Views: 7 Author: Site Editor Publish Time: 2025-05-30 Origin: Site
Stainless steel is an alloy steel with iron (Fe) as its base, enhanced by the addition of alloying elements such as chromium (Cr), nickel (Ni), and molybdenum (Mo) to improve its corrosion resistance and mechanical properties. Its key characteristic is the formation of a dense chromium oxide film (Cr₂O₃) on the surface, which protects it from rust and chemical corrosion.
Due to its unique corrosion resistance and high strength, stainless steel is widely used in modern industry. From the façades of skyscrapers to the internal structures of food processing equipment, its applications are broad and continuously expanding. In addition to its excellent physical and chemical properties, stainless steel is also favored for its attractive appearance and long service life, making it a common choice in households, medical devices, and the chemical industry.
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Before selecting a stainless steel material, it is essential to clearly define the application requirements, including temperature, corrosive environment, mechanical load, hygiene standards, and more. These factors directly influence the choice of alloy type and material properties.
Temperature
High-temperature applications require stainless steels with excellent heat resistance, such as austenitic stainless steels, while low-temperature environments may necessitate materials with good toughness at cryogenic temperatures. Elevated temperatures can accelerate corrosion and may lead to oxidation, creep, and other degradation, while low temperatures can result in brittleness. Frequent temperature fluctuations can also cause thermal fatigue.
Corrosive Environment
Corrosive media place high demands on the corrosion resistance of stainless steel.
- Chloride Content: Chloride ions are a major cause of pitting and crevice corrosion in stainless steels, commonly found in seawater, saline solutions, and chlorine-based disinfectants.
- Oxidizing or Reducing Conditions: The redox potential of the medium plays a role in determining material performance and degradation mechanisms.
Mechanical Load
The mechanical load of the application determines the required hardness, strength, and other mechanical properties of the stainless steel. These can be adjusted through alloy composition and heat treatment.
- Vibration or Impact: Materials should have sufficient fatigue strength and impact toughness under dynamic loads.
- Stress Corrosion Cracking (SCC) Risk: In specific environments (e.g., high-temperature water containing chlorides), certain stainless steels are susceptible to SCC under tensile stress.
Hygiene Requirements
In industries such as medical and food processing, stainless steels with high hygienic standards are required, such as AISI 316L. These grades ensure that the material does not contaminate products and complies with stringent cleanliness standards.
1. Austenitic Stainless Steel
Austenitic stainless steels are the most common type, characterized by high levels of nickel and chromium. They often contain additional elements such as molybdenum and manganese to enhance performance.
Characteristics:Excellent corrosion resistance, toughness, and weldability; non-magnetic.
Applications:Widely used in food processing, chemical equipment, medical devices, and architectural decoration.
2. Martensitic Stainless Steel
Martensitic stainless steels contain higher carbon content and can achieve superior hardness and strength through heat treatment.
Characteristics: High hardness and wear resistance; magnetic; relatively lower corrosion resistance.
Applications: Commonly used in knives, valves, bearings, turbine blades, and other applications requiring high strength and wear resistance.
3. Ferritic Stainless Steel
Ferritic stainless steels have high chromium content but low nickel content, often alloyed with molybdenum to enhance corrosion resistance.
Characteristics: Good corrosion and oxidation resistance; strong magnetism; lower toughness and weldability.
Applications: Frequently used in automotive exhaust systems, household appliances, and architectural applications.
3. Duplex Stainless Steel
Combining the advantages of both austenitic and ferritic stainless steels, duplex grades offer superior strength and corrosion resistance, especially stress corrosion cracking resistance. Their microstructure consists of approximately equal parts austenite and ferrite, with high levels of molybdenum (Mo) and nitrogen (N).
Characteristics:High strength, excellent corrosion resistance, outstanding resistance to stress corrosion cracking.
Applications:Ideal for harsh environments such as marine engineering, petrochemical plants, and wastewater treatment systems.
4. Precipitation-Hardening Stainless Steel
Precipitation-hardening stainless steels achieve high strength and hardness through the addition of elements like copper and aluminum, followed by heat treatment that forms fine precipitates.
Characteristics: Extremely high strength, good corrosion resistance, but relatively difficult to machine.
Applications: Commonly used in high-tech industries such as aerospace, nuclear power, and advanced machinery.
