F6NM (UNS S41500) Super Martensitic Stainless Steel

Product Description

F6NM is a premium super martensitic stainless steel with carefully balanced additions of nickel (3.50-5.50%) and molybdenum (0.50-1.00%), specifically engineered to deliver an exceptional combination of high strength, superior toughness at sub-zero temperatures, and excellent corrosion resistance. This advanced alloy features a very low carbon content (0.05% max), which significantly enhances weldability while maintaining the beneficial properties of martensitic microstructure. F6NM (UNS S41500) represents a major metallurgical advancement over conventional martensitic stainless steels, offering substantially improved toughness, superior corrosion resistance in aggressive environments, and exceptional resistance to sulfide stress cracking (SSC). Qualified to NACE MR0175/ISO 15156 standards, this sophisticated alloy provides reliable performance in sour service conditions, making it the material of choice for critical components in demanding oil and gas applications, particularly in subsea and downhole environments where component failure can have severe consequences.

Applications

F6NM super martensitic stainless steel is specifically designed for applications requiring an optimal combination of high strength, excellent toughness, and superior corrosion resistance, particularly in oil and gas production environments. Its primary applications include:

• Valves and valve components for severe service conditions
• Actuators for subsea and topside applications
• Subsea connectors and components
• Downhole tools and equipment
• Completion equipment for sour service environments
• Wellhead components and Christmas trees
• Pump shafts and impellers for corrosive service
• Subsea manifold components
• High-pressure flow control equipment
• Drill and completion risers
• Bolting for critical subsea applications
• Intervention tools for hostile environments

The exceptional combination of mechanical properties and corrosion resistance makes F6NM particularly valuable for applications where other stainless steels would be susceptible to stress corrosion cracking or would not provide adequate mechanical properties in demanding environments.

Standards and Specifications

F6NM super martensitic stainless steel complies with the following international standards and specifications:

• UNS S41500
• NACE MR-0175/ISO 15156 (Materials for use in H₂S-containing environments in oil and gas production)
• W1.4313 (European designation, similar)
• ASTM A182/A182M (Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service)
• ASTM A217/A217M Grade CA6NM (Standard Specification for Steel Castings, Martensitic Stainless and Alloy, for Pressure-Containing Parts, Suitable for High-Temperature Service)
• ASTM A276 Type 415 (Standard Specification for Stainless Steel Bars and Shapes)
• ASTM A479/A479M Type XM-19 (Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels)
• API 6A (Specification for Wellhead and Christmas Tree Equipment)
• API 17D (Specification for Subsea Wellhead and Christmas Tree Equipment)

Chemical Composition and Grade Comparison

Chemical Composition (WT%)

Element	Min	Max
C	–	0.05
Si	–	0.60
Mn	0.50	1.00
P	–	0.030
S	–	0.030
Cr	11.5	14.0
Ni	3.50	5.50
Mo	0.50	1.00

Grade Equivalents and Similar Materials

Standard	Designation	Notes
UNS	S41500	Primary designation for F6NM
ASTM	Type 415	Wrought version
ASTM Cast	CA6NM	Cast equivalent
European	W1.4313	Similar composition
European	X3CrNiMo13-4	Similar composition

Comparison with Similar Grades

Property	F6NM (S41500)	F6NM Cast (CA6NM)	AISI 410	17-4PH
Carbon Content	≤0.05%	≤0.06%	0.08-0.15%	≤0.07%
Nickel Content	3.50-5.50%	3.50-4.50%	≤0.75%	3.00-5.00%
Toughness	Excellent	Very Good	Fair	Good
Corrosion Resistance	Very Good	Very Good	Moderate	Good
Weldability	Excellent	Good	Fair	Fair
Typical Yield Strength	75,000 PSI	70,000 PSI	65,000 PSI	105,000 PSI

Mechanical Properties

F6NM offers exceptional mechanical properties in both the solution annealed and double tempered condition:

Typical Mechanical Properties in Solution Annealed Condition

Property	Value	Metric Equivalent
0.2% Yield Strength	75,000 PSI Min	≥ 517 MPa
Tensile Strength	95,000 PSI Min	≥ 655 MPa
Elongation	18% min	18% min
Reduction of Area	35% min	35% min
Hardness	23 HRC	~253 BHN
Charpy V Notch @ -60 DEG C	42/34 Joules	42/34 J

Physical Properties

Property	Value
Density	7.75 g/cm³ at 20°C
Elastic modulus at 20°C	200 GPa
Thermal conductivity at 20°C	25 W/m·K
Specific heat capacity at 20°C	460 J/kg·K
Electrical resistivity at 20°C	0.60 μΩ·m
Thermal expansion coefficient (20-100°C)	10.5 × 10⁻⁶ /K
Magnetic permeability	Ferromagnetic

Available Dimensions

SHUNFU METAL supplies F6NM (UNS S41500) super martensitic stainless steel in the following dimensions:

• Round Bars: Diameter range from 10 mm to 350 mm (0.394″ to 13.8″)
• Flat Bars: Thickness from 5 mm to 100 mm (0.197″ to 4″), width according to customer requirements
• Forgings: Custom sizes according to customer specifications
• Plates: Thickness from 5 mm to 100 mm (0.197″ to 4″)
• Seamless Tubes: Outside diameter from 10 mm to 250 mm (0.394″ to 9.8″) with various wall thicknesses
• Custom Components: Machined according to customer drawings and specifications

Materials are supplied in the solution annealed and double tempered condition. Custom dimensions and specifications are available upon request to meet specific project requirements. All products are fully tested and certified to meet or exceed relevant industry standards, including NACE MR0175/ISO 15156 requirements for sour service applications.

