC + Aged 480°C/3h/AC)
| Property | Value | Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 1725 MPa (≥ 250 ksi) | AMS 6512 |
| Yield Strength 0.2% (Rp0.2) | ≥ 1655 MPa (≥ 240 ksi) | AMS 6512 |
| Elongation (4D) | ≥ 6% | AMS 6512 |
| Reduction of Area | ≥ 35% | AMS 6512 |
| Hardness | 48–52 HRC | — |
| Fracture Toughness KIC | ≥ 80 MPa√m | ASTM E399 |
| Young's Modulus | ~186 GPa (27 × 10³ ksi) | — |
Elevated-Temperature Strength Retention (Aged Condition, Typical)
| Temperature | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
|---|---|---|---|
| 20°C | 1800 | 1750 | 8 |
| 200°C (392°F) | 1650 | 1580 | 8 |
| 300°C (572°F) | 1480 | 1400 | 9 |
| 400°C (752°F) | 1250 | 1150 | 12 |
| 500°C (932°F) | 900 | 800 | 15 |
Service temperature limit: Above ~400°C, the Ni₃Mo precipitates coarsen rapidly — the alloy over-ages and loses 30–50% of its room-temperature strength within 1,000 hours. For service above 400°C, consider a nickel-base superalloy (Inconel 718) or hot-work tool steel (H13).
Physical Properties
| Property | Value | Unit |
|---|---|---|
| Density | 8.00 | g/cm³ |
| Solidus Temperature | ~1430 | °C |
| Thermal Conductivity (20°C) | ~25 | W/m·K |
| Specific Heat | ~460 | J/kg·K |
| Mean Thermal Expansion (20–200°C) | ~10.1 | μm/m·°C |
| Electrical Resistivity | ~0.60 | μΩ·m |
| Magnetic (Annealed) | Ferromagnetic | — |
Heat Treatment
The Simple Two-Step Cycle
Step 1 — Solution Annealing:
| Parameter | Specification |
|---|---|
| Temperature | 815–830°C (1500–1525°F) |
| Soak Time | 1 hour per 25 mm section thickness |
| Atmosphere | Air, vacuum, or inert gas |
| Cooling | Air cool to room temperature — no quench required |
Metallurgical objective: Austenitize the alloy, dissolve any prior precipitates, and produce a fully martensitic structure on cooling. The air cool is sufficient because the high nickel content suppresses the diffusion-controlled ferrite/pearlite transformation and guarantees martensite formation at cooling rates as slow as still-air cooling for sections up to 100 mm.
Step 2 — Precipitation Aging:
| Parameter | Specification |
|---|---|
| Temperature | 480–500°C (900–930°F) |
| Soak Time | 3–6 hours (3 h standard; 6 h for peak-aged properties) |
| Cooling | Air cool |
Metallurgical objective: Precipitate nanometer-scale Ni₃Mo and Ni₃Ti intermetallic particles uniformly throughout the martensitic lath structure. The aging temperature is precisely below the austenite reversion temperature (~600°C for 18Ni250) — ensuring the martensitic matrix remains unchanged while the precipitates form. The aging contraction is <0.1% and is isotropic.
Production Process
1. Round Bars & Forgings
- Melting: VIM + VAR mandatory. VIM ensures carbon ≤0.02% and Ti ±0.03% precision. VAR eliminates centerline segregation. Air-melt or single-vacuum-melt material does not meet AMS 6512.
- Hot Forging: Ingot homogenized at 1200–1250°C (above the Ni₃Mo solvus ~1150°C) then forged at 1100–1200°C with minimum 4:1 reduction. Finishing temperature ≥ 900°C.
- Solution Annealing: 815–830°C, air cool. Hardness check — annealed hardness 28–33 HRC confirms full martensitic transformation.
- UT & Finishing: 100% ultrasonic immersion testing, ASTM E399 KIC fracture toughness verification on sample coupons per heat-treatment lot.
