Stainless steel is all around you, used in countless industries and everyday items. But do you know the different grades it comes in? Each grade, from austenitic to martensitic, has unique properties for specific uses. In this article, you’ll discover the key grades, their features, and where they’re commonly used.
Principal Categories of Stainless Steel
The cardinal grades of stainless steel encompass austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel and precipitation-hardening stainless steel. every grade is possessed of inimitable virtues and finds specific applications.
Austenitic Stainless Steel Grades
Austenitic stainless steel is widely used in many fields for its excellent corrosion resistance and excellent processing properties. Nickel plays a key role in it, giving the material good toughness and corrosion resistance.
304 stainless steel
- Composition: Mainly contains 18-20% chromium (Cr) and 8-10% nickel (Ni), and the rest is mostly iron (Fe) and very small amounts of other impurity elements.
- Data example: In a typical 304 stainless steel tableware, the ratio of chromium to nickel is strictly controlled within the above range. The chromium element forms a dense chromium oxide protective film, which effectively blocks daily corrosive media such as water vapor and salt,the nickel element ensures the stability of the tableware structure, making it not easy to deform and damage.
- Characteristics: Good tolerance to most common acid, alkali, and salt corrosive agents.
- Advantages: In the food processing industry, such as the storage tanks of the milk production line, it can be in contact with dairy products for a long time without corrosion, ensuring food safety and hygiene.
316 stainless steel
- Composition: The chromium content is 16-18%, the nickel content is 10-14%, and it also contains 2-3% molybdenum (Mo).
- Data example: Taking the 316 stainless steel pipe in the marine environment as an example, the precise addition of molybdenum enables it to effectively cope with high concentrations of chloride in seawater. In seawater, chloride ions are extremely corrosive, but 316 stainless steel can prevent pitting and crevice corrosion with this combination of ingredients, ensuring long-term stable operation of the pipeline.
- Features: Due to the reinforcement of molybdenum, the corrosion resistance is significantly improved compared to 304 stainless steel, especially suitable for chloride-containing environments.
- Advantages: When transporting chloride-containing corrosive liquids in the chemical industry, the service life of its pipeline can be greatly extended compared to 304 stainless steel pipelines.
321 stainless steel
- Composition: Contains 17-19% chromium, 9-12% nickel and 0.2-0.5% titanium (Ti).
- Data example: In some high-temperature components of aerospace engines, chromium and nickel provide basic corrosion resistance and structural strength, and titanium combines with carbon to form stable carbides.
- Features: The addition of titanium makes it extremely stable in high-temperature environments and can prevent embrittlement caused by carbide precipitation.
- Advantages: In high-temperature and high-pressure chemical reactors, it can still maintain good strength and toughness during long-term high-temperature operation, avoiding safety hazards caused by changes in material structure.
310 stainless steel
- Composition: The chromium content is about 25%, and the nickel content is as high as 20%.
- Data example: In the heating elements of industrial high-temperature furnaces, high contents of chromium and nickel enable it to withstand long-term high-temperature baking at over 1000°C. Features: It has extremely strong high-temperature resistance and can work stably in ultra-high temperature environments for a long time.
- Advantages: It is often used in key components of industrial furnaces, such as furnace tubes. In the glass manufacturing industry, 310 stainless steel furnace tubes in high-temperature furnaces can withstand high-temperature erosion and thermal stress when glass raw materials are melted. Its excellent performance ensures the continuous and stable glass production process,in the heat treatment industry, the heating chamber components used in high-temperature annealing equipment for metal parts can provide a uniform and stable high-temperature environment for parts, ensuring the quality and effect of the heat treatment process.
309 stainless steel
- Composition: Contains 23-25% chromium and 12-15% nickel.
- Data example: In the burner components of large boilers, chromium elements show excellent antioxidant ability in the oxidizing environment of high-temperature combustion. After testing, after being exposed to 800°C and 10% oxygen for 500 hours, the thickness of the oxide film only increased by about 0.05 mm. The nickel element gives good high-temperature strength and creep resistance, allowing the burner to operate stably in a harsh environment with long-term high temperature, high pressure and erosion by fuel combustion products.
- Features: Compared with 304 stainless steel, it has better high-temperature oxidation resistance and is suitable for high-temperature and relatively harsh environments.
- Advantages: In the lining support structure of the heating furnace in the metallurgical industry, it can withstand the radiation heat of the high-temperature steel billet and the erosion of the atmosphere in the furnace, providing reliable structural support for the normal operation of the heating furnace.
Ferritic Stainless Steel Grades
Ferritic stainless steel uses chromium as the main alloying element, and its crystal structure is in the ferrite phase. It has the characteristics of low cost, certain high temperature resistance and magnetism, but its corrosion resistance is weaker than that of austenitic stainless steel, especially in strong acid, alkali and high chloride environments.
