2-1. Ferritic steels Chromium-free stainless steels with more than 14% chromium, any carbonaceous chromium-containing stainless steels with 27% chromium, and the addition of molybdenum, titanium, tantalum, silicon, aluminum, The tungsten, vanadium and other elements of stainless steel, the chemical composition of the ferrite element is dominant, the matrix is ​​ferritin. The microstructure of the steel in the quenched (solid solution) state is ferrite, and a small amount of carbides and intermetallic compounds can be seen in the annealed and aged steel.
Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and the like belong to this class. Ferritic stainless steels have high corrosion resistance and oxidation resistance because of their high chromium content, but they have poor mechanical properties and process properties. They are mostly used in acid-resistant structures that are not stressed and used as anti-oxidation steels. 2-2. Ferritic-martensitic steels are ya (or δ) two-phase state at high temperatures, yM transition occurs during rapid cooling, ferrite is still retained, and martensite and ferrite are present at room temperature. With different composition and heating temperatures, the amount of ferrite in the structure can vary from a few percent to several tens of percent. 0Crl3 steel, lCrl3 steel, 2Cr13 steel with lower chrome upper limit and lower carbon limit, Cr17Ni2 steel, Cr17wn4 steel, and many modified 12% chrome hot strength steels developed on the basis of ICrl3 steel (this kind of steel is also called heat-resistant stainless steel. Many of the steel grades, such as Cr11MoV, Cr12WMoV, Crl2W4MoV, 18Crl2WMoVNb, etc., are dry. Ferritic-martensitic steels can partially undergo quench hardening, so higher mechanical properties can be obtained. However, their mechanical properties and process properties are largely influenced by the content and distribution of ferrite in the tissue. The amount of chromium contained in this type of steel is 12 to 14% and 15 to 18% in two series. The former has the ability to resist the atmosphere and weak corrosive media, and has good shock absorption and a small coefficient of linear expansion; the latter's corrosion resistance is comparable to that of ferritic acid-resistant steel with the same amount of chromium, but to some extent It also retains some of the disadvantages of high-chromium ferritic steels. 2-3. Martensitic steels of this type are in the y-phase zone at normal quenching temperatures, but their y-phase is only stable at high temperatures, and M-points are generally around 3,00°C, so they transform to martensite upon cooling. Such steels include 2Cr13, 2Cr13Ni2, 3Cr13 and partially modified 12% chromium hot strength steels, such as 13Cr14NiWVBA, Cr11Ni2MoWVB steel and so on. Martensitic stainless steel mechanical properties, corrosion resistance, process performance and physical properties, and chromium containing 12 to 14% ferritic - martensitic stainless steel similar. Since there is no free ferrite in the structure, the mechanical properties are higher than those of the above steels, but the heat sensitivity during heat treatment is low. 2-4. The martensite-carbide steel Fe-C alloy has a carbon dissociation point of 0.83%. In stainless steel, chromium shifts S to the left, containing 12% chromium and more than 0.4% carbon (Figure 11-3). , as well as steels containing 18% chromium and more than 0.3% carbon (Tu Bu) 3) are all hypereutectoid steels. Such steels are heated at normal quenching temperatures and secondary carbides cannot completely dissolve in austenite, so the quenched structure is composed of martensite and carbides. There are not many stainless steel grades belonging to this category, but some stainless steels with relatively high carbon content, such as 4Crl3, 9Cr18, 9Crl8MoV, 9Crl7MoVCo steel, etc., 3Crl3 steel with a limited carbon content quenched at a lower temperature may also appear Such an organization. Due to the high carbon content, although the above 9Cr18 and other three steels contain more chromium, their corrosion resistance is only comparable to stainless steel containing 12 to 14% of niobium. The main purpose of this type of steel is to require highly hard and wear-resistant parts such as cutting tools, bearings, springs and medical equipment. 