2. Plates
- Hot Rolling: Slab at 1100–1200°C. Finishing temperature ≥ 900°C.
- Solution Annealing: 815–830°C, air cool. Uniform cooling is sufficient.
- Aging: 480–500°C / 3–6 h. Hardness verification per lot.
- Leveling & NDE: Precision leveling. Ultrasonic testing per ASTM A435.
Industry Applications
| Industry | Typical Component | Why 18Ni250? |
|---|---|---|
| Aerospace — Landing Gear | Main landing gear struts, axle beams, torque links | ≥1725 MPa + KIC ≥80 MPa√m; fatigue life 2× 300M at equivalent strength; no quench distortion |
| Rocket & Missile | Solid rocket motor cases, missile airframes, pressure vessels | Highest strength-to-weight ratio of any weldable steel; room-temperature aging avoids thermal distortion of thin-wall vessels |
| Tooling & Dies | Aluminum die-casting dies, extrusion tooling, plastic injection mold cores | Age-hardens at 480°C with <0.1% contraction — enables machining to final dimensions in soft condition then aging with zero post-treatment grinding |
| High-Performance Gears & Shafts | Helicopter transmission shafts, racing transmission gears | Surface nitriding at 480°C (coincident with aging cycle) produces hard case + high-strength core in single thermal cycle |
| Centrifuge & Rotating Equipment | Ultracentrifuge rotors, high-speed spindles | High strength permits higher rotational speeds; fracture toughness prevents catastrophic burst failures |
| Ordnance & Defense | Gun barrels, breech components, armor-piercing penetrator bodies | High strength + good toughness at high strain rates; weldable for field repair |
Quality Assurance: 7-Stage Zero-Defect Inspection
- Raw Material Purity: Incoming Ni, Co, Mo, FeTi analyzed by ICP-OES. Carbon content of all charge materials ≤0.010% — pre-melt carbon inventory determines final carbon ≤0.03%.
- VIM + VAR Melt Chemistry: VIM carbon ≤0.02% (internal target). VAR ingot macro-etched for segregation. Titanium verified ±0.03% of target.
- Hot Working Surveillance: IR pyrometry, reduction ≥4:1, processing charts archived.
- Solution Anneal: 815–830°C furnace chart ±5°C. Hardness 28–33 HRC confirmed per lot.
- Aging Verification: 480–500°C digital chart. Aged hardness 48–52 HRC. Room-temperature tensile + KIC fracture toughness per heat-treatment lot.
- Non-Destructive Examination: 100% UT per AMS-STD-2154 Class A for aerospace forgings. MPI on finished components.
- Documentation: EN 10204 3.1 + fracture toughness report. SGS/TÜV witness available.
Frequently Asked Questions
Q1: What is 18Ni250 used for?
Aerospace landing gear, rocket motor cases, tooling (die-casting dies, extrusion tooling), high-performance shafts and gears, ultracentrifuge rotors, and defense applications — anywhere ≥1725 MPa tensile strength must coexist with weldability, toughness, and near-zero heat-treatment distortion.
Q2: What does "Maraging 250" mean?
"Maraging" = martensite + aging. "250" = nominal tensile strength of 250 ksi (1725 MPa). The alloy achieves this strength by aging nanometer-scale Ni₃Mo/Ni₃Ti precipitates in a soft martensitic matrix — completely different from the carbon-dependent hardening of conventional steels.
Q3: What is the density of 18Ni250?
8.00 g/cm³ (0.289 lb/in³) — similar to most steels, slightly denser than Inconel 718 (8.19) due to the cobalt and molybdenum content. Weight estimation: Mass (kg) = 8.00 × Volume (cm³) ÷ 1000.
Q4: What is the tensile strength of 18Ni250?
Minimum ≥ 1725 MPa (≥ 250 ksi) in the aged condition per AMS 6512. Typical values 1780–1850 MPa. In the solution-annealed condition (before aging): approximately 950–1050 MPa — the aging treatment adds ~800 MPa of strength.
