Abstract
Rare earth (RE) elements are beneficial to improving corrosion properties in low-carbon and low-alloy steels. In this paper, corrosion performance of Q235B steel and Q355B steel samples after RE alloying under wet-dry cycle immersion conditions were analyzed. Experimental results show that corrosion rate was significantly decreased. It was probably due to the grain refinement by RE alloying, which increased the density of protective rust layers and improved corrosion resistance. The formation of small-sized spherical RE inclusions also inhibited the precipitation of MnS and weakened micro galvanic corrosion. Additionally, RE atoms tended to segregate towards grain boundaries and a RE concentration region is formed between rust layers and matrix to impede the access from contacting corrosive ions. A corrosion resistance schematic of RE atom segregation was proposed based on microstructure morphology and element distribution results.
Highlights
Low-carbon and low-alloy steels have been widely used as structural materials due to their excellent engineering properties
When these two kinds of construction steels exposed to atmospheric corrosion environment, they are prone to be attacked and corrosion will result in potential safety problems and economic losses [1,2]
It is found that more pores and exfoliating of outer rust layer appear on the sample surface in Q235B and Q355B steels with the local exfoliating of outer rust layer appear on the sample surface in Q235B and Q355B steels with the extension of test time
Summary
Low-carbon and low-alloy steels have been widely used as structural materials due to their excellent engineering properties When these two kinds of construction steels exposed to atmospheric corrosion environment, they are prone to be attacked and corrosion will result in potential safety problems and economic losses [1,2]. The atmospheric corrosion originates from pitting corrosion and spreads to the entire surface to form uniform corrosion It is well-known that manganese sulfide (MnS) often provides initiation sites for pitting corrosion and aluminium oxide (Al2 O3 ) has been considered to cause destructive effects on corrosion resistance of steels [12,13,14]. Many investigators have shown effects of RE elements on microstructure and inclusions in steels, few studies have focused on the influence of RE alloying such as segregation of RE atoms in steels under wet-dry cycle immersion conditions. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA) and auger electron spectroscopy (AES) were conducted to investigate the mechanism of improving corrosion resistance by the method of RE alloying
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