Why does metal rust and why doesn t stainless steel rust?

Metal rust is an oxidation reaction, the more carbon different steels contain, the easier it is to oxidize and rust, the reason why stainless steel can not rust is because it contains [chromium].

Usually the chromium content must reach 13 25 (weight ratio) to change the oxidation of the steel surface.

If we insert a freshly cut stainless steel plate into the water, a layer of chromium oxide will immediately form on the surface in less than a second, and this layer of oxide can slow down the oxidation rate of steel by at least 10,000 times, at this rate, it will take at least a million years to corrode a steel plate one centimeter thick.

However, stainless steel does not really rust, if you use a microscope to observe, there are actually many small rust spots on its surface;

If you look closely, these spots contain sulfur, and the presence of sulfur is inevitable in the manufacture of steel.

These stainless steels are fine when exposed to air, but they rust quickly when left in water. At this time, a trace amount of [molybdenum] can be added, for example, the steel nails that are driven into the bone during fractures contain molybdenum, but such stainless steel ** is much higher.

Stainless steel will be from trace amounts"Manganese sulfide"Rust is starting to get there, but how did they start?

Recent studies have found that it is not these sulfur atoms that turn into sulfuric acid in water that causes corrosion, but that during the manufacturing and cooling of stainless steel, the chromium in the steel moves to some places, partially replacing the position of manganese sulfide, which in turn causes the chromium content in the vicinity to become low.

And when the chromium content is less than 13, the stainless steel will rust.

Try to create a good environment in the production process, ventilate and dry, have low humidity to avoid moisture, and use processing aids with good anti-rust effect.

Rust is due to the redox reaction that occurs in the air, and there are many types of it.

Stainless steel increases the electric potential of iron because of the addition of chromium, which is not easy to rust, but ordinary stainless steel is only relative, and it will rust in an alkaline environment.

Metals rust because of the presence of water vapor and oxygen, which work together with iron to oxidize iron.

Stainless steel is not because of the addition of carbon, but metals such as chromium nickel. The addition of carbon creates a galvanic cell reaction that accelerates rusting.

Metal rust is actually because it contains more carbon, under the action of air and water, it is easy to electrochemical corrosion (commonly known as rust), and stainless steel is processed from ordinary metal, which also contains some substances with more stable structure, stainless steel in addition to iron, but also contains chromium and nickel with strong corrosion resistance. The chromium content is generally more than 13, and the nickel content is also about 10%, so it can make stainless steel not easy to rust. The carbon content of steel is general, and the carbon content of iron is generally 2, and attention should be paid to the conversion of carbon in iron as much as possible during processing.

Metals rust because redox reactions occur, such as iron oxidation to iron oxide.

Stainless steel is not easily oxidized because a certain amount of carbon is added to the iron during processing, which changes the internal structure of the metal.

Stainless steel has excellent corrosion resistance, mainly because of chromium. When chromium comes into contact with air or water, a dense layer of chromium trioxide will be formed on the surface, and this oxide film is very thin, so it will not affect the metallic luster of the surface.

After the oxide film is formed, it will not continue to react with water and air, which is the reason why stainless steel is stainless steel. If the surface layer is damaged by abrasion, the surrounding water and oxygen will cause the oxide film to form rapidly again, so that the stainless steel has a strong self-"stainless repair ability".

Austenitic stainless steel microstructure.

However, stainless steel stainless steel is not absolute, taking austenitic stainless steel as an example, if the material is heated to a high temperature of 450 to 900, the structure will change, and chromium carbide will be formed along the edge of the crystal, resulting in the inability to form a protective layer of chromium oxide at the edge of the crystal, thereby reducing the corrosion resistance, this corrosion is called "intergranular corrosion". In order to avoid intergranular corrosion, parts that need to be welded at high temperatures are usually made of stainless steel with lower carbon content of 304L and 316L (L refers to lower carbon content). , welcome the industry, find fault and complain.

There are many reasons for the rust of stainless steel, such as the accumulation of dust containing other metal elements on the surface, and the phenomenon of electrochemical corrosion will occur when it is exposed to humidity for a long time. In addition, organic juice adheres to the surface of stainless steel or it is placed in polluted air, which is easy to corrode and rust.

Stainless steel rust causes.

