Stainless steel can be divided into different types according to its microstructure and composition, and each type of stainless steel has different performance and application. This article will focus on five common types of stainless steel: austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel and precipitation hardening stainless steel.
1. Austenitic Stainless Steel
Austenitic stainless steel is a type of stainless steel characterized by an austenitic crystal structure. The main alloying elements of austenitic stainless steel are chromium (Cr) and nickel (Ni), of which chromium is usually above 18% and nickel is generally above 8%. Due to its high nickel content, austenitic stainless steel usually has good corrosion resistance, ductility and low-temperature toughness.
The crystal structure of austenitic stainless steel is face-centered cubic (FCC), which gives it high plasticity and ductility, enabling it to maintain good mechanical properties under extreme conditions.
Classification Of Austenitic Stainless Steel：
Austenitic stainless steel can be divided into the following types according to its chemical composition and performance characteristics:
304 stainless steel (1.4301): an alloy of 18% chromium and 8% nickel, with good comprehensive performance, suitable for various mildly corrosive environments.
316 stainless steel (1.4401): 2%-3% molybdenum is added to 304, which significantly improves the ability to resist chloride corrosion and is suitable for more corrosive places such as marine environments and chemical equipment.
321 stainless steel (1.4541): titanium is added, which has better resistance to intergranular corrosion and is often used in high-temperature equipment.
904L stainless steel (1.4539): contains higher alloying elements such as copper, providing stronger corrosion resistance, and is often used in seawater cooling systems, acidic gas treatment and other environments.
Characteristics Of Austenitic Stainless Steel:
- Strong corrosion resistance: Austenitic stainless steel has good corrosion resistance to most acidic and alkaline environments, especially strong corrosion resistance to chlorides.
- Good processability: Due to the high ductility of the austenitic structure, austenitic stainless steel is very suitable for processing processes such as stamping, drawing, and welding.
- Good low-temperature toughness: Austenitic stainless steel can still maintain good toughness in low-temperature environments and is suitable for use in low-temperature equipment.
- High heat treatment difficulty: Although austenitic stainless steel has excellent performance under normal conditions, it is difficult to heat treat, especially at high temperatures, it is prone to intergranular corrosion.
Application Areas Of Austenitic Stainless Steel:
- Food and pharmaceutical industries: 304 and 316 stainless steel are widely used in food processing equipment, pharmaceutical equipment, and drinking water treatment facilities.
- Chemical and petrochemical industries: Corrosion resistance makes it suitable for chemical containers, reactors, pipelines and other equipment.
- Building decoration and home appliance industries: Austenitic stainless steel has a beautiful appearance and corrosion resistance, and is often used in building exterior walls, bridges and various home appliance parts.
- Medical devices: Due to its excellent biocompatibility, austenitic stainless steel is widely used in surgical instruments, artificial joints, etc.
2.Ferritic Stainless Steel
Ferritic stainless steel is a type of stainless steel with a ferrite crystal structure. Its main alloying element is chromium (Cr), the chromium content is usually between 10.5% and 30%, and the nickel content is low (usually less than 1%). Ferritic stainless steel has a lower price and better oxidation resistance, and is particularly suitable for environments with high temperature and low corrosion resistance requirements.
Classification Of Ferritic Stainless Steel:
430 stainless steel (1.4016): The chromium content is about 17%, with good corrosion resistance and oxidation resistance, and is widely used in kitchen equipment, automobile exhaust systems, etc.
446 stainless steel (1.4762): It has a higher chromium content (about 24% to 27%), so it has better high temperature resistance and is often used in boilers, stoves, rocket engines, etc.
439 stainless steel (1.4510): Contains 16%-18% chromium, mainly used in automobiles, boilers and heat exchangers, with good corrosion resistance and weldability.
Characteristics Of Ferritic Stainless Steel
- Strong high temperature resistance: Ferritic stainless steel has strong oxidation resistance in high temperature environments, and is particularly suitable for high temperature working environments.
