AISI Grade 18Ni (350) Maraging Steel, Aged

AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm Product Information -:- For detailed product information, please contact sales. -: AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm Synonyms -:- For detailed product information, please contact sales. -:

AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm Product Information -:- For detailed product information, please contact sales. -: # AISI Grade 18Ni (350) Maraging Steel, Aged ## Peak-Hardened Round Bar - 16 mm Diameter | RT | Longitudinal Testing --- ### **Product Overview** This specification covers **AISI Grade 18Ni (350) Maraging Steel** in the **fully precipitation-hardened (aged) condition**, supplied as **16 mm (0.63 inch) diameter round bars**. This represents the **highest strength commercially available grade** in the standard 18% nickel maraging steel family. The material has undergone complete solution annealing and aging to achieve its ultimate strength potential, with mechanical properties certified at **room temperature (RT)** in the **longitudinal direction**. The 16 mm diameter ensures excellent through-hardening and property uniformity, making this product form ideal for machining high-stress, weight-critical components. --- ### **Chemical Composition (Weight %) - Premium High-Strength Grade** | Element | Specification Range | Typical Analysis | Critical Function for 350 Grade | | :--- | :--- | :--- | :--- | | **Nickel (Ni)** | 18.00 – 19.00 | 18.5 | Forms the tough martensitic matrix; essential for fracture toughness at ultra-high strength. | | **Cobalt (Co)** | **11.50 – 12.50** | 12.0 | **Key differentiator.** Elevated Co reduces solubility of Mo in martensite, dramatically increasing driving force for precipitation and enabling >2400 MPa strength. | | **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. | | **Silicon (Si)** | ≤ 0.10 | 0.05 | Residual. | | **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**. --- ### **Standard Heat Treatment for Peak Properties** 1. **Solution Annealing:** 815-830°C (1500-1525°F) for 1 hour, air cooled. *Produces uniform, soft martensite.* 2. **Aging (Peak Hardening):** 480°C (900°F) for 3-6 hours, air cooled. *Precipitates a high density of fine Ni₃(Mo,Ti) intermetallics, achieving peak strength.* *Material is supplied in this final, aged condition.* --- ### **Mechanical Properties at Room Temperature (Longitudinal Direction)** *Guaranteed minimum values are typical for 16 mm round bar. Properties represent the pinnacle of commercial steel strength.* | Property | Minimum Guaranteed Value | Typical Achieved Value | Test Standard | | :--- | :--- | :--- | :--- | | **Ultimate Tensile Strength (UTS)** | 2340 MPa (339 ksi) | 2400 – 2450 MPa (348 – 355 ksi) | ASTM E8 | | **0.2% Yield Strength (YS)** | 2240 MPa (325 ksi) | 2300 – 2350 MPa (334 – 341 ksi) | ASTM E8 | | **Elongation in 4D (50 mm)** | 6% | 7 – 9% | ASTM E8 | | **Reduction of Area (RA)** | 25% | 30 – 40% | ASTM E8 | | **Hardness** | 54 HRC | 55 – 57 HRC | ASTM E18 | | **Fracture Toughness (K_IC)** | **30 MPa√m** | 35 – 50 MPa√m | ASTM E399 | | **Modulus of Elasticity** | 180 GPa | 185 – 190 GPa | ASTM E111 | | **Impact Energy (Charpy V)** | **15 J** | 20 – 30 J | ASTM E23 | **Critical Performance Notes:** * **Strength vs. Toughness Trade-off:** The exceptional strength comes with significantly **lower fracture toughness** compared to 18Ni(300) (KIC ~75-90 MPa√m). Design must account for this inherent brittleness. * **Notch Sensitivity:** Highly notch-sensitive. Sharp geometric transitions must be avoided. * **Property Uniformity:** 16 mm diameter ensures full hardening with minimal gradient from surface to core. --- ### **Physical Properties (Aged Condition, 20°C/RT)** | Property | Value | | :--- | :--- | | **Density** | 8.03 – 8.05 g/cm³ | | **Thermal Conductivity** | 18 – 20 W/(m·K) | | **Specific Heat Capacity** | 460 J/(kg·K) | | **Coefficient of Thermal Expansion** | 10.5 – 11.0 x 10⁻⁶ /K (20-100°C) | | **Electrical Resistivity** | 0.65 – 0.75 μΩ·m | | **Magnetic Properties** | Ferromagnetic | --- ### **International Standards & Designations** | Standard | Designation | Notes | | :--- | :--- | :--- | | **AMS (Aerospace)** | **AMS 6518** | Most common spec: *Maraging Steel, 18Ni 11.5Co 4.8Mo 1.4Ti (0.10Al) (0.020C)* | | **Proprietary** | VascoMax 350, Marval 18-350 | Common trade names. | | **UNS** | Often shared with 300 grade (K92890) | Must specify chemistry/strength requirements. | | **MIL-S** | MIL-S-46850 (may be invoked) | Covers maraging steels; specific grade must be stated. | | **Customer-Specific** | Boeing, Airbus, NASA specifications | Often govern procurement for critical applications. | *Note: There is no generic ASTM standard specifically for 18Ni(350); it is typically supplied to proprietary or AMS specifications.