2-5. Steels such as austenitic steels contain a large amount of elements for expanding the y-zone and austenite stabilizing. They are all y-phase at high temperatures. Since the Ms points are below room temperature when cooled, they have an austenite structure at room temperature. Chromium-nickel stainless steels such as 18-8, 18-12, 25-20, and 20-25Mo, and low nickel stainless steels such as Cr18Mnl0Ni5, Cr13Ni4Mn9, Cr17Ni4Mn9N, and Cr14Ni3Mnl4Ti steel in which manganese is substituted for manganese and added nitrogen are all included in this category. Austenitic stainless steels have many advantages that have been described previously. Although the mechanical properties are relatively low, and ferritic stainless steels cannot be heat-treated, they can be hardened by cold working to increase their strength. The disadvantage of this kind of steel is that it is sensitive to intergranular corrosion and stress corrosion, and it needs to be eliminated by appropriate alloy additives and technological measures. 2-6. The effect of austenite-ferritic steels on the expansion of the y-zone and the stabilization of austenite elements is not sufficient to give the steel a pure austenitic structure at normal or very high temperatures. Therefore, austenite- In the ferrite multiphase state, the ferrite content can also be varied within a wide range depending on the composition and the heating temperature. There are many stainless steels belonging to this category, such as low-carbon 18-8 chromium-nickel steel, 18-8 chromium-nickel steel with titanium, niobium, and molybdenum, and ferrite, especially in the structure of cast steel. Chromium-manganese stainless steels (such as Cr17Mnll) with chromium greater than 14 to 15% and carbon below 0.2%, and most chromium manganese nitrogen stainless steels currently studied and applied. Compared with pure austenitic stainless steels, these steels have many advantages such as high yield strength, high resistance to intergranular corrosion, low sensitivity to stress corrosion, low tendency to generate hot cracks during welding, and good casting fluidity. and many more. The disadvantages are that the pressure processing performance is poor, the point corrosion tendency is large, the c-phase brittleness is easy to occur, and the weak magnetic properties are exhibited under the strong magnetic field. All these advantages and disadvantages originate from the ferrite in the tissue. 2-7. The Ms point of such steels as those of austenitic martensite-martensite steels is lower than room temperature. After solid solution treatment, they are austenite and easy to form and weld. Martensitic transformation can usually be made by two processes. First, after the solution treatment is heated at 700-800 degrees, austenite is transformed into a stable state due to the precipitation of chromium carbide, Ms point is increased to above room temperature, and converted to martensite upon cooling; secondly, it is directly after solution treatment. Cools to between Ms and Mf, transforming austenite to martensite. The latter method can obtain higher corrosion resistance, but the interval between solution treatment and cryogenic treatment should not be too long, otherwise the deep cold strengthening effect will be reduced due to the austenite aging stability. After the above treatment, the steel is further aged by 400-500 degrees, so that the precipitated intermetallic compound is further strengthened. Typical steels of this type include 17Cr-7Ni-A1, 15Cr-9Ni-A1, 17Cr-5Ni-Mo, 15Cr-8Ni-Mo-A1, and so on. This kind of steel is also called austenitic-martensite aging stainless steel, and since the steel actually has a different amount of ferrite in addition to austenite and martensite, it is also called semi-autumn. Precipitation hardening stainless steel. This kind of steel is a new type of stainless steel developed and applied in the late 1950s. Their general characteristics are high strength (C up to 100 to 150) and good thermal strength, but due to the low chromium content and the precipitation of chromium carbide during heat treatment. Therefore, the corrosion resistance is lower than standard austenitic stainless steel. It can also be said that the high strength of this kind of steel is obtained at the expense of a part of corrosion resistance and other properties (such as non-magnetic). At present, these steels are mainly used in aviation industry and rocket ** production, general machinery manufacturing Applications are not yet universal, and there is also a series of ultra high strength steels that are included in the classification.
