What are the matters needing attention when purchasing stainless steel profiles
Publisher：Jiangsu Farrand Metal Products Co., Ltd. Release time：2025-07-08 13:15:06 Number of clicks：
Close
If a magnet attracts technetium, it is definitely not stainless steel. This is the biggest misunderstanding in the minds of Chinese people! It can be said that if you go to any hardware store, the boss will tell you this. If you believe it, then in fact you are wrong. What a magnet can attract doesn't necessarily mean it's not stainless steel. Stainless steel can be classified into many types, among which the commonly used classification methods include austenitic, ferritic, duplex, martensitic, and precipitation-hardening. (Don't ask me what these terms mean; just remember them. They are all terms in metallography.) Among them, only austenitic stainless steel is non-magnetic, but this type of stainless steel accounts for the vast majority of the stainless steel market (previously over 70%, now only an estimated 60%, and in the future it will fall below 50%), and is the most widely used. All other steel materials are magnetic, which is why stainless steel is identified by magnetism in the domestic Chinese market. However, all other types of stainless steel are magnetic. For instance, many times when you go to a high-end restaurant and try out those shiny stainless steel knives and forks with a magnet, they are often magnetic. In fact, that is very likely to be martensitic stainless steel. Also, the stainless steel used in car exhaust pipes is magnetic; it is ferritic.
Austenitic stainless steel often requires the addition of Ni. Currently, the price of Ni is very high worldwide. Therefore, one of the main development trends of stainless steel at present is how to save nickel. One good way is to develop excellent ferritic stainless steel and duplex stainless steel. So in the future, there will inevitably be more stainless steels that magnets can attract.
2. Does stainless steel definitely never rust?
There is another major misconception among the public that stainless steel will never rust. In fact, I have taken on far too many cases of stainless steel rusting. Among all the stainless steel rusting incidents I have taken over, a large proportion are due to users' insufficient understanding of stainless steel. When selecting and using materials, they did not consider the characteristics of stainless steel and used it randomly and excessively, resulting in abnormal rusting of stainless steel.
As is well known, in a normal atmospheric environment, as long as the stainless steel is qualified (in compliance with national standards), it will not rust. This is because stainless steel contains an important alloying element, Cr (the Cr content in stainless steel must be above 13%, otherwise its excellent corrosion resistance cannot be guaranteed). Cr can form a dense passivation film on the surface of stainless steel, protecting it from corrosion.
However, in many cases, stainless steel can still suffer from local corrosion due to damage to the surface passivation film. There are many types of local corrosion, including pitting corrosion, crevice corrosion, intergranular corrosion, stress corrosion and galvanic corrosion (the above are referred to as the five major local corrosions of stainless steel). Among them, the most common ones we encounter in the home appliance, decoration and tableware industries are pitting corrosion and crevice corrosion. The causes of these two types of corrosion are the same and both are closely related to Cl-. To avoid this, first of all, it is necessary to pay attention to keeping stainless steel in a Cl- environment for a long time as much as possible. Secondly, it is important to ensure that the environment where stainless steel is used is clean to prevent the accumulation of dirt. Additionally, it is necessary to avoid scratches on the surface of stainless steel. The surface of stainless steel often forms a new passive film after being scratched. However, the newly formed passive film on the scratch is generally fragile, and the scratch is prone to create geometric crevices, which can easily lead to crevice corrosion and rusting.
Because there are many types of stainless steel and various types of corrosion, and each type is different, it cannot be generalized. However, if it is necessary to specify where rust is prone to occur, I can offer a rather practical but not necessarily scientifically rigorous suggestion:
1) If this place refers to a spatial area. Generally, places with a higher content of Cl- are more prone to rust, and damp areas are also more likely to rust. For instance, Shanghai, which is close to the sea, has a relatively high content of Cl- and is very humid, making it prone to rust.
2) If it refers to any part of the product. Generally speaking, the connection parts of the product are prone to corrosion due to the gaps at the connection parts. The deformed parts are prone to corrosion due to residual stress and phase transformation induced by deformation. The welded parts are prone to corrosion due to unreasonable welding processes. Places where dirt and grime accumulate are prone to corrosion due to lack of oxygen and the gaps between dirt and stainless steel. The scratched area is prone to corrosion. Areas that are frequently washed and hit by hard objects are prone to rust due to erosion and corrosion. www.boismarinecreation.com wuxi stainless steel company
3. Which type of stainless steel is the best stainless steel?
The reason why this issue is also brought up as a misunderstanding of everyone is that in fact, asking this question itself involves a misunderstanding. That is, there must be the best stainless steel that nothing can corrode it. In fact, this idea is incorrect. At least, as far as I know, there is no such perfect stainless steel. Each type of stainless steel has its specific application field and design purpose. When developing and designing materials, it is impossible to take everything into account. Cost, corrosion resistance, formability and welding are often difficult to balance. Even if we only consider corrosion resistance, it is impossible for the product development and component design to take into account all types of corrosion. However, it can only be achieved through selective selection and emphasis, such as adding Mo to enhance pitting resistance, and adding Ti and Nb to improve intergranular corrosion resistance, etc. In fact, based on the differences in these components, stainless steel is divided into many grades, with as many as hundreds of types. Among them, the ones we encounter most frequently are as follows:
304 is the most classic stainless steel that we encounter the most. It has a Cr content of 17% to 19% and a Ni content of 8 to 11%. Currently, its market price is approximately 30,000 to 40,000 yuan per ton.
