AISI Grade 18Ni (350) Maraging Steel solution annealed

AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours Product Information -:- For detailed product information, please contact sales. -: AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours Synonyms -:- For detailed product information, please contact sales. -:

AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours Product Information -:- For detailed product information, please contact sales. -: # AISI Grade 18Ni (350) Maraging Steel ## Fully Precipitation-Hardened Condition: Extended Aging Treatment --- ### **Product Overview** This specification covers **AISI Grade 18Ni (350) Maraging Steel** in its **peak precipitation-hardened (aged) condition**, achieved through a **standard solution annealing followed by an extended aging treatment**. The material has undergone the complete heat treatment cycle: **solution annealing at 815°C (1500°F) for 1 hour, air cooling, followed by aging at 480°C (900°F) for 6 hours**. This **extended aging duration (6 hours vs. typical 3-4 hours)** is specifically employed to ensure complete precipitation transformation in **thick sections or for applications demanding absolute microstructural stability**. This product delivers the **highest strength level** (Yield Strength > 2300 MPa) commercially available in the maraging steel family, with optimized toughness for this strength regime. --- ### **Chemical Composition (Weight %) - Premium High-Strength Grade** | Element | Specification Range (AMS 6518) | Typical Analysis | Critical Function | | :--- | :--- | :--- | :--- | | **Nickel (Ni)** | 18.00 – 19.00 | 18.5 | Forms the tough, ductile martensitic matrix; essential for base toughness. | | **Cobalt (Co)** | **11.50 – 12.50** | 12.0 | **Key Differentiator.** Elevated Co content reduces solubility of Mo in martensite, dramatically increasing driving force for precipitation and enabling ultimate strength >2400 MPa UTS. | | **Molybdenum (Mo)** | 4.60 – 5.20 | 4.9 | Primary precipitation hardener; forms coherent Ni₃Mo particles. | | **Titanium (Ti)** | **1.20 – 1.45** | 1.35 | **Key Differentiator.** Substantially increased vs. 300 grade. Forms abundant Ni₃Ti precipitates, contributing massively to strength. | | **Aluminum (Al)** | 0.05 – 0.15 | 0.10 | Deoxidizer; forms minor Ni₃Al precipitates. | | **Carbon (C)** | ≤ 0.030 | 0.010 | Maintained at ultra-low levels to preserve toughness and weldability. | | **Manganese (Mn)** | ≤ 0.10 | 0.05 | Residual element. | | **Silicon (Si)** | ≤ 0.10 | 0.05 | Residual element. | | **Boron (B)** | ≤ 0.005 | 0.003 | Enhances hardenability and grain boundary strength. | | **Zirconium (Zr)** | ≤ 0.02 | 0.01 | Grain refiner. | | **Sulfur (S)** | ≤ 0.010 | 0.003 | Impurity control. | | **Phosphorus (P)** | ≤ 0.010 | 0.005 | Impurity control. | | **Iron (Fe)** | Balance | Balance | Base element. | **Core Distinction from 18Ni(300):** The combined elevation of **Cobalt (~12% vs. ~9%)** and **Titanium (~1.35% vs. ~0.65%)** provides the chemical potential for approximately **15-20% higher yield strength**. --- ### **Optimized Heat Treatment Cycle** 1. **Solution Annealing:** * **Temperature:** 815°C ± 10°C (1500°F) * **Time:** **1 hour** - Standard duration for thorough austenitization and homogenization. * **Cooling:** Air Cool (or forced air). * ***Result:*** Produces a soft, uniform, and stress-relieved lath martensite structure with all alloying elements in solid solution. Hardness approximately 30-34 HRC. 2. **Extended Aging (Peak Hardening):** * **Temperature:** 480°C ± 5°C (900°F) - Standard peak-aging temperature. * **Time:** **6 hours** - **Critical Extended Duration.** Represents 150-200% of typical aging time. * **Cooling:** Air Cool. * ***Metallurgical Outcome:*** The extended time at peak aging temperature ensures: * **Complete Precipitation:** Maximum possible transformation of supersaturated elements into strengthening intermetallics (Ni₃Mo, Ni₃Ti). * **Microstructural Stability:** Achieves a more stable precipitate size distribution, slightly coarsened but still coherent, which can improve resistance to over-aging in service. * **Uniformity in Thick Sections:** For heavy forgings or large components, the extended time guarantees the thermal center reaches full aging potential. * **Stress Relief:** More thorough relief of residual stresses from prior processing. --- ### **Mechanical Properties (Peak-Aged Condition - Longitudinal)** *Typical achieved properties after the 815°C/1h + 480°C/6h cycle. Properties represent the pinnacle of commercial steel strength.