Reviewed · 2026-08-03
Stainless Steel
Stainless steels are iron-based alloys whose chromium enables a self-repairing passive film in suitable environments. They are selected by metallurgical family, exact grade, product standard, condition, fabrication route, surface state and exposure—not by the word “stainless” alone.
Classification basis
The primary classification follows room-temperature microstructure and strengthening route; corrosion behavior still varies substantially within each family.
Compare austenitic, ferritic, martensitic, duplex and precipitation-hardening families before moving to a grade or product specification.
A familiar grade name never replaces the governing product specification and certified documentation.01
Explore subcategories
Austenitic Stainless Steel
They are distinguished from ferritic and duplex grades by matrix/phase constitution and from martensitic or PH grades by strengthening route; cold work can still raise strength and magnetic response.
→Stainless steelFerritic Stainless Steel
Ferritic grades are not simply low-cost 304 substitutes: toughness, weldability, forming, section thickness, chromium/molybdenum content and stabilization determine suitability.
→Stainless steelMartensitic Stainless Steel
Grade name alone does not define performance: annealed machinable stock, hardened product and tempered component can have completely different properties.
→Stainless steelDuplex Stainless Steel
“Duplex” is a family, not one performance level: lean duplex, standard 2205 and super duplex 2507 differ in alloy content, corrosion resistance, fabrication window and cost.
→Stainless steelPrecipitation-Hardening Stainless Steel
PH grades differ from martensitic grades because final strengthening relies on precipitation aging, although some grades also form martensitic matrices; the exact condition designation is essential.
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Representative grades and systems
| Grade / system | Use as a selection entry point |
|---|---|
| 201 | Define chlorides, acids, temperature, deposits, cleaning and crevice conditions before ranking grades. |
| 304/304L | Confirm strength, toughness, forming, welding, machining and heat-treatment requirements for the product section. |
| 316/316L | Use the governing product specification and certified test report for acceptance; cross-standard names are only comparison aids. |
| 409 | Define chlorides, acids, temperature, deposits, cleaning and crevice conditions before ranking grades. |
| 430 | Confirm strength, toughness, forming, welding, machining and heat-treatment requirements for the product section. |
| 410 | Use the governing product specification and certified test report for acceptance; cross-standard names are only comparison aids. |
| 420 | Define chlorides, acids, temperature, deposits, cleaning and crevice conditions before ranking grades. |
| 2205 | Confirm strength, toughness, forming, welding, machining and heat-treatment requirements for the product section. |
| 2507 | Use the governing product specification and certified test report for acceptance; cross-standard names are only comparison aids. |
| 17-4 PH | Define chlorides, acids, temperature, deposits, cleaning and crevice conditions before ranking grades. |
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Property framework
Chromium-supported passivity provides corrosion resistance only within an appropriate environment and surface condition.
Strength ranges from highly formable annealed sheet to heat-treated martensitic and precipitation-hardened products.
Magnetic response, thermal expansion, work hardening and weld behavior depend on family, grade and processing history.
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Common product forms
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Applications
- Food, pharmaceutical and hygienic equipment
- Chemical, water, marine and energy systems
- Architecture, transportation and durable consumer equipment
- Define chlorides, acids, temperature, deposits, cleaning and crevice conditions before ranking grades.
- Confirm strength, toughness, forming, welding, machining and heat-treatment requirements for the product section.
- Use the governing product specification and certified test report for acceptance; cross-standard names are only comparison aids.
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Standards and designation systems
ASTM A240/A240M is a major flat-product specification; pipe, bar, wire and forgings use different standards.
UNS, EN, JIS and GB designations must be mapped with the exact product standard and requirements.
Design and fabrication codes may add toughness, corrosion, welding, inspection or certification requirements.
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Procurement checklist
- Specify grade, product standard, dimensions, tolerances, condition and finish.
- State inspection, PMI, NDE, corrosion tests, MTC type and traceability when required.
- Describe application, fabrication route, destination, quantity, packing and delivery schedule in the RFQ.
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Sources and editorial review
worldstainless · Technical overview, accessed 2026
Nickel Institute · Technical Guide 9014, 2020
ASTM International · A240/A240M-26 scope page