316 is resistant to seawater corrosion and has more Mo than 304. Its price is over 60,000 yuan. 301 and 302 have a higher C content than 304, but their corrosion resistance is correspondingly slightly lower.
321 with Ti and Nb added to enhance weldability was once quite popular in China, but it is now gradually fading out. I guess these are the few types that everyone has encountered most frequently.
4. How to identify different types of stainless steel
Is this issue also considered a misunderstanding? Yes. Because it is very difficult for you to distinguish different types of stainless steel just by the naked eye. It's almost impossible. Apart from being able to simply distinguish whether it belongs to austenitic stainless steel or other types based on magnetic properties, even experts in stainless steel, even those who have been working on it all their lives, are unable to tell the difference. The distinction can only be made through special instruments. Of course, insiders can make a rough estimate based on factors such as price, magnetism, and place of origin, but they can never give you a very clear and reliable answer.
Which types of stainless steel should be avoided if possible?
1. Stainless steel that is too cheap. Although this statement is a bit excessive, it definitely has some truth to it. Take buying a stainless steel sink as an example. If one weighs over 10 kilograms when carried in hand (do you have it?) I'm not sure. If a stainless steel sink with a faucet weight of around 300 yuan is sold for less than 300 yuan and the boss tells you it has no magnetism, it must be made of stainless steel. So, tx, you mustn't buy it under any circumstances. Why? Didn't we tell you the current market price of 304 earlier? Although it's only the price in the second half of last year, I believe the price this year should only be higher than this. 30,000 yuan per ton, that's just the factory price. If you don't buy a hundred tons, you won't be able to get this price. It's 30 yuan per kilogram. (So expensive. Do you know why stainless steel hardware is so expensive now?) Then, light materials
The material cost is as high as 300 yuan for a 10-kilogram sink. Add in the losses, processing costs, transportation, taxes, the profit the boss needs to earn, management fees, and so on. Can you possibly buy it for less than 400 yuan? So, there is only one possibility: adulteration.
2. Don't buy 200 stainless steel. As we talked about the issue of adulteration earlier, let's move on to the next topic. In fact, the reason why I want to post here is that I have considered that stainless steel is needed in many places during decoration, and many people, including salespeople, may be kept in the dark. The main purpose of Posting this is to tell everyone not to blindly believe in magnetic identification methods and not to be deceived by intentional or unintentional sales.
It seems I've said a lot of nonsense again. Now let's get to the point. Since 2000, due to taking advantage of the magnetic psychology of domestic users, many low-quality low-Ni stainless steels have emerged in China. They are called 200 (actually, they should be called the new 200 series). These stainless steels have a very low Ni content. If the Ni content is too low, there will be a problem: stainless steel with low Ni content is prone to ferritic (ferritic stainless steels all contain very little or no Ni), and thus cannot take advantage of people's magnetic psychology for promotion and publicity. So, manufacturers have no choice but to take another step - reducing the Cr content and increasing the C and N content, because in this way they can obtain the austenite structure again (so professional. If you don't understand, there's no need to ask why it's like this. I can still explain it clearly, but I think it's unnecessary). However, this has led to a very serious problem. As those who have read the previous posts know, the corrosion resistance of stainless steel (which may not be very scientific, but it can be said this way) is closely related to the Cr content. The higher the Cr content, the better the corrosion resistance. In addition, a high C% content can have a significant negative impact on the corrosion resistance of stainless steel. Moreover, it is difficult for the N% content to be high (if it is too high, it will become nitrogen gas overflow. Of course, high N is an important development direction for stainless steel), and if it is too high, the formability will be poor. As a result, this leads to the low corrosion resistance of this type of stainless steel (it is still much better than ordinary steel, but much worse than the previous 304 and others. I am conducting research in this area to see exactly how much the corrosion resistance of the two differs).
Product Recommendation
304 hot-rolled stainless steel plate 
316 hot-rolled stainless steel plate 
Processing of stainless steel square tubes 
Zhangpu Stainless Steel 
310s hot-rolled stainless steel plate
3 / 3
Scan the code
Scan the code