Because of the name stainless steel, many people will think that stainless steel will not rust, and if it rusts, it is not real stainless steel. But in fact, this idea is very one-sided, and stainless steel will also show signs of rust under certain conditions.

Stainless steel rusts, most likely due to the accumulation of dust containing other metal elements on its surface, so that in a humid environment for a long time, the chain traces and the condensation of stainless steel will connect the two into a microbattery, resulting in galvanic corrosion. In addition, if the surface of stainless steel is attached to melon and vegetable juice, noodle soup, etc., it is easy to form organic acids when encountering water and oxygen, and corrosion and rust will occur in the long run.

Finally, if stainless steel is placed in polluted air and encounters condensation, liquids such as sulfuric acid and nitric acid will be formed, causing chemical corrosion. Therefore, when we use stainless steel, we must clean and scrub frequently, remove attachments, and place them in a normal environment to protect the shed.

In everyday life, stainless steel can be found everywhere. So the question is, do you know why stainless steel rusts? What are the conditions in daily life that are easy to cause stainless steel to rust? Next, let me give you a brief introduction.

The reason why stainless steel rusts is that its corrosion resistance will change with factors such as the steel itself, the state of the reinforcement, and the environment in which it is used. For example, 304 steel pipe has the advantage of rust resistance in a dry atmosphere, but if it is used in a coastal city, it is easy to rust because the air contains a lot of salt.

Which situations in daily life are easy to cause stainless steel to rust.

Although there are many ways in which the table can be destroyed, the following situations are more common in daily life:

1. In the process of kitchen decoration, it is inevitable that cement and oil will remain around the sink, and if it is not cleaned immediately, it is likely to cause rust or mold;

2. In daily life, if the indoor dust containing minerals and acids and alkalis floats on the surface of the sink, coupled with the humidity of the air, it will also lead to the appearance of "floating rust".

During use:

1. Kitchen knives, scissors and other products placed on the surface of the sink for a long time will also lead to mildew and discoloration of stainless steel;

2. In addition, if the cleaning agent and sauce remain in the sink, it will also cause mold on the surface of the sink over time;

3. Due to the poor water quality in most areas of the country, coupled with the fact that most of the water pipes are galvanized pipes, and the iron content in the water is high, if there are many water stains left in the sink, it will rust after a long time. Especially for new house decoration, if the water stains on the sink are not cleaned in time, it will easily cause rust.

Summary: After reading the above introduction, I believe you have a further understanding of why stainless steel rusts. If you need to know more about it, please continue to ******, and more exciting content will be presented to you in the future.

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Because of the chromium added to the composition of stainless steel, it can form a passivation film on the surface of stainless steel, prevent the metal matrix from being damaged, enhance corrosion resistance, so the surface will not rust. But stainless steel can also rust in some special environments, such as:

In humid conditions and salty sea fog, stainless steel surfaces can rust. 1. When cleaning and maintaining stainless steel, rags and stainless steel oil should be used, and the oil should be poured on the rag first, and attention should be paid not to put too much stainless steel oil to avoid too much waste. Then wipe the stainless steel surface with a rag, wait until the stain is wiped clean, and then rinse it again with clean water.

2. When maintaining stainless steel products, we must do a good job of daily cleaning, and when cleaning stainless steel, you can use a relatively mild method. For example, you can use hot water or a clean, soft cloth to wipe the surface, and if there is oil on the surface, you can use a detergent to completely remove the stain from stainless steel. 3. If there are water stains on the surface of the stainless steel, resulting in rust on the surface, you can use a milder detergent to wipe it.

If you have cooked stainless steel, you can soak it in soapy water before washing it with a sponge pad. 4. The surface of stainless steel should avoid contact with acid and alkaline liquids to avoid being corroded, and the surface can not be scrubbed with vinegar. Stainless steel surfaces should also not be cleaned with bleach or disinfectant water, and should be cleaned with a neutral liquid.

Metals rust and non-rust are relative, there can be no metal that is absolutely rust-free, and even gold and platinum, which are the least likely to rust, will corrode and rust when they encounter solutions with particularly strong metal dissolving capabilities, such as aqua regia.

Stainless steel is also rusty.

The reason why it does not rust is because a layer of chromium oxide film will be formed on the surface of stainless steel, but once it is damaged, it cannot prevent the oxidation of iron, and the stainless steel will rust.