* --- ### **Primary Applications** This material is reserved for applications where **maximum strength-to-weight ratio is the dominant design criterion**, and where its lower toughness can be managed through meticulous design and quality control. 1. **Aerospace & Defense (Primary Use):** * **Rocket Motor Cases:** For solid and liquid propellant rockets where chamber pressure demands ultimate strength. * **Missile & Ordnance Components:** Penetrators, casings, and structural elements. * **Aircraft Landing Gear Components:** Ultra-high-strength pins, bolts, and linkages in advanced designs. * **Spacecraft & Satellite Components:** Where minimizing mass is critical (e.g., deployment mechanisms, fittings). 2. **Tooling & Industrial:** * **Extrusion Dies & Mandrels** for high-strength alloys (e.g., titanium, nickel superalloys). * **High-Pressure Isostatic Press (HIP) Tooling.** * **Precision Shafts & Spindles** in high-load machinery. 3. **High-Performance Racing & Automotive:** * **Connecting Rod Bolts, Head Studs** in top-tier motorsport. * **Critical Fasteners** in safety-critical assemblies. --- ### **Fabrication & Handling in Aged Condition - Extreme Difficulty** **GENERAL WARNING:** Machining aged 18Ni(350) is one of the most challenging metalworking tasks. * **Machining Strategy:** * **Tooling:** **Cubic Boron Nitride (CBN)** or **Ceramic** inserts are **strongly recommended**. Premium submicron carbide can be used with extreme care. * **Parameters:** Very low feeds and speeds. High-pressure coolant is **essential**. * **Operations:** Grinding and Electrical Discharge Machining (EDM) are preferred for finishing. * **Joining:** * **Welding:** **Not recommended** in the aged condition. Must be welded in solution-annealed state followed by full re-aging. * **Mechanical Fastening:** Primary joining method. Use large bearing areas and smooth radii. * **Corrosion & Protection:** * **Not corrosion resistant.** Requires immediate protection after final machining. * **Standard Coatings:** Electroless Nickel, High-quality cadmium-titanium plate (with mandatory post-plate bake for hydrogen embrittlement relief). --- ### **Quality Assurance & Certification** Given the criticality of applications, certification is exhaustive. 1. **Material Test Report:** EN 10204 3.1 or 3.2, detailing heat chemistry and **longitudinal** mechanical tests. 2. **Heat Treatment Record:** Full documentation of solution and aging cycles. 3. **Non-Destructive Testing:** 100% **Ultrasonic Testing (UT)** is standard for bar stock to detect internal flaws. 4. **Microcleanliness Report:** Per ASTM E45, often with stringent limits on inclusions. 5. **Fracture Toughness Report:** KIC or JIC data is frequently required. --- ### **Design & Procurement Critical Considerations** * **Toughness is Limited:** The **fracture toughness (KIC) is the defining design limit**, not yield strength. **Leak-Before-Break** design principles are often inapplicable. * **Stress Corrosion Cracking (SCC):** While maraging steels have good SCC resistance, the extreme strength of 350 grade increases susceptibility. Environmental control is vital. * **Cost:** Material and processing costs are **significantly higher** than 18Ni(300), driven by high Cobalt content. * **Availability:** Not an off-the-shelf item; requires ordering from specialized mills. --- ### **Summary** The **16 mm aged 18Ni (350) maraging steel round bar** represents the **absolute frontier of strength in wrought alloy steel**. It is a **specialist material** whose use is justified only when the performance requirement unequivocally demands strength levels beyond the capability of 18Ni(300) or other ultra-high-strength steels. Its successful implementation requires: 1. **Fracture mechanics-based design** accounting for low toughness. 2. **Perfect fabrication quality** with no allowable defects. 3. **Rigorous environmental protection** in service. It is the material of choice when the design imperative is: **"The highest possible strength, and we will engineer everything else around that constraint."** -:- For detailed product information, please contact sales. -: AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm Specification Dimensions Size： Diameter 20-1000 mm Length <7352 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, Aged, at RT, tested longitudinal, round bar 16 mm Properties -:- For detailed product information, please contact sales. -:

Applications of AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm -:- For detailed product information, please contact sales. -: Chemical Identifiers AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm -:- For detailed product information, please contact sales. -:

Packing of AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm -:- 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 3823 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