Abstract:

In this paper,the influences of Sn on the mechanical properties and CO₂ corrosion resistance of the Q125-grade oil tube used for ERW were investigated by means of SEM,TEM,EBSD and electrochemical measurement. The results show that Sn has no influence on the microstructure of the steel as well as the forms and sizes of precipitates,so that there is no obvious change of the steel strength. However,the activity of the tested steel changes after the addition of a little Sn,which results in the negative shift of corrosion potential,the decrease in corrosion current density,the increase in the polarization resistance of electrode reaction and the deceleration of the corrosion,thus improving the corrosion resistance of the tube. Moreover,it is found that,with the addition of Sn,both the proportion of small-angle grain boundary and the corrosion resistance of the steel improve,while the proportion of large-angle grain boundary decreases,which results in a decrease in the elongation and impact energy of the steel.

Key words: ERW tube, corrosion behavior, large-angle grain boundary, polarization curve