Mechanism of Grooving Corrosion Resistance in Cu-Ti Added High Frequency Electric Resistance Welded Steel Pipes

摘要

The effect of the sulfides on corrosion andthe observation of the microstructure of the inclusionsespecially, the sulfides, were investigated toelucidate the mechanism of the grooving corrosionresistance in Cu-Ti added high frequency electricresistance welded steel pipes. Main conclusions are asfollows. (1) The constitution of the sulfides changesfrom MnS to Cu_xS+MnS and Ti_2S by the addtion of Cuand Ti and the relative small sulfides less than 0.1#mu#m Increase. (2) MnS overall covered with Cu_xSprecipitates in Cu-Ti added steel. Cu_xS in Cu-Ti addedsteel more precipitates than that in Cu-Ti free steelbecause of the difference in cu content. (3) Cu_xS+MnSand Ti_2S are not corroded in 3% sodium chloridesolution (NaCl) from the in-situ observation.Therefore, it was supposed that the grooving corrosionof the welded portion because the constitution and themorphology of the sulfides varied by the addition ofcu and Ti. That is, it is caused by preventing MnS itselffrom dissolving for the environment by the formation of Cu_xS.