Mechanisms of pitting induced by containing Ce inclusions in X100 pipeline steel

Abstract

Rare earth cerium (Ce) can reduce the pitting susceptibility and occurrence probability of X100 pipeline steel in a simulated marine environment by altering the characteristics and quantity of inclusions. To elucidate the effects of containing Ce inclusions on pitting, X-ray micro-computer tomography observations, field emission scanning electron microscopy with energy dispersive spectroscopy analyses, scanning Kelvin probe microscopy tests, conductive atomic force microscopy analyses, and a series of immersion tests were carried out. The results show that after adding 0.0049 wt%Ce, the number of inclusions per unit volume decreases from 224 to 24. Moreover, the mechanism of pitting induced by inclusions after Ce modification has changed fundamentally. The local corrosion of containing Ce inclusions is mainly caused by chemical process rather than the previous combined of electrochemical and chemical process, and this change effectively slows down the rate of initiation and propagation of pitting.

Keywords

• X100 pipeline steel
• Rare earth inclusion
• XRM
• AFM
• Pitting