Corrosion resistance of stainless steel Type and definition of corrosion
A stainless steel can have good corrosion resistance in many media, but in some other media, corrosion may occur due to low chemical stability. Therefore, a stainless steel cannot resist corrosion on all media. In many industrial applications, stainless steel provides satisfactory corrosion resistance. According to the experience of use, in addition to mechanical failure, the corrosion of stainless steel is mainly manifested in: a serious form of corrosion of stainless steel is local corrosion (ie, stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue, and crevice corrosion) . The failure caused by these localized corrosion accounts for almost half of the failure cases. In fact, many failures can be avoided through reasonable selection. Metal corrosion, according to the mechanism can be divided into special corrosion, chemical corrosion and electrochemical corrosion three. Most of the metal corrosion in actual life and engineering practice belongs to electrochemical corrosion. Stress Corrosion Cracking (SCC): This is a general term used to refer to alloys that are exposed to stress due to the expansion of the cracks in corrosive environments. Stress corrosion cracking has a brittle fracture morphology, but it can also occur in tough materials. The prerequisite for stress corrosion cracking is the presence of tensile stress (whether residual or applied stress, or both) and the presence of specific corrosive media. The formation and expansion of the pattern are approximately perpendicular to the tensile stress direction. The stress value that causes stress corrosion cracking is much lower than the stress value required for the material to break when no corrosive medium is present. Microscopically, a crack that passes through a grain is called a transgranular crack, and a crack that spreads along a grain boundary is called an intergranular crack. When stress corrosion cracking expands to a depth (here, the load-bearing material section When the stress reaches its fracture stress in air, the material breaks down as normal cracks (in ductile materials, usually through polymerization of microscopic defects). Therefore, the section of the part that fails due to stress corrosion cracking will contain characteristic areas of stress corrosion cracking and "dendrite" areas associated with micro-defective polymerization. Point corrosion: Point corrosion refers to the fact that most of the surface of the metal material is not corroded or corroded to a small extent, but localized corrosion is highly dispersed. The size of the common corrosion point is less than 1.00mm, and the depth is often larger than the surface pore size, and lighter ones have shallow pits. Seriously even perforations are formed. Intergranular corrosion: The grain boundary is a boundary between dislocations of crystal grains with different crystallographic orientations. Therefore, they are favorable for the segregation of various solute elements in the steel or precipitation of metal compounds (such as carbides and δ phases). District city. Therefore, in some corrosive media, it is not surprising that the grain boundaries may be etched first. This type of corrosion is known as intergranular corrosion, and most metals and alloys may exhibit intergranular corrosion in certain corrosive media. Intergranular corrosion is a selective corrosion damage. It differs from general selective corrosion in that the locality of corrosion is microscopic and not macroscopically local. Crevice corrosion refers to the occurrence of spot-like or ulcer-like macroscopic pits at the crevices of metal components, which is a form of localized corrosion that may occur in the gaps in solution stagnant or in the surface of the shield. Such gaps may be formed at the metal to metal or metal and non-metal joints, for example, where rivets, bolts, gaskets, valve seats, loose surface deposits, and marine organisms are in contact with the candle. Total corrosion: This is a term used to describe the phenomenon of corrosion that occurs across the surface of the alloy in a relatively homogenous manner. When total corrosion occurs, the village material gradually thins due to corrosion, and even material corrosion fails. Stainless steel may exhibit general corrosion in strong acids and alkalis. The problem of failure caused by extensive corrosion is not a cause for concern, since the corrosion can usually be predicted by simple immersion tests or by referring to literature on corrosion. Uniform corrosion: It refers to the phenomenon that all metal surfaces exposed to corrosive media are corroded. According to different conditions of use, different indicators are required for corrosion resistance. Generally, they can be divided into two categories: 1. Stainless steel refers to steel that is resistant to corrosion in the atmosphere and in weakly corrosive media. Corrosion rates of less than 0.01 mm/year are considered “completely corrosion resistantâ€; corrosion rates of less than 0.1 mm/year are considered “corrosion resistantâ€. 