Under normal circumstances, stainless steel will not rust. However, if it is not properly used or maintained, or the environment in which stainless steel is located is too harsh, stainless steel may rust. When we see yellow or orange rust spots on the steel surface, we can quickly confirm that this is a sign of rust.
Why does stainless steel rust? First of all, let's understand the structure of stainless steel:
Stainless steel is a crystal solid, composed of atoms, arranged like a toy. Besides iron, it also contains metal components such as chromium, nickel and titanium. Chromium and nickel elements have anti-rust function, forming a protective film-passivation film to prevent stainless steel from rusting.
Generally speaking, stainless steel will not rust as long as this film is not damaged, cracked or contaminated by impurities. However, if the passivation film is damaged due to improper use or maintenance, stainless steel will rust.
Under what circumstances will stainless steel rust?
There are three basic substances that can destroy the passive surface of stainless steel and corrode it.
Mechanical abrasion
Refers to things that scratch the steel surface, such as steel brushes, wire brushes, metal fragments, etc.
water
The hardness of the water flowing from our tap is different. Because the living area is different, it may be hard water or soft water. Hard water contains impurities. After heating, impurities will remain motionless and form precipitates, which will destroy the passivated surface and rust stainless steel.
Note: Other sediments generated during food processing or service must also be removed in time.
bleaching agent
Can be seen everywhere. It exists in water, food and salt. The worst kind comes from household and industrial cleaners.
Why does stainless steel rust?
Why does stainless steel rust? When brown rust spots (spots) appear on the surface of stainless steel pipes, people are greatly surprised: they think that "stainless steel does not rust, and it is not stainless steel that rusts, but it may be steel." In fact, this is a one-sided misunderstanding of stainless steel. Stainless steel rusts under certain conditions.
Stainless steel not only has the ability to resist atmospheric oxidation, that is, rust prevention, but also has the ability to corrode in the medium containing acid, alkali and salt, that is, corrosion resistance. However, its corrosion resistance varies with the chemical composition of steel itself, the state of mutual reinforcement, the use conditions and the types of environmental media. For example, 304 steel pipe has absolutely excellent anticorrosion ability in dry and clean atmosphere, but in sea fog with high salt content, if it is moved to coastal areas, it will soon rust; 3 16 steel pipe performed well. Therefore, not all kinds of stainless steel can resist corrosion and rust in any environment.
Stainless steel forms a very thin, firm and stable chromium-rich oxide film (protective film) on its surface to prevent oxygen atoms from continuing to permeate and oxidize, thus gaining corrosion resistance. Once this film is destroyed for some reason, oxygen atoms in air or liquid will continue to penetrate or iron atoms in metal will continue to separate to form loose iron oxide, and the metal surface will continue to be corroded. There are many forms of damage to this surface film, and the following are common in daily life:
1. Dust containing other metal elements or attachments of different metal particles are deposited on the surface of stainless steel. In humid air, the condensed water between accessories and stainless steel connects them into a miniature battery, which causes electrochemical reaction and destroys the protective film. This is called electrochemical corrosion.
2. Organic fruit juice (such as melons, vegetables, noodle soup, phlegm, etc.). ) attached to the surface of stainless steel, organic acids will be formed in the presence of water and oxygen, which will corrode the metal surface for a long time.
3. Substances containing acid, alkali and salt (such as alkali water and lime water splashing for wall decoration) are attached to the surface of stainless steel, causing regional corrosion.
4. In polluted air (such as air containing a lot of sulfides, carbon oxides and nitrogen oxides), condensed water will form sulfuric acid, nitric acid and acetic acid, causing chemical corrosion.
All the above conditions will lead to the damage of the protective film on the stainless steel surface, leading to corrosion. Therefore, in order to ensure that the metal surface is bright and will not be corroded, we suggest:
1. The surface of decorative stainless steel must be cleaned and scrubbed frequently to remove attachments and external factors causing decoration.
2. 3 16 stainless steel should be used in coastal areas, which can resist seawater corrosion. 3. The chemical composition of some stainless steel pipes in the market can't meet the corresponding national standards and the material requirements of 304. So it will also cause rust, which requires users to carefully choose products from reputable manufacturers.