- Good corrosion resistance: Ferritic stainless steel has good corrosion resistance to general acids, alkalis, and oxidizing substances, especially at high temperatures.
- Poor weldability: Ferritic stainless steel is prone to cracks during welding, so it has high requirements for welding technology.
- Poor ductility: Compared with austenitic stainless steel, ferritic stainless steel has poor ductility and is not suitable for complex stamping and stretching processes.
Application Areas Of Ferritic Stainless Steel
- Automotive industry: widely used in automobile exhaust pipes, automobile parts, etc.
- Kitchen equipment: such as sinks, stoves, tableware, etc.
- Boilers and heat exchangers: suitable for high temperature environments, such as boiler linings, heat exchangers, etc.
- Architectural decoration: used for high temperature resistant decorative applications, such as roofs, exterior walls, etc.
3.Martensitic Stainless Steel
Martensitic stainless steel is a type of stainless steel with martensitic crystal structure as the main microstructure. Its alloy composition usually contains 12% to 18% chromium and a lower amount of nickel. Due to its high hardness and strength, martensitic stainless steel is often used in high-strength and wear-resistant applications, but its corrosion resistance is poor.
Classification Of Martensitic Stainless Steel:
410 stainless steel (1.4006): Contains 12%-14% chromium and a higher carbon content, with good wear resistance and moderate corrosion resistance. Commonly used in the manufacture of knives, mechanical parts, etc.
420 stainless steel (1.4021): Contains more carbon than 410 stainless steel, has higher hardness and wear resistance, and is suitable for knives, surgical instruments, etc.
440C stainless steel (1.4125): Contains up to 1.2% carbon, has very high hardness and wear resistance, and is suitable for the manufacture of high-hardness tools and bearings.
Characteristics Of Martensitic Stainless Steel:
- High strength and hardness: Martensitic stainless steel can obtain extremely high hardness and strength after heat treatment, which is suitable for applications with wear resistance and high strength requirements.
- Poor corrosion resistance: Compared with austenitic and ferritic stainless steels, martensitic stainless steels have poor corrosion resistance, especially in humid or corrosive environments.
- Low ductility: Due to its high hardness, martensitic stainless steels have poor ductility and are difficult to cold work.
Application Areas Of Martensitic Stainless Steels
- Knives and cutting tools: Martensitic stainless steels are widely used in knives, scalpels, scissors, scrapers and other tools that require sharp edges.
- Bearings and mechanical parts: Martensitic stainless steels are suitable for mechanical parts such as bearings and gears that require high strength and wear resistance.
- Medical equipment: such as surgical instruments, dental instruments, etc.
- Pump bodies and valves: Used in pump bodies, valves and other parts that require high pressure resistance and wear resistance in industries such as petrochemicals and nuclear power plants.
4.Duplex Stainless Steel
Duplex stainless steel is a type of stainless steel with a dual crystal structure of austenite and ferrite. Its microstructure is usually composed of 50% austenite phase and 50% ferrite phase. Duplex stainless steel combines the advantages of two phases, and can maintain good corrosion resistance and high crack resistance while ensuring high strength.
Classification Of Duplex Stainless Steel:
2205 duplex stainless steel (1.4462): It has 22% chromium and 5% nickel, and nitrogen is added. It has very good corrosion resistance and resistance to stress corrosion cracking. It is often used in marine, petroleum and chemical engineering.
2507 duplex stainless steel (1.4410): It contains higher chromium (25%) and nickel (7%), and also contains a higher amount of molybdenum. It has stronger corrosion resistance and is suitable for extreme corrosive environments, such as marine engineering, oil and gas industry, etc.
Characteristics Of Duplex Stainless Steel:
- Excellent corrosion resistance: The corrosion resistance of duplex stainless steel is better than that of conventional ferritic stainless steel and close to that of austenitic stainless steel, especially in chloride corrosion and acidic environments.
