Is stainless steel easy to rust? Why not learn about our 304 stainless steel
There are three main factors that affect stainless steel corrosion:
1. The content of alloying elements.
Generally speaking, the content of chromium is 10.5%, and the steel is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, the content of nickel in 304 material is 8-10%, and the content of chromium is 18-20%. Such stainless steel will not rust under normal circumstances.
2. The smelting process of the manufacturer will also affect the corrosion resistance of stainless steel.
A large stainless steel plant with good smelting technology, advanced equipment and advanced technology can ensure the control of alloy elements, the removal of impurities, and the control of billet cooling temperature. On the contrary, some small steel mills have backward equipment and backward technology. During the smelting process, impurities cannot be removed, and the products produced will inevitably rust.
3. The external environment, the climate is dry and ventilated, and the environment is not easy to rust.
The air humidity is high, continuous rainy weather, or environmental areas with high pH in the air are prone to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.
How to deal with rust spots on stainless steel?
1. Chemical method
Use pickling paste or spray to assist the re-passivation of the rusted part to form a chromium oxide film to restore the corrosion resistance. After pickling, in order to remove all contaminants and acid residues, it is very important to rinse properly with clean water. After all treatment, re-polish with polishing equipment, and seal with polishing wax.
2. Mechanical method
Sandblast cleaning, blast cleaning with glass or ceramic particles, annihilation, brushing and polishing. It is possible to mechanically wipe away contamination from previously removed material, polishing material, or submerged material. All kinds of contamination, especially foreign iron particles, can be a source of corrosion, especially in humid environments.
Stainless steel grades and properties commonly used in instruments
1. 304 stainless steel is one of the most widely used austenitic stainless steels. It is suitable for the manufacture of deep-drawn parts and acid pipelines, containers, structural parts, various instrument bodies, etc. It can also be used to manufacture non-magnetic , cryogenic equipment and components.
2. 304L stainless steel. In order to solve the problem of ultra-low carbon austenitic stainless steel developed due to the precipitation of Cr23C6 causing serious intergranular corrosion tendency of 304 stainless steel under some conditions, its sensitized state intergranular corrosion resistance is significantly better than that of 304 stainless steel. Except for the slightly lower strength, other properties are the same as 321 stainless steel. It is mainly used for corrosion-resistant equipment and components that cannot be subjected to solution treatment after welding, and can be used to manufacture various instrument bodies.
3. 304H stainless steel. The internal branch of 304 stainless steel has a carbon mass fraction of 0.04%-0.10%, and its high temperature performance is better than that of 304 stainless steel.
4. 316 stainless steel. Adding molybdenum on the basis of 10Cr18Ni12 steel makes the steel have good resistance to reducing medium and pitting corrosion. In seawater and various other media, the corrosion resistance is better than 304 stainless steel, mainly used for pitting-resistant materials.
5. 316L stainless steel. Ultra-low carbon steel, with good resistance to sensitized intergranular corrosion, is suitable for the manufacture of welded parts and equipment with thick section dimensions, such as corrosion-resistant materials in petrochemical equipment.
6. 316H stainless steel. The internal branch of 316 stainless steel has a carbon mass fraction of 0.04%-0.10%, and its high temperature performance is better than that of 316 stainless steel.
7. 317 stainless steel. The pitting corrosion resistance and creep resistance are better than 316L stainless steel, which is used in the manufacture of petrochemical and organic acid corrosion resistant equipment.
8. 321 stainless steel. Titanium-stabilized austenitic stainless steel, adding titanium to improve intergranular corrosion resistance, and has good high-temperature mechanical properties, can be replaced by ultra-low carbon austenitic stainless steel. Except for special occasions such as high temperature or hydrogen corrosion resistance, it is generally not recommended for use.
9. 347 stainless steel. Niobium-stabilized austenitic stainless steel, adding niobium to improve intergranular corrosion resistance, the corrosion resistance in acid, alkali, salt and other corrosive media is the same as 321 stainless steel, good welding performance, can be used as corrosion-resistant material and anti-corrosion Hot steel is mainly used in thermal power and petrochemical fields, such as making containers, pipes, heat exchangers, shafts, furnace tubes in industrial furnaces, and furnace tube thermometers.
10. 904L stainless steel. Super complete austenitic stainless steel is a kind of super austenitic stainless steel invented by OUTOKUMPU in Finland. , It has good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid and phosphoric acid, and also has good resistance to crevice corrosion and stress corrosion resistance. It is suitable for various concentrations of sulfuric acid below 70 °C, and has good corrosion resistance in acetic acid and mixed acid of formic acid and acetic acid at any concentration and temperature under normal pressure. The original standard ASMESB-625 classifies it as nickel-based alloys, and the new standard classifies it as stainless steel. There are only similar grades of 015Cr19Ni26Mo5Cu2 steel in China. A few European instrument manufacturers use 904L stainless steel as the key material. For example, the measuring tube of E+H's mass flowmeter is made of 904L stainless steel, and the case of Rolex watches is also made of 904L stainless steel.
11. 440C stainless steel. Martensitic stainless steel has the highest hardness among hardenable stainless steels and stainless steels, with a hardness of HRC57. Mainly used to make nozzles, bearings, valve cores, valve seats, sleeves, valve stems, etc.
12. 17-4PH stainless steel. Martensitic precipitation hardening stainless steel with a hardness of HRC44 has high strength, hardness and corrosion resistance and cannot be used at temperatures above 300°C. It has good corrosion resistance to the atmosphere and diluted acid or salt. Its corrosion resistance is the same as that of 304 stainless steel and 430 stainless steel. It is used to manufacture offshore platforms, turbine blades, valve cores, valve seats, sleeves, valve stems Wait.