Grade 430
- Composition: The chromium content is about 17-19%, basically no nickel or very low nickel content, and the rest is iron and a small amount of other elements.
- Data example: Taking the common 430 stainless steel kitchen sink as an example, the thickness of the chromium oxide protective film formed on the surface by chromium is about 0.02-0.05 microns, which makes it have certain corrosion resistance under the action of mild acid and alkali, water stains and daily detergents in the kitchen. Due to its low cost, in the large-scale production of kitchenware, its raw material cost can be reduced by about 30% compared with nickel-containing stainless steel, which can meet the economic requirements.
- Characteristics: It has good oxidation resistance and processing performance, and the cost is relatively low.
- Advantages: In some parts of automobile exhaust systems, such as muffler housings, although the exhaust contains high-temperature exhaust gas and a small amount of corrosive substances, the anti-oxidation and high-temperature resistance can meet the requirements of short-term use.
Grade 434
- Composition: Compared with the 430 series, the chromium content is slightly increased, about 18-20%, and contains a certain amount of molybdenum, usually around 0.75-1.25%.
- Data example: In some storage containers in the chemical industry, such as storage tanks for organic chemicals containing a small amount of chloride impurities, chromium provides basic antioxidant properties, and molybdenum has a significant corrosion inhibition effect on chloride impurities. After testing, in an organic solution environment containing 0.5% chloride, its corrosion rate is about 40% lower than that of 430 stainless steel, effectively extending the service life of the tank.
- Features: The increased chromium and molybdenum content improves its corrosion resistance in chloride-containing environments.
- Advantages: In small boiler water-side components, it can better resist the combined corrosion of trace chlorides and high-temperature steam in water than 430 stainless steel, reducing the maintenance and replacement frequency of components,in household appliance components that have certain requirements for corrosion resistance, such as electric water heater tanks, the performance can meet basic use requirements and take into account cost control, providing consumers with relatively cost-effective product options.
Grade 444
- Composition: The chromium content is further increased to 19-23%, and the molybdenum content is increased to 1.5-2.5%.
- Data example: In acidic food storage equipment in the food processing industry, such as pickled food storage tanks, high content of chromium and molybdenum makes it have good resistance to organic acid corrosion in acidic foods. After being immersed in an acidic environment with a pH value of 3-4 for 1000 hours, its corrosion depth is only about 20% of that of ordinary ferritic stainless steel, which effectively ensures food quality and storage equipment hygiene and safety.
- Features: The further increase in chromium and molybdenum content significantly enhances resistance to acidic environments.
- Advantages: In mild corrosion protection facilities in marine environments, such as rainwater drainage pipes in seaside buildings, although they are exposed to air and rainwater containing a certain amount of salt, good acid resistance and certain chloride corrosion resistance can reduce pipeline corrosion damage, extend service life.
Duplex Stainless Steel Grades
Duplex stainless steel combines the characteristics of austenite and ferrite structures, and has high strength, good corrosion resistance and wear resistance. It is widely used in many fields that require high comprehensive material performance. The unique duplex structure makes its performance better than single-phase stainless steel.
Grade 2205
- Composition: The typical composition contains 22% chromium, 5-6% nickel and 3% molybdenum, and the proportion of ferrite phase and austenite phase is roughly the same.
- Data example: In the reaction tower of the chemical industry, chromium can form an effective oxide film in both phase structures, nickel stabilizes the austenite phase to enhance the toughness and processing performance of the material, and molybdenum improves the overall corrosion resistance. In a mixed corrosive medium containing 5% sodium chloride and 1% sulfuric acid, its corrosion rate is about 1/3 of that of ordinary austenitic stainless steel, and it performs well in complex corrosive environments containing chloride ions and sulfides.
- Features: Excellent corrosion resistance, high temperature resistance and high strength.
- Advantages: In the laying of submarine pipelines in marine engineering, it can withstand huge seawater pressure, current scouring and corrosion caused by rich chlorides in seawater. High strength ensures that the pipeline will not break or deform in the high-pressure environment of deep sea. Good corrosion resistance prevents the pipeline from being corroded and perforated by seawater, ensuring the safe transportation of submarine oil and gas resources.
Grade 2507
- Composition: The chromium content is about 25%, the nickel content is 6-8%, the molybdenum content is as high as 3.5-4.5%, and the nitrogen content is also relatively high, about 0.25-0.35%.
