Stainless steel is ubiquitous in industries such as machining, equipment manufacturing, food processing, chemicals, and new energy. While many engineers are familiar with grades 304 and 316, they often encounter pitfalls when selecting from the dozens of available grades. Stainless steel is not "rust-proof"; it relies on chromium to form a passivating film for corrosion resistance, while alloying elements like nickel, molybdenum, titanium, and manganese determine properties such as corrosion resistance, high-temperature performance, machinability, and strength.
This article compiles the 18 most commonly used stainless steel grades in industrial settings-categorized into austenitic, ferritic, martensitic, duplex, and precipitation-hardening steels-and outlines their characteristics, limitations, and typical applications to serve as a reference for material selection.
I. Austenitic Stainless Steels (201, 301, 303, 304, 304L, 316, 316L, 321, 309S, 310S, 904L) Austenitic grades account for over 70% of the market. They are weakly magnetic or non-magnetic at room temperature, offer excellent weldability and formability, cannot be hardened by quenching, and rely on cold working to increase strength. 1. 201: An economical grade with high manganese and low nickel content; low cost. Corrosion resistance is relatively weak; prone to rusting in humid or salt-spray environments. Commonly used for indoor decorative tubing, hardware, and general decorative parts; unsuitable for outdoor or coastal environments. 2. 301: Exhibits outstanding work-hardening effects; strength and hardness increase significantly after cold rolling. Used for springs, rail transit components, and elastic parts. 3. 303: A free-machining grade with added sulfur to improve machinability. Corrosion resistance is slightly inferior to 304; suitable for high-volume turning operations to produce bolts, bushings, and valve components. 4. 304: The industry standard; features an 18-8 chromium-nickel ratio and balanced overall properties; easy to bend and weld. Suitable for kitchenware, food processing equipment, general piping, and equipment housings. Limitation: Not resistant to seawater or high-chloride environments. 5. 304L: An extra-low carbon version with a carbon content of ≤0.03%. Offers strong resistance to intergranular corrosion after welding; the preferred choice for welded thick-plate components; strength is slightly lower than 304. Suitable for petrochemical equipment, heat exchangers, and welded structural parts. 6. 316: Contains molybdenum; offers superior resistance to pitting and chloride-ion corrosion compared to 304. Suitable for coastal equipment, marine applications, and equipment handling standard chemical media. 7. 316L: Low-carbon version of 316; currently the most widely used grade in marine and chemical applications. Does not require post-weld solution treatment; offers excellent resistance to intergranular corrosion; suitable for marine components, pharmaceutical equipment, and seawater piping. 8. 321: Contains titanium to inhibit intergranular precipitation. Suitable for welded components operating at high temperatures (430°C–900°C) where post-weld heat treatment is not feasible; applications include exhaust pipes and boiler heat-exchange components. Titanium content makes it unsuitable for food-contact applications. 9. 309S: Medium-temperature heat-resistant steel with high chromium and nickel content; offers strong oxidation resistance. Used for industrial furnace linings and high-temperature heat-treatment tooling. 10. 310S: High-temperature austenitic steel; maximum service temperature reaches 1100°C. Suitable for furnace chambers, high-temperature kiln components, and radiant tubes; relatively high cost. 11. 904L (Super Austenitic): High nickel and molybdenum content; resistant to highly corrosive media such as concentrated sulfuric acid and phosphoric acid. Suitable for highly corrosive chemical equipment and high-end instrument components; high cost. II. Ferritic Stainless Steels (409L, 430): Magnetic, nickel-free, and low-cost; cannot be hardened by quenching; offers better thermal conductivity and stress-corrosion cracking resistance than austenitic grades, but has poorer weld toughness. 12. 409L: Steel specifically for automotive exhaust systems; offers high-temperature oxidation resistance and excellent cost-performance; used for exhaust pipes and mufflers. 13. 430: The most common ferritic grade; often referred to as "stainless iron." Suitable for indoor appliance casings and decorative panels. Prone to pitting and rusting in chloride-rich environments; not suitable for coastal areas. III. Martensitic Stainless Steels (410, 420, 440C): Strongly magnetic; hardness and wear resistance can be enhanced through quenching and tempering; corrosion resistance is inferior to that of austenitic grades; primarily selected for hardness and wear resistance. 14. 410: Basic martensitic grade; good strength, moderate corrosion resistance; suitable for valve components, pump shafts, and fasteners. 15. 420: Cutlery-grade steel; achieves high hardness after quenching; suitable for knives, scissors, and medical cutting instruments. 16. 440C: High-carbon martensitic grade; one of the hardest stainless steels; exceptional wear resistance, though corrosion resistance is limited; suitable for high-end bearings, cutting tools, and valve seals. IV. Duplex Stainless Steels (2205, 2507): Composed of roughly equal parts austenite and ferrite; yield strength is approximately double that of austenitic grades; exhibits outstanding resistance to chloride-induced stress corrosion cracking; higher cost. 17. 2205: General-purpose duplex steel; suitable for seawater, desulfurization, papermaking, and chemical industry heat exchangers; serves as a substitute for 316L in harsh, chloride-rich environments. 18. 2507 (Super Duplex Steel): Higher molybdenum content; superior pitting corrosion resistance; suitable for high-salinity environments, offshore oil and gas applications, and seawater desalination equipment. V. Supplementary Precipitation-Hardening Stainless Steel (17-4PH/630): Although not included in the previous list of 18 types, 17-4PH is frequently used in engineering; it achieves ultra-high strength through aging treatment and is utilized in aerospace applications, high-end valves, and high-strength structural components. Summary of key selection criteria: 1. Standard indoor environments: Prioritize 304; choose 201 for indoor decorative applications with budget constraints. 2. Welding of thick plates: Prioritize 304L or 316L to prevent intergranular corrosion. 3. Coastal areas, chloride exposure, or seawater: Upgrade progressively from 316L to 2205, then to 2507. 4. High-temperature conditions: 321 for medium temperatures; 309S/310S for high temperatures. 5. Large-scale machining (turning): Choose 303. 6. Applications requiring hardness and wear resistance (e.g., cutting tools): Martensitic grades 420 or 440C. 7. Highly corrosive chemical media: 904L or super duplex stainless steel. Many failure cases stem not from poor steel quality, but from the selection of the wrong grade. There is no "universal" stainless steel grade; a comprehensive assessment considering the medium, temperature, chloride levels, welding processes, and costs is essential to avoid issues such as rusting or cracking.
