Quick Answer
Quick Answer
ASTM A240 covers chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels and general applications. It defines chemical composition limits and mechanical property minimums for over 50 grades, from common austenitic types like 304 and 316L to duplex and ferritic alloys.
ASTM A240/A240M is one of the most widely cited stainless steel product standards in global fabrication. Issued by ASTM International, it governs flat-rolled stainless product in three forms: plate (thickness ≥ 4.75 mm or width ≥ 600 mm), sheet (thickness < 4.75 mm, width ≥ 600 mm), and strip (width < 600 mm). The M suffix in A240M indicates the SI unit version; both versions are maintained in parallel.
Scope and Applicability
A240 applies to heat-resisting chromium steels and chromium-nickel stainless steels intended for:
- Pressure vessels and pressure-retaining components
- General corrosion-resistant applications
- Food-processing and pharmaceutical equipment
- Architectural and structural applications (where grades permit)
The standard does not cover bar, rod, wire, or pipe forms. Those are addressed by separate ASTM standards (A276 for bar, A312 for pipe).
Grade Coverage
A240 includes more than 50 UNS-designated grades organized into families:
| Family | Typical Grades | UNS Numbers |
|---|---|---|
| Austenitic (300-series) | 304, 304L, 316, 316L, 317L, 321, 347 | S30400, S30403, S31600, S31603... |
| Ferritic (400-series) | 430, 439, 444 | S43000, S43035, S44400 |
| Martensitic | 410, 420 | S41000, S42000 |
| Duplex | 2205, 2507 | S32205, S32750 |
| Lean Duplex | LDX 2101, 2304 | S32101, S32304 |
| Super Austenitic | 904L, 6% Mo grades | N08904, S31254 |
Chemical Composition Requirements
The following table shows the composition limits for the most commonly ordered grades. All values are wt% maximum unless a range or minimum is noted.
| Grade | C max | Mn max | Si max | Cr | Ni | Mo | N |
|---|---|---|---|---|---|---|---|
| 304 | 0.07 | 2.00 | 0.75 | 17.5–19.5 | 8.0–10.5 | — | — |
| 304L | 0.030 | 2.00 | 0.75 | 17.5–19.5 | 8.0–12.0 | — | — |
| 316 | 0.07 | 2.00 | 0.75 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | — |
| 316L | 0.030 | 2.00 | 0.75 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | — |
| 316Ti | 0.08 | 2.00 | 0.75 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | — |
| 2205 | 0.030 | 2.00 | 1.00 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | 0.14–0.20 |
Note: P and S are controlled in all grades (typically P ≤ 0.045, S ≤ 0.030 for most grades). Refer to the current edition of A240 for complete limits.
Mechanical Property Requirements
Mechanical properties are determined by tensile testing per ASTM A370. Minimum requirements for key grades:
| Grade | Tensile Str. min (MPa) | Yield Str. 0.2% min (MPa) | Elongation min % | Hardness max |
|---|---|---|---|---|
| 304 | 515 | 205 | 40 | 92 HRB |
| 304L | 485 | 170 | 40 | 88 HRB |
| 316 | 515 | 205 | 40 | 95 HRB |
| 316L | 485 | 170 | 40 | 95 HRB |
| 2205 | 620 | 450 | 25 | 31 HRC |
| 2507 | 795 | 550 | 15 | 32 HRC |
Elongation is measured on a 50 mm gauge length for sheet/strip and a 200 mm gauge length for plate, unless otherwise specified.
Heat Treatment
A240 requires that all austenitic grades be supplied in the annealed condition unless otherwise specified on the purchase order. The standard defines the minimum annealing temperature for each grade family:
- Austenitic 300-series: solution anneal at ≥ 1040 °C (1900 °F), water quench or rapid air cool
- Ferritic 400-series: anneal at 760–900 °C depending on grade
- Duplex grades: solution anneal at ≥ 1020–1080 °C, rapid quench
Improper annealing leads to sensitization (chromium carbide precipitation at grain boundaries), which severely reduces intergranular corrosion resistance. The MTC should confirm the heat-treatment temperature and method.
Testing and Inspection Requirements
Each heat of material requires the following minimum tests:
- Chemical analysis — one per heat (ladle analysis). Product analysis may be required if specified.
- Tensile test — one test specimen per lot (lot = same heat and same heat treatment condition).
- Hardness test — Brinell or Rockwell per ASTM E18/E10; frequency defined in the standard.
- Surface and visual inspection — all material.
Optional tests (if invoked on the purchase order):
- Intergranular corrosion test (ASTM A262)
- Ferrite measurement (duplex grades)
- Charpy impact at sub-zero temperatures
- Ultrasonic examination
Ordering Information
A complete A240 purchase order should specify:
- ASTM A240 (edition year if required)
- Grade designation (e.g., Type 316L)
- Dimensions: thickness × width × length (or coil weight)
- Finish: No. 1, 2B, 2D, BA, No. 4, No. 8 (mirror)
- Quantity (kg or sheets)
- Any supplementary requirements (S1 through S13)
- Certification requirements (e.g., EN 10204 3.1 test report)
Reading the MTC for A240 Material
When verifying a mill test certificate for A240 material, confirm:
- The standard designation matches the purchase order (including grade)
- Heat number is traceable to physical markings on the material
- Chemical analysis values fall within the A240 limits for the specified grade
- Mechanical test results meet the minimums in the table above
- Annealing condition is stated
- The certificate is signed/stamped by the mill's authorized representative
TestCert automates this check by storing A240 composition and mechanical limits as structured data, flagging any value that falls outside the specification without requiring manual reference to the standard text.
Frequently Asked Questions
What is the difference between ASTM A240 Grade 304 and Grade 304L?
The primary difference is carbon content. Grade 304L has a maximum carbon of 0.030 wt% versus 0.07 wt% for 304. The lower carbon in 304L reduces the risk of sensitization during welding, making it preferred for welded components that will be used in corrosive environments without post-weld annealing.
Does ASTM A240 cover duplex stainless steel?
Yes. A240 includes duplex grades such as 2205 (UNS S32205) and super duplex 2507 (UNS S32750). These grades have higher yield strength than austenitic grades and improved chloride stress corrosion resistance, but require careful heat treatment control.
What surface finish designations are used in ASTM A240?
Common finishes include: No. 1 (hot-rolled, annealed, descaled), 2D (cold-rolled, annealed, dull), 2B (cold-rolled, annealed, light skin-pass — most common), BA (bright annealed), No. 4 (brushed), and No. 8 (mirror polished). The finish must be specified on the purchase order.
Is ASTM A240 the same as ASME SA-240?
They are nearly identical. ASME SA-240 is ASTM A240 adopted into the ASME Boiler and Pressure Vessel Code Section II, Part A. SA-240 may include additional ASME-specific requirements. For pressure-vessel fabrication requiring ASME code compliance, SA-240 must be invoked, not A240. See our comparison page for full details.
How many test specimens are required per heat under A240?
A240 requires one tensile test specimen per lot, where a lot is defined as all material of the same heat, same product form, same nominal thickness, and same heat treatment condition. For large heats, multiple lots may be required.
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