Types of Stainless Steel

Stainless steel is a widely used material known for its resistance to corrosion, durability, and versatility. Its unique properties are derived from the addition of chromium and other elements, which enhance its strength and resistance to various environmental conditions.

This blog provides a comprehensive overview of the types of stainless steel, their compositions, physical properties, and applications, along with a comparison of common grades to help you select the right type for your needs.

Families of Stainless Steel

Stainless steels are categorized into five main families based on their microstructure and alloy content:

1. Austenitic Stainless Steel
2. Ferritic Stainless Steel
3. Martensitic Stainless Steel
4. Duplex Stainless Steel
5. Precipitation-Hardening Stainless Steel

1. Austenitic Stainless Steel

Austenitic stainless steels are known for their high chromium (16-26%) and nickel (6-22%) content, often containing molybdenum (0-7%) and nitrogen. They have a face-centered cubic (FCC) microstructure, which remains stable at all temperatures, making them non-magnetic. Their excellent corrosion resistance, especially against chloride-induced corrosion, combined with their superb formability and weldability, make them a popular choice.

Composition and Properties:

• Primary Elements: High chromium (16-26%) and nickel (6-22%) content. Often contains molybdenum (0-7%) and nitrogen.
• Microstructure: Face-centered cubic (FCC), which remains stable at all temperatures.
• Magnetism: Non-magnetic.
• Corrosion Resistance: Excellent, especially against chloride-induced corrosion.
• Formability and Weldability: Excellent.

Common Grades:

• 304 (18/8): Contains 18% chromium and 8% nickel. Known for good corrosion resistance, formability, and weldability.
• 316: Enhanced with 2-3% molybdenum for better resistance to chlorides and industrial solvents.

Physical Properties:

• Tensile Strength: 515-720 MPa
• Maximum Use Temperature: 870-925°C (1600-1700°F)
• Melting Point: 1400-1450°C (2550-2650°F)

Applications:

• Food processing equipment, chemical containers, architectural applications, and medical devices.

Advantages:

• Excellent corrosion resistance.
• High ductility and formability.
• Stable at various temperatures.

Disadvantages:

• Higher cost due to nickel content.
• Susceptible to stress corrosion cracking under certain conditions.

2. Ferritic Stainless Steel

Ferritic stainless steels are characterized by their chromium content (10.5-30%) and low carbon content (less than 0.1%). They have a body-centered cubic (BCC) microstructure, making them magnetic with moderate corrosion resistance, generally lower than austenitic but good against stress corrosion cracking.

Composition and Properties:

• Primary Elements: Chromium (10.5-30%), low carbon (less than 0.1%).
• Microstructure: Body-centered cubic (BCC).
• Magnetism: Magnetic.
• Corrosion Resistance: Moderate, generally lower than austenitic but good against stress corrosion cracking.

Common Grades:

• 430: Contains 16-18% chromium. Used for good corrosion resistance and formability in less demanding environments.
• 409: Contains 10.5-11.75% chromium, often used in automotive exhaust systems.

Physical Properties:

• Tensile Strength: 380-550 MPa
• Maximum Use Temperature: 800-850°C (1470-1560°F)
• Melting Point: 1425-1510°C (2600-2750°F)

Applications:

• Automotive trim, exhaust systems, industrial machinery, and kitchenware.

Advantages:

• Lower cost due to low nickel content.
• Good resistance to oxidation and stress corrosion cracking.

Disadvantages:

• Lower corrosion resistance compared to austenitic stainless steel.
• Limited weldability and formability.

3. Martensitic Stainless Steel

Martensitic stainless steels are known for their higher carbon content (0.1-1.2%) and chromium (12-18%). They can be heat-treated to form a martensitic structure, enhancing hardness and strength. These steels are magnetic and offer moderate corrosion resistance, which can be improved with higher chromium content.

Composition and Properties:

• Primary Elements: Chromium (12-18%), higher carbon content (0.1-1.2%).
• Microstructure: Can be heat-treated to form a martensitic structure, enhancing hardness and strength.
• Magnetism: Magnetic.
• Corrosion Resistance: Moderate, but can be improved with higher chromium content.

Common Grades:

• 410: Contains 11.5-13.5% chromium, known for its high strength and hardness.
• 420: Contains 12-14% chromium, used in cutlery and surgical instruments.

Physical Properties:

• Tensile Strength: 500-1000 MPa (depending on heat treatment)
• Maximum Use Temperature: 700-815°C (1290-1500°F)
• Melting Point: 1450-1510°C (2640-2750°F)

Applications:

• Cutlery, surgical instruments, valves, and pumps.

Advantages:

• High strength and hardness.
• Good wear resistance.

Disadvantages:

• Lower corrosion resistance compared to austenitic and ferritic steels.
• Brittle at low temperatures, less ductile.

4. Duplex Stainless Steel

Duplex stainless steels offer a balance between austenitic and ferritic structures, with high chromium (19-28%), molybdenum (up to 5%), and lower nickel content. Their mixed microstructure provides superior corrosion resistance, especially against chloride-induced stress corrosion cracking and pitting.

