Stainless Steel Plate: Grades 304, 316, 321 — Properties, Specifications & Applications
Stainless steel plate is specified whenever carbon steel cannot survive the operating environment — corrosive chemicals, high temperatures with repeated thermal cycling, marine and coastal exposure, hygienic food and pharmaceutical processing, or simply where a project demands a material that will not rust for decades.
Choosing the wrong grade means either spending too much (specifying 316 where 304 would do) or watching your equipment corrode within months (using 304 in a chloride environment that demands 316). The difference between 304, 316, and 321 comes down to chemistry — specifically the amounts of molybdenum, titanium, and carbon — and understanding what each element does is the key to getting the specification right.
This guide covers the grades, chemical composition, mechanical properties, corrosion resistance, and applications for the stainless steel plates most commonly ordered for industrial projects.
Understanding the Grades
All three grades — 304, 316, and 321 — belong to the austenitic family (300 series) of stainless steels. Austenitic stainless steels are non-magnetic (in the annealed condition), highly formable, weldable, and corrosion-resistant. They get their corrosion resistance from chromium (which forms a passive oxide layer on the surface) and their austenitic structure from nickel.
The differences between grades come from the addition of specific alloying elements:
304 — the baseline. 18% chromium, 8% nickel. No significant additions.
316 — adds 2–3% molybdenum for superior resistance to chlorides and pitting.
321 — adds titanium (min 5× carbon content) for resistance to intergranular corrosion at high temperatures.
Chemical Composition
Element | 304 | 304L | 316 | 316L | 321 |
|---|---|---|---|---|---|
Carbon (C) max | 0.08% | 0.030% | 0.08% | 0.030% | 0.08% |
Chromium (Cr) | 18.0–20.0% | 18.0–20.0% | 16.0–18.0% | 16.0–18.0% | 17.0–19.0% |
Nickel (Ni) | 8.0–10.5% | 8.0–12.0% | 10.0–14.0% | 10.0–14.0% | 9.0–12.0% |
Molybdenum (Mo) | — | — | 2.0–3.0% | 2.0–3.0% | — |
Titanium (Ti) | — | — | — | — | 5×C min |
Manganese (Mn) max | 2.0% | 2.0% | 2.0% | 2.0% | 2.0% |
Silicon (Si) max | 0.75% | 0.75% | 0.75% | 0.75% | 0.75% |
Phosphorus (P) max | 0.045% | 0.045% | 0.045% | 0.045% | 0.045% |
Sulfur (S) max | 0.030% | 0.030% | 0.030% | 0.030% | 0.030% |
What "L" means: The "L" grades (304L, 316L) have lower maximum carbon content (0.030% vs 0.08%). This prevents chromium carbide precipitation during welding — a phenomenon called sensitization — which depletes chromium from grain boundaries and makes the steel vulnerable to intergranular corrosion in the heat-affected zone. For any stainless steel plate that will be welded, always specify the L grade (304L or 316L). The cost difference is negligible; the performance difference in welded joints is significant.
Mechanical Properties
Property | 304/304L | 316/316L | 321 |
|---|---|---|---|
Tensile strength, min | 515 MPa (75 ksi) | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
Yield strength (0.2%), min | 205 MPa (30 ksi) | 205 MPa (30 ksi) | 205 MPa (30 ksi) |
Elongation in 50mm, min | 40% | 40% | 40% |
Hardness, max | 201 HBW | 217 HBW | 217 HBW |
Max continuous service temp | 870°C (1,600°F) | 870°C (1,600°F) | 925°C (1,700°F) |
Sensitization range | 425–870°C | 425–870°C | Resistant (Ti-stabilized) |
Density | 8.0 g/cm³ | 8.0 g/cm³ | 8.0 g/cm³ |
Magnetic | No (annealed) | No (annealed) | No (annealed) |
Key takeaway: All three grades have virtually identical tensile and yield strength at room temperature. The differences show up in corrosion resistance and high-temperature behavior — not in mechanical strength.