- High strength and high pressure resistance: Due to its unique structure, duplex stainless steel combines the advantages of austenite and ferrite, and its strength is much higher than that of single austenitic stainless steel or ferritic stainless steel, making it suitable for use in environments with high pressure and high temperature.
- Good crack resistance and stress corrosion cracking resistance: Compared with austenitic stainless steel, duplex stainless steel has better resistance to stress corrosion cracking (SCC), so it is suitable for use in harsh industrial environments.
- Excellent processability and weldability: The processability and weldability of duplex stainless steel are relatively good, but still slightly inferior to austenitic stainless steel
Application Areas Of Duplex Stainless Steel
- Marine engineering: Applied in offshore platforms, submarine pipelines, ship structures and other fields.
- Oil and gas: Duplex stainless steel is widely used in corrosion-resistant pipelines, storage tanks, heat exchangers and other equipment.
- Power industry: Especially in equipment in nuclear power plants and thermal power plants, duplex stainless steel is often used in steam pipes, boiler components and other parts.
5.Precipitation Hardening Stainless Steel
Precipitation hardening stainless steel is a special stainless steel that can significantly improve its strength and hardness through the precipitation hardening mechanism in heat treatment. This type of steel usually contains elements such as chromium, nickel, copper, and aluminum. By controlling the heat treatment temperature and time, the second phase particles dissolved in the matrix in the alloy are precipitated, thereby greatly improving the mechanical properties of the material. Precipitation hardening stainless steel not only has high strength and hardness, but also maintains relatively good corrosion resistance.
Classification Of Precipitation Hardening Stainless Steel
17-4 PH (630 stainless steel): Contains elements such as chromium, nickel, and copper, has high strength and good corrosion resistance, and is mainly used in aerospace, nuclear energy, chemical and other industries.
15-5 PH: Contains a small amount of niobium and molybdenum, has good strength and corrosion resistance, and is mainly used in chemical equipment, aerospace, etc.
13-8 Mo: Adds molybdenum and a certain amount of niobium, has high strength and fatigue resistance, and is often used in high-pressure vessels, pneumatic equipment and other fields.
PH 800: With high strength and high toughness, it is widely used in the manufacture of high-temperature and high-pressure equipment.
Characteristics Of Precipitation Hardening Stainless Steel:
- Extremely high strength and hardness: Through the precipitation hardening process, precipitation hardening stainless steel can significantly improve the strength and hardness of the material without sacrificing corrosion resistance.
- Good corrosion resistance: Precipitation hardening stainless steel has relatively good corrosion resistance, especially in neutral, weakly acidic and weakly alkaline environments.
- Good fatigue resistance and wear resistance: Due to its excellent hardness and strength, precipitation hardening stainless steel has good fatigue resistance and wear resistance.
- Strong adjustability: Through different heat treatment processes, the mechanical properties of precipitation hardening stainless steel can be adjusted as needed to meet the needs of different applications.
Application Areas Of Precipitation Hardening Stainless Steel
- Aerospace: Precipitation hardening stainless steel is used to manufacture high-strength and high-corrosion-resistant parts such as aircraft engine parts, turbine blades, nozzles, and fuselages.
- Nuclear energy industry: In high-temperature and high-radiation environments such as nuclear reactors and nuclear power plants, precipitation hardening stainless steel can provide higher strength and corrosion resistance.
- Oil and gas: Suitable for the manufacture of high-pressure and high-strength equipment such as oil drilling platforms, high-pressure oil and gas pipelines, and pump bodies.
- High-pressure vessels and chemical equipment: Precipitation hardening stainless steel is mainly used in chemical reactors, storage tanks, reactors and other equipment.
From austenitic stainless steel, ferritic stainless steel, martensitic stainless steel to duplex stainless steel and precipitation hardening stainless steel, each type of stainless steel has its own unique chemical composition, microstructure and performance characteristics to adapt to different working environments and application requirements. It is critical to choose the right type of stainless steel according to specific usage requirements.
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