316 stainless steel, 18cr-12ni-2.5mo, due to the addition of Mo, its corrosion resistance, atmospheric corrosion resistance and high temperature strength are particularly good, which can be used under harsh conditions; Excellent work hardening (non-magnetic). Seawater equipment, chemical, dye, papermaking, oxalic acid, fertilizer and other production equipment; Photography, food industry, coastal facilities, ropes, CD rods, bolts, nuts. Chemical composition of 316 stainless steel: C ≤ 0.08, Si ≤ 1.00, Mn ≤ 2.00, P ≤ 0.035, s ≤ 0.03, ni:10.0-14.0, cr:16.0-18.5, mo:2.0-3.0. Mechanical properties of 316 stainless steel: tensile strength (MPA) 620 min, yield strength (MPA) 310 min, elongation (%) 30 min, area reduction (%) 40 min, density of 316 stainless steel 8.03 g/cm3, which is generally used for austenitic stainless steel.
Stainless steel is generally the general term of stainless steel and acid resistant steel. Stainless steel refers to the steel that is resistant to the corrosion of weak media such as atmosphere, steam and water, while acid resistant steel refers to the steel that is resistant to the corrosion of chemical corrosive media such as acid, alkali and salt. Since the advent of stainless steel at the beginning of this century, the invention of stainless steel is a major achievement in the history of world metallurgy. The development of stainless steel has laid an important material and technological foundation for the development of modern industry and scientific and technological progress. There are many kinds of stainless steel with different properties. It has gradually formed several categories in the process of development. According to the structure, it can be divided into four categories: martensitic stainless steel (including precipitation hardening stainless steel), ferritic stainless steel, austenitic stainless steel and austenitic plus ferritic duplex stainless steel; According to the main chemical composition in steel or some characteristic elements in steel, it is divided into chromium stainless steel, chromium nickel stainless steel, chromium nickel molybdenum stainless steel, low-carbon stainless steel, high molybdenum stainless steel, high-purity stainless steel, etc; According to the performance characteristics and uses of steel, it is divided into nitric acid resistant stainless steel, sulfuric acid resistant stainless steel, pitting corrosion resistant stainless steel, stress corrosion resistant stainless steel, high-strength stainless steel, etc; According to the functional characteristics of steel, it is divided into low-temperature stainless steel, non-magnetic stainless steel, free cutting stainless steel, superplastic stainless steel, etc. The commonly used classification method is based on the characteristics of steel structure and chemical composition, as well as the combination of the two. It is generally divided into martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, duplex stainless steel and precipitation hardening stainless steel, or into chromium stainless steel and nickel stainless steel.
Stainless steel is generally used in corrosion-resistant environments, as well as medical devices and daily necessities.
According to the main chemical composition, it is divided into chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel; It can also be divided into acid resistant stainless steel and heat-resistant stainless steel according to their performance characteristics; It is usually classified by metallographic structure. According to the metallographic structure, it is classified into: ferritic (f) stainless steel, martensitic (m) stainless steel, austenitic (a) stainless steel, AUSTENITIC FERRITIC (A-F) duplex stainless steel, austenitic martensitic (A-M) duplex stainless steel and precipitation hardening (PH) stainless steel.
Ferritic type
Its internal microstructure is ferrite, and its chromium content is in the range of 11.5% – 32.0%. With the increase of chromium content, its acid resistance is also improved. Adding molybdenum (MO) can improve its acid corrosion resistance and stress corrosion resistance. The national standard grades of this kind of stainless steel are 00Cr12, 1Cr17, 00cr17mo, 00cr30mo2, etc.
Martensitic type
Its microstructure is martensite. The mass fraction of chromium in this kind of steel is 11.5% – 18.0%, but the maximum mass fraction of carbon can reach 0.6%. The increase of carbon content improves the strength and hardness of steel. A small amount of nickel added to this kind of steel can promote the formation of martensite and improve its corrosion resistance at the same time. This kind of steel has poor weldability. Steel plates listed in national standards include 1Cr13, 2 Cr13, 3 Cr13, 1 Cr17Ni2, etc.
Austenite type
Its microstructure is austenite. It is a stainless steel with austenite structure formed by adding appropriate nickel (the mass fraction of nickel is 8%~25%) to high chromium stainless steel. Austenitic stainless steel is based on cr18ni19 iron-based alloy. On this basis, with different applications, it has developed into chromium nickel austenitic stainless steel series as shown in Figure 1-2.
Austenitic stainless steel is generally a kind of corrosion-resistant steel, which is the most widely used steel. Among them, 18-8 stainless steel is the most representative. It has better mechanical properties and is convenient for machining, stamping and welding. It has excellent corrosion resistance and heat resistance in oxidizing environment. However, it is particularly sensitive to the medium containing chloride ions (cl-) in the solution and is prone to stress corrosion. 18-8 stainless steel is divided into three grades according to the carbon content in its chemical composition: general carbon content (WC ≤ 0.15%), low carbon grade (WC ≤ 0.08%) and ultra-low carbon grade (WC ≤ 0.03%). For example, 1Cr18Ni9Ti, 0Cr18Ni9 and 00cr17ni14m02 steel plates in China’s national standards belong to the above three grades. Many countries in the world feel the shortage of nickel reserves. In order to save nickel, manganese and nitrogen were used to replace some nickel in 18-8 stainless steel as early as the 1940s and 1950s. The grades of steel plates developed and listed in national standards include 1Cr17Mn6Ni5N and 0Cr19Ni9N.
