The Difference Between Austenitic Stainless Steel and Martensitic Stainless Steel

Stainless steel fasteners are highly durable and can withstand extreme temperatures, making them suitable for use in a wide range of industries and applications. Some of the most common reasons for using stainless steel fasteners are their corrosion resistance, durability, aesthetics and strength. While most users of stainless steel fasteners are familiar with these benefits as a whole, far fewer people are know what the different types of stainless steel are and how their properties may affect any given application.

The two most common types of stainless steel used in fastener production are Austenitic Stainless Steel and Martensitic Stainless Steel. The main difference between Austenitic Stainless Steel and Martensitic Stainless Steel is their composition and microstructure, which gives them different mechanical and physical properties.

Austenitic Stainless Steel contains high levels of chromium and nickel, and sometimes molybdenum, which makes it highly resistant to corrosion and oxidation. This type of stainless steel has a face-centered cubic (FCC) crystal structure, which gives it good ductility, toughness, and excellent formability. Austenitic stainless steel is often used in applications that require good corrosion resistance, such as in food processing, chemical, and pharmaceutical industries. There are several types of Austenitic Stainless Steel, including:

  1. AISI 304: This is the most common type of Austenitic Stainless Steel, containing 18% chromium and 8% nickel, which gives it another name people use, 18-8 Stainless Steel. It has good corrosion resistance, formability, and weldability, and is often used in applications that require general corrosion resistance, such as in food processing, chemical, and architectural industries.

  2. AISI 316: This type of Austenitic Stainless Steel contains 16% to 18% chromium, 10% to 14% nickel, and 2% to 3% molybdenum. It has better corrosion resistance than AISI 304, especially in chloride environments, and is often used in applications that require high corrosion resistance, such as in marine, medical, and chemical industries.

  3. AISI 321: This type of Austenitic Stainless Steel contains 17% to 19% chromium, 9% to 12% nickel, and 0.3% to 0.7% titanium. It has good corrosion resistance and high-temperature strength, making it suitable for use in applications that require resistance to high temperatures, such as in exhaust systems and jet engines.

  4. AISI 347: This type of Austenitic Stainless Steel contains 17% to 19% chromium, 9% to 13% nickel, and 0.3% to 0.7% columbium. It has similar properties to AISI 321 but has better corrosion resistance in high-temperature applications.

  5. AISI 201: This type of Austenitic Stainless Steel contains 16% to 18% chromium and 3.5% to 5.5% nickel. It has lower corrosion resistance than AISI 304 but is more affordable and has good formability and weldability. It is often used in applications that require low to moderate corrosion resistance, such as in automotive trim and kitchenware.

On the other hand, Martensitic Stainless Steel contains high levels of carbon and low levels of nickel, which gives it high strength, hardness, and wear resistance. This type of stainless steel has a body-centered cubic (BCC) crystal structure, which makes it less ductile than Austenitic Stainless Steel. Martensitic stainless steel is often used in applications that require high strength and wear resistance, such as in knives, tools, and turbine blades. The types of Martensitic Stainless Steel include:

  1. AISI 410: This type of Martensitic Stainless Steel contains 11.5% to 13.5% chromium and has a moderate level of corrosion resistance. It is often used in applications that require high strength, hardness, and wear resistance, such as in cutlery, pumps, and valves.

  2. AISI 420: This type of Martensitic Stainless Steel contains 12% to 14% chromium and 0.15% to 0.40% carbon. It has higher corrosion resistance than AISI 410 and is often used in applications that require high strength, hardness, and wear resistance, such as in surgical instruments, dental equipment, and turbine blades.

  3. AISI 440: This type of Martensitic Stainless Steel contains 16% to 18% chromium and 0.75% to 1.20% carbon. It has the highest level of hardness and wear resistance among Martensitic Stainless Steel, making it suitable for use in high-performance cutting tools, bearings, and valves.

  4. AISI 431: This type of Martensitic Stainless Steel contains 15% to 17% chromium, 1.25% to 2.50% nickel, and 0.12% to 0.22% carbon. It has good corrosion resistance and high strength, making it suitable for use in pumps, valves, and marine applications.

In summary, Austenitic Stainless Steel and Martensitic Stainless Steel have different compositions and microstructures, which give them different properties. Austenitic Stainless Steel is highly corrosion-resistant, ductile, and formable, while Martensitic Stainless Steel is highly wear-resistant, hard, and strong. The choice between the two types of stainless steel depends on the specific application requirements and conditions.

If you need help choosing which type of stainless steel fasteners you should use in your application, contact Mudge Fasteners at (800) 634-0406 for assistance from one of our helpful fastener experts.

Kyle Domer