Things about food grade stainless steel
1. Main components of stainless steel
The main components of stainless steel are iron, chromium, nickel, and a small amount of carbon and other elements
2. Stainless steel classification
According to material organization structure
Austenitic stainless steel
martensitic stainless steel
ferritic stainless steel
Austenitic-ferritic duplex stainless steel
precipitation hardened stainless steel
The most common one is austenitic stainless steel, and the output of austenitic stainless steel accounts for about 75% to 80% of the total stainless steel output.
3. Austenitic stainless steel
The classic first-generation austenitic stainless steel is called 18-8 steel (that is, our common 304 stainless steel, 18-8 means that the chromium content is about 18%, and the nickel content is 8% to 10%), which is the most typical Represents steel type, other austenites are developed on the basis of 18-8.
Commonly used austenitic stainless steels include:
2XX series (chromium-nickel-manganese austenitic stainless steel, the most common 201, 202)
3XX series (chromium-nickel austenitic stainless steel, the most common 304, 316)
The 2XX series originated during World War II. As a strategic material, nickel was strictly controlled in various countries (nickel is very expensive). In order to solve the serious shortage of nickel supply, the United States first developed 2XX series stainless steel products with low nickel content. The emergency and supplementary product of the 3XX series, the 2XX series is developed by adding manganese and/or nitrogen to steel instead of the precious metal nickel. The corrosion resistance of the 2XX series is not as good as that of the 3XX series, but both are non-magnetic, so domestic Many unscrupulous merchants pass off 201 stainless steel as inferior quality as 304 stainless steel. However, excessive intake of manganese in the human body can cause damage to the nervous system, so the 2XX series cannot be used for tableware.
4. What are the differences between 304, SUS304, 06Cr19Ni10 and S30408?
These are the different names of 18-8 austenitic stainless steel in different countries, 304 (American standard, also known as the American name), SUS304 (Japanese standard, also known as the Japanese name), 06Cr19Ni10 (Chinese standard, also known as the Chinese name), S30408 (S30408 is the UNS number of 06Cr19Ni10, and American 304 also has the corresponding UNS number S30400). There will be slight differences in the standards of different countries, but after all, these can be generally considered to be the same material.
5. Which is better, 304 stainless steel or 316 stainless steel?
The 316 stainless steel we usually refer to refers to 316L. "L" is the abbreviation of "LOW" in English, which means "low carbon". Compared with 304, 316 stainless steel has increased nickel content, reduced carbon content, and newly added molybdenum (304 does not contain molybdenum). The addition of nickel and molybdenum greatly enhances its corrosion resistance and high temperature resistance. Of course, the cost Also higher. 316 is mainly used in marine, high-temperature distillation, special medical equipment and other equipment that require corrosion resistance and high temperature resistance, so 304 is sufficient for ordinary food contact.
6. What is food grade stainless steel?
Food-grade stainless steel refers to stainless steel that complies with the national mandatory standard GB4806.9-2016 "National Food Safety Standard Metal Materials and Products for Food Contact".
From the above, we can see that the country has two main requirements for food-grade stainless steel: first, the raw materials must meet the requirements, and second, the heavy metal precipitation of these raw materials must meet food-grade standards.
Many friends will ask whether 304 stainless steel is food-grade stainless steel?
The answer is: 304 stainless steel is "not equal to" food-grade stainless steel. 304 is an American standard. Naturally, the word "304" as an American standard cannot appear in Chinese standards, but generally speaking, "specially treated 304 stainless steel" is food grade stainless steel. Grade stainless steel, ordinary 304 stainless steel is not food grade stainless steel, 304 stainless steel has a wide range of industrial uses, and most of them are not food grade.
7. How to treat food grade stainless steel stamps
Take electric kettles as an example. Many of the big brand kettles we buy have food-grade stainless steel stamps on the inner wall. Are those with the stamps food-grade stainless steel? The answer is: no. Food-grade stainless steel stamps are not national standards. They are added by each company for marketing purposes, and the styles of the stamps vary from company to company. (Think about it silently, even if the country does issue standards, it is impossible for the words 304, an American standard, to appear in the mark), so the presence or absence of a steel seal cannot be used as a standard for identifying food-grade stainless steel.