2. Corrosion resistant steels are steels that are resistant to corrosion in a variety of aggressive media. 2. Corrosion Resistance of Various Stainless Steels 304 is a versatile stainless steel that is widely used to make equipment and components that require good overall performance (corrosion resistance and formability). 301 stainless steel shows a remarkable work hardening phenomenon when it is deformed, and is used in various occasions where higher strength is required. 302 stainless steel is essentially a variant of 304 stainless steel with a higher carbon content, which can be obtained with higher strength by cold rolling. 302B is a kind of stainless steel with high silicon content. It has high resistance to high temperature oxidation. The 303 and 303Se are free-cutting stainless steels containing * and selenium, respectively, and are used in applications requiring high cutting power and high lightness. 303Se stainless steel is also used to make parts that require hot boring because the stainless steel has good hot workability under these conditions. 304L is a variant of 304 stainless steel with a low carbon content and is used where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, and the precipitation of carbides may result in intergranular corrosion of the stainless steel in some environments (weld erosion). 304N is a nitrogen-containing stainless steel that is added to improve the strength of the steel. 305 and 384 stainless steels contain high nickel, which has a low work-hardening rate and are suitable for various occasions requiring high cold formability. 308 stainless steel is used to make the electrode. 309, 310, 314 and 330 stainless steels have relatively high contents of nickel and chromium in order to improve the oxidation resistance and creep strength of steel at high temperatures. The 30S5 and 310S are variants of the 309 and 310 stainless steels. The only difference is that the carbon content is low, in order to minimize the precipitation of carbides near the weld. 330 stainless steel has a particularly high resistance to carburization and thermal shock resistance. Type 316 and 317 stainless steels contain aluminum and therefore have much greater resistance to pitting corrosion in marine and chemical industry environments than 304 stainless steels. Among them, Type 316 stainless steel consists of variants including low-carbon stainless steel 316L, nitrogen-containing high-strength stainless steel 316N and high-combined free-cutting stainless steel 316F. 321, 347, and 348 are stainless steels stabilized with titanium, niobium, tantalum, and niobium, respectively, and are suitable for use as welded components at high temperatures. 348 is a stainless steel suitable for the nuclear power industry. It has certain restrictions on the amount of helium and drill.
Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and the like belong to this class. Ferritic stainless steels have high corrosion resistance and oxidation resistance because of their high chromium content, but they have poor mechanical properties and process properties. They are mostly used in acid-resistant structures that are not stressed and used as anti-oxidation steels. 2-2. Ferritic-martensitic steels are ya (or δ) two-phase state at high temperatures, yM transition occurs during rapid cooling, ferrite is still retained, and martensite and ferrite are present at room temperature. With different composition and heating temperatures, the amount of ferrite in the structure can vary from a few percent to several tens of percent. 0Crl3 steel, lCrl3 steel, 2Cr13 steel with lower chrome upper limit and lower carbon limit, Cr17Ni2 steel, Cr17wn4 steel, and many modified 12% chrome hot strength steels developed on the basis of ICrl3 steel (this kind of steel is also called heat-resistant stainless steel. Many of the steel grades, such as Cr11MoV, Cr12WMoV, Crl2W4MoV, 18Crl2WMoVNb, etc., are dry. Ferritic-martensitic steels can partially undergo quench hardening, so higher mechanical properties can be obtained. However, their mechanical properties and process properties are largely influenced by the content and distribution of ferrite in the tissue. The amount of chromium contained in this type of steel is 12 to 14% and 15 to 18% in two series. The former has the ability to resist the atmosphere and weak corrosive media, and has good shock absorption and a small coefficient of linear expansion; the latter's corrosion resistance is comparable to that of ferritic acid-resistant steel with the same amount of chromium, but to some extent It also retains some of the disadvantages of high-chromium ferritic steels. 