Why does stainless steel rust?
Steel resistant to weak corrosive media such as air, steam and water and chemical corrosive media such as acid, alkali and salt. Also known as stainless acid-resistant steel. In practical application, steel resistant to weak corrosive medium is usually called stainless steel, while steel resistant to chemical medium is called acid-resistant steel. Because of the different chemical composition, the former is not necessarily resistant to the corrosion of chemical media, while the latter is generally stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel. Chromium is the basic element for corrosion resistance of stainless steel. When the chromium content in steel reaches about 12%, chromium reacts with oxygen in corrosive medium to form a thin oxide film (self-passivation film) on the steel surface, which can prevent further corrosion of steel matrix. Besides chromium, commonly used alloying elements are nickel, molybdenum, titanium, niobium, copper, nitrogen and so on. To meet the requirements of various uses for stainless steel structure and efficiency. Stainless steel is usually divided into: ① ferritic stainless steel according to the matrix structure. Chromium 12% ~ 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its chloride stress corrosion resistance is better than other kinds of stainless steel. ② Austenitic stainless steel. It contains more than 18% chromium, about 8% nickel and a few elements such as molybdenum, titanium and nitrogen. Good comprehensive performance, corrosion resistance to various media. ③ Austenite-ferrite duplex stainless steel. It has the advantages of austenitic and ferritic stainless steel and is superplastic. ④ Martensite stainless steel. High strength, but poor plasticity and weldability.
Stainless steel is a modern material with a history of 60 years.
Since the invention of stainless steel at the beginning of this century, stainless steel has combined the image of modern materials with excellent reputation in architectural application, which has made its competitors envious.
austenitic stainless steel
Stainless steel with austenitic structure at room temperature. When the chromium content is about 18%, the nickel content is about 8% ~ 10%, and the carbon content is about 0. 1%, the steel has a stable austenite structure. Austenitic Cr-Ni stainless steel includes the famous 18Cr-8Ni steel and the high Cr-Ni series steel developed by adding Mo, Cu, Si, Nb and Ti. Austenitic stainless steel is nonmagnetic and has high toughness and plasticity, but its strength is low, so it can not be strengthened by phase transformation, but only by cold working. If sulfur, calcium, selenium, tellurium and other elements are added, it has good cutting performance. This steel can not only resist the corrosion of oxidizing acid medium, but also resist the corrosion of sulfuric acid, phosphoric acid, formic acid, acetic acid and urea if it contains elements such as Mo and Cu. If the carbon content in this steel is less than 0.03% or contains Ti and Ni, its intergranular corrosion resistance can be significantly improved. High silicon austenitic stainless steel has good corrosion resistance in concentrated nitric acid. Austenitic stainless steel is widely used in all walks of life because of its comprehensive and good comprehensive properties.
As long as the steel grade is selected correctly, processed properly and maintained properly, stainless steel will not be corroded, pitted, rusted and worn. Stainless steel is also one of the strongest building metal materials. Because stainless steel has good corrosion resistance, it can permanently maintain the integrity of engineering design. Chromium-containing stainless steel also has both mechanical strength and high ductility, which is easy to manufacture and meets the needs of architects and structural designers.
In architecture, building and structural industries, the key to the success of stainless steel lies in its good corrosion resistance.
Stainless steel brand grouping
200 Series-Cr-Ni-Mn Austenitic Stainless Steel
300 series-Cr-Ni austenitic stainless steel
Model 30 1- has good ductility and is used for molding products. It can also be rapidly hardened by machining. Good weldability. Wear resistance and fatigue strength are better than 304 stainless steel.
Type 302-corrosion resistance is the same as that of 304, and its strength is better because of its relatively high carbon content.
Type 303-with a small amount of sulfur and phosphorus, it is easier to cut than type 304.
Model 304- General Model; Namely 18/8 stainless steel. GB brand is 0Cr 18Ni9.
Model 309- has better temperature resistance than 304.
