Do you know how to prevent and control intergranular corrosion?

Intergranular corrosion (IGC) is a critical issue for austenitic stainless steels, and effective measures must be taken to prevent and control it. Based on its mechanism, the following strategies are widely adopted:

1.Use of Ultra-Low Carbon Stainless Steel

Reducing the carbon content to below 0.03% prevents the formation of chromium carbides (Cr23C6) and eliminates chromium-depleted zones, which are the main cause of intergranular corrosion. Ultra-low carbon stainless steels, such as 00Cr17Ni14Mo2, are ideal for this purpose. For applications requiring moderate strength, good plasticity, and lower costs, 0Cr18Ni9 is a practical choice.

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2.Stabilized Stainless Steel

Using stabilized stainless steel, which contains titanium (Ti) or niobium (Nb), is another effective solution. These elements have a strong affinity for carbon, forming stable carbides (TiC or NbC) instead of chromium carbides. Unlike Cr23C6, TiC and NbC have much lower solubility in austenite at solution treatment temperatures. As a result, stabilized stainless steels, such as 1Cr18Ni9Ti or 1Cr18Ni9Nb, can operate at temperatures between 500°C and 700°C without a tendency for intergranular corrosion.

3.Solution Treatment

Austenitic stainless steels are prone to sensitization during welding due to the high temperatures in the weld pool and heat-affected zones (HAZ). To address this, a solution treatment can be applied:

Non-stabilized stainless steels are heated to 1000–1120°C, held for 1–2 minutes per millimeter of thickness, and then rapidly cooled.

Stabilized stainless steels are treated at 950–1050°C.

This process dissolves carbides and prevents their re-precipitation, reducing the susceptibility to intergranular corrosion.

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4.Proper Welding Techniques

Improper welding practices can expose the material to sensitization temperatures, increasing its sensitivity to intergranular corrosion. To mitigate this:

Minimize heat input during welding. Argon arc welding is preferred over manual arc welding due to its lower heat input.

Use ultra-low carbon stainless steels or stabilized stainless steels with Ti or Nb as welding materials.

For welding rods, select ultra-low carbon or Nb-containing electrodes.

Ensure quick operation and rapid cooling to limit the time the material spends in the sensitization temperature range.

By implementing these measures, intergranular corrosion can be effectively prevented and controlled, ensuring the durability and performance of austenitic stainless steels in various applications.