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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:
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Yield strength: 500 – 800 MPa (depending on grade, e.g., EA4T higher than 4140).
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Tensile strength: 700 – 1,050 MPa.
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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:
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Hardness: 200–300 HV (for pure MoS₂ flame-sprayed) or 400–600 HV when blended with Mo or Ni-based binders.
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Coefficient of friction: 0.03–0.08 (dry sliding), much lower than steel-on-steel (~0.5–0.8).
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Wear resistance: Significantly reduces surface scoring and fretting at bearing seats or coupling zones.
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Temperature resistance: Stable lubrication effect up to ~400–450 °C in air.
3. Combined Effect on Axles
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The axle’s structural strength remains the same (defined by forged steel).
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The MoS₂ coating increases surface life by lowering wear, galling, and seizure risks.
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This is critical in areas like:
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Journal seats (where bearings sit on axles).
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Coupling interfaces (shafts with press fits).
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Keyed or spline connections (reducing fretting).
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