Most of the stainless steels we see every day are nickel-chromium stainless steels of the same grade as 302 and 304, and chromium stainless steels of 1-4 Cr 13 (commonly called "stainless steel iron"). In China, there are more than 100 kinds of stainless steel, and the properties and values of stainless steel vary greatly with the elements and contents in the steel. Therefore, the identification of stainless steel must be carefully studied, and the mark of steel grade must be clear, and it can be correctly identified through comprehensive tests and other methods.
At present, we mainly have the following methods to identify stainless steel:
Stainless steel monolithic products generally come from steel mills ordered or imported from abroad, as well as the backlog and backlog of processed products in society. Different sources of stainless steel have different identification methods.
1. Generally, it is only necessary to check the marks on the steel or packaging according to the quality certificate of the imported or steel mill.
The quality certificate is the supplier's confirmation and guarantee of the inspection results of this batch of products. Therefore, the quality certificate not only states the name, specification, number of delivered pieces, weight and delivery status of the materials, but also states all inspection results of the specified guaranteed items.
Similarly, in order to facilitate management, avoid confusion and prevent use accidents caused by confusion, manufacturers indicate signs such as brand number, batch number, status, specification, quantity and manufacturer's code on materials or packaging. The marks marked on it shall be consistent with the contents of the quality certificate. There are three commonly used marking methods: coloring (painting on the designated part of the material to indicate its brand) and printing (stamping or spray printing on the designated part of the material to indicate the brand, specification and heat number, etc. Materials, commonly used in thick steel plates or large and medium-sized steel beams), and listed (hanging signs indicate the brand, batch number, specification, quantity, etc. Bound or boxed material).
Signs of stainless steel are generally printed on the market.
2. Social backlog and stainless steel backlog. According to the length of the backlog and the quality of storage, there are generally two situations:
First, the backlog is not long and it is well kept. The processing unit not only keeps the original or copy of the quality certificate, but also has a complete and clear mark on the steel or packaging. For the identification of this kind of stainless steel, it is also necessary to check the signs on the steel or packaging according to the quality certificate.
The other is that the backlog is long, the storage is not perfect, there is no quality certificate, and the signs on steel or packaging are not obvious or fall off. For the identification of this kind of stainless steel, it is mainly necessary to conduct in-depth investigation and study and consult the original documents of the processing unit. Generally speaking, invoices and other original documents are marked with steel numbers. If there is no record of steel grade, it is necessary to consult the local price information at that time to determine the steel grade at the price. This is an effective method to determine the steel grade, but it is often prone to arrogance. Therefore, it is necessary to master the identification method of physical objects.
Physical identification is a concrete method to determine whether a commodity (including whole material, scrap, waste, etc.) is stainless steel and what kind of stainless steel it belongs to with the help of simple instruments when the steel grade (No.) is unknown.
It should be pointed out that sensory identification can not distinguish specific steels (types), but can only basically distinguish three categories: chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel. The identification methods are as follows:
Color discrimination
The surface color of stainless steel after pickling is silvery white and smooth: the color of Cr-Ni stainless steel is silvery white and emerald; Chrome stainless steel is white and slightly gray; The color of Cr-Mn-N stainless steel is similar to that of Cr-Ni stainless steel. Surface colors of stainless steel without pickling: chrome nickel steel is brownish white, chrome steel is brownish black, and chrome manganese nitrogen is black (these three colors refer to the colors with heavy oxidation). Cold-rolled non-annealed Cr-Ni stainless steel with silvery white reflective surface.
Identify with a magnet
Magnets can basically distinguish two kinds of stainless steel. Because chromium stainless steel can be attracted by magnets in any state; Chromium-nickel stainless steel is generally non-magnetic in annealed state, and some will be magnetic after cold working. But high manganese steel with high manganese content is nonmagnetic; The magnetic properties of Cr-Ni-N stainless steel are complicated: some are nonmagnetic, some are magnetic, some are nonmagnetic in the longitudinal direction and some are magnetic in the transverse direction. Therefore, although magnets can basically distinguish chromium stainless steel from chromium-nickel stainless steel, they cannot correctly distinguish some special steel grades, let alone specific steel grades.
Identification with copper sulfate
Oxygen on steel >>
Question 2: How to distinguish the quality and type of stainless steel? The quality of stainless steel is invisible to the naked eye.
It's funny to say that holding a magnet upstairs.
Which country's magnet can absorb steel? The surface gloss will not come out.
Because people are too poisonous now.
You can make mud look better than gold.
Generally, you can only test.
