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Guide to Austenitic Stainless Steel
Table of Contents
Austenitic stainless steel is one of the five families of stainless steel (along with ferritic, martensitic, duplex, and precipitation-hardened). Why is austenitic stainless steel called by that name? Stainless steel is named according to its crystalline structure. The primary crystalline structure of austenitic stainless steel is austenite, a face-centred cubic. Its uppermost feature is non-magnetic and can’t be hardened by heat treatment. Therefore, the industry refers to its processing sheet as cold-rolled steel.
Austenitic stainless steel is highly corrosion-resistant and versatile for various applications. In addition to being resistant to corrosion by oxidising acid media, it can also resist the corrosion of sulfuric acid, phosphoric acid, formic acid, acetic acid, urea, etc., if elements such as Mo and Cu are added. Austenitic stainless steel with high silicon content has good corrosion resistance to concentrated nitric acid.
Austenitic Stainless Steel Composition
The austenitic stainless steel series, comprising the 200 and 300 series, relies on specific alloying elements to achieve its signature face-centred cubic (FCC) structure, corrosion resistance, and mechanical properties. Here are the common elements and their roles:
Core Elements (Cr, Ni, C)
Their core elements are Cr, Ni, and C. Chromium (Cr: 15–32%) will form a passive oxide layer for corrosion resistance. It also stabilizes austenite and enhances oxidation resistance at high temperatures. Nickel (Ni: 8–37%) is the primary austenite stabilizer, ensuring FCC structure at all temperatures. It boosts ductility, toughness, and resistance to reducing acids. Carbon (C: ≤0.08%) is an element that stabilises austenite in austenitic stainless steel. However, the content should be minimised to prevent carbide precipitation during welding (“sensitisation”).
Key Alloying Additions (Mn, N, Mo)
Mn, N, and Mo are the key alloying additions. Manganese (Mn: 2–20%) can enhance nitrogen solubility and work-hardening capability. Also, the 200 series of austenitic stainless steel partially replaces nickel for cost reduction. Nitrogen (N: 0.1–0.6%) increases strength and pitting resistance (PREN = %Cr + 3.3%Mo + 16%N). Molybdenum (Mo: 0–7%) is added in 316 (2–3%), 317 (3–4%), and super austenitic grades (6–7%) for chloride resistance. It mitigates pitting/crevice corrosion in aggressive environments.
Specialized Additives (Si, Cu, Ti, Nb)
Specialized additives in austenitic stainless steels address specific weaknesses or environmental challenges that the base alloy (Fe-Cr-Ni-Mn) cannot handle alone. The common specialized additives include silicon, aluminum, and copper.
Adding silicon and aluminum enhances oxidation resistance in heat-resistant grades (e.g., 309/310, which is often used in furnace parts). Copper (Cu: 1–4%) can improve resistance to sulfuric/phosphoric acids in alloys like 904L. Ti and Nb are stabilizers. They can prevent chromium carbide formation in welded components.
Austenitic Stainless Steel Properties
Austenitic stainless steel is known for its excellent corrosion resistance, high strength, and ductility. Due to its wide range of properties and versatile applications, it is the most commonly used type of stainless steel.
Austenitic stainless steels exhibit unique properties due to their face-centred cubic (FCC) crystal structure, high alloy content, and non-magnetic nature. They are known for their excellent corrosion resistance, high strength, and ductility.
1. High corrosion resistance
General resistance is oxidation resistance. Austenitic stainless steel is Cr-rich, forming a protective oxide layer on the surface when exposed to oxygen. This oxide layer is a barrier against corrosive elements, such as water and chemicals (organic acids, nitric acid, and alkalis), making austenitic stainless steel suitable for harsh environments.
Excellent localized corrosion resistance is significant. We use the Pitting Resistance Equivalent Number (pren), a calculated value used to predict the resistance of stainless steel to localized pitting corrosion, to show the localized corrosion resistance for austenitic stainless steel. A higher PREN indicates superior pitting resistance.
304: PREN ≈ 19
316: PREN ≈ 26
254 SMO (6% Mo): PREN > 43
Note: If a stainless steel has good resistance to pitting and crevice corrosion, it will be ideal for applications in marine environments or where exposure to chlorides is common. (PREN = %Cr + 3.3 x (%Mo + 0.5 x %W) + 16 x %N. Calculator)
2. Good Strength
While not as strong as other types of stainless steel such as martensitic or precipitation-hardening grades, austenitic stainless steel still offers good levels of strength and toughness. Its strength can be further increased through cold working, surface treatment, or by adding alloying elements like nickel or molybdenum.
Moderate yield strength (typically 170–350 MPa annealed).
Strength ↑ significantly during cold working (e.g., cold-rolled 301 reaches >1,000 MPa).
Retains ductility down to cryogenic temperatures (–196°C).
3. Ductility & Formability
Austenitic stainless steels are also highly ductile, meaning they can be deformed without breaking. This makes them easy to form into various shapes and sizes using techniques such as bending, rolling, or welding. Due to their lower work hardening rate, they are also more easily machinable than other types of stainless steel.
Austenitic stainless steel has exceptional elongation (40–60%), ideal for deep drawing, bending, and stamping. While it has lower yield strength/stiffness than carbon steels, it has less springback during forming.
4. Great Toughness
Austenitic stainless steel has high impact resistance (e.g., >100 J at –196°C for 304L), suitable for LNG/space applications.
