Effects of rare earth elements on corrosion behaviors of low‐carbon steels and weathering steels

Abstract

The effects of rare earth elements on the corrosion properties of low‐carbon steel and weathering steel were investigated. To elucidate the roles of rare earth elements (Ce and La) and the corrosion behavior of steels, salt spray tests, electrochemical techniques, X‐ray diffractometer, scanning electron microscopy, Electron Probe Micro Analysis (EPMA), and Auger Electron Spectroscopy (AES) were conducted. The results showed that the addition of rare earth elements enhances the corrosion resistance of both low‐carbon steels and weathering steels, indicated by lower corrosion current density and salt spray corrosion rate after rare earth alloying. On the one hand, rare earth elements modify the morphology of inclusions and thus slow down the micro‐area electrochemical corrosion, which improves the electrochemical corrosion resistance of these two steels. On the other hand, rare earth atoms tend to segregate toward the interface between the rust layer and the matrix. Hence, salt spray corrosion resistance is improved due to the enhancement of adhesion and compactness of the rust by the addition of rare earth elements.

Effects of Rare Earth (Ce and La) on Steel Corrosion Behaviors under Wet-Dry Cycle Immersion Conditions

“…Rust layers can effectively prevent the Corrosion rates obtained in wet-dry cycle immersion tests are shown in Figure 2. The corrosion rates (g•m −2 •h −1 ) of these four steels are calculated from the following Equation (1) [22,23]:…”

“…The main corrosion phases are all composed of γ-FeOOH, α-FeOOH, Fe 3 O 4 and γ-Fe 2 O 3 . According to previous study, γ-FeOOH is firstly formed and then transforms to α-FeOOH and Fe3O4 during the atmospheric corrosion of steels [7,23,25,26]. α-FeOOH is the most stable hydroxy iron oxide and the main phase in protective rust layers.…”

“…A completely intergranular fracture surface covered by grain boundaries has been produced and the change of Ce content in each layer under different ion sputtering time is analyzed as shown in Figure 7. According to previous study, the kinetic energy range of Ce is chosen from 52 eV to 115 eV including three typical Auger peaks of Ce at 68 eV, 87 eV and 104 eV, respectively [23]. Although the spectra lines have a certain deviation from the standard map, the tested Auger peaks of Ce in Q235BM steel are at 68 eV, 87 eV and 103 eV, which are consistent with typical peaks in Auger Electron Spectroscopy Reference Manual [27].…”

“…Whereas, no obvious Auger peaks of La are found by AES, although La atoms should have the similar Auger peaks as Ce atoms in theory. Previous study has explained this phenomenon due to the minimum level to be effectively detected and the difficulty to be distinguished from Ce [23]. Although the peaks of La are not obvious as Ce, La atoms are still believed to segregate towards grain boundaries for its similar chemical properties to Ce atoms.…”

“…Although the peaks of La are not obvious as Ce, La atoms are still believed to segregate towards grain boundaries for its similar chemical properties to Ce atoms. Many researchers believe that RE atoms tend to segregate towards grain boundaries or interfaces such as surfaces or grain boundaries due to their large radius [18,23]. Whether segregation of RE elements towards interfaces occurs or not, an AES experiment has been performed for the specimens with RE addition to test this finding.…”