8. Let's talk about stainless steel testing fluid
Nowadays, you can buy a lot of stainless steel testing solutions online. The principle is very simple: the solution reacts chemically with certain components of different types of stainless steel, causing the color of the solution to change. Testing fluids are usually divided into two types:
No power required
energized type
Types that do not require electricity, such as: manganese (Mn) detection liquid, mainly used to detect 304 stainless steel (201, 202 has high manganese content, mainly for some unscrupulous businesses to use 201, 202 as 304)
Electrical type, such as: molybdenum (Mo) detection liquid, mainly used to detect 316 stainless steel (molybdenum is a precious metal and other stainless steel does not contain molybdenum, mainly for some unscrupulous merchants who use 304 to pass it off as 316)
This type of testing solution has three disadvantages:
Will slightly corrode the stainless steel surface
Coated stainless steel cannot be tested (coated stainless steel must be filed off before testing)
Just a rough inspection, just a rough inspection, just a rough inspection, say important things three times
Take the manganese (Mn) testing liquid as an example. If it is qualified, it means that the manganese content meets the requirements. It is not known whether other elements meet the national standards. In other words, these testing liquids still have a certain effect on some routine fraud.
9. How to ensure that you buy food-grade stainless steel
There is only one way: buy products from regular big brands.
Taking the electric kettle as an example, the main body of the part in contact with water should be food-grade stainless steel. Because the national mandatory standard GB4806.9-2016 is "mandatory", buying regular big brand products must meet food grade requirements.
10. Reasons why stainless steel "does not rust"
The main reason why stainless steel does not rust is due to the chromium in it. The presence of chromium forms a dense chromium-rich oxide film on the surface of stainless steel, which can prevent corrosion and rust. The passive film of stainless steel is an oxygen hydrocarbon-based, water, and chromium compound. If there are scratches on the surface, the protective film will fall off, but the surrounding water and oxygen will regenerate it and maintain corrosion resistance, so that the stainless steel surface has the ability to maintain itself. Restorative Power".
11. Introduction to 443 stainless steel
443 stainless steel is a type of ferritic stainless steel. It is now generally used to replace 304 stainless steel. Its anti-rust ability and processing performance are equivalent to 304, and its thermal conductivity is better than 304. It is widely used in electrical appliances, kitchen equipment, elevators and other fields.
12. Why do some stainless steel tableware have a "smell"?
Sometimes when our hands come into contact with metal, there will be a metallic smell on our hands. This is mainly because when the skin comes into contact with the surface of the metal, the oxidized fat on the skin is catalyzed by the trace metal ions and decomposes into small molecules of aldehydes and ketones, which you smell. , in fact, it is similar to the smell of blood and iron.
During the production process of stainless steel tableware, in order to make the product have certain special properties, such as anti-corrosion or acid and alkali resistance, after it is formed and condensed, it will be polished by pouring water and polishing liquid through mechanical processing. Especially the engine oil and other substances attached during the finishing process after molding will produce "odor". If you use food-grade stainless steel tableware such as 304 and 316, there will still be an obvious "odor" after cleaning, indicating the quality of the stainless steel. not to standard.
13. How to quickly remove dirt on the surface of stainless steel?
Our commonly used stainless steel pots, faucets and other stainless steel utensils will produce dirt on the surface after long-term use, and they are particularly difficult to remove. Especially stainless steel pots often turn yellow and black, which affects their appearance.
The method of decontamination is also relatively simple: use a special stainless steel cleaner, and thick oil dirt can be easily removed with an emery sponge.
14. Is 304 stainless steel non-magnetic?
Austenitic stainless steel (represented by 304) is non-magnetic or has weak magnetism. Due to component segregation or improper heat treatment during smelting, a small amount of martensite or ferrite structure will appear in austenitic 304 stainless steel, so that weak magnetism will appear in 304 stainless steel. In addition, after cold working of 304 stainless steel, the organizational structure will also transform to martensite. The greater the cold working deformation, the more martensitic transformation, and the stronger the magnetism. Ferrite (mainly 430, 409L, 439 and 445NF, etc.) and martensite (represented by 410) are generally magnetic.
15. Is stainless steel necessarily rust-free?
There are many types of stainless steel, and different types of stainless steel have different corrosion resistance. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment. For example, 304 has strong corrosion resistance, but it will still be corroded if it is often exposed to salt water and seawater environments. In this case, 316 should be used. However, if 304 rusts under normal daily use conditions, it can only mean that the product process is not up to standard or the content of metallic chromium and other additives is insufficient.
16. The surface of the stainless steel basin turns black after being wiped with paper. Is it safe to use?
Supermarket shopping often comes with some small gifts. After wiping some stainless steel basins with paper, there will be a layer of black stuff on the paper. After washing it many times, it still cannot be cleaned. This black layer may be polishing wax. (There is also a saying that it is a mixture of polishing wax and metal powder). Polishing wax is a toxic substance that is difficult to dissolve in water. Normally, stainless steel product polishing wax should be cleaned before leaving the factory. If products with polishing wax flow into In the hands of consumers, let alone whether the stainless steel itself reaches food grade, at least it shows that there are problems with the quality control of the manufacturer. It is recommended not to use such products to contact food or throw them away directly.
