Stainless steel is the abbreviation of stainless and acid-resistant steel. The steel that is resistant to weak corrosive media such as air, steam, and water or has stainless is called stainless steel; Corroded steel is called acid-resistant steel.
Stainless steel refers to steel that is resistant to weak corrosive media such as air, steam, and water, and chemically corrosive media such as acid, alkali, and salt, also known as stainless acid-resistant steel. In practical applications, the steel that is resistant to weak corrosive media is often called stainless steel, and the steel that is resistant to chemical media corrosion is called acid-resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter is generally stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.
Similar Articles:
- 304 stainless steel
- Stainless steel casting
- Knowledge of stainless steel
- Carbon steel VS stainless steel
- Process flow of stainless steel precision casting
- Classification and performance of stainless steel grades
Usually divided into:
Usually, according to the metallographic structure, ordinary stainless steel is divided into three categories: austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. Based on these three basic metallographic structures, for specific needs and purposes, dual-phase steels, precipitation-hardening stainless steels, and high-alloy steels with an iron content of less than 50% are derived.
- Austenitic stainless steel.
The matrix is dominated by austenite structure (CY phase) of face-centered cubic crystal structure, non-magnetic, and is mainly strengthened by cold working (and may lead to certain magnetic properties) stainless steel. The American Iron and Steel Institute is designated by numbers in the 200 and 300 series, such as 304.
- Ferritic stainless steel.
The matrix is dominated by the ferrite structure ((a phase) of the body-centered cubic crystal structure, which is magnetic and generally cannot be hardened by heat treatment but can be slightly strengthened by cold working. The American Iron and Steel Institute is marked with 430 and 446.
- Martensitic stainless steel.
The matrix is a martensitic structure (body-centered cubic or cubic), magnetic, and its mechanical properties can be adjusted by heat treatment. The American Iron and Steel Institute is designated by the numbers 410, 420, and 440. Martensite has an austenite structure at high temperature, and when cooled to room temperature at an appropriate rate, the austenite structure can be transformed into martensite (ie, hardened).
- Austenitic-ferritic (duplex) stainless steel.
The matrix has both austenite and ferrite two-phase structure, and the content of the less-phase matrix is generally more than 15%. It is magnetic and can be strengthened by cold working. 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, dual-phase steel has high strength and the resistance to intergranular corrosion and chloride stress corrosion, and pitting corrosion is significantly improved.
- Precipitation hardening stainless steel.
The matrix is an austenite or martensitic structure and can be hardened by precipitation hardening. The American Iron and Steel Institute is marked with a 600 series number, such as 630, which is 17-4PH.
Generally speaking, in addition to alloys, the corrosion resistance of austenitic stainless steel is relatively excellent. In a less corrosive environment, ferritic stainless steel can be used. In a mildly corrosive environment, if the material is required to have high For strength or high hardness, martensitic stainless steel and precipitation hardening stainless steel can be used.
What kind of stainless steel is not easy to rust?
Three main factors affect stainless steel corrosion:
- 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.
- 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 alloying elements, the removal of impurities, and the control of the cooling temperature of the billet, so the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. 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.
- The external environment, the climate is dry and ventilated, and the environment is not easy to rust.
The air humidity is high, and 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?
- 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, 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. For local slight rust spots, you can also use a 1:1 mixture of gasoline and engine oil to wipe off the rust spots with a clean rag.
- 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. Therefore, mechanically cleaned surfaces should preferably be properly cleaned in dry conditions. The use of mechanical methods can only clean the surface, and cannot change the corrosion resistance of the material itself. Therefore, it is recommended to re-polish with polishing equipment after mechanical cleaning and seal with polishing wax.
Stainless steel grades and properties commonly used in instruments
- 304 stainless steel. It is one of the most widely used and widely used austenitic stainless steel. 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, low-temperature equipment and part.
- 304L stainless steel. 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.
- 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.
- 316 stainless steel. Adding molybdenum based on 10Cr18Ni12 steel makes the steel has 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.
- 316L stainless steel. Ultra-low carbon steel has good resistance to sensitized intergranular corrosion and is suitable for the manufacture of welded parts and equipment with thick section dimensions, such as corrosion-resistant materials in petrochemical equipment.
- 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.
- 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.
- 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.
- 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.
- 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. China only has similar grades of 015Cr19Ni26Mo5Cu2 steel. A few European instrument manufacturers use 904L stainless steel as the key material. For example, the measuring tube of the E+H mass flowmeter is made of 904L stainless steel, and the case of Rolex watches is also made of 904L stainless steel.
- 440C stainless steel. Martensitic stainless steel has the highest hardness among hardenable stainless steel and stainless steel, with a hardness of HRC57. Mainly used to make nozzles, bearings, valve cores, valve seats, sleeves, valve stems, etc.
- 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, and valve stems Wait.
Recent Articles：
- Casting technical requirements and analysis of common problems of steel castings
- What is the role of Mo in high manganese steel casting production?
- What effect does carbon have on cast steel and iron during smelting?
- Prevention and Analysis of Stainless Steel Casting Defects
- Causes of cracks in steel castings