Intergranular corrosion of stainless steelIt is a localized selective corrosion that occurs along the boundaries of metal grains, resulting in the loss of intergranular bonding force and a sharp decrease in material strength, but the surface may still remain bright. It is a highly concealed and harmful form of corrosion.

　　Intergranular corrosion of stainless steelPreventive measures and material selection:

1. Material selection

Ultra low carbon stainless steel:

304L (0.03% C), 316L (0.03% C): Excellent resistance to intergranular corrosion, suitable for welding structures.

Stabilized stainless steel:

321 (containing Ti), 347 (containing Nb): Suppressing chromium carbide precipitation through TiC/NbC, suitable for high temperature environments.

Dual phase stainless steel:

Like 2205 (austenite+ferrite): ferrite quickly supplements chromium, balancing corrosion resistance and mechanical properties.

2. Process optimization

Heat treatment control:

Avoid slow cooling in the range of 450-850 ℃, and rapid cooling or solution treatment after welding.

Welding specifications:

Using small wire energy input (such as argon arc welding) to reduce the residence time of the heat affected zone in the sensitization zone.

Impurity control:

Limit the content of impurities such as P and Si to reduce the risk of grain boundary segregation.

3. Design improvement

Structural optimization: Avoid dead corners caused by medium retention in design and reduce the risk of local corrosion.

Coating protection: Coating or lining is used in corrosive media to isolate stainless steel from contact with the medium.