Intergranular corrosion is the most common corrosion form of austenitic stainless steel. So what is the mechanism of intergranular corrosion?
Mechanism of Intergranular Corrosion of Stainless Steel
Intergranular corrosion is a common form of localized corrosion, where corrosion occurs along the boundaries or adjacent regions of metal or alloy grains, while the actual grains are slightly corroded. This type of corrosion weakens the bonding between grains, and severe intergranular corrosion can result in the loss of the metal's strength and ductility, causing it to fracture under normal load.
304 Stainless Steel Excellent Resistance to Intergranular Corrosion
Grade 304 stainless steel is a widely used austenitic stainless steel alloy. It contains 18-20% chromium and 8-10.5% nickel, which provides excellent corrosion resistance.
The typical chemical composition of 304 material is as follows: Carbon ≤ 0.08%, Silicon ≤ 1.00%, Manganese ≤ 2.00%, Phosphorus ≤ 0.045%, Sulfur ≤ 0.030%, Chromium: 18.00-20.00%, Nickel: 8.00-10.50%.
1.Intergranular corrosion is related to the carbon content in 304 stainless steel.High carbon content leads to the combination of chromium and carbon at the grain boundaries to form chromium carbides, which consume chromium elements and result in the loss of corrosion resistance ability at the grain boundaries , making intergranular corrosion more likely to occur.Therefore, reducing the carbon content in 304 stainless steel can improve its resistance to intergranular corrosion.
2.The excellent resistance to intergranular corrosion of 304 stainless steel is mainly due to the presence of more than 17% chromium element, which forms a dense chromium oxide layer on its surface, effectively preventing intergranular corrosion in acidic media.
In addition, the presence of about 8% nickel in 304 stainless steel provides excellent corrosion resistance and heat resistance, which enables it to be used stably in harsh environments for a long time. Therefore, 304 stainless steel is widely used in fields such as chemical industry, petroleum, shipbuilding, light industry, and food.
3.Heat treatment
Proper heat treatment can improve the intergranular corrosion resistance of 304 stainless steel.The common method of heat treatment is solution annealing,which involves heating the 304 stainless steel at high temperatures and then cold it rapidly,which can help eliminate chromium carbides at grain boundaries,to improve intergranular corrosion resistance.
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