* | Property | Typical Achieved Value | Test Standard | Notes | | :--- | :--- | :--- | :--- | | **Ultimate Tensile Strength (UTS)** | 2400 – 2450 MPa (348 – 355 ksi) | ASTM E8 | Slightly higher than minimum guaranteed values. | | **0.2% Yield Strength (YS)** | 2300 – 2350 MPa (334 – 341 ksi) | ASTM E8 | **Primary design value.** | | **Elongation in 50 mm (2")** | 6 – 8% | ASTM E8 | Good ductility for this strength level. | | **Reduction of Area** | 25 – 35% | ASTM E8 | | | **Hardness** | 55 – 57 HRC | ASTM E18 | | | **Fracture Toughness (K_IC)** | 30 – 45 MPa√m | ASTM E399 | **Critical property.** Significantly lower than 18Ni(300). Design is fracture-controlled. | | **Modulus of Elasticity** | 185 – 190 GPa (26.8 – 27.5 × 10⁶ psi) | ASTM E111 | | | **Fatigue Strength (10⁷ cycles, R=0.1)** | ~550 – 650 MPa | ASTM E466 | Highly surface-finish sensitive. | **Effect of Extended Aging (6h vs. 3-4h):** * **Strength:** May show a **slight decrease (1-3%)** compared to a theoretically optimal 3-4h peak due to very early stages of over-aging/coarsening. * **Toughness:** May show a **slight increase (5-10%)** in fracture toughness for the same reason. * **Stability:** Improved resistance to further microstructural change during moderate temperature exposure. --- ### **Physical Properties (Aged Condition, 20°C)** | Property | Value | | :--- | :--- | | **Density** | 8.03 – 8.05 g/cm³ (0.290 lb/in³) | | **Melting Range** | 1400 – 1430°C (2550 – 2610°F) | | **Thermal Conductivity** | 18 – 20 W/(m·K) | | **Specific Heat Capacity** | 460 J/(kg·K) | | **Coefficient of Thermal Expansion** | 10.5 – 11.0 × 10⁻⁶ /°C (20-100°C) | | **Electrical Resistivity** | 0.65 – 0.75 μΩ·m | | **Magnetic Properties** | Ferromagnetic (Martensitic) | --- ### **Dimensional Change During Aging** * **Linear Growth:** Predictable expansion of **approximately 0.06 – 0.08%**. * **Distortion:** Minimal if uniformly heated and cooled; complex parts may require fixturing. --- ### **International Standards Compliance** This heat treatment cycle is specified to achieve the properties mandated by high-performance standards. | Standard Body | Standard Number | Title / Notes | | :--- | :--- | :--- | | **SAE Aerospace (AMS)** | **AMS 6518C** | *Maraging Steel, 18Ni 11.5Co 4.8Mo 1.4Ti (0.10Al) (0.020C), Solution Heat Treated, Precipitation Hardenable.* This is the primary governing spec for 18Ni(350). The 6-hour aging may be called out as a specific requirement for certain applications or sections. | | **Proprietary Specifications** | VascoMax 350, Marval 18-350 | Common trade names; often supplied with certified heat treatment per customer order. | | **Customer-Specific** | Boeing, Airbus, NASA, ESA Specifications | Often govern procurement, explicitly defining aging time and temperature parameters. | | **General Reference** | MIL-S-46850 | May be invoked; specific grade and heat treatment must be stated. | --- ### **Primary Applications** This material is specified for the most demanding applications where **maximum strength-to-weight ratio is the paramount design driver**. 1. **Aerospace & Defense (Primary Use):** * **Solid Rocket Motor Cases and Nozzle Components:** Where high chamber pressure demands ultimate strength. * **Missile Airframes and Warhead Casings.** * **Aircraft Landing Gear Ultra-High-Strength Components:** Pins, bolts, and linkages. * **Spacecraft Fittings and Deployment Mechanisms** where mass minimization is critical. 2. **Tooling & High-Pressure Equipment:** * **Extrusion Dies and Mandrels** for titanium and nickel superalloys. * **Die Inserts for High-Pressure Die Casting.** * **Components for Isostatic Pressing (HIP) Tooling.** 3. **High-Performance Racing & Specialized Machinery:** * **Critical Fasteners** (e.g., connecting rod bolts, head studs) in top-tier motorsport. * **High-Load, Minimal-Deflection Shafts and Spindles.** --- ### **Fabrication Considerations (In Aged Condition)** **Machining:** * **Extremely Difficult.