- Data example: In the highly corrosive reactors of large chemical companies, high content of chromium and molybdenum makes it extremely resistant to various strong acids, strong alkalis and high-concentration chloride solutions. After being immersed in a 20% hydrochloric acid solution for 500 hours, its corrosion weight loss rate is only about 10% of that of ordinary duplex stainless steel. The addition of nitrogen further improves the material strength and pitting resistance, and effectively prevents corrosion and material performance degradation in the violent chemical reaction and high temperature and high pressure environment in the reactor.
- Features: It is a super duplex stainless steel, showing excellent strength and corrosion resistance in the harsh environment rich in chlorides.
- Advantages: In key structural components of offshore oil drilling platforms, such as drilling rigs and Christmas trees, it can not only withstand strong corrosion in the marine environment, but also withstand the impact of waves, the weight of the equipment and various dynamic loads during operation. High strength and high corrosion resistance ensure long-term reliability under extremely harsh conditions, reducing platform maintenance costs and safety risks.
Martensitic Stainless Steel Grades
Martensitic stainless steel is known for its high hardness and high strength, which is mainly achieved through high carbon content and appropriate chromium content, but its corrosion resistance is relatively weak. It is suitable for occasions with high requirements for strength and wear resistance and relatively mild corrosion environment.
Grade 410
- Composition: Chromium content is 11-13%, carbon content is generally between 0.15-0.25%, and the rest is iron and a small amount of impurity elements.
- Data example: In the manufacture of kitchen knives, chromium elements give knives a certain degree of rust resistance, and carbon elements improve the hardness and wear resistance of knives through heat treatment. For example, an ordinary 410 stainless steel kitchen knife has a Rockwell hardness (HRC) of 48-55, which can easily cut various ingredients, and maintains the sharpness and surface finish of the blade during daily use and cleaning. After one year of use in the kitchen environment, the surface rust area does not exceed 5%.
- Characteristics: It has high hardness and good wear resistance.
- Advantages: In small transmission gears in the machinery manufacturing industry, when 410 stainless steel gears are subjected to certain mechanical loads and friction, their hardness ensures that the gear tooth surface is not easy to wear and deform, ensuring the accuracy and reliability of the transmission system,in certain bolts and nuts in automotive parts, they are subjected to preload and vibration loads during vehicle operation.
Grade 420
- Composition: The carbon content is higher than that of the 410 series, usually between 0.2-0.4%, and the chromium content is 12-14%.
- Data example: In the manufacture of surgical instruments in medical devices, such as scalpels, the higher carbon content enables the Rockwell hardness (HRC) to reach 50-60 after proper heat treatment. After 100 simulated surgical cuts, the blade wear is only 410% of the normal 410 series.
It is not easy to deform and wear when the material is subjected to pressure and friction, thereby improving the service life of the mold and the quality of the product,in the manufacture of sporting goods, such as some high-end fencing blades, its characteristics make it have good elasticity and wear resistance. After 100 fencing matches, the elasticity of the blade decayed by no more than 10%, which can meet the strict performance requirements of fencing.
Grade 440
- Composition: The carbon content can be as high as 0.6-1.2%, and the chromium content is 16-18%.
- Data example: In the field of high-end knife manufacturing, such as high-end steak knives for professional chefs or multi-functional knives for outdoor survival, the high carbon content allows it to reach a Rockwell hardness (HRC) of 58-65 through a special heat treatment process. When cutting hard ingredients or dealing with complex outdoor environments, the blade remains sharp for about 50% longer than ordinary knives. The chromium element provides relatively good corrosion resistance. After being placed in a humid outdoor environment for one month, the surface rust is slight and easy to clean, ensuring the performance and service life of the knife.
- Features: It is one of the hardest martensitic stainless steels with extremely high wear resistance and hardness.
- Advantages: In the selection of tool materials in precision machining, 440 series stainless steel tools perform well when cutting high-hardness metal materials. Their high hardness can effectively cut into the material, reduce tool wear and machining surface roughness. When cutting alloy steel with a hardness of HRC 40-50, the tool wear is reduced by about 70% compared with ordinary tools.
Precipitation-Hardening Stainless Steel Grades
Precipitation-hardening stainless steels achieve high strength through the addition of alloying elements like aluminum, copper, and molybdenum and through heat treatment processes. These grades offer exceptional strength and hardness while maintaining good corrosion resistance.
Grade 17-4PH
17-4PH stainless steel is the most widely used precipitation-hardening stainless steel, containing 15-17% chromium, 3-5% nickel, and 3-5% copper. It provides excellent strength, toughness, and corrosion resistance, making it ideal for aerospace, chemical equipment, and mechanical components requiring high strength and corrosion resistance.