Question 3: How to distinguish the quality of stainless steel People often think that magnets adsorb stainless steel to verify its quality and authenticity, and that without magnetism, it is good goods and genuine products. If a smoker is magnetic, it is considered a fake. In fact, this is an extremely one-sided and unrealistic way to identify mistakes.
There are many kinds of stainless steel, which can be divided into several types according to the structure at room temperature:
1. Austenite types: such as 304, 32 1, 3 16, 3 10, etc.
2. Martensite or ferrite type: such as 430, 420, 4 10, etc.
Austenite is nonmagnetic or weakly magnetic, while martensite or ferrite is magnetic.
Stainless steel usually used as decorative tube sheet is mostly austenitic 304 material, which is generally non-magnetic or weakly magnetic. However, due to the fluctuation of chemical composition or different processing conditions caused by smelting, magnetism may appear, but this cannot be considered as counterfeiting or unqualified. What is the reason?
The austenite mentioned above is nonmagnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to composition segregation or improper heat treatment during smelting, a small amount of martensite or ferrite structure will be produced in austenitic 304 stainless steel. In this way, 304 stainless steel will have weak magnetism.
In addition, the microstructure of 304 stainless steel will also transform into martensite after cold working. The greater the cold deformation, the more martensite transformation and the stronger the magnetic properties of steel. Like a batch of steel belts, φ 76 tubes and φ 9.5 tubes are produced, and there is no obvious magnetic induction. Due to the large bending deformation and obvious magnetic induction, the rectangular tube produced by the company is more deformed than the circular tube, especially at the corner, with more intense deformation and more obvious magnetism.
In order to completely eliminate the magnetism of 304 steel caused by the above reasons, stable austenite structure can be restored by high temperature solution treatment, thus eliminating magnetism.
In particular, the magnetism of 304 stainless steel caused by the above reasons is completely different from that of 430, carbon steel and other stainless steels, that is to say, the magnetism of 304 steel is always weak.
This tells us that if stainless steel has weak magnetism or no magnetism at all, it should be judged as 304 or 3 16 material; If it is the same as carbon steel, it shows strong magnetism, because it is judged that it is not made of 304 material.
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 has the ability to resist atmospheric oxidation, that is, rust prevention, and also has the ability to resist corrosion in the medium containing acid, alkali and salt, that is, corrosion resistance. However, its corrosion resistance varies with the chemical composition of its steel, 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, 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 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 are adhered to the surface of stainless steel (such as alkali water and lime water splashing for wall decoration), causing local 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 the permanent brightness of the metal surface, it will not ... >>
Question 4: How to distinguish the quality of stainless steel products? There is also a kind of stainless steel tableware, that is, knives, forks, spoons, chopsticks and other tableware that come into direct contact with food. These two types of stainless steel products are within the national standards for food safety stainless steel products, but stainless steel products for tableware containers have higher requirements for steel. "Because cooking processes such as steaming, boiling, frying and frying require high temperature and corrosion resistance of cookware, such containers generally require the use of austenitic steel, that is, the content of nickel and chromium is relatively high. Usually, the content of chromium is between 18%-20%, which has strong rust prevention ability. Nickel content is between 8%- 10%, and it has strong corrosion resistance. The stainless steel products for tableware have not so high requirements for steel. Austenitic ferritic steel can be used, and the requirements for nickel content are relatively loose. However, the contents of nickel and chromium are not stated in the stainless steel products on the market at present. How do consumers distinguish high-quality and inferior stainless steel products? In this regard, relevant experts have given you the following tips: 1. Test with a magnet. The products that can't be adsorbed are of high quality, but those that can be firmly adsorbed are definitely not good stainless steel, which proves that its nickel content is low, that is, its corrosion resistance is poor. When testing, the most accurate method is to suck the bottom of stainless steel container, because the edge of the container sometimes becomes magnetic because of polishing, and it can also be sucked when testing. However, this method is not suitable for stainless steel products with manganese added. If the manganese content is lower than 2% required by the national standard, the magnet testing method will be effective. However, if this standard is not followed, the added manganese exceeds the standard limit, and the magnet can't absorb it. Therefore, magnet detection is not a foolproof method, and its premise is that the product quality of the enterprise is qualified. 2. Don't choose things that are too cheap. It is best not to buy the so-called stainless steel products in the hands of stall vendors. There are many kinds of stalls in the street, and bosses often attract consumers at very low prices. In fact, most of the things on the stalls are fake, and the real stainless steel products are not so cheap, because the price of the products is determined according to the cost of making materials. Light "stainless steel" is definitely not edible stainless steel, and may even be transformed from abandoned chemical iron drums. Don't buy those fake and shoddy products for cheap. 3. weigh yourself. Under normal circumstances, qualified stainless steel tableware brands will be heavier than unqualified ones. Precautions for the use of stainless steel tableware containers 1. No salt, soy sauce, vinegar, vegetable soup, etc. For a long time, because these foods contain a lot of electrolytes. If stored for a long time, stainless steel will react with these electrolytes electrochemically like other metals, so that harmful metal elements can be dissolved out. 2. Don't use stainless steel pot to cook traditional Chinese medicine, because traditional Chinese medicine contains a variety of alkaloids, organic acids and other components, especially under heating conditions, it is difficult to avoid not reacting with it, which will invalidate the medicine and even generate some more toxic complexes. 3. Do not use strong alkaline or oxidizing chemicals, such as baking soda, bleaching powder, sodium hypochlorite, etc. Used for washing, because these substances are strong electrolytes and will also react electrochemically with stainless steel. 4. Don't burn in the air. Compared with iron products and aluminum products, stainless steel cookware has lower thermal conductivity and slower heat transfer time. Empty burning will cause the chrome coating on the surface of the cooker to age and fall off. 5. Keep the cooker clean and scrub it frequently, especially after storing vinegar, soy sauce and other seasonings, and clean it in time to keep the cooker dry.