Composition and Properties:

• Primary Elements: Balanced amounts of austenitic and ferritic structures, with high chromium (19-28%), molybdenum (up to 5%), and lower nickel content.
• Microstructure: Mixed austenitic and ferritic phases.
• Magnetism: Slightly magnetic.
• Corrosion Resistance: Superior, especially against chloride-induced stress corrosion cracking and pitting.

Common Grades:

• 2205: Contains 22% chromium, 5% nickel, and 3% molybdenum, offering excellent strength and corrosion resistance.

Physical Properties:

• Tensile Strength: 600-800 MPa
• Maximum Use Temperature: 315-675°C (600-1250°F)
• Melting Point: 1350-1400°C (2460-2550°F)

Applications:

• Chemical processing, oil and gas industry, marine environments, and desalination plants.

Advantages:

• Higher strength than austenitic and ferritic steels.
• Excellent resistance to stress corrosion cracking and pitting.

Disadvantages:

• Difficult to weld.
• Higher cost due to complex alloy content.

5. Precipitation-Hardening Stainless Steel

Precipitation-hardening stainless steels are characterized by their chromium (15-17.5%), nickel (3-7%), and additional elements like aluminum, copper, and niobium. These steels can be heat-treated to precipitate intermetallic compounds, enhancing strength. Some grades are magnetic, and they offer good to excellent corrosion resistance depending on the grade.

Composition and Properties:

• Primary Elements: Chromium (15-17.5%), nickel (3-7%), and additional elements like aluminum, copper, and niobium.
• Microstructure: Can be heat treated to precipitate intermetallic compounds, enhancing strength.
• Magnetism: Some grades are magnetic.
• Corrosion Resistance: Good to excellent, depending on the grade.

Common Grades:

• 17-4 PH: Contains 17% chromium and 4% nickel, with copper for high strength and hardness.

Physical Properties:

• Tensile Strength: 930-1310 MPa (after heat treatment)
• Maximum Use Temperature: 300-550°C (570-1020°F)
• Melting Point: 1400-1450°C (2550-2650°F)

Applications:

• Aerospace components, nuclear waste casks, and high-performance equipment.

Advantages:

• High strength and hardness.
• Good corrosion resistance.

Disadvantages:

• Complex heat treatment process.
• Higher cost.

Detailed Comparison of Common Grades: 304 vs. 316

304 Stainless Steel:

• Composition: 18% chromium, 8% nickel.
• Tensile Strength: 515 MPa.
• Corrosion Resistance: Good, suitable for general applications.
• Applications: Kitchen equipment, food processing, architectural trim.
• Positives: Excellent formability and weldability, good corrosion resistance.
• Negatives: Less resistant to chloride-induced pitting and stress corrosion cracking.

316 Stainless Steel:

• Composition: 16-18% chromium, 10-14% nickel, 2-3% molybdenum.
• Tensile Strength: 515 MPa.
• Corrosion Resistance: Excellent, especially in chloride environments.
• Applications: Marine equipment, chemical processing, medical devices.
• Positives: Superior corrosion resistance, especially to chlorides, and excellent durability.
• Negatives: Higher cost due to molybdenum content.

Choosing the Right Stainless Steel

Corrosion Resistance:

• 304 vs. 316: 304 is sufficient for general use but 316 is better for environments with high exposure to chlorides, such as coastal areas or chemical processing plants. Use 316 for applications requiring greater corrosion resistance.

Mechanical Properties:

• 304 vs. 316: Both offer similar tensile strength, but 316 provides better resistance to pitting and crevice corrosion. Select 316 for more demanding environments.

Formability and Weldability:

• Austenitic Steels (304, 316): Offer excellent formability and weldability, making them suitable for complex shapes and structures.
• Ferritic and Martensitic Steels: Generally harder to form and weld. Use austenitic grades if fabrication complexity is high.

Cost:

• 304: More cost-effective for general applications.
• 316: Higher initial cost but offers better long-term performance in harsh environments. Assess the total cost of ownership considering longevity and maintenance.

Temperature Resistance:

• High-Temperature Applications: Austenitic and ferritic steels are stable at higher temperatures. For applications like heat exchangers or furnace parts, consider grades like 310 or 446.

Conclusion

Stainless steel offers a diverse range of properties suitable for various industrial applications. By understanding the differences in composition, physical properties, and suitability for specific environments, you can make informed decisions to select the best type of stainless steel for your project. Whether you need the excellent corrosion resistance of austenitic steel, the high strength of martensitic steel, or the balanced properties of duplex steel, there is a stainless steel type that fits your requirements.

If you have a stainless steel project and need expert guidance, YENA Engineering B.V. is here to help. Our team of experienced engineers can provide you with detailed technical data, specific use case recommendations, and personalized support to ensure you choose the best material for your needs. Contact us today to learn more about how we can assist with your stainless steel requirements.