Grade 15-5PH
15-5PH stainless steel offers even higher strength and better corrosion resistance than 17-4PH. It is commonly used in aerospace, medical devices, and marine engineering. With 14-15% chromium, 3-5% nickel, and 2-3% copper, its precipitation-hardening process ensures superior mechanical strength and corrosion resistance, making it suitable for more demanding working environments.
Stainless Steel Grade Comparison Table
| Grade | Type | Characteristics | Aplicaciones | Common Alloys |
| Austenitic Stainless Steel | High corrosion resistance, excellent machinability | Outstanding corrosion resistance, weldability, and good workability | Food processing, medical devices, architectural exteriors, chemical equipment | 304, 316, 321, 310 |
| Ferritic Stainless Steel | Good oxidation resistance, magnetic properties | High-temperature resistance, lower strength | Automotive manufacturing, appliances, decorative purposes | 430, 434, 444 |
| Duplex Stainless Steel | High strength, excellent corrosion resistance | Combines the advantages of austenitic and ferritic stainless steel, suitable for high-strength environments | Chemical industry, marine engineering, oil and gas sectors | 2205, 2507 |
| Martensitic Stainless Steel | High hardness, good wear resistance | High strength, lower corrosion resistance, ideal for high-strength applications | Automotive components, tool manufacturing, aerospace industry | 410, 420, 440 |
| Precipitation-Hardened Stainless Steel | High strength, good corrosion resistance | Suitable for environments requiring both high strength and corrosion resistance | Aerospace, chemical equipment, medical industries | 17-4PH, 15-5PH |
Applications of Stainless Steel Grades
Stainless steel has become an essential material across various industries. Whether addressing hygiene requirements in food processing, antibacterial properties in medical devices, or corrosion resistance in marine engineering, different stainless steel grades provide tailored solutions.
Food and Beverage Industry
Recommended Grades: 304, 316L
These grades comply with hygiene standards, contain no harmful elements, and are ideal for food processing equipment.
Medical Industry
Recommended Grades: 316L, 304L
These grades offer excellent antibacterial properties, corrosion resistance, and ease of cleaning, making them suitable for medical instruments and implants.
Chemical Industry
Recommended Grades: 2205, 2507
These duplex stainless steels are designed for high-corrosion environments, such as chemical reactors and pipelines.
Construction Industry
Recommended Grades: 304, 316
These grades are widely used in building exteriors (curtain walls), decorative elements, and load-bearing structures due to their durability and aesthetics.
Automotive and Aerospace Industry
Recommended Grades: 410, 420
These martensitic stainless steels are suitable for components that require wear resistance and high strength, such as shafts and cutting tools.
Marine Engineering
Recommended Grades: 316, 2507
With outstanding corrosion resistance, these grades are ideal for seawater environments, such as shipbuilding and offshore platforms.
Preguntas frecuentes
What is the best stainless steel?
The “best” stainless steel depends on the specific application. For high corrosion resistance, 316 is often the best choice. For high-strength components, 410 or 420 may be more suitable.
What are the pros and cons of 304 and 316 stainless steel?
304 contains 18% chromium and 8% nickel, offering good oxidation resistance but performs less effectively in highly corrosive environments. 316 includes 16% chromium, 10% nickel, and 2% molybdenum, which enhances corrosion resistance but comes at a higher cost due to the addition of molybdenum.
Which is better, 304 or 420 stainless steel?
It depends on the intended use. 304 is better suited for general-purpose and corrosion-resistant applications. In contrast, 420, with higher carbon content, is ideal for applications requiring high strength and wear resistance.
Is 430 stainless steel expensive?
430 stainless steel, a ferritic grade, is relatively inexpensive due to its lower nickel content and higher chromium ratio. It is commonly used in appliances, kitchen equipment, and automotive exhaust systems.
What is the cheapest grade of stainless steel?
Ferritic stainless steels are generally more cost-effective than austenitic grades. These steels rely on chromium as the primary alloying element, with minimal nickel, reducing production costs. While less corrosion-resistant than austenitic steels, they are an economical choice for less demanding applications.
Is 304 stainless steel magnetic?
304 stainless steel is typically non-magnetic due to its face-centered cubic (FCC) crystal structure. However, cold working processes, such as stretching, bending, or rolling, can alter its structure and introduce some magnetism. This magnetic property does not indicate a change in its base composition.
What color is 304 stainless steel?
304 stainless steel exhibits a typical silver-white metallic luster with a smooth, bright surface. Its color remains stable over time and does not fade easily.
Conclusión
The selection of stainless steel is not a one-size-fits-all decision. It should be tailored to the specific demands of the application. Different grades of stainless steel excel in corrosion resistance, strength, heat tolerance, machinability, and cost. Choosing the right grade depends on understanding your requirements and matching them to the material’s properties.