Question 5: What method is used to distinguish true and false stainless steel People often think that "stainless steel" means "stainless steel". If it rusts, it must be a fake and shoddy product. This understanding is of course too simple. First of all, stainless steel is not absolutely stainless, but relatively stainless under certain conditions. If users use it improperly and use it in an environment or under conditions beyond their corrosion resistance, it will naturally rust. Second, the stainless steel used in the product is corroded and rusted, or it may be because the manufacturer's material selection is unreasonable, that is, the manufacturer chooses an inappropriate stainless steel brand as the raw material for its products, or the manufacturer's production and processing technology is not up to standard. In addition, the manufacturer did choose fake stainless steel that did not meet the authoritative standards of relevant countries or industries as raw materials. In any case, these are what manufacturers have to face and solve when purchasing and processing. In view of the fact that inferior stainless steel is still produced and sold in the market at present, as well as market cheating behaviors such as shoddy and forged quality certificates, how to take the initiative in the procurement of stainless steel materials, quickly see through these cheating behaviors and avoid the harm of fake and shoddy stainless steel? Even as an expert, it is difficult to distinguish the true and false stainless steels from the appearance. Is there any simple method? Some people say: this is very simple, use a magnet to suck! What can't be absorbed is good, it is "stainless steel", and what can be absorbed is poor, it is "stainless steel"! At present, this statement and practice seems to be very popular, and even scientific and technological publications and TV programs have implemented this law. Experts in the industry deny that this statement and practice is unscientific and extremely wrong. At present, among the five types of stainless steel developed and applied in the world, only austenitic stainless steel (numerous 300 series brands and 200 series brands) often has no magnetism (or its magnetism is weak after processing), while ferritic stainless steel (numerous 400 series brands), duplex stainless steel, martensitic stainless steel and precipitation hardening stainless steel all have magnetism. No matter whether it is magnetic or not, each stainless steel has its own characteristics and scope of application. 300 series austenitic stainless steel is the most widely used, and the proportion of stainless steel with magnetic modern ferrite is increasing, which can partially replace 300 series austenitic stainless steel in kitchen utensils, household appliances, decoration, automobile exhaust system, petrochemical industry and other civil and industrial fields. For 200-series austenitic stainless steel whose magnet can't attract, manganese and nitrogen are used instead of nickel, which reduces the cost and improves the strength compared with the corresponding 300-series steel. However, due to the decline of corrosion resistance, its application fields are narrow, often those fields that require high strength, non-magnetism and low corrosion resistance, such as springs and electronic equipment. As for the so-called "200 series stainless steel" popular in China market, its corrosion resistance and use value are lower. These products are not produced according to the existing national standards, but according to their very loose enterprise standards, reducing the content of nickel and chromium in steel and increasing the content of manganese. Some even reduce nickel to below 1%, chromium to below 10%, and manganese to above 14%, and their pitting equivalent is extremely low, far from reaching the corresponding national standards. In terms of corrosion resistance, these products can't even be called stainless steel, nor can they be called 200 series stainless steel at all. In the current stainless steel market in China, it can be said that there are almost no real 200 series stainless steels. The so-called "200 series stainless steel" on the market is the biggest problem steel and fake steel at present, but it is just like 300 series austenitic stainless steel that is nonmagnetic austenitic steel! It can be said that in the current China market, using magnet attraction to identify the quality of stainless steel often connives at fake and shoddy stainless steel and crowd out high-quality magnetic ferritic steel. At the same time, due to cost factors, it will crowd out nonmagnetic 300-series austenitic stainless steel, and may even make this fake and shoddy steel pass off as nonmagnetic 300-series austenitic stainless steel for industrial use. Obviously, it is impossible to identify the authenticity of stainless steel by magnetic attraction. Is there any other practical and simple method? The answer is yes. This paper introduces a simple method, that is, identification with stainless steel measuring solution, that is, by observing the color change characteristics of the measuring solution in the process of dissolving the measured steel, to determine or distinguish some situations of the measured steel. The "color change" is usually related to the specific elements such as nickel (Ni), molybdenum (Mo) and manganese (Mn) in the tested steel. At present, there are many stainless steel measuring liquid products on the domestic market, some of which are imported from Japan and many of which are made in China. Especially in the developed areas of domestic stainless steel industry and stainless steel waste recycling industry, such as Dai Nan, Wuxi, Foshan, Zhejiang, etc. & gt
Question 6: How to distinguish the quality of stainless steel? When buying stainless steel doors, you should pay special attention to the following points:
1: Choose stainless steel doors produced by manufacturers with quality assurance.
