Abstract
An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-resistant steel (CR steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless steel (SS steel) was evaluated for comparison. Moreover, the passive film with CR steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott‑Schottky approach. The results showed that the excellent passivity of CR steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR steel. A passive film growth model for CR steel was proposed.
Highlights
The corrosion of steel is one of the most important factors for the damage of reinforced concrete structures
The cross section of the passive film after 10-day passivation and 30-day chloride induction was examined by scanning transmission electron microscopy (STEM)/focused ion beam (FIB) (Focused Ion Beam)
The EDS (Energy Dispersive Spectrometer) analysis was performed in scanning transmission electron microscopy (STEM) mode using a probe diameter of 1–2 nm
Summary
The corrosion of steel is one of the most important factors for the damage of reinforced concrete structures. A protective passive film is usually formed on the steel surface in the high alkaline concrete environment. The high corrosion resistance of stainless steel is attributed to the compact dual-layer passive film on the steel surface. The high alloy content of stainless steel leads to excellent corrosion resistance, but results in high cost and bad weldability [5]. With proper processing and metallographic microstructure, the low alloy content can provide adequate corrosion resistance in high alkaline environments, which leads to low cost and good weldability. Due to the distinct composition and microstructure, the passive film growth mechanism of CR steel has to be studied thoroughly. The objective of this work is to investigate the passive film growth mechanism and the effect of substrate composition of new 10% Cr alloyed corrosion-resistant steel (CR). Various methods are applied, such as electrochemical methods (open-circuit potential, linear polarization resistance, electrochemical impedance spectroscopy, and Mott-Schottky curves), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM)
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