2-3. Martensitic steels of this type are in the y-phase zone at normal quenching temperatures, but their y-phase is only stable at high temperatures, and M-points are generally around 3,00°C, so they transform to martensite upon cooling. Such steels include 2Cr13, 2Cr13Ni2, 3Cr13 and partially modified 12% chromium hot strength steels, such as 13Cr14NiWVBA, Cr11Ni2MoWVB steel and so on. Martensitic stainless steel mechanical properties, corrosion resistance, process performance and physical properties, and chromium containing 12 to 14% ferritic - martensitic stainless steel similar. Since there is no free ferrite in the structure, the mechanical properties are higher than those of the above steels, but the heat sensitivity during heat treatment is low. 2-4. The martensite-carbide steel Fe-C alloy has a carbon dissociation point of 0.83%. In stainless steel, chromium shifts S to the left, containing 12% chromium and more than 0.4% carbon (Figure 11-3). , as well as steels containing 18% chromium and more than 0.3% carbon (Tu Bu) 3) are all hypereutectoid steels. Such steels are heated at normal quenching temperatures and secondary carbides cannot completely dissolve in austenite, so the quenched structure is composed of martensite and carbides. There are not many stainless steel grades belonging to this category, but some stainless steels with relatively high carbon content, such as 4Crl3, 9Cr18, 9Crl8MoV, 9Crl7MoVCo steel, etc., 3Crl3 steel with a limited carbon content quenched at a lower temperature may also appear Such an organization. Due to the high carbon content, although the above 9Cr18 and other three steels contain more chromium, their corrosion resistance is only comparable to stainless steel containing 12 to 14% of niobium. The main purpose of this type of steel is to require highly hard and wear-resistant parts such as cutting tools, bearings, springs and medical equipment. 2-5. Steels such as austenitic steels contain a large amount of elements for expanding the y-zone and austenite stabilizing. They are all y-phase at high temperatures. Since the Ms points are below room temperature when cooled, they have an austenite structure at room temperature. Chromium-nickel stainless steels such as 18-8, 18-12, 25-20, and 20-25Mo, and low nickel stainless steels such as Cr18Mnl0Ni5, Cr13Ni4Mn9, Cr17Ni4Mn9N, and Cr14Ni3Mnl4Ti steel in which manganese is substituted for manganese and added nitrogen are all included in this category. Austenitic stainless steels have many advantages that have been described previously. Although the mechanical properties are relatively low, and ferritic stainless steels cannot be heat-treated, they can be hardened by cold working to increase their strength. The disadvantage of this kind of steel is that it is sensitive to intergranular corrosion and stress corrosion, and it needs to be eliminated by appropriate alloy additives and technological measures. 2-6. The effect of austenite-ferritic steels on the expansion of the y-zone and the stabilization of austenite elements is not sufficient to give the steel a pure austenitic structure at normal or very high temperatures. Therefore, austenite- In the ferrite multiphase state, the ferrite content can also be varied within a wide range depending on the composition and the heating temperature. There are many stainless steels belonging to this category, such as low-carbon 18-8 chromium-nickel steel, 18-8 chromium-nickel steel with titanium, niobium, and molybdenum, and ferrite, especially in the structure of cast steel. Chromium-manganese stainless steels (such as Cr17Mnll) with chromium greater than 14 to 15% and carbon below 0.2%, and most chromium manganese nitrogen stainless steels currently studied and applied. Compared with pure austenitic stainless steels, these steels have many advantages such as high yield strength, high resistance to intergranular corrosion, low sensitivity to stress corrosion, low tendency to generate hot cracks during welding, and good casting fluidity. and many more. The disadvantages are that the pressure processing performance is poor, the point corrosion tendency is large, the c-phase brittleness is easy to occur, and the weak magnetic properties are exhibited under the strong magnetic field. All these advantages and disadvantages originate from the ferrite in the tissue. 