2: Pay attention to the purchase of locks in the same direction as your door opening.
3. Pay attention to the width of your door frame. The ball lock and handle lock on the door should not be less than 90cm.
4. Pay special attention when installing stainless steel doors: only one end with insurance can be removed before installation. Never remove the end with a key and install it. You'd better read the instructions carefully.
5: Do not drip engine oil into the lock cylinder. If the key doesn't open flexibly, you can put some pencil scraps in the keyhole.
6. If you accidentally turn the indoor safety 90 degrees clockwise, it will become a permanent insurance and can only be opened with a key. Turn the safety 90 degrees counterclockwise to recover.
7: Do not wipe the lock body and handle with a wet cloth to avoid rust.
8: When closing the door, it is best to hold the handle, screw the locking bolt into the lock body, and then let go after closing the door. Don't slam the door hard, otherwise it will shorten the service life of the lock.
But also from the following aspects.
1. Wear resistance.
Related to wear resistance is the material of stainless steel doors. When buying, ask the dealer what material it is, such as the difference between cast iron and steel mentioned above, and pay attention to it.
2. feel it.
The handle of stainless steel door is determined by the spring, and the quality of the spring determines the handle and service life when it is used. Some lock springs are not good, which easily leads to the handle drooping, thus ending the life of stainless steel doors. Try the toughness of stainless steel door springs yourself when buying. A good spring brings a very soft feeling, neither too soft nor too hard.
3. electroplating.
In the process of purchasing, we should also look at the coating of stainless steel doors, that is, consider whether the handles of stainless steel doors will fade. Generally speaking, the protective layer of a good stainless steel door, that is, the coating, will not be easily oxidized and worn. The coating of stainless steel door handle is related to the overall beauty of the room, so this point can not be ignored.
Generally speaking, the safety factor of modern stainless steel doors has little to do with the complexity of switching operation procedures. A simple lock is not necessarily unsafe, nor is it necessarily safe to open a very complicated lock.
Looking at the lock depends not only on the feel, but also on whether there is quality guarantee, which usually lasts for five years.
When you choose a lock according to the situation at home, you should also pay attention to whether the lock is installed in the same way as the general one. If it is different, the merchant will generally indicate it when you buy it. For example, locks are not installed from front to back, but from back to front. If the lock is damaged due to a program error when you install it at home, it is not a quality problem of the lock and is not covered by the warranty, which means that the merchant will not return it.
In addition, you can't ignore health factors when purchasing accessories. For example, the bathroom is suitable for copper locks. Although the stainless steel door lock looks clean, it actually breeds thousands of germs, including Gram bacteria, Escherichia coli, Streptococcus and so on. The bacteria on brass door locks are much less than those on stainless steel door locks, because copper has bactericidal effect. So I suggest you install a brass door lock in the bathroom at home, which is good for your health.
Question 7: How to identify the material of stainless steel;
Stainless steel monolithic products generally come from steel mills ordered or imported from abroad, as well as the backlog and backlog of processed products in society. Different sources of stainless steel have different identification methods.
1. Generally, it is only necessary to check the marks on the steel or packaging according to the quality certificate of the imported or steel mill.