Q5: What is the yield strength of 18Ni250?
Minimum ≥ 1655 MPa (≥ 240 ksi). The yield-to-tensile ratio is approximately 0.95 — exceptionally high, indicating that the alloy transitions from elastic to plastic deformation at a stress very close to its ultimate tensile strength.
Q6: What is the fracture toughness of 18Ni250?
KIC ≥ 80 MPa√m at 1725 MPa tensile — approximately 30–50% higher than 300M (KIC ~55–65 MPa√m at equivalent strength). This means the critical flaw size for brittle fracture is approximately 2× larger, providing more forgiving inspection intervals.
Q7: How does 18Ni250 compare to 300M?
| Property | 18Ni250 | 300M (4340M) | Advantage |
|---|---|---|---|
| Tensile Strength | ≥1725 MPa | ≥1930 MPa | 300M — slightly higher |
| Fracture Toughness (KIC) | ≥80 MPa√m | ~60 MPa√m | 250 — 30% tougher |
| Weldability | Good | Poor (H₂ cracking) | 250 — field-repairable |
| Quench Distortion | Near-zero (air cool) | Significant (oil quench) | 250 — 40–80 h machining saved |
| Cost | 3–5× 300M | Baseline | 300M — cheaper raw material |
Q8: What heat treatment does 18Ni250 require?
(1) Solution anneal at 815–830°C / 1 h / air cool. (2) Age at 480–500°C / 3–6 h / air cool. No oil or water quench. No tempering. The simplicity is the value proposition.
Q9: Is 18Ni250 weldable?
Yes — one of the few ultra-high-strength steels that is readily weldable. GTAW with matching 18Ni250 filler. Weld in the solution-annealed condition, then post-weld age at 480°C for full strength recovery.
Q10: What is the price of 18Ni250 per kg?
\$30–55/kg EXW for round bars — reflecting the 18% Ni + 8% Co content and the mandatory VIM+VAR melting. Contact sales@hangboalloy.com for firm quotation.
Q11: What is the difference between 18Ni250 and 18Ni300?
18Ni300 has higher cobalt (9%) and titanium (0.5–0.8%) for tensile ≥2000 MPa, but slightly lower KIC (~70 MPa√m). 18Ni250 is the balanced strength-toughness grade; 300 is for maximum strength.
Q12: What product forms does Shanghai Hangbo supply?
Round bars (Ø10–300 mm), forgings (discs, blocks), plates (5–100 mm). Supplied solution-annealed for customer machining/aging, or fully aged with certified properties.
Q13: Does Shanghai Hangbo ship internationally?
Yes — FOB/CIF/DAP to 40+ countries. VIM+VAR production lead time 10–14 weeks.
Q14: Can 18Ni250 be nitrided?
Yes, and the gas nitriding temperature (~500°C) coincides perfectly with the aging cycle, enabling case hardening + bulk aging in a single thermal operation.
Q15: Why is carbon kept below 0.03% in 18Ni250?
Carbon forms brittle Fe₃C (cementite) at prior-austenite grain boundaries, reducing fracture toughness and promoting intergranular fracture. Maraging steels achieve strength through intermetallic precipitates, not carbon — eliminating carbon is a feature, not a compromise.
Q16: Does 18Ni250 rust?
Yes. It is a steel (~65% Fe) with no chromium content (Cr ≤0.1%). All components must be cadmium-plated, nickel-plated, painted, or oil-protected for corrosion protection.
Contact Shanghai Hangbo Alloy Group
| Channel | Details |
|---|---|
| Company | Shanghai Hangbo Alloy Group Co., Ltd. — China Supplier |
| Website | www.nickel-alloy.com |
| sales@hangboalloy.com | |
| WhatsApp (Lisa) | +86 13611656360 |
| Address | Shanghai, China |
