What is the principle by which 316L steel resists oxidation at high temperatures

The oxidation resistance of 316L stainless steel at high temperatures mainly relies on its special alloy composition and the physical and chemical changes that occur in these components at high temperatures. The specific principle is as follows:

The role of chromium

Formation of a passivation film: Chromium is an important alloy element in 316L stainless steel, with a content generally ranging from 16% to 18%. In high-temperature environments, chromium reacts with oxygen preferentially and forms a dense chromium oxide (Cr₂O₃) passivation film on the surface of the stainless steel. This passivation film is very thin, usually only a few nanometers to several tens of nanometers thick, but it has good stability and continuity, which can separate the metal substrate from the outside oxygen and prevent oxygen from further reacting with the internal metal atoms, thereby slowing down the oxidation rate.

Self-repairing ability: Even in high-temperature conditions, the passivation film may be partially damaged due to some mechanical actions or other factors. However, due to the presence of chromium, it will quickly re-oxidize in an oxygen-containing environment to repair the damaged area, allowing the passivation film to continue to exert its protective effect.

The role of nickel

Improvement of alloy stability: The content of nickel in 316L stainless steel is usually between 10% and 14%. It can enhance the thermodynamic stability of the stainless steel and reduce the free energy of the alloy, making the alloy less likely to react with oxygen at high temperatures. From the perspective of crystal structure, nickel can expand the austenite phase region, allowing the stainless steel to maintain a stable austenite structure at high temperatures, which has good toughness and oxidation resistance.

Promotion of passivation film formation: Nickel can also work in synergy with elements such as chromium to promote the formation and stability of the oxide chromium passivation film. During high-temperature oxidation, nickel can adjust the composition and structure of the passivation film, making it more dense and uniform, and enhancing the protective ability of the passivation film on the metal substrate.

The role of molybdenum

Enhancement of resistance to pitting and crevice corrosion: 316L stainless steel contains 2% - 3% of molybdenum. In high-temperature oxidation environments, molybdenum can improve the resistance to pitting and crevice corrosion of the stainless steel. Because molybdenum can be enriched in the passivation film, it can change the electronic structure and chemical composition of the passivation film, making it have higher resistance and lower ion diffusion coefficient, thereby hindering the invasion of corrosive media and reducing the occurrence of pitting and crevice corrosion, indirectly improving the overall oxidation resistance of the stainless steel at high temperatures.

Improvement of the stability of the oxidation film: Molybdenum can work together with chromium, nickel, and other elements to form a more complex and stable oxide film structure. At high temperatures, this oxide film containing molybdenum can withstand higher temperatures and greater stress, and is less likely to crack or flake, thus maintaining good oxidation resistance.

The synergistic effect of alloy elements

Optimization of crystal structure: The alloy elements such as chromium, nickel, and molybdenum in 316L stainless steel cooperate with each other to optimize the crystal structure of the stainless steel. They form a uniform and stable solid solution structure in the alloy, which can reduce crystal defects and decrease the atomic diffusion rate, making it difficult for oxygen and other oxidizing media to diffuse through the defects and gaps in the crystal structure, thereby improving the oxidation resistance of the stainless steel at high temperatures.

Adjustment of the growth mechanism of the oxide film: The presence of multiple alloy elements changes the growth mechanism of the oxide film. During high-temperature oxidation, the interaction between alloy elements causes the growth of the oxide film to be more uniform and orderly, and the ion diffusion and chemical reactions in the oxide film are more stable, resulting in an oxide film with better protective performance and the ability to effectively prevent further oxidation at high temperatures.