Research On Corrosion Of The Carbon Steel Welded Joint In The Ammonium Sulfite Solution

Aiming at the fact of serious corrosion of carbon steel welded joint in the ammonium sulfite solution during the paper-making of using ammonium sulfite, the corrosion behavior of them was researched. On the base of adopting galvano-chemistry test, corrosion speed of the welded joint in different temperature, concentration and pH solution was got. The influence of the three factors on corrosion speed being discussed, corrosion regularity thus is obtained. The corrosion speed of carbon steel in different temperature and concentration was also measured by gravimetric method, though which the test result of galvano-chemistry was proved. Using metallographic analysis, original structure and surface deficiency were obtained, the influence of the structure on corrosion speed was settled, the surface macrography patterns of welded joint in different temperature and concentration were got. Microscopic patterns after corrosion in different condition were gained by SEM, though which the influence of temperature, concentration and structure on corrosion was easily observed.The results show the microstructures of welded joint were of obvious difference after steel Q235 being welded by J420, which lead to the corrosion of weld seam is the quickest, base metal is slowest and heat-affected zone .Heightening temperature and concentration can accelerate corrosion speed. The variation of cathode curves wasn't obvious, but passivation occurs in the anode. With the variation of ammonium sulfite pH changing from acidity to alkality, passivation occurs in the anode and the corrosion speed is reduced.