** One of the most challenging machining operations. * **Tooling:** **Cubic Boron Nitride (CBN)** or **Ceramic** inserts are strongly recommended. Premium carbide can be used with extreme care. * **Strategy:** Low feeds/speeds, high-pressure coolant, rigid setups. **Grinding** and **Electrical Discharge Machining (EDM)** are preferred finishing methods. **Joining:** * **Welding:** **Not recommended** in the aged condition. Must be performed in the solution-annealed state, followed by a full re-solution and re-aging cycle (including the 6-hour hold). * **Adhesive Bonding:** A viable method with proper surface preparation. * **Mechanical Fastening:** The primary joining method. Requires careful design to prevent bearing failure. **Corrosion Protection:** * **Not corrosion resistant.** Requires immediate and effective protective coatings. * **Standard Coatings:** **Electroless Nickel (EN)** or **Cadmium-Titanium plating** (with mandatory post-plate baking to relieve hydrogen embrittlement). --- ### **Quality Assurance & Documentation** 1. **Material Test Report:** Must conform to EN 10204 3.1 or 3.2, detailing heat chemistry and mechanical properties **achieved after the specified 6-hour aging cycle**. 2. **Heat Treatment Certification:** Furnace charts or equivalent documentation verifying both the solution anneal (815°C/1h) and the extended age (480°C/6h) were performed as specified. 3. **Non-Destructive Testing:** Typically required for finished components; Ultrasonic Testing (UT) is common for detecting internal flaws. --- ### **Rationale for the 6-Hour Aging Cycle** The selection of a 6-hour aging time over the more common 3-4 hours is driven by specific technical needs: 1. **Assurance for Thick Sections:** For components with substantial mass (>50 mm thickness), the extended time guarantees the thermal core reaches full aging potential, ensuring property uniformity. 2. **Maximized Stability:** In applications where the component might see intermittent exposure to temperatures near 300-400°C in service, the slightly coarsened, more stable precipitate structure from extended aging offers better property retention. 3. **Process Robustness:** Provides a wider processing window, making the heat treatment less sensitive to minor furnace temperature variations. --- ### **Summary** **AISI Grade 18Ni (350) Maraging Steel**, processed via **solution annealing at 815°C for 1 hour and aging at 480°C for 6 hours**, represents the **pinnacle of strength in wrought alloy steels**. This extended aging variant is selected when the application demands not only the ultimate strength but also an added margin of microstructural stability and through-thickness property uniformity. Its use is justified in extreme performance applications where the performance benefit outweighs the significant challenges and costs associated with its fabrication and the inherent design constraints imposed by its relatively low fracture toughness. It is a material that delivers uncompromising strength for those who can master its complexities. -:- For detailed product information, please contact sales. -: AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours Specification Dimensions Size： Diameter 20-1000 mm Length <7356 mm Size:We can customized as required Standard： Per your request or drawing We can customized as required Properties（Theoretical） Chemical Composition -:- For detailed product information, please contact sales. -: AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours Properties -:- For detailed product information, please contact sales. -:

Applications of AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours -:- For detailed product information, please contact sales. -: Chemical Identifiers AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours -:- For detailed product information, please contact sales. -:

Packing of AISI Grade 18Ni (350) Maraging Steel solution annealed at 815°C (1500°F) for 1 hour, air cooled, aged at 480°C (900°F) for 6 hours -:- For detailed product information, please contact sales. -: Standard Packing: -:- For detailed product information, please contact sales. -: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3827 gallon liquid totes Special package is available on request. E FORUs’ is carefully handled to minimize damage during storage and transportation and to preserve the quality of our products in their original condition