Product introduction
309 stainless steel. 309S stainless steel -- S30908 (American AISI, ASTM) 309S. 309S stainless steel is mostly produced by steel plants, which has good corrosion resistance and high temperature resistance. It can withstand high temperature of 980 ° C. It is mainly used in boiler, chemical industry and other industries. 309 has no sulfur content compared with 309S.
Chinese name: 309 stainless steel
Characteristics and application: better corrosion resistance and heat resistance than 0Cr19Ni9
Corresponding Chinese brand: 0Cr23Ni13

Basic information
309 stainless steel. 309S stainless steel -- S30908 (American AISI, ASTM) 309S.
The American Iron and Steel Institute uses three digits to mark various standard grades of malleable stainless steel. Among them: ① Austenitic stainless steels are marked with 200 and 300 series numbers, for example, some common austenitic stainless steels are marked with 302, 304, 316 and 310, and ② ferritic and martensitic stainless steels are marked with 400 series numbers. ③ Ferritic stainless steels are marked with 430 and 446, while martensitic stainless steels are marked with 410, 420 and 440C. Duplex (austenite ferrite), ④ stainless steels, precipitation hardening stainless steels and high alloys with iron content less than 50% usually use patent names or trade names.

Chemical composition
① The international chemical element symbols and national symbols are used to represent the chemical composition, and the Arabic letters are used to represent the composition content: for example, China and Russia 12CrNi3A ② use fixed digit numbers to represent the steel series or numbers; For example, the United States, Japan, 300 series, 400 series and 200 series; ③ The serial number is composed of Latin letters and order, which only represents the purpose. Numbering rules in China ① use element symbols ② use, Chinese pinyin, open hearth steel: P, rimmed steel: F, killed steel: B, Class A steel: A, T8: special 8, GCr15: ball
◆ Bonded steel, spring steel, such as 20CrMnTi 60SiMn, (expressed in parts per ten thousand)
◆ Stainless steel, alloy tool steel (expressed in thousandths), such as one thousandth of 1Cr18Ni9 (0.1% C), stainless C ≤ 0.08%, such as 0Cr18Ni9, ultra-low carbon C ≤ 0.03%, such as 0Cr17Ni13Mo

Stainless steel knowledge
Stainless steel refers to steel that is resistant to weak corrosion media such as air, steam and water and chemical etching media such as acid, alkali and salt, also known as Stainless acid resistant Steel. In practical applications, steel resistant to weak corrosion medium is often called stainless steel, while steel resistant to chemical medium is called acid resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical medium corrosion, while the latter is generally stainless. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel.
Stainless steel is often divided into martensitic steel, ferritic steel, austenitic steel, etc. according to the structure state. In addition, it can be divided into chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel according to composition.
1. Ferritic stainless steel: containing 12%~30% chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its chloride stress corrosion resistance is superior to other types of stainless steel. This category includes Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Ferritic stainless steel has good corrosion resistance and oxidation resistance due to its high chromium content, but its mechanical and technological properties are poor. It is mostly used for acid resistant structures with little stress and as oxidation resistant steel. This kind of steel can resist the corrosion of atmosphere, nitric acid and saline solution, and has good high-temperature oxidation resistance and small thermal expansion coefficient. It is used in nitric acid and food factory equipment, and can also be used to make parts working under high temperature, such as gas turbine parts.
2. Austenitic stainless steel: it contains more than 18% chromium, about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and can resist corrosion of various mediums. Common grades of austenitic stainless steel include 1Cr18Ni9, 0Cr19Ni9, etc. The wC of 0Cr19Ni9 steel is less than 0.08%, and the steel grade is marked as "0". This kind of steel contains a lot of Ni and Cr, which makes the steel austenitic at room temperature. This kind of steel has good plasticity, toughness, weldability and corrosion resistance. It has good corrosion resistance in oxidizing and reducing media. It is used to make acid resistant equipment, such as corrosion resistant containers and equipment linings, transmission pipelines, nitric acid resistant equipment parts, etc. Austenitic stainless steel generally adopts solution treatment, that is, the steel is heated to 1050~1150 ℃, and then cooled by water to obtain single-phase austenitic structure.
3. Austenitic ferritic duplex stainless steel: It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity. A stainless steel in which the austenite and ferrite structures account for about half of each other. With low C content, Cr content is 18%~28% and Ni content is 3%~10%. Some steels also contain alloy elements such as Mo, Cu, Si, Nb, Ti and N. This kind of steel has the characteristics of both austenitic and ferritic stainless steels. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and has improved intergranular corrosion resistance and welding performance. At the same time, it maintains the 475 ℃ brittleness of ferritic stainless steels, high thermal conductivity and superplasticity. Compared with austenitic stainless steel, it has higher strength and better resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel is a nickel saving stainless steel with excellent pitting corrosion resistance.
4. Martensitic stainless steel: high strength, but poor plasticity and weldability. The common brands of martensitic stainless steel are 1Cr13, 3Cr13, etc. Because of its high carbon content, it has high strength, hardness and wear resistance, but its corrosion resistance is slightly poor. It is used on some parts with high mechanical performance requirements and general corrosion resistance requirements, such as springs, turbine blades, hydraulic compressor valves, etc. This kind of steel is used after quenching and tempering.
Stainless steel action
Stainless steel will not produce corrosion, pitting, rust or wear. Stainless steel is also one of the metal materials with high strength used in construction. As stainless steel has good corrosion resistance, it can make structural components permanently maintain the integrity of engineering design. Chromium containing stainless steel also integrates mechanical strength and high extensibility, which is easy to process and manufacture components and can meet the needs of architects and structural designers.

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