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Does Stainless Steel Tarnish


In daily life, we sometimes see colorful patterns on the surface of stainless steel utensils. For this phenomenon, it may be that the surface of the utensils is stained with oil, or it may be obtained through special treatment. Discoloration of the surface.

The oxide film on the surface of stainless steel is a five-color transparent film, and its color can be explained by the gloss and the principle. When parallel light shines on the surface of the oxide film, some light (L2) undergoes specular reflection (L5) on the surface of the oxide film and refraction (1) at the same time, enters the oxide film, and then reflects back from the lower surface (L4); Similarly, another part of light L1 also produces the above reflection and refraction phenomenon. The specularly reflected light of light L1 and the light of light L2 refracted into the oxide film and then reflected back from the lower surface together constitute dry and light L6. When both peaks and peaks or valleys and valleys are stacked, the light wave oscillation is strengthened; on the contrary, when the two peaks and valleys are stacked, the light wave oscillation is weakened. White light is a compound light composed of seven colors of red, orange, yellow, green, blue, blue, and purple. When the above-mentioned interaction occurs, which color of light waves will be strengthened? 303 stainless steel rods, first of all Depends on the thickness of the oxide film. That is, when white light passes through an oxide film of a certain thickness, the light wave oscillation of a certain wavelength in between is strengthened, and the oxide film presents the color of light corresponding to this wavelength; when white light passes through an oxide film of another thickness, the other The light oscillation of one wavelength is strengthened, and the oxide film shows another color.

#1 Experimental Discussion On High Temperature Discoloration Of Stainless Steel

From the analysis of the above-mentioned discoloration principle, it can be known that the basic cause of discoloration is the dryness and discoloration caused by the oxidation of the stainless steel surface, which leads to the change in the thickness of the passivation film (oxide film). Therefore, how to improve the oxidation resistance of materials is the basic measure to solve the high temperature discoloration of stainless steel.

(1) The Influence Of Chemical Elements

The carbon content of stainless steel is low, and carbon atoms are easy to disperse into the stainless steel matrix during the oxidation process in a high-temperature environment, so the oxidation process of stainless steel is accompanied by the carburizing process. Experimentally select steels with different contents of chromium, silicon, nickel, etc. A high temperature cycle experiment was carried out. After the test, measure the carbon content increase ratio of each steel type, and use the carburizing amount to judge the oxidation degree of stainless steel. Figure 2 shows the results of carburizing experiments of different steel types.

In order to further verify the influence of silicon element on carburization resistance, only silicon element is adjusted in SUS310S steel, and then high temperature cycle experiment is carried out. Figure 3 shows the effect of silicon content on carburization resistance. It is not difficult to see from the two sets of experimental results that when the mass fraction of chromium element is increased to more than 22% or the mass fraction of silicon element is increased to more than 2%, the high temperature oxidation resistance of the material is significantly improved.

(2) The Influence Of Oxide Film

The fine oxide film of stainless steel can prevent the oxidant from invading the sub-surface of stainless steel and hinder the continuous occurrence of oxidation, otherwise the loose oxide film will lead to continuous oxidation and thickening. In the continuous production line, the surface of stainless steel is forcibly oxidized by continuous pickling, so as to improve the fineness of the oxide film on the surface of stainless steel. Correlation tests were carried out on the product after the acid concentration was correlated and adjusted for high temperature oxidation resistance, oxide film thickness and chemical composition of the oxide film. The analysis results show that the adjustment of the acid concentration has no significant effect on the composition of the oxide film and the thickness of the oxide film. It is still deepened and oxidized when used in a higher temperature environment, showing discoloration.

#2 Why Does The Surface Of 304 Stainless Steel Pipe Change Color When Exposed To High Temperature?

#Stainless steel tube# Generally speaking, products made of high-quality 304 stainless steel tubes will not appear blackened on the surface. If the 304 stainless steel pipe products become dark or black during long-term use, it is because the 304 stainless steel pipe produces an oxide film under the action of air. The main function of this oxide film is to prevent the metal in 304 stainless steel from being oxidized. So what are the principles and influencing factors of high temperature discoloration on the surface of 304 stainless steel pipes?

The oxide film on the surface of the stainless steel welded pipe is actually a five-color transparent film, and its color change is affected by the principle of light interference. In light interference, the color that appears is mainly due to the change in the thickness of the oxide film on the surface. Therefore, the oxidation resistance of 304 stainless steel pipe is an effective teaching method to solve its high temperature discoloration.

The main factors affecting the oxidation resistance of stainless steel are chemical elements, oxide film and surface roughness.

1.Chemical Elements

The carbon content of the stainless steel plate material is relatively low. In a high-temperature working environment, carbon atoms are easy to diffuse into the stainless steel matrix during the oxidation reaction process. Therefore, the oxidation treatment process of stainless steel is accompanied by the carburizing process.

Therefore, steels with different chromium, silicon and nickel contents can be selected for high temperature cycle test. After the experimental research is over, measure the proportion of enterprises passing through the increase of carbon content in various steels, and judge the degree of oxidation technology of the material according to the amount of carburizing.

In order to verify the effect of silicon on the carburizing properties of stainless steel, the proportion of silicon in 310S stainless steel was adjusted, and a high temperature cycle test was carried out. The final test results show that when the mass fraction of chromium element can be increased to more than 22% or the mass fraction of silicon element can be gradually increased to more than 2%, the high temperature oxidation resistance of the steel pipe is obviously improved.

2.The Effect Of Oxide Film

The tough oxide film on the surface can prevent the oxidant from invading the stainless steel substrate, that is, to prevent the oxidation from continuing, while the loose oxide film will make the oxide film continue to thicken. In the continuous production line, the continuous pickling treatment method is used to perform forced oxidation on the surface of the stainless steel plate, so that the research on the compactness of the oxide film on the surface of the stainless steel plate can be enhanced.

3.The Effect Of Surface Roughness

Oxidation of 304 stainless steel pipes in high temperature environments will thicken the oxide film on the surface. This development, as well as the direct economic relationship between the anti-oxidation capacity of the material itself and the heat absorption capacity of the material, the surface roughness of the surface and the degree of anti-color, will affect the heat absorption capacity and discoloration degree of the unit building area of the pipeline.

Practical research shows that when the surface roughness of the thin-walled stainless steel pipe is less than 0.022 μm, its heat absorption capacity can be significantly reduced, the steel pipe will not be further oxidized, and the thickness of the oxide film remains basically unchanged under high-temperature working environments. The degree of discoloration is also very slight.

In fact, the material of the stainless steel water pipe itself will not change color, but due to contact with the air, there are impurities in the air, which will cause yellowing, blackening and discoloration. Hope the above content can help you.

#3 Will Stainless Steel Be Corroded And Discolored By Dripping Water?

Won’t. Stainless steel has the ability to resist atmospheric oxidation, that is, stainless, and also has the ability to be corroded in media containing acids, alkalis, and salts, that is, corrosion resistance. Moreover, the commonly used stainless steel products are polished, so the stainless steel will not fade.

The invention and use of stainless steel can be traced back to the First World War. British scientist Henry Brellley was commissioned by the British government’s military arsenal to study the improvement of weapons. At that time, the barrels of rifles used by soldiers were extremely prone to wear and tear, and Brellley wanted to invent an alloy steel that was not easy to wear.

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