• The axle itself is not made of molybdenum disulfide (MoS₂).
  Railway axles are forged steels (such as 42CrMo4, EA4T, or 4140).

• MoS₂ is used only as a coating or additive (flame-sprayed or solid-lubricant layer), not as the structural material.

So the strength of the axle comes from the steel, while the MoS₂ layer improves tribological performance (friction and wear).

1. Axle Strength (Steel Core)

Typical forged steel axles used in rail applications have:

• Yield strength: 500 – 800 MPa (depending on grade, e.g., EA4T higher than 4140).

• Tensile strength: 700 – 1,050 MPa.

• Fatigue strength: Designed for >10⁷ load cycles under bending/torsion.

These properties define the axle’s ability to carry train loads and withstand impacts.

2. MoS₂ Coating Contribution

MoS₂ coatings (flame-sprayed or bonded layers) provide:

• Hardness: 200–300 HV (for pure MoS₂ flame-sprayed) or 400–600 HV when blended with Mo or Ni-based binders.

• Coefficient of friction: 0.03–0.08 (dry sliding), much lower than steel-on-steel (~0.5–0.8).

• Wear resistance: Significantly reduces surface scoring and fretting at bearing seats or coupling zones.

• Temperature resistance: Stable lubrication effect up to ~400–450 °C in air.

3. Combined Effect on Axles

• The axle’s structural strength remains the same (defined by forged steel).

• The MoS₂ coating increases surface life by lowering wear, galling, and seizure risks.

• This is critical in areas like:

  • Journal seats (where bearings sit on axles).

  • Coupling interfaces (shafts with press fits).

  • Keyed or spline connections (reducing fretting).

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