2-7. The Ms point of such steels as those of austenitic martensite-martensite steels is lower than room temperature. After solid solution treatment, they are austenite and easy to form and weld. Martensitic transformation can usually be made by two processes. First, after the solution treatment is heated at 700-800 degrees, austenite is transformed into a stable state due to the precipitation of chromium carbide, Ms point is increased to above room temperature, and converted to martensite upon cooling; secondly, it is directly after solution treatment. Cools to between Ms and Mf, transforming austenite to martensite. The latter method can obtain higher corrosion resistance, but the interval between solution treatment and cryogenic treatment should not be too long, otherwise the deep cold strengthening effect will be reduced due to the austenite aging stability. After the above treatment, the steel is further aged by 400-500 degrees, so that the precipitated intermetallic compound is further strengthened. Typical steels of this type include 17Cr-7Ni-A1, 15Cr-9Ni-A1, 17Cr-5Ni-Mo, 15Cr-8Ni-Mo-A1, and so on. This kind of steel is also called austenitic-martensite aging stainless steel, and since the steel actually has a different amount of ferrite in addition to austenite and martensite, it is also called semi-autumn. Precipitation hardening stainless steel. This kind of steel is a new type of stainless steel developed and applied in the late 1950s. Their general characteristics are high strength (C up to 100 to 150) and good thermal strength, but due to the low chromium content and the precipitation of chromium carbide during heat treatment. Therefore, the corrosion resistance is lower than standard austenitic stainless steel. It can also be said that the high strength of this kind of steel is obtained at the expense of a part of corrosion resistance and other properties (such as non-magnetic). At present, these steels are mainly used in aviation industry and rocket ** production, general machinery manufacturing Applications are not yet universal, and there is also a series of ultra high strength steels that are included in the classification.
Corrosion resistance of stainless steel Type and definition of corrosion
A stainless steel can have good corrosion resistance in many media, but in some other media, corrosion may occur due to low chemical stability. Therefore, a stainless steel cannot resist corrosion on all media. In many industrial applications, stainless steel provides satisfactory corrosion resistance. According to the experience of use, in addition to mechanical failure, the corrosion of stainless steel is mainly manifested in: a serious form of corrosion of stainless steel is local corrosion (ie, stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue, and crevice corrosion) . The failure caused by these localized corrosion accounts for almost half of the failure cases. In fact, many failures can be avoided through reasonable selection. Metal corrosion, according to the mechanism can be divided into special corrosion, chemical corrosion and electrochemical corrosion three. Most of the metal corrosion in actual life and engineering practice belongs to electrochemical corrosion. Stress Corrosion Cracking (SCC): This is a general term used to refer to alloys that are exposed to stress due to the expansion of the cracks in corrosive environments. Stress corrosion cracking has a brittle fracture morphology, but it can also occur in tough materials. The prerequisite for stress corrosion cracking is the presence of tensile stress (whether residual or applied stress, or both) and the presence of specific corrosive media. The formation and expansion of the pattern are approximately perpendicular to the tensile stress direction. The stress value that causes stress corrosion cracking is much lower than the stress value required for the material to break when no corrosive medium is present. Microscopically, a crack that passes through a grain is called a transgranular crack, and a crack that spreads along a grain boundary is called an intergranular crack. When stress corrosion cracking expands to a depth (here, the load-bearing material section When the stress reaches its fracture stress in air, the material breaks down as normal cracks (in ductile materials, usually through polymerization of microscopic defects). Therefore, the section of the part that fails due to stress corrosion cracking will contain characteristic areas of stress corrosion cracking and "dendrite" areas associated with micro-defective polymerization. Point corrosion: Point corrosion refers to the fact that most of the surface of the metal material is not corroded or corroded to a small extent, but localized corrosion is highly dispersed. The size of the common corrosion point is less than 1.00mm, and the depth is often larger than the surface pore size, and lighter ones have shallow pits. Seriously even perforations are formed. Intergranular corrosion: The grain boundary is a boundary between dislocations of crystal grains with different crystallographic orientations. Therefore, they are favorable for the segregation of various solute elements in the steel or precipitation of metal compounds (such as carbides and δ phases). District city. Therefore, in