Model 3 16— The second most widely used steel, after 304, is mainly used in food industry and surgical equipment. Molybdenum is added to obtain a special corrosion-resistant structure. Because it has better chloride corrosion resistance than 304, it is also used as "marine steel". SS3 16 is usually used in nuclear fuel recovery devices. 18/ 10 stainless steel usually meets this application level. [ 1]
The performance of model 32 1- is similar to that of model 30, but the risk of welding corrosion is reduced due to the addition of titanium. ......
Will stainless steel rust?
When brown rust spots (spots) appear on the surface of stainless steel, people are greatly surprised: they think that "stainless steel does not rust, and rust is not stainless steel, but may be a problem with steel". In fact, this is a one-sided misunderstanding of stainless steel. Stainless steel rusts under certain conditions.
Stainless steel not only has the ability to resist atmospheric oxidation, that is, rust prevention, but also has the ability to corrode in the medium containing acid, alkali and salt, that is, corrosion resistance. However, its corrosion resistance varies with the chemical composition, processing state, service conditions and environmental medium types of its steel. For example, 304 stainless steel has absolutely excellent corrosion resistance in dry and clean atmosphere, but in sea fog containing a lot of salt, if it is moved to coastal areas, it will soon rust; While 3 16 stainless steel performed well. Therefore, not all kinds of stainless steel can resist corrosion and rust in any startup environment.
Stainless steel forms a very thin, firm and stable chromium-rich oxide film (protective film) on its surface, which prevents oxygen atoms from continuing to infiltrate and oxidize and gains corrosion resistance. Once this film is destroyed for some reason, oxygen atoms in air or liquid will continue to infiltrate or iron atoms in metal will continue to precipitate to form loose iron oxide, and the metal surface will continue to be corroded. This surface film is damaged in many forms, the following are common in daily life:
Dust containing other metal elements or attachments of different metal particles are deposited on the surface of stainless steel. In humid air, the condensed water between accessories and stainless steel connects them into a miniature battery, which causes electrochemical reaction and destroys the protective film. This is called electrochemical corrosion. For example, the new house has just been renovated, and there are metal chips deposited on the surface of the sink in the water pipe, which is easy to cause floating rust.
Organic fruit juice (such as melons, vegetables, noodle soup, phlegm, etc. ) adheres to the surface of stainless steel and forms organic acids in the presence of water and oxygen. Organic acids will corrode metal surfaces for a long time.
The adhesion of stainless steel surface contains acid, alkali and salt substances (such as alkaline water and lime water splashing for wall decoration), which causes regional corrosion. Usually in decoration, workers do not clean the sink in time after use, which leads to the corrosion of the surface by acid and alkali substances.
In polluted air (such as air containing a lot of sulfides, carbon oxides and nitrogen oxides), condensed water forms sulfuric acid, nitric acid and acetic acid, causing chemical corrosion.
All the above conditions will lead to the damage of the protective film on the stainless steel surface, leading to corrosion. Therefore, in order to ensure that the metal surface is bright and will not be corroded, we suggest:
1. Stainless steel surface must be cleaned and scrubbed frequently to remove the attachments and external factors that lead to corrosion.
2. The chemical composition of some stainless steel in the market can't meet the corresponding national standards, so it will rust, which requires users to carefully choose the products of reputable manufacturers.
Why does 304 stainless steel rust?
