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Decarburization in Fasteners: Causes, Effects, and How to Prevent It

In the world of high-performance fasteners, precision and material integrity are non-negotiable. One often overlooked, yet critical, phenomenon that can compromise fastener strength and performance is decarburization.

In this blog, we explore what decarburization is, how it occurs, its impact on fastener performance, and how to detect and prevent it.

What Is Decarburization?

Decarburization refers to the loss of carbon from the surface layer of a steel component, typically during heat treatment processes like forging, annealing, or hardening. Since carbon plays a key role in providing hardness and strength to steel, its depletion can drastically alter mechanical properties at the surface.

How Does Decarburization Happen?

Decarburization typically occurs when steel is exposed to high temperatures in the presence of oxygen or other reactive gases. Common scenarios include:

  • Improper control during forging or heat treatment
  • Exposure to oxidizing environments (air, CO2, water vapor)
  • Lack of protective atmospheres in furnaces

Prolonged heating at high temperatures

Effects of Decarburization on Fasteners

Using fasteners with a decarburized surface can have serious consequences:

  • Reduced Surface Hardness: A decarburized layer is softer and more prone to wear and galling.
  • Decreased Fatigue Resistance: Surface decarb creates stress risers and lowers resistance to cyclic loads.
  • Risk of Failure in Service: Particularly in critical applications like Oil & Gas, Power, or Heavy Machinery, a decarburized fastener can lead to premature failure.
  • Poor Thread Performance: Threads may deform under load or during tightening.

How to Prevent Decarburization

  1. Controlled Heat Treatment: Use inert atmospheres (like nitrogen or vacuum) or controlled carburizing environments.
  2. Protective Coatings: Applying anti-scale compounds or coatings prior to heat treatment.
  3. Shorter Soaking Times: Minimizing exposure to high temperatures.
  4. Post-Forging Inspection: Especially for critical components.

At Industrial Engineering Works (IEW), we ensure that our heat treatment vendors follow tightly controlled processes and atmospheres to eliminate risk of surface decarburization.

How to Detect Decarburization

Several methods exist to detect and measure decarburization:

  • Microstructural Analysis (Metallography): A cross-sectional cut is polished and etched to reveal the depth of decarburized zones under a microscope.
  • Hardness Testing (Micro Hardness or Case Depth Analysis): Surface and subsurface hardness profiles are measured.
  • Spectroscopy/Surface Carbon Analysis: Determines chemical composition across depth.

According to ASTM F2328 and ISO 898-1, there are clear criteria on allowable decarburization limits for fasteners depending on the grade and class.

Final Thoughts

Decarburization may not be visible to the naked eye, but its impact can be catastrophic in high-stress applications. At IEW, our quality assurance practices are built to detect and prevent even the smallest deviations that could affect performance.

If you’re sourcing fasteners for mission-critical use, ensure decarburization is being accounted for in the quality checks. After all, strength starts at the surface.

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