some corrosive media, it is not surprising that the grain boundaries may be etched first. This type of corrosion is known as intergranular corrosion, and most metals and alloys may exhibit intergranular corrosion in certain corrosive media. Intergranular corrosion is a selective corrosion damage. It differs from general selective corrosion in that the locality of corrosion is microscopic and not macroscopically local. Crevice corrosion refers to the occurrence of spot-like or ulcer-like macroscopic pits at the crevices of metal components, which is a form of localized corrosion that may occur in the gaps in solution stagnant or in the surface of the shield. Such gaps may be formed at the metal to metal or metal and non-metal joints, for example, where rivets, bolts, gaskets, valve seats, loose surface deposits, and marine organisms are in contact with the candle. Total corrosion: This is a term used to describe the phenomenon of corrosion that occurs across the surface of the alloy in a relatively homogenous manner. When total corrosion occurs, the village material gradually thins due to corrosion, and even material corrosion fails. Stainless steel may exhibit general corrosion in strong acids and alkalis. The problem of failure caused by extensive corrosion is not a cause for concern, since the corrosion can usually be predicted by simple immersion tests or by referring to literature on corrosion. Uniform corrosion: It refers to the phenomenon that all metal surfaces exposed to corrosive media are corroded. According to different conditions of use, different indicators are required for corrosion resistance. Generally, they can be divided into two categories: 1. Stainless steel refers to steel that is resistant to corrosion in the atmosphere and in weakly corrosive media. Corrosion rates of less than 0.01 mm/year are considered “completely corrosion resistantâ€; corrosion rates of less than 0.1 mm/year are considered “corrosion resistantâ€. 2. Corrosion resistant steels are steels that are resistant to corrosion in a variety of aggressive media. 2. Corrosion Resistance of Various Stainless Steels 304 is a versatile stainless steel that is widely used to make equipment and components that require good overall performance (corrosion resistance and formability). 301 stainless steel shows a remarkable work hardening phenomenon when it is deformed, and is used in various occasions where higher strength is required. 302 stainless steel is essentially a variant of 304 stainless steel with a higher carbon content, which can be obtained with higher strength by cold rolling. 302B is a kind of stainless steel with high silicon content. It has high resistance to high temperature oxidation. The 303 and 303Se are free-cutting stainless steels containing * and selenium, respectively, and are used in applications requiring high cutting power and high lightness. 303Se stainless steel is also used to make parts that require hot boring because the stainless steel has good hot workability under these conditions. 304L is a variant of 304 stainless steel with a low carbon content and is used where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, and the precipitation of carbides may result in intergranular corrosion of the stainless steel in some environments (weld erosion). 304N is a nitrogen-containing stainless steel that is added to improve the strength of the steel. 305 and 384 stainless steels contain high nickel, which has a low work-hardening rate and are suitable for various occasions requiring high cold formability. 308 stainless steel is used to make the electrode. 309, 310, 314 and 330 stainless steels have relatively high contents of nickel and chromium in order to improve the oxidation resistance and creep strength of steel at high temperatures. The 30S5 and 310S are variants of the 309 and 310 stainless steels. The only difference is that the carbon content is low, in order to minimize the precipitation of carbides near the weld. 330 stainless steel has a particularly high resistance to carburization and thermal shock resistance. Type 316 and 317 stainless steels contain aluminum and therefore have much greater resistance to pitting corrosion in marine and chemical industry environments than 304 stainless steels. Among them, Type 316 stainless steel consists of variants including low-carbon stainless steel 316L, nitrogen-containing high-strength stainless steel 316N and high-combined free-cutting stainless steel 316F. 321, 347, and 348 are stainless steels stabilized with titanium, niobium, tantalum, and niobium, respectively, and are suitable for use as welded components at high temperatures. 348 is a stainless steel suitable for the nuclear power industry. It has certain restrictions on the amount of helium and drill.
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