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Intergranular corrosion of metal surface seen at x2000 magnitude

Intergranular Corrosion

What is Intergranular Corrosion?

The Basics of Intergranular Corrosion

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The Basics of Intergranular Corrosion

Intergranular corrosion is a type of localized corrosion that occurs preferentially along the grain boundaries of a metal or alloy, leading to the weakening and potential failure of the material. This metal failure mode is usually limited to specific alloy systems and environments such as hot chloride corrosion of austenitic stainless steel or ammonia cracking of brass, and sulfide cracking of bronze alloys.
Intergranular corrosion may be defined as corrosion arising preferentially at grain boundaries, typically with subtle or negligible attack on the adjacent grains and is sometimes referred to as grain boundary corrosion and intercrystalline corrosion.

Several factors influence the occurrence and severity of intergranular corrosion in industrial applications. Some key variables include:

  • Grain Boundary Properties: The presence and nature of precipitates along grain boundaries can impact the electrochemical potential difference between the grain boundary and the bulk material, promoting corrosion.
  • Welding and Heat Treatments: The heat input during welding and subsequent heat treatments can lead to sensitization of the material, making it more susceptible to intergranular corrosion.
  • Low Chromium Content: Chromium depleted zones in certain grades of stainless steels (and only stainless steel) caused by improper welding or prolonged heat treatments can increase the likelihood of corrosion occurring.

The typical method for controlling intergranular corrosion is to replace the material with a more corrosion-resistant alloy. Other mitigation strategies may include:

  • Proper Heat Treatment: Control heat treatment processes, such as annealing or stress-relieving, to avoid sensitization and promote the formation of stable grain boundary phases.
  • Welding Techniques: Utilize welding techniques, such as low heat input processes and the use of filler metals with low sensitization potential, to reduce the risk of corrosive activity.
  • Protective Coatings: Apply protective coatings or surface treatments, such as electroplated chromium or conversion coatings, to improve the corrosion resistance and provide a thin yet dense and very hard barrier to the base material.

Armoloy's Solution to Corrosion

Armoloy offers multiple metal surface treatments with varying levels of protection from the common causes of intergranular corrosion. Offering both broad-spectrum and industry-specific applications, our protective metallic coatings add significant value through increased performance and decreased revenue losses from unplanned maintenance and downtime.

Our protective coatings ensure a thin, precise coat that won’t impact production, but will improve surface hardness and prevent environmental defects. Beyond increasing wear life, Armoloy tailors our metallic coatings based on the specific requirements of your application and industry.

The best practice to avoid this form of metal failure is to understand the factors that encourage corrosive activity, and the mitigation strategies available to reduce the risk of corrosion from causing detrimental effects to industrial applications.

Beyond the Lab: Metal Failures in Narrative Form

Other Metal Failure Modes

Other common metal failures include:

Corrosion can also result from, or be a precursor to, other potential metal failures

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