Heat Treatment

F6NM achieves its optimal properties through a carefully controlled heat treatment process:

• Solution Annealing: 950-1050°C (1740-1920°F) followed by rapid cooling in air or oil
• Double Tempering: Primary tempering at 580-620°C (1075-1150°F) followed by secondary tempering at 550-590°C (1020-1095°F)
• Stress Relieving (when required): 550-600°C (1020-1110°F) for stress relief without significant changes to mechanical properties

The double tempering process is critical for F6NM to achieve the optimal combination of strength, toughness, and corrosion resistance. This process ensures the transformation of retained austenite to tempered martensite, resulting in a homogeneous microstructure with excellent mechanical properties and corrosion resistance.

Corrosion Resistance

F6NM super martensitic stainless steel offers excellent corrosion resistance properties:

• General Corrosion: Superior resistance to atmospheric corrosion, fresh water, and mildly corrosive industrial environments.
• Pitting Corrosion: Good resistance to pitting corrosion in chloride-containing environments, significantly better than conventional martensitic stainless steels like AISI 410.
• Stress Corrosion Cracking (SCC): Enhanced resistance to chloride-induced SCC compared to standard martensitic and many austenitic stainless steels.
• Sulfide Stress Cracking (SSC): Excellent resistance to SSC in sour environments, qualified according to NACE MR0175/ISO 15156 standards for oil and gas production applications.
• Crevice Corrosion: Improved resistance to crevice corrosion compared to conventional martensitic stainless steels.
• CO₂ Corrosion: Outstanding resistance to carbon dioxide (sweet) corrosion, making it suitable for sweet oil and gas production environments.

The improved corrosion resistance of F6NM compared to conventional martensitic stainless steels is primarily attributed to its higher nickel and molybdenum content, combined with very low carbon content and controlled heat treatment.

Weldability and Fabrication

F6NM offers excellent fabrication characteristics, particularly compared to conventional martensitic stainless steels:

• Weldability: Excellent weldability due to low carbon content, significantly reducing the risk of cold cracking. Preheating is typically not required for thin sections, though mild preheating (150-200°C) may be beneficial for thicker sections.
• Welding Processes: Compatible with GTAW (TIG), GMAW (MIG), SMAW (Stick), SAW (Submerged Arc) welding processes. Matching filler metals (e.g., E410NiMo or custom F6NM fillers) are recommended.
• Post-Weld Heat Treatment: Post-weld heat treatment (tempering at 580-620°C) is recommended for critical applications to restore corrosion resistance and toughness.
• Machinability: Good machinability, comparable to or better than austenitic stainless steels. Standard tooling and moderate cutting speeds can be used.
• Formability: Good hot formability. Moderate cold formability in the annealed condition.
• Surface Finishing: Excellent response to polishing, grinding, and other surface finishing operations.

The superior weldability of F6NM compared to conventional martensitic stainless steels makes it particularly valuable for fabricated components in critical applications where welds must maintain both mechanical integrity and corrosion resistance.

Key Advantages of F6NM

F6NM super martensitic stainless steel offers several key advantages over conventional martensitic and other stainless steels:

• Exceptional Low-Temperature Toughness: Maintains excellent impact properties down to -60°C (-76°F), making it suitable for arctic and deepwater applications.
• Superior Weldability: Dramatically improved weldability compared to conventional martensitic grades, reducing fabrication costs and increasing reliability.
• Excellent Corrosion Resistance: Enhanced resistance to pitting, SSC, and general corrosion compared to conventional 12% Cr martensitic stainless steels.
• High Strength: Maintains high strength levels comparable to conventional martensitic stainless steels while offering superior toughness and corrosion resistance.
• NACE MR0175 Qualification: Qualified for sour service applications according to strict industry standards.
• Cost-Effective Alternative: Offers a more economical alternative to duplex stainless steels or nickel alloys in many applications while providing adequate performance.
• Magnetic Properties: Unlike austenitic stainless steels, F6NM is ferromagnetic, making it suitable for applications requiring magnetic properties.

Why Choose SHUNFU METAL for F6NM

When sourcing F6NM (UNS S41500) super martensitic stainless steel for your critical applications, SHUNFU METAL delivers superior quality and service. Our inventory of F6NM meets the most stringent industry standards and undergoes comprehensive quality control to ensure consistent performance in demanding environments. We provide complete material traceability and certification, including:

• Material test reports (MTR) documenting chemical composition
• Mechanical property certification including impact testing at specified temperatures
• Heat treatment documentation
• Non-destructive testing results (ultrasonic, magnetic particle, liquid penetrant)
• NACE MR0175/ISO 15156 compliance certification
• Positive material identification (PMI) testing reports
• Microstructure examination reports when required

Our technical experts can assist you in selecting the optimal heat treatment condition and product form of F6NM for your specific application requirements, ensuring maximum performance and service life of your equipment. With competitive pricing, reliable global shipping, and responsive customer service, we aim to be your trusted partner for specialty stainless steel solutions in the oil and gas, valve manufacturing, and subsea equipment industries.

Contact us today with your F6NM requirements. Our team is ready to provide detailed quotations and technical support to help you select the ideal material specification for your valves, actuators, subsea equipment, or other demanding applications in corrosive environments.