1. Introduction to MP35N Alloy

MP35N (UNS R30035) is a unique, multi-phase cobalt-nickel-chromium-molybdenum superalloy. Its exceptional combination of properties stems from a specialized thermomechanical processing sequence that induces a synergistic strengthening mechanism involving both solid solution strengthening and precipitation hardening. This makes MP35N fasteners the premier choice for the most demanding applications where ultra-high strength, supreme toughness, and outstanding corrosion resistance are simultaneously required.

2. Chemical Composition (ASTM F562 / AMS 5844)

The nominal chemical composition of MP35N alloy is as follows:

• Cobalt (Co): 35% (Balance)

• Nickel (Ni): 35%

• Chromium (Cr): 20%

• Molybdenum (Mo): 10%

• Titanium (Ti): ≤ 1.0%

• Iron (Fe): ≤ 1.0%

• Manganese (Mn): ≤ 0.15%

• Silicon (Si): ≤ 0.15%

• Carbon (C): ≤ 0.025%

• Phosphorus (P): ≤ 0.015%

• Sulfur (S): ≤ 0.010%

• Boron (B): ≤ 0.015%

3. Mechanical and Physical Properties

MP35N achieves its legendary properties through a specific cold work + aging heat treatment process.

A. Key Mechanical Properties (Typical for Aged Condition):

• Ultimate Tensile Strength (UTS): 260 - 300 ksi (1790 - 2070 MPa)

• Yield Strength (0.2% Offset): 240 - 285 ksi (1655 - 1965 MPa)

• Elongation: 8% - 15%

• Reduction of Area: 35% - 50%

• Hardness: 45 - 52 HRC

• Fatigue Strength (Endurance Limit): Exceptionally high, a key reason for its use in dynamic components.

• Fracture Toughness (KIC): Remarkably high for its strength level, providing exceptional damage tolerance.

B. Corrosion Resistance:
MP35N offers unparalleled resistance to a wide range of corrosive environments:

• Stress Corrosion Cracking (SCC): Immune in chloride, hydrogen sulfide, and seawater environments.

• Pitting & Crevice Corrosion: Excellent resistance, surpassing most stainless steels and nickel alloys.

• General Corrosion: Outstanding resistance to oxidizing and reducing acids, salt spray, and sour gas (H2S) services.

C. Physical Properties:

• Density: 0.297 lb/in³ (8.22 g/cm³)

• Melting Range: 2370 - 2520°F (1300 - 1385°C)

• Magnetic Permeability: Essentially non-magnetic (<1.005 μ)

4. MP35N Fastener Product Range

Leading MP35N bolt manufacturers produce a comprehensive range of high-performance components, including:

• MP35N Bolts: General term for externally threaded fasteners.

• MP35N Studs and Bolts: Critical for flange connections in subsea, aerospace, and high-pressure systems. Dual-ended studs are common.

• MP35N Screws: A broad category covering various head styles.

• MP35N Socket Head Cap Screws: Extremely popular for aerospace and medical applications due to their high tensile capability and compact head design. They are often manufactured to exacting standards like ASME B18.3.

• Other forms include nuts, washers, threaded rods, and custom-engineered fasteners.

5. Specifications and Standards

The procurement and manufacturing of MP35N fasteners are governed by several critical aerospace, military, and industry specifications. Key among them is the MP35N bolt spec:

• AMS 5844: Covers bar, wire, and forging stock.

• ASTM F562: Standard specification for wrought cobalt-35nickel-20chromium-10molybdenum alloy for surgical implants (also widely used for fasteners).

• AS/EN/NAS/MS Standards: Specific fastener standards (e.g., NASM 25027 for socket head capscrews) often reference the material per AMS 5844.

• Customer-Specific Drawings: Many applications require fasteners manufactured to proprietary engineering drawings with stringent lot traceability and testing requirements.

6. Application Sectors

MP35N fasteners are specified where failure is not an option:

• Aerospace: Landing gear components, engine mounts, flight-critical linkages, and spacecraft systems.

• Oil & Gas (Subsea & Downhole): Christmas tree components, wellhead equipment, riser connectors, and instrumentation in sour service environments.

• Medical & Surgical: Implantable devices, surgical tooling, and dental instruments due to its biocompatibility and strength.

• Marine & Naval: Critical seawater piping systems, submarine components, and shipboard hardware.

• High-Performance Automotive & Racing: Critical suspension and drivetrain components.

7. Sourcing and Manufacturing

Identifying qualified MP35N bolt suppliers is crucial. A reputable MP35N bolt manufacturer will possess:

• Specialized Metallurgical Expertise: Deep understanding of the complex cold work and aging processes.

• Advanced Manufacturing Capabilities: Precision machining and grinding of this ultra-high-strength material.

• Stringent Quality Systems: Compliance with AS9100, ISO 9001, and NADCAP accreditations (especially for heat treatment and testing).

• Full Traceability: Ability to provide mill certifications, heat treat records, and full chemical/mechanical test reports for each lot.

• Testing Facilities: In-house capability for mechanical testing, corrosion testing (e.g., ASTM G48), and metallography.

Conclusion

MP35N fasteners represent the pinnacle of fastener technology, offering an unmatched synergy of extreme strength, toughness, and corrosion resistance. When application demands exceed the capabilities of stainless steels (like A286), nickel alloys (like Inconel 718), or even titanium alloys, MP35N bolts, MP35N studs and bolts, and MP35N socket head cap screws become the engineering material of choice. Successfully implementing these components requires partnering with highly specialized MP35N bolt suppliers who can navigate the complexities of the MP35N bolt spec and deliver parts with guaranteed performance and reliability.