5. Excellent thermal conductivity
Austenitic stainless steels have excellent thermal conductivity and low thermal expansion coefficients. This makes them ideal for cryogenic applications where materials must withstand extreme temperatures without losing structural integrity.
Typical Grades of Austenitic Stainless Steel
Austenitic stainless steels are classified primarily into 200-series (manganese-based) and 300-series (nickel-based) subgroups, with further specialization into five sub-groups based on alloying elements and performance characteristics. Nickel-based austenitic stainless steel means that the primary stabilizer of stainless steel is Ni. Similarly, the stabilizer of manganese-based austenitic stainless steel is Mn.
Type 1. Cr-Mn Grades (200 Series)
These grades contain lower amounts of nickel than the AISI 300 series and are often called “chromium-manganese-nickel” alloys. This makes them suitable for applications requiring high strength and toughness while maintaining good corrosion resistance.
The structure of 200-series stainless steel is obtained by adding manganese and nitrogen. It has a small amount of nickel content, making it a cost-effective nickel-chromium austenitic type stainless steel. The AISI 200 series includes grades such as 201, 202, and 205. Compared with the AISI 300 series, it has a higher manganese content, which helps improve its strength and work-hardening rate.
Composition: Low nickel (3.5–7.5%), high manganese (5.5–20%), nitrogen (0.1–0.25%), and chromium (16–19%).
Key Grades: 201, 202, 204Cu, 205.
Properties: Higher yield strength than 300-series, cost-effective, moderate corrosion resistance, magnetic after cold working.
Applications: Cookware, automotive trim, and indoor water tanks.
Type 2. Cr-Ni Grades (Standard 300 Series)
The AISI 300 series is the larger subgroup. Its versatile, austenitic Cr-Ni alloys balance strength, corrosion resistance, and formability. 18/8 stainless steel, also called grade 304 or A2, is the common austenitic stainless steel. With their excellent corrosion resistance, non-magnetic properties, and good formability and weldability, AISI 300 series stainless steels are widely used in various industries.
Composition: Nickel (8–10.5%), chromium (18–20%), low carbon (<0.08%).
Key Grades: 304 (18/8 steel), 304L (low carbon), 321 (Ti-stabilized), 347 (Nb-stabilized).
Properties: Non-magnetic when annealed, excellent formability/weldability, good general corrosion resistance.
Applications: Food processing equipment, architectural cladding, medical devices.
Type 3. Cr-Ni-Mo Grades (Molybdenum-Enhanced)
Cr-Ni-Mo grades refer to a group of stainless steel grades to which molybdenum has been added. The above words mention that Mo can improve the pitting and crevice corrosion resistance of stainless steel, particularly in chloride-containing environments. The typical Cr-Ni-Mo series stainless steel is AISI 316 and 316L. These steels are used in a wide range of applications, including chemical processing equipment, food and beverage processing, pharmaceutical manufacturing, and marine environments.
Composition: Added molybdenum (2–3%), chromium (16–18%), nickel (10–14%).
Key Grades: 316 and 317 families.
Properties: Superior chloride/pitting resistance (PREN ≈ 26–30), higher strength.
Applications: Marine hardware, chemical tanks, offshore structures.
Type 4. High-Performance Austenitics (Super Austenitic)
High-performance austenitic steels are a subclass of austenitic stainless steels designed to offer exceptional corrosion resistance, high strength, and good weldability, especially in aggressive environments where standard stainless steels would fail.
Composition: Elevated chromium (17–25%), nickel (14–25%), molybdenum (3–7%), nitrogen (0.15–0.6%).
Key Grades: 904L, 254 SMO (6% Mo), Ultra 654 SMO (7% Mo).
Properties: Exceptional corrosion resistance (PREN >40), stress-corrosion cracking immunity.
Applications: Desalination plants, sulfuric acid reactors, pharmaceutical tubing.
Type 5. Precipitation Hardening AISI 660
AISI 660, or Grade EN 1.4980, is a precipitation hardening stainless steel. This type of steel is unique in its ability to develop high strength through a heat treatment process called aging. It belongs to the austenitic family and comprises iron, carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, titanium, aluminum, vanadium, and boron.
Used for service temperatures up to 700 °C (1,300 °F), AISI 660 finds extensive use in industries such as aerospace (standardized in AMS 5731, AMS 5732, AMS 5737, and AMS 5525 standards), oil and gas, chemical processing, and power generation.
Type 6. High-Temperature Austenitic Stainless Steel
Heat-resistant austenitic stainless steel is a type of austenitic stainless steel specifically designed to withstand high temperatures and maintain its mechanical properties. Unlike regular austenitic grades, it adds elements such as titanium, molybdenum, and niobium. These elements act as stabilizers at high temperatures and improve the material’s creep resistance. Heat-resistant grades like Grade 309 and 310 can be used at elevated temperatures, usually above 800 °C (1,500 °F). However, other heat-resistant grades are generally used at above 600 °C (1,100 °F).
Composition: High chromium (20–26%), nickel (12–35%), silicon/cerium for oxidation resistance.
Key Grades: 310, 309, Therma MA (Ce-stabilized).
Properties: Oxidation resistance up to 1150°C, creep strength.
Applications: Furnace parts, heat exchangers, jet engine components.
See Also
David Tan
Stainless Steel Materials & Products Expert. With 20+ years of experience in stainless steel, specialize in various stainless steel surface treatments and stainless steel fabricating. Familiar with multiple stainless steel characteristics and applications.
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