Abstract
Martensitic stainless steel parts used in carbonaceous atmosphere at high temperature are subject to corrosion which results in a large amount of lost energy and high repair and maintenance costs. This work therefore proposes a model for surface development and corrosion mechanism as a solution to reduce corrosion costs. The morphology, phase, and corrosion behavior of steel are investigated using GIXRD, XANES, and EIS. The results show formation of nanograin–boundary networks in the protective layer of martensitic stainless steel. This Cr2O3–Cr7C3 nanograin mixture on the FeCr2O4 layer causes ion transport which is the main reason for the corrosion reaction during carburizing of the steel. The results reveal the rate determining steps in the corrosion mechanism during carburizing of steel. These steps are the diffusion of uncharged active gases in the stagnant–gas layer over the steel surface followed by the conversion of C into C4− and O into O2− at the gas–oxide interface simultaneously with the migration of Cr3+ from the metal-oxide interface to the gas-oxide interface. It is proposed that previous research on Al2O3 coatings may be the solution to producing effective coatings that overcome the corrosion challenges discussed in this work.
Highlights
Corrosion has had environmental and economic impacts for decades
Absorption near–edge structure (XANES), and the electrochemical behavior is investigated by electrochemical impedance spectroscopy (EIS)
The grazing incidence X-ray diffraction (GIXRD) and XANES results show the generation of a mixed Cr2O3–Cr7C3–nanograin film on top of the FeCr2O4 layer that has developed on the surface of the steel carburized at high temperature
Summary
Corrosion has had environmental and economic impacts for decades. The high cost of corrosion has been reported as approximately 3.5–4.5% of the United States’ GNP or more than 3% of the world’s GDP1–3. Our current study reports on this nanoscale mechanism and the complete corrosion mechanism corresponding to surface development of martensitic stainless steel in low oxygen–partial pressured carburizing. Morphology, phase, phase portion and corrosion behavior of the steel surface can be investigated using these techniques to determine the surface development and complete corrosion mechanism (atomic, nanoscale and microscale) and can lead to a solution of the corrosion problem. The GIXRD and XANES results show the generation of a mixed Cr2O3–Cr7C3–nanograin film on top of the FeCr2O4 layer that has developed on the surface of the steel carburized at high temperature. The carburizing of a commercial martensitic stainless steel, Fe–13.60Cr–0.33C–0.37Mn–0.28Si–0.28Ni (wt%), was done in a low oxygen–partial pressured system using the current heating technique[17] (detailed in Methods and Supplementary Section 1). EIS works in the frequency domain and determines the net impedance in an electrochemical process through the kinetics of charge transfer and electrochemical reaction[26,27,28,29]
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