Nitrogen corrosion

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This post was last edited by JFTANG726 on 2009-12-6 at 16:02. At normal temperatures, nitrogen does not cause corrosion to steel; it is often used for nitrogen sealing to protect equipment. However, in ammonia synthesis plants (or other hydrogen-nitrogen-ammonia environments), in addition to hydrogen corrosion, ammonia decomposes at temperatures of 400–600°C under the catalysis of iron to produce active nitrogen atoms. These nitrogen atoms penetrate into the steel and dissolve into the ferrite phase, forming nitrogen-containing α-Fe. When the nitrogen concentration exceeds the saturation limit, it reacts with Fe to form interstitial nitrides of the γ′ phase; once the concentration in the γ′ phase reaches saturation, the ε phase is formed. This creates a nitrided layer within a certain depth range on the surface of the steel. The nitridized layer is hard and brittle, which reduces the ductility and strength of the steel, and cracks tend to form at stress concentration areas. This is what is known as “nitridation embrittlement”. Let’s discuss nitrogen-induced embrittlement!