SS 431 Round 1.4057 X17CrNi16-2 Bars

Product Description

AISI 431 (WNr. 1.4057 / X17CrNi16-2) is a high-chromium, low-nickel, martensitic stainless steel. It is widely regarded as the most corrosion-resistant grade within the martensitic family. By combining high tensile strength and torque resistance with superior toughness, it is the preferred choice for hardware in marine and aerospace environments.

Technical Profile: SS 431 / 1.4057

Chemical Composition (%)

The addition of Nickel (unique for most martensitic grades) improves the material's toughness and corrosion resistance compared to 410 or 420.

Mechanical Properties (Condition QT 800)

431 is almost always supplied in a Quenched and Tempered (QT) condition. The "800" designation typically refers to the minimum tensile strength.

• Tensile Strength ($R_m$): 800 a 1,050 MPa

• Yield Strength ($R_{p0.2}$): $\ge 600$ MPa

• Hardness (Brinell): 235 a 285 HBW

• Impact Strength (Charpy V): $\ge 25$ J (at room temperature)

• Elongation ($A_5$): $\ge 12\%$

Key Characteristics

• Superior Corrosion Resistance: Due to its 16% Chromium content, it offers excellent resistance to marine atmospheres, salt spray, and many organic acids. It performs significantly better than 410 or 416.

• High Strength and Toughness: The nickel content prevents the extreme brittleness often seen in high-carbon martensitic steels, allowing it to withstand high-impact loads.

• Magnetic: Like all martensitic grades, 431 is strongly magnetic.

• Heat Resistance: Maintains good mechanical properties and oxidation resistance up to approximately $700A \text{C}$, though it is primarily used for structural strength at lower temperatures.

Common Applications

Grade 431 is the standard for high-performance shafting and marine hardware:

• Marine Engineering: Propeller shafts, pump shafts, and outboard motor components.

• Aerospace: High-strength bolts, fasteners, and aircraft structural parts.

• Chemical Industry: Valve stems, mixer shafts, and specialized laboratory equipment.

• General Industry: Gears, drive shafts, and heavy-duty nuts/bolts.

Global Designations

Fabrication and Heat Treatment

• Machinability: Comparable to a 4140 low-alloy steel. It is more difficult to machine than 416 due to its toughness; using carbide tooling and slower speeds is recommended.

• Welding: Generally not recommended because it is air-hardening. If welding is necessary, it requires extensive pre-heating to $200A \text{C} a 300A \text{C}$ and immediate post-weld heat treatment (annealing or tempering) to prevent cracking.

• Heat Treatment:

  • Hardening: $950A \text{C} a 1050A \text{C}$, followed by oil or air quench.

  • Tempering: Usually performed between $600A \text{C} a 700A \text{C}$. Avoid tempering in the $400A \text{C} a 550A \text{C}$ range to prevent "temper embrittlement," which severely reduces impact toughness.