Stainless Steel F6NM 415 Round UNS 41500 Bars

Product Description

UNS S41500, commonly known by its forging grade designation F6NM, is a low-carbon, 13% Chromium martensitic stainless steel with additions of Nickel and Molybdenum. It is essentially the ASTM/UNS equivalent to the European EN 1.4313 (X3CrNiMo13-4).

F6NM is engineered to solve the inherent brittleness found in standard 400-series martensitic steels, offering a unique combination of high tensile strength, exceptional notch toughness, and improved weldability.

Technical Profile: F6NM (UNS S41500)

Chemical Composition (%)

The "NM" in F6NM stands for Nickel and Molybdenum. The low carbon content is the secret to its superior ductility and resistance to cracking.

Mechanical Properties (Typical ASTM A182 Requirements)

F6NM is typically supplied in the Quenched and Double Tempered condition to ensure the transformation of retained austenite and to maximize impact toughness.

• Tensile Strength ($R_m$): $\ge 790$ MPa (115 ksi)

• Yield Strength (0.2% Offset): $\ge 620$ MPa (90 ksi)

• Elongation: $\ge 15\%$

• Hardness (Brinell): 295 HBW max (typically maintained between 230–285 HBW for NACE compliance)

• Impact Toughness (Charpy V-Notch): Exceptionally high, even at sub-zero temperatures (down to $-60°\text{C}$).

Key Characteristics

• Corrosion & Erosion Resistance: Superior to Grade 410 in CO2 and H2S environments. It is highly resistant to cavitation, making it the premier choice for high-velocity fluid environments.

• NACE MR0175 Compliance: When heat-treated correctly to a hardness below 23 HRC, F6NM is suitable for sour gas service in the oil and gas industry.

• Weldability: Unlike most martensitic steels, F6NM has excellent weldability due to its low carbon content, which prevents the formation of hard, brittle martensite in the heat-affected zone.

• Magnetic: The alloy is ferromagnetic.

Common Applications

F6NM round bars are used for critical components in "heavy" industrial sectors:

• Oil & Gas: Valve bodies, flanges, hangers, and wellhead components for high-pressure service.

• Power Generation: Turbine runners, Pelton wheels, and wicket gates for hydroelectric plants.

• Pump & Compressor Industry: High-performance shafts, impellers, and wear rings.

• Marine: Large-scale propeller shafting and offshore structural connectors.

Global Designations & Standards

Processing & Heat Treatment

1. Hardening: Heat to $950°\text{C} – 1050°\text{C}$ followed by air or oil quenching.

2. Double Tempering:

   • First Temper: $600°\text{C} – 650°\text{C}$ (to transform the structure).

   • Second Temper: $590°\text{C} – 620°\text{C}$ (to achieve final mechanical properties and stress relief).

3. Machining: F6NM is tougher than 410 but machines well with rigid setups. It has a tendency to work-harden, so constant feeds and adequate coolant are essential.