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Corrosion Resistance of the Welded Joint of Submarine Pipeline Steel with Ferrite Plus Bainite Dual‐Phase Microstructure
Author(s) -
Wang YiPeng,
Zuo XiuRong,
Li JinLing
Publication year - 2015
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201400309
Subject(s) - materials science , metallurgy , corrosion , microstructure , bainite , pitting corrosion , ferrite (magnet) , base metal , dual phase steel , optical microscope , scanning electron microscope , welding , composite material , austenite , martensite
In this work, the corrosion resistance of the welded joint and base metal of submarine X65 pipeline steel with ferrite plus bainite dual‐phase microstructure was investigated by electrochemical and immersion tests. The corrosion product films were characterized using X‐ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and optical microscopy. To research the development of pitting corrosion in each zone, pitting diameter statistics were finished under optical microscopy and the forming mechanism of pitting induced by inclusion was analyzed. The experimental results proved that the corrosion resistance of the welded joint was better than that of the base metal, both from the general corrosion and pitting corrosion standpoint. In the welded joint, the weld metal has the best corrosion resistance, and then was the heat affected zone (HAZ). However, there was little difference between parent metal (near HAZ) and base metal (far HAZ) on the corrosion resistance. XRD and EDS analysis showed that the composition of the outer rust layer was mainly composed of Fe 2 O 3 , Fe 3 O 4 , FeOOH, and Fe(OH) 3 , and the inner layer was consisted of Fe 2 O 3 , Fe 3 O 4 , and a little FeOOH. Combined with the microstructure of the each zones, it can be concluded that the best corrosion resistance of the weld metal attributes to the refined grain size. Due to a creation of a galvanic effect between the ferrite and bainite, the dual‐phase microstructure of the base metal and parent metal displayed weak corrosion resistance.