Corrosion Resistance Comparison
This is where grade selection really matters:
Environment | 304 | 316 | 321 | Winner |
|---|---|---|---|---|
Atmospheric (urban, industrial) | Good | Excellent | Good | 316 |
Fresh water | Excellent | Excellent | Excellent | All equal |
Seawater / marine | Poor (pitting) | Good | Poor | 316 mandatory |
Chloride solutions | Poor | Good | Poor | 316 mandatory |
Dilute organic acids | Good | Good | Good | All equal |
Nitric acid | Excellent | Good | Good | 304 |
Sulfuric acid | Poor | Moderate | Poor | Neither (use higher alloys) |
Caustic (NaOH) | Good | Good | Good | All equal |
High-temp oxidation (>500°C) | Good | Good | Excellent | 321 preferred |
Polythionic acid (refinery) | Susceptible | Susceptible | Resistant | 321 mandatory |
Intergranular corrosion (welded) | Susceptible (use 304L) | Susceptible (use 316L) | Resistant (Ti-stabilized) | 321 or L grades |
The simple decision rules:
No chlorides, no high temperature, general corrosion resistance needed → 304/304L (cheapest, most available)
Chlorides present (seawater, coastal, swimming pools, chemical plants with chloride solutions) → 316/316L (molybdenum provides pitting resistance)
Continuous high temperature above 500°C with thermal cycling, or refinery service with polythionic acid risk → 321 (titanium prevents sensitization)
Welded fabrication in any grade → always specify L grade (304L or 316L) unless using 321
Plate Specifications and Standards
Standard | Scope |
|---|---|
ASTM A240 | SS plate, sheet, and strip for pressure vessels and general applications — the primary standard |
ASTM A167 | SS plate for general applications (older standard, being replaced by A240) |
EN 10088-2 | European standard for SS flat products (plate, sheet, strip) |
JIS G4304/G4305 | Japanese standards for SS hot-rolled and cold-rolled plate/sheet |
ASME SA240 | ASME Boiler & Pressure Vessel Code equivalent of ASTM A240 (for ASME code-stamped equipment) |
ASTM A240 is the standard you need for virtually all industrial stainless steel plate procurement. It covers chemical composition, mechanical properties, and testing requirements for all austenitic grades including 304, 304L, 316, 316L, 321, 310, 317L, 904L, and duplex grades.
Available Sizes
Parameter | Typical Range |
|---|---|
Thickness | 1.0mm to 150mm (3/64" to 6") |
Width | 1,000mm, 1,219mm (4'), 1,500mm, 2,000mm, 2,500mm |
Length | 2,000mm, 2,438mm (8'), 3,000mm, 6,000mm (20'), custom lengths |
Surface finish | No.1 (hot-rolled, annealed, pickled — standard for plate), 2B (cold-rolled, smooth), No.4 (brushed), BA (mirror) |
Edge | Mill edge (standard for plate), slit edge, sheared edge |
Standard mill plate dimensions: 1,500mm × 6,000mm or 2,000mm × 6,000mm in hot-rolled No.1 finish. Larger sizes and custom cutting available on request.
For pressure vessel and equipment fabrication: Plates are typically ordered to the exact dimensions required for the fabrication, with mill test certificates specifying the heat number, chemical composition, and mechanical test results per ASTM A240.
Grade Selection Guide: Which Grade for Which Application?
Application | Recommended Grade | Why |
|---|---|---|
Food processing equipment | 304L or 316L | Hygienic, easy to clean, corrosion-resistant. 316L for dairy, brewing, or acidic foods. |
Chemical processing tanks | 316L | Chloride and acid resistance. Use 317L or higher alloys for aggressive chemicals. |
Pharmaceutical equipment | 316L | Hygienic, corrosion-resistant, ASME BPE compliant surface finish |
Marine / coastal structures | 316 or 316L | Molybdenum resists chloride pitting. 304 will pit in marine environments. |
Pressure vessels (general) | 304L or 316L | Per ASME Section VIII. L grade for welded construction. |
Heat exchangers (general) | 316L | Corrosion resistance + weldability |
Heat exchangers (high-temp refinery) | 321 | Resists sensitization and polythionic acid cracking |
Expansion joints / bellows | 321 or 316L | 321 for high-temp cycling, 316L for corrosive service |
Exhaust systems / furnace parts | 321 or 310 | 321 up to 925°C, 310 for higher temperatures |
Architectural / decorative | 304 (No.4 or BA finish) | Appearance, corrosion resistance, lowest cost |
Water treatment equipment | 316L | Chlorinated water environments demand chloride resistance |
Nuclear components | 304L or 316L | Per ASME Section III requirements |
Tank fabrication (general storage) | 304L | Cost-effective, good corrosion resistance for most stored fluids |
Offshore platform structures | 316L or duplex 2205 | Marine chloride environment |
Pulp and paper industry | 316L or 317L | Chloride-containing bleaching chemicals |
304 vs 316: How to Decide
This is the #1 question buyers ask. Here is the practical decision framework:
Choose 304/304L when:
The environment has no significant chloride exposure
The application involves fresh water, mild chemicals, or atmospheric exposure (non-coastal)
Budget is a primary concern — 304 is typically 15–25% cheaper than 316
The application is architectural, structural, or general-purpose
Choose 316/316L when:
Chlorides are present in any concentration (seawater, brackish water, road salt, chlorinated water)
The application involves chemical processing with acids or aggressive solutions
The plate will be used in marine, coastal, or offshore environments
Food/pharmaceutical regulations specify 316 grade
The higher cost is justified by significantly longer service life in the specific environment
When in doubt, specify 316L. The price premium over 304L is 15–25%, but the corrosion performance in any environment containing chlorides is dramatically better. In environments where 304 would need replacement in 5 years, 316 will last 20+ years — making it far more economical over the lifecycle.
