Scientists have uncovered a complex relationship between oxygen exposure and corrosion resistance in Super 13Cr stainless steel, a material crucial for industrial applications. The study, conducted under high-temperature conditions of 120°C, demonstrates that the steel's protective capabilities are highly sensitive to oxygen levels in its environment.
Research findings show that when exposed to low oxygen partial pressures (0.03 MPa), the steel's protective layer, known as the passive film, becomes more stable and effective. This enhanced protection is evidenced by higher open circuit potential measurements and increased linear resistance, suggesting improved corrosion resistance under these conditions. The protective film forms a dual-layer structure, with chromium oxides dominating the inner layer and iron oxides forming the outer layer.
The investigation revealed that increasing oxygen levels beyond 0.06 MPa triggers a significant change in the steel's behavior. At these higher pressures, the protective film begins to deteriorate, showing reduced stability and weakened corrosion resistance. The metal's surface experiences accelerated dissolution rates, compromising its structural integrity.
When oxygen partial pressure reaches 1 MPa, the steel undergoes a dramatic transformation from passive protection to active corrosion. Under these conditions, the protective film completely breaks down, leading to the formation of a two-layered corrosion product structure. The outer layer becomes porous and primarily consists of iron oxides, while the inner layer maintains a more compact structure dominated by chromium oxides.
The research team employed advanced analytical techniques, including electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy, to characterize these changes. Their measurements indicate that the donor density within the passive film - a key indicator of its protective capability - varies significantly with oxygen exposure, ranging from 0.76 to 2.14 × 10²² per cubic centimeter.
Industry implications of these findings are substantial, particularly for applications where Super 13Cr stainless steel operates in oxygen-rich environments. The study suggests that careful control of oxygen exposure is essential for maintaining the material's protective properties, with optimal performance achieved at relatively low oxygen partial pressures.
The research provides crucial insights for engineers and manufacturers working with Super 13Cr stainless steel in high-temperature environments, offering specific guidelines for oxygen exposure levels to maximize corrosion resistance and extend material lifespan.