The quality certificate is the supplier's confirmation and guarantee of the inspection results of this batch of products. Therefore, the quality certificate not only indicates the name, specification, number of delivered pieces, weight and delivery status of the materials. But also all the inspection results of the specified guarantee items must be stated.
Similarly, in order to facilitate management, avoid confusion and prevent use accidents caused by confusion. The manufacturer shall indicate the brand, batch number, status, specification, quantity and manufacturer's code on the materials or packages. The mark marked on it shall be consistent with the record of the quality certificate. There are three common marking methods:
(1) Coloring-Paint the designated part of the material with the color indicating its brand;
(2) Print —— Stamp or spray print the specified parts of the material, indicating the brand, specification and heat number of the material.
Wait a minute. Stamping is often used on thick steel plates or large and medium-sized steel beams.
(3) Label-A label indicating the brand, batch number, specification and quantity is hung on the bundled or boxed materials.
Signs of stainless steel are generally printed on the market.
2. Social backlog and stainless steel backlog. According to the length of inventory backlog and the quality of inventory, there are generally two situations:
First, the backlog is not long, and it is well managed. Processing units not only keep the original quality certificate or
Copy, and the steel or including the logo on it is complete and clear. For the identification of this kind of stainless steel, it is also necessary to check the signs on the steel or packaging according to the warranty.
The other is that the backlog is long, the storage is not perfect, there is no quality certificate, and the signs on steel or packaging are not obvious or fall off. For the identification of this kind of stainless steel, it is mainly necessary to conduct in-depth investigation and study and consult the original documents of the processing unit. Generally speaking, invoices and other original documents are marked with steel numbers. If there is no steel grade to remember, you must also consult the local price tag information at that time to determine the steel grade through the price. This is an effective method to determine the steel grade, but it is often prone to arrogance. Therefore, it is necessary to master the identification method of physical objects.
(2) Physical identification of stainless steel:
Physical identification is a concrete method to determine whether a commodity (including whole material, scrap, waste, etc.) is stainless steel and what kind of stainless steel it belongs to with the help of simple instruments when the steel grade (No.) is unknown.
It should be pointed out that sensory identification can not distinguish specific steels (types), but can only basically distinguish three categories: chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel. The identification methods are as follows:
1. Color difference:
The surface color of stainless steel after pickling is silvery white and smooth: the color of Cr-Ni stainless steel is silvery white and emerald; Chrome stainless steel is white and slightly gray; The color of Cr-Mn-N stainless steel is similar to that of Cr-Ni stainless steel. Surface color of stainless steel without pickling: Cr-Ni steel is brownish white; Chrome steel is brownish black; Chromium, manganese and nitrogen are black (these three colors refer to the colors with heavy oxidation). Cold-rolled non-annealed Cr-Ni stainless steel with silvery white reflective surface. Stainless steel, except Yuangang, is generally white after pickling.
2. Identification with copper sulfate:
The method is to remove the oxide layer on the steel, drop a drop of water on it and wipe it with copper sulfate. If it does not change color after wiping, it is generally stainless steel; Such as purple: high manganese steel is nonmagnetic, while ordinary steel or low alloy steel is magnetic.
3. Identify with a magnet:
Magnets can basically distinguish two kinds of stainless steel. Because chromium stainless steel can be attracted by magnets in any state; Chromium-nickel stainless steel is generally non-magnetic in annealed state, and some will be magnetic after cold working. But high manganese steel with high manganese content is nonmagnetic; The magnetic properties of Cr-Ni-N stainless steel are complicated: some are nonmagnetic, some are magnetic, some are nonmagnetic in the longitudinal direction and some are magnetic in the transverse direction. Therefore, although magnets can basically distinguish chromium stainless steel from chromium-nickel stainless steel, they cannot correctly distinguish some special steel grades, let alone specific steel grades.
For special steel grades, we still need to use the following three methods to identify them.
1) grinding identification:
Grinding identification is to grind stainless steel on a grinding machine and observe its sparks. Such as sparks >>
Question 8: How to tell the good from the bad in stainless steel pot? Generally, the easiest way to judge whether stainless steel pot is good or bad is to attract stainless steel pot with magnets. What attracts is stainless steel, and what does not attract is stainless steel. Stainless steel has better antirust effect than stainless steel. Looking at the price, we can see that stainless steel is much more expensive than stainless iron.
Question 9: How to distinguish the quality of stainless steel? Hello, the better the stainless steel, the stronger the corrosion resistance, and it is not easy to rust. You can tell from the length of time. The common one is 20 1.304.6438+06. In addition, only professional machinery and chemicals can be used for testing.