What Documentation to Request
When procuring stainless steel plate, always request:
EN 10204 Type 3.1 Mill Test Certificate (MTC) — showing heat number, chemical composition (actual analysis vs specification limits), and mechanical test results (tensile, yield, elongation, hardness). This is the minimum for any industrial plate purchase.
PMI (Positive Material Identification) test — for critical applications, PMI testing using handheld XRF or OES analyzers verifies that the plate is actually the grade specified. PMI prevents material mix-ups, which can be catastrophic in chemical and refinery service. Many EPC contractors and national oil companies require PMI as standard.
Surface inspection report — for plates used in food, pharmaceutical, or pressure vessel applications, verify the surface finish meets the required standard (Ra value for surface roughness if specified).
Ultrasonic testing (UT) — for thick plates (typically >25mm) used in pressure vessel fabrication, UT per ASTM A578 or SA578 verifies the plate is free from internal laminations and inclusions.
Supply from Kasko Makine
Kasko Makine supplies stainless steel plate in all common grades and sizes for fabrication, construction, and industrial projects:
Grades: 304, 304L, 316, 316L, 321, 310S, 317L, 904L, duplex 2205, super duplex 2507
Standard: ASTM A240 / ASME SA240, EN 10088-2
Thickness: 1.0mm to 150mm
Widths: 1,000mm, 1,219mm, 1,500mm, 2,000mm, 2,500mm
Lengths: 2,000mm, 2,438mm, 3,000mm, 6,000mm, custom cut
Surface finish: No.1 (HR), 2B (CR), No.4 (brushed), BA (bright annealed)
Cutting services: Plasma, laser, waterjet, and shear cutting to your dimensions
We also supply stainless steel pipe (ASTM A312), stainless steel fittings (ASTM A403), stainless steel flanges (ASTM A182), and stainless steel fasteners (ASTM A193 B8/B8M) — complete stainless steel material packages for your fabrication project.
All plate supplied with EN 10204 Type 3.1 mill test certificates. PMI testing, UT inspection, and third-party verification available on request.
FAQ SCHEMA
Q: What is the difference between 304 and 316 stainless steel plate?
A: The key difference is molybdenum. 316 contains 2–3% molybdenum, which gives it significantly better resistance to chloride corrosion and pitting. 304 has no molybdenum. Choose 304 for non-chloride environments where cost matters. Choose 316 for any application involving seawater, coastal exposure, chlorinated water, or chemical processing with chloride solutions.
Q: What does the "L" mean in 304L and 316L?
A: The "L" stands for low carbon. 304L and 316L have a maximum carbon content of 0.030% compared to 0.08% for standard 304 and 316. The lower carbon prevents chromium carbide precipitation (sensitization) during welding, which protects against intergranular corrosion in the weld heat-affected zone. Always specify L grades for welded stainless steel fabrication.
Q: When should I use 321 stainless steel instead of 304 or 316?
A: Use 321 when the application involves continuous exposure to temperatures in the 425–870°C range, where 304 and 316 are susceptible to sensitization and intergranular corrosion. 321 is titanium-stabilized, which prevents chromium carbide formation at elevated temperatures. Common applications include refinery heat exchangers, exhaust manifolds, furnace parts, and expansion joints subject to thermal cycling.
Q: What is the standard specification for stainless steel plate?
A: ASTM A240 (and its ASME equivalent SA240) is the primary specification for stainless steel plate, sheet, and strip for pressure vessels and general applications. It covers chemical composition, mechanical properties, and testing requirements for all common grades including 304, 304L, 316, 316L, 321, 310S, and duplex grades.
Q: How much more does 316 stainless steel plate cost than 304?
A: 316/316L plate typically costs 15–25% more than 304/304L of the same thickness and size. The premium is due to the molybdenum and higher nickel content in 316. However, in chloride-containing environments, 316 lasts significantly longer than 304 — often 4× or more — making it far more cost-effective over the lifecycle despite the higher purchase price.
Q: What documentation should I receive with stainless steel plate?
A: At minimum, an EN 10204 Type 3.1 Mill Test Certificate (MTC) showing the heat number, actual chemical composition, and mechanical test results. For critical applications, also request PMI (Positive Material Identification) testing, ultrasonic testing (UT) per ASTM A578 for thick plates, and surface finish verification.
Request stainless steel plate pricing — send us your grade, thickness, width, length, quantity, and any special requirements (surface finish, testing, cutting) to info@kaskomakine.com or WhatsApp +90 (537) 521 13 99. We respond within 24 hours and deliver to fabrication shops and project sites across Africa, the Middle East, Central Asia, and beyond.