304 material rusts, which may be due to the following reasons: 1: There are chloride ions in the service environment. Chloride ion exists widely, such as salt/sweat/seawater/sea breeze/soil and so on. In the presence of chloride ion, stainless steel corrodes quickly, even exceeding ordinary low carbon steel. Therefore, there is a requirement for the use environment of stainless steel, which needs to be wiped frequently to remove dust and keep it clean and dry. (This will give him a "misuse". There is an example in the United States: an enterprise uses oak containers to hold solutions containing chloride ions. The container has been used for nearly a hundred years, and it was planned to be replaced in the 1990s. Because the oak material is not modern enough, the container leaked due to corrosion 16 days after it was replaced with stainless steel. 2: Without solid solution treatment. The alloy elements are not dissolved in the matrix, which leads to low alloy content and poor corrosion resistance in the matrix. 3. This material without titanium and niobium has a natural tendency of intergranular corrosion. Adding titanium and niobium and stabilizing treatment can reduce intergranular corrosion. It is a kind of high alloy steel resistant to air or chemical corrosive medium. Stainless steel is a kind of steel with beautiful surface and good corrosion resistance. Without surface treatment such as color electroplating, it gives full play to the inherent surface properties of stainless steel and is used in many aspects, usually called stainless steel. High alloy steels such as 13 Cr steel and 18-8 Cr-Ni steel are its representative properties. From the metallographic point of view, because stainless steel contains chromium, a very thin chromium film is formed on the surface, which isolates the oxygen invading the steel and plays a role in corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 12% chromium. 304 is a general-purpose stainless steel, which is widely used to manufacture devices and parts that require good comprehensive performance (corrosion resistance and formability). 304 stainless steel is a stainless steel brand produced according to American ASTM standard. 304 is equivalent to China's 0Cr19Ni9 (0Cr18Ni9) stainless steel. 304 contains 19% chromium and 9% nickel. 304 is the most widely used stainless steel/heat resistant steel. Used in food production plants/Xitong Chemical Plant/nuclear energy, etc. : 304 corresponds to China brand 0cr 18ni9, 1cr 18ni9ti, with carbon content ≤ 0.08%. 304l is a variant of 304 stainless steel with low carbon content, which is used in welding occasions. The low carbon content minimizes carbide precipitation in the heat affected zone near the weld, which may lead to intergranular corrosion (welding corrosion) of stainless steel in some environments. The above information is provided by Shanghai Shiqiang Stainless Steel Material Factory, and the reference website is shsqbxg.
Why does stainless steel rust?
Stainless steel is the abbreviation of stainless and acid-resistant steel, and steel or stainless steel resistant to weak corrosive media such as air, steam and water is called stainless steel. Steel resistant to chemical corrosive media (acid, alkali, salt and other chemical corrosion) is called acid-resistant steel. Their corrosion resistance is different due to their different chemical compositions. Ordinary stainless steel is generally not resistant to chemical medium corrosion, and acid-resistant steel is generally stainless.
The invention and use of stainless steel can be traced back to the First World War. Henry buhrer, a British scientist, was commissioned by the British Arsenal to study the improvement of weapons. At that time, the rifle bore used by soldiers was very easy to wear, and buhrer wanted to invent an alloy steel that was not easy to wear.
The stainless steel invented by buhrer Leigh was patented in Britain in 19 16, and mass production began. Since then, stainless steel accidentally found in garbage has swept the world, and Henry buhrer Leigh is also known as the "father of stainless steel". During the First World War, British guns on the battlefield were always transported back to the rear because the bore was worn out and could not be used. The military production department ordered buhrer Li, a high-strength wear-resistant alloy steel, to study and solve the problem of gun bore wear. Li and his assistant collected various types of steel and alloy steel with different properties produced at home and abroad, conducted efficiency tests on machines with different properties, and then chose more suitable steel to make guns. One day, they experimented with a domestic alloy steel containing a lot of chromium. After the wear-resistant experiment, it was found that this alloy was not wear-resistant, which indicated that guns could not be made. So they recorded the experimental results and threw things at the corner. One day a few months later, an assistant came to Bougel with a shiny piece of steel and said, "Sir, this is the alloy steel that Mr. Mullah sent me when I was cleaning the warehouse. Do you want to try it and see what special effect it has? " "good!" Buhrer looked at the bright steel and said happily.
The experimental results show that it is a stainless steel that is not afraid of acid, alkali and salt. This kind of stainless steel was invented by Mullah in Germany in 19 12. However, the mullahs don't know what this stainless steel is for.
Li thought: "This kind of steel which is not wear-resistant but corrosion-resistant can't be used to make guns. Can it be used as tableware? " He did as he said, and made stainless steel fruit knives, forks, spoons, fruit bowls and folding knives.
Chromium 15% ~ 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its chloride stress corrosion resistance is better than other types of stainless steel, including Crl7, Cr 17Mo2Ti, Cr25, Cr25Mo3Ti and Cr28. Ferritic stainless steel has good corrosion resistance and oxidation resistance because of its high chromium content, but its mechanical efficiency and process efficiency are poor, so it is mostly used in acid-resistant structures with less stress and as oxidation-resistant steel. This kind of steel can resist the corrosion of atmosphere, nitric acid and brine solution, and has the characteristics of good oxidation resistance at high temperature and low thermal expansion coefficient. It can be used in nitric acid and food factory equipment, and can also be used to manufacture parts that work at high temperature, such as gas turbine parts.
