How To Distinguish Stainless Steel 304 And 202?

- Jun 28, 2018 -

First, stainless steel is what steel?

Stainless steel is a kind of steel, steel is called steel containing carbon (C) below 2%, more than 2%

It is iron. The addition of chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), titanium (Ti), molybdenum (Mo) and other alloying elements to the steel during the smelting process improves the properties of the steel and renders the steel corrosion resistant. (that is, not rust) is what we often say stainless steel.

Second, why do stainless steels have different steel numbers?

Stainless steel in the smelting process, due to the addition of different alloy elements, different varieties of different amounts.

Its characteristics are also different, in order to distinguish it is crowned with a different steel number, the following is a common decorative stainless steel different steel "alloy element" content table is for reference only:

Steel No. Carbon (C) Silicon (Si) Manganese (Mn) Phosphorus (P) Sulfur (S) Chromium (Cr) Nickel (Ni) Molybdenum (Mo) Copper (Cu)

304 ≤ 0.08 ≤ 1.00 ≤ 2.00 ≤ 0.045 ≤ 0.03 18-20 8-10

301 ≤ 0.15 ≤ 1.00 ≤ 2.00 ≤ 0.045 ≤ 0.03 16-18 6-8

202 ≤ 0.15 ≤ 1.00 7.5-10 ≤ 0.05 ≤ 0.03 17-19 4-6

201 ≤ 0.15 ≤ 1.00 5.5-7.5 ≤ 0.05 ≤ 0.03 16-18 3.5-5.5


Third, what kind of stainless steel is not easy to rust?

There are three main factors that affect stainless steel corrosion:

First, the content of alloying elements, generally speaking, the content of chromium is not easily rusted in 10.5% of steel. Chrome-nickel

The higher the content is, the better the corrosion resistance is. For example, the 304 material nickel content is 8-10%, and the chromium content is 18-20%. Such stainless steel will not rust under normal circumstances.

Second, the smelting process of the production company will also affect the corrosion resistance of stainless steel. The large stainless steel plant with good smelting technology, advanced equipment and advanced technology is able to guarantee the control of alloy elements, the removal of impurities, and the control of the cooling temperature of the billet. The CNC WeChat number cncdar is therefore stable and reliable in product quality, and its internal quality is good. , not easy to rust. Conversely, some small steel plants are behind and the process is behind. During the smelting process, impurities cannot be removed and the products will inevitably rust.

Third, the external environment, climate, dry and ventilated environment is not easy to rust. Humidity in the air, continuous rainy weather, or air in areas with high pH, it is easy to rust. 304 stainless steel, if the surrounding environment is too bad it will rust.

Fourth, stainless steel is not with magnetic, without magnetic is a good stainless steel? If the microstrip is magnetic, is it not 304?

Many customers went to the market to buy stainless steel. They brought a small magnet. When they looked at the goods, they took a look and thought they couldn't suck it.

It is a good stainless steel. Without magnetic, it will not rust. In fact, this is a misunderstanding. The stainless steel band is not magnetic, which is determined by the organizational structure. Molten steel will form “ferrite” due to the different solidification temperatures in the solidification process.

"Austenitic," "Martensitic," and other structural stainless steels, where "ferritic" and "martensitic" stainless steels are magnetic. The "austenitic" stainless steel has a combination of its mechanical properties and good processability weldability, but only the "ferritic" stainless steel with magnetic properties is stronger than the "austenitic" stainless steel. Currently, the so-called 200 series and 300 series stainless steels with high manganese content and low nickel content that are in circulation in the market are not magnetic, and their performance is greatly different from that of high nickel containing 304. Instead, 304 is subjected to stretching and annealing. , polishing, casting and other processing processes will also be micro-magnetic, so the use of stainless steel tape without magnetic to determine the quality of stainless steel is a misunderstanding, but also unscientific.


5. Why does stainless steel rust?

When the brown rust (spot) appears on the surface of stainless steel, people are greatly surprised: "Stainless steel does not rust, rust is not stainless steel, and there may be a problem with the steel." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation - that is, stainless, but also has the ability to resist corrosion in the medium containing acid, alkali, salt, corrosion resistance. However, the corrosion resistance of the steel varies with the chemical composition of the steel itself, the mutual state, the conditions of use, and the type of environmental media. Such as 304 material, in the dry and clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the sea area, in the sea fog containing a lot of salt, will quickly rust. Therefore, it is not any kind of stainless steel that can resist corrosion and rust at any time.

Stainless steel is based on the surface of the formation of a very thin and strong and stable chromium-rich oxide film (protective film), to prevent the continued penetration of oxygen atoms, continue to oxidize, CNC WeChat number cncdar and get the ability to resist corrosion. Once for some reason, this kind of film is constantly destroyed, air or liquid neutralizes oxygen atoms will continue to infiltrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, the metal surface will be constantly Corrosion. This type of surface film is damaged in many forms, and is common in daily life as follows:


1. The surface of stainless steel deposits deposits containing other metallic elements such as dust or dissimilar metallic particles, in wet conditions

In the air, the condensate between the attached matter and the stainless steel, connecting the two into a microbattery, triggering an electrochemical reaction.

Should the protective film be destroyed, it is called electrochemical corrosion.

2. The surface of stainless steel adheres to the organic matter juice (such as melon vegetables and noodles, etc.) and is formed under the conditions of water and oxygen.

Organic acids form organic acids that attack metal surfaces for long periods of time.

3, stainless steel surface adhesion with acid, alkali, salt substances (such as the decoration of the wall of alkali water, lime water spray test) caused

Local corrosion.

4. In contaminated air (atmosphere containing large amounts of sulfides, oxides, and hydrogen oxide), in the event of condensation,

Sulfuric acid, nitric acid, and acetic acid are formed to cause chemical corrosion.

The above conditions can cause damage to the stainless steel surface protective film, causing corrosion. Therefore, to ensure that the metal surface is permanently bright and does not rust, we recommend:

1 The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove attachments and eliminate the external factors that cause corrosion.

2 There is a 201 and 202 stainless steel on the market that tends to rust in the waterfront area and is suitable for use in industrial pollution and air corrosion environments.

3 The sea area uses 304 stainless steel, and 304 can resist seawater corrosion.

Sixth, but how does stainless steel rust appear?

a) Chemical methods:

Using a pickling paste or spray to aid the re-passivation of the rusted area to form a chromium oxide film to restore corrosion resistance

Capacity, after pickling, it is very important to rinse properly with clean water in order to remove all contaminants and acid residues. After everything is processed, it is polished again with a polishing device and closed with a polishing wax. For those with slight rust on the spot, a 1:1 mixture of petrol and oil can be used to wipe off rust with a clean rag.

b) Mechanical method:

Blast cleaning, shot blasting with glass or ceramic particles, annihilation, brushing and polishing. Mechanically available

It can wipe away the contamination caused by previously removed materials, polishing materials or annihilation materials. All kinds of pollution, especially foreign iron particles, can be a source of corrosion, especially in humid environments. Therefore, the mechanical cleaning surface should preferably be cleaned in a dry condition. The mechanical method can only clean the surface and cannot change the corrosion resistance of the material itself. It is therefore recommended to re-polish with a polishing machine after mechanical cleaning and close it with a polishing wax.

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