The principle and influencing factors of the high-temperature color change on the surface of stainle

The surface oxide film of stainless steel welded pipes is actually a five-color transparent film. Its color variation is influenced by the principle of light interference. During light interference, which color is actually displayed mainly depends on the change in the thickness of the surface oxide film. Therefore, the oxidation resistance of 304 stainless steel pipes is an effective method to solve their color change at high temperatures. 

The factors influencing oxidation resistance mainly include the influence of chemical elements, the influence of the oxide film, and the influence of surface roughness. 

1. Chemical element 

The carbon content in 304 tubes is relatively low. In high-temperature environments, carbon atoms are prone to diffuse into the stainless steel matrix structure during the oxidation process. Therefore, the oxidation process of the tube also involves the carbon diffusion process. 

Therefore, the test can be conducted on steels with different contents of chromium, silicon, and nickel for high-temperature cycling experiments. After the test, the increase ratio of carbon content in various types of steel will be measured, and the degree of oxidation of the materials will be judged based on the carbonizing amount. 

In order to deeply verify the influence of silicon element on the carburization resistance performance of stainless steel products tubes, only the proportion of silicon element was adjusted in 310S, and then a high-temperature cycling test was conducted. The final test results showed that when the mass fraction of chromium element was increased to above 22% or the mass fraction of silicon element was increased by more than 2%, the high-temperature oxidation resistance performance of the steel tubes significantly improved. 

2. Oxide Film Impact 

The superficial tough oxide film can prevent the oxidizing agent from penetrating into the stainless steel matrix, that is, it can prevent the oxidation from continuing to occur. However, the loose oxide film will cause the oxide film to continue to thicken. In a continuous production line, a forced oxidation operation is carried out on stainless steel pipes using the continuous pickling method to enhance the density of the oxide film. 

3. Surface Roughness Impact 

In a high-temperature environment, the oxidation of 304 stainless steel pipes will thicken the surface oxide film. This situation is directly related to the material's own oxidation resistance and its heat absorption capacity. Surface roughness, surface reflectance, etc. will affect the heat absorption per unit area of the pipe and thus influence the degree of color change. 

Practice has shown that when the surface roughness of the thin-walled stainless steel pipe is lower than 0.022 μm, its heat absorption capacity significantly decreases. The pipe will not further oxidize, and the thickness of the oxide film in a high-temperature environment remains basically unchanged, with a very slight color change.