If the chromium content is not up to standard, it will rust.
Why do stainless steel screws rust?
You can coat it with a layer, so it won't rust. At present, high-demand bolts are made of xylan coating and PTFE coating. You can try it sometime.
Why does 304 stainless steel rust?
Under normal circumstances, stainless steel will not rust. However, if it is not properly used or maintained, or the environment in which stainless steel is located is too harsh, stainless steel may rust. When we see yellow or orange rust spots on the steel surface, we can quickly confirm that this is a sign of rust.
Why does stainless steel rust? First of all, let's understand the structure of stainless steel:
Stainless steel is a crystal solid, composed of atoms, arranged like a toy. Besides iron, it also contains metal components such as chromium, nickel and titanium. Chromium and nickel elements have anti-rust function, forming a protective film-passivation film to prevent stainless steel from rusting.
Generally speaking, stainless steel will not rust as long as this film is not damaged, cracked or contaminated by impurities. However, if the passivation film is damaged due to improper use or maintenance, stainless steel will rust.
Why does stainless steel rust? Will 304 stainless steel rust?
First of all, clarify a concept that stainless steel cannot rust, but it is difficult to rust. There are several possibilities for 304 stainless steel to rust:
1. chloride ion
Chloride ion exists widely, such as salt/sweat/seawater/sea breeze/soil and so on. In the presence of chloride ion, stainless steel corrodes quickly, even exceeding ordinary low carbon steel. Therefore, there is a requirement for the use environment of stainless steel, which needs to be wiped frequently to remove dust and keep it clean and dry. (This will give him a "misuse". There is an example in the United States: an enterprise uses oak containers to hold solutions containing chloride ions. The container has been used for nearly a hundred years, and it was planned to be replaced in the 1990s. Because the oak material is not modern enough, the container leaked due to corrosion 16 days after it was replaced with stainless steel.
2. Solution annealing
The alloy elements are not dissolved in the matrix, which leads to low alloy content and poor corrosion resistance in the matrix.
3. Intergranular corrosion
This material without titanium and niobium has a tendency of intergranular corrosion. Adding titanium and niobium and stabilizing treatment can reduce intergranular corrosion. It is a kind of high alloy steel resistant to air or chemical corrosive medium. Stainless steel is a kind of steel with beautiful surface and good corrosion resistance. Without surface treatment such as color electroplating, it gives full play to the inherent surface properties of stainless steel and is used in many aspects, usually called stainless steel. High alloy steels such as 13 Cr steel and 18-8 Cr-Ni steel are its representative properties. From the metallographic point of view, because stainless steel contains chromium, a very thin chromium film is formed on the surface, which isolates the oxygen invading the steel and plays a role in corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 12% chromium. Used where welding is needed. The low carbon content minimizes carbide precipitation in the heat affected zone near the weld, which may lead to intergranular corrosion (welding corrosion) of stainless steel in some environments.
4. Surface phenomenon
Surface mark refers to the linear or point dent defect on the surface of 304 stainless steel after deep processing or grinding.
Cause: There are foreign bodies on the surface and die surface, and there are scars on the surface of blank holder.
Countermeasures: remove foreign bodies and scars before processing, or remove orange peel by full grinding.
Orange peel phenomenon refers to the phenomenon that the surface of 304 stainless steel molded products produces the same shape as orange peel under grinding or other conditions.
Reason: insufficient grinding, the bigger the processing, the more serious the orange peel, the coarse particle size of raw materials and the softening of heat treatment.
Countermeasures: Fully grind the deep-processed products, select suitable heat treatment conditions and control the particle size of raw materials.
Why does stainless steel rust?
Because moisture contains corrosive elements. Corrosive substances will corrode and rust as we often say if they stay on the metal surface for a long time. Not only stainless steel will rust, but also copper will rust. Only in the aspect of antibody aging produced by corrosive elements in water, the composition of stainless steel and copper is different from that of iron.