Designations | ASTM | EN | C, ≤ | Mn, ≤ | P, ≤ | S, ≤ | Si, ≤ | Cr | Ni | Mo | N, ≤ | Other Elements |
≤, UOS | ||||||||||||
Austenitic stainless steel | 304 | 1.4301 | 0.08 | 2 | 0.05 | 0.03 | 1 | 18.0-20.0 | 8.0-11.0 | – | – | – |
304L | 1.4307 | 0.035 | 2 | 0.045 | 0.03 | 1 | 18.0-20.0 | 8.0-13.0 | – | – | – | |
316 | 1.4401 | 0.08 | 2 | 0.045 | 0.03 | 1 | 16.0-18.0 | 11.0-14.0 | 2.00-3.00 | – | – | |
316L | 1.4404 | 0.035 | 2 | 0.045 | 0.03 | 1 | 16.0-18.0 | 10.0-14.0 | 2.00-3.00 | – | – | |
904L | 1.4539 | 0.02 | 2 | 0.045 | 0.04 | 1 | 19.0-23.0 | 23.0-28.0 | 4.00-5.00 | 0.1 | Cu 1.00-2.00 | |
Ferritic Stainless Steel | 409 | 1.4512 | 0.03 | 1 | 0.04 | 0.015 | 1 | 10.50-12.50 | – | 6 x (C+N) to 0.65 | – | |
430 | 1.4016 | 0.12 | 1 | 0.04 | 0.03 | 1 | 16.0-18.0 | – | – | – | – | |
444 | 1.4521 | 0.025 | 1 | 0.04 | 0.03 | 1 | 17.5-19.5 | 1 | 1.75-2.50 | 0.035 | Ti+Cb 0.20+4 × (C+N)-0.80 | |
Martensitic stainless steels | 410 | 1.4006 | 0.08-0.15 | 1 | 0.04 | 0.03 | 1 | 11.5-13.5 | – | – | – | – |
420 | 1.4021 | 0.15, ≥ | 1 | 0.04 | 0.03 | 1 | 12.0-14.0 | – | – | – | – | |
440C | 1.4125 | 0.95-1.20 | 1 | 0.04 | 0.03 | 1 | 16.0-18.0 | – | ≤0.75 | – | – | |
Duplex stainless steels | 2205 | 1.4462 | 0.03 | 2 | 0.03 | 0.02 | 1 | 22.0-23.0 | 4.5-6.5 | 3.0-3.5 | 0.14-0.20 | – |
2507 | 1.4410 | 0.03 | 1.2 | 0.035 | 0.02 | 0.8 | 24.0-26.0 | 6.0-8.0 | 3.0-5.0 | 0.24-0.32 | – | |
PH | 15-5 PH / 631 | 1.4568 | 0.07 | 1 | 0.04 | 0.03 | 1 | 14.0-15.5 | 3.5-5.5 | – | – | 2.5-4.5 Cu; 0.15-0.45 Nb |
17-4 PH / 630 | 1.4542 | 0.07 | 1 | 0.04 | 0.03 | 1 | 15.5-17.5 | 3.0-5.0 | – | – | 3.0-5.0 Cu; 0.15-0.45 Nb |
304 vs. 316 stainless steel
The difference between 304 and 316 stainless steel lies in their composition and performance. 304 stainless steel has good toughness in non-extreme environments, low cost, and is suitable for the food industry. 316 stainless steel has 2% molybdenum added, which has better corrosion resistance and is particularly suitable for marine environments and high-temperature equipment.
304 and 316 food-grade stainless steels have their own advantages. When choosing, multiple factors such as the use environment, cost budget, and performance requirements should be fully considered to ensure that the selected material can meet actual needs and has a high cost-effectiveness.
Which is better, 304 or 410 stainless steel?
304 stainless steel contains more nickel (Ni) than 410, giving it superior corrosion resistance, oxidation resistance, and better stability. It's widely used in industrial applications, home decor, and everyday tableware.
In contrast, 410 stainless steel has a higher carbon content, which provides better strength and hardness, along with stronger magnetic properties. It's suitable for industrial tools like bolts, nuts, pump parts, and rulers.
In actual engineering, the selection of stainless steel structural materials depends on the equipment being designed and its use requirements. Material selection includes a comprehensive understanding of the availability, source, delivery time, product shape and size of the material. Simply put, the factors that should be considered when selecting materials for components of a device or equipment are: the compatibility of the material with the process fluid; the compatibility of the material with other component materials; the difficulty and complexity of manufacturing and processing using processing methods (such as machining, rolling, forging, hot and cold forming) and metal connection methods (such as welding, screw connection, etc.); the strength and ability to withstand operating temperatures, loads and pressures; cost; feasibility.
-Pipe and Tube (EN 10216-5, ASTM A213, ASTM A249, A312, A790,)
-Forged Fitting and Flange (ASTM A182 , ASTM A105,ASTM B564 )
-Butt Weld Fittings (ASTM A234, ASTM A403,ASTM A815)
-Round bar , Billet (ASTM A276, ASTM A479)
- Plate, Sheet, Strip(ASTM A240, EN 10028-7, A480)
-Bolting, Nuts（ASTM A193, A194, A320）
1. Why are my stainless welds rusting?
Stainless steel resists rusting because chromium reacts with oxygen to form a dense, protective chromium oxide layer on the surface. However, stainless steel welds can rust due to the precipitation of carbides and the heat generated during welding, which can lead to the formation of iron oxides on the weld surface.
Even a weld that appears perfect in its as-welded state may begin to rust within 24 hours, especially at the boundary of the heat-affected zone (HAZ), where issues like undercutting can occur.
Therefore, after welding, it is essential to grind, pickle, polish, or clean the welded area to allow a new chromium oxide layer to reform and restore corrosion resistance.
2. What are the 4 types of stainless steel?
There isn't a single "best" grade of stainless steel; the ideal choice depends on the specific application and environment. However, 304 stainless steel is generally considered the most common and versatile due to its balance of corrosion resistance, formability, and affordability.
