Quick Answer
Quick Answer
ASTM A36 covers a single carbon-steel grade with a minimum yield strength of 250 MPa (36 ksi) and a UTS range of 400–550 MPa. ASTM A572 covers five high-strength low-alloy (HSLA) grades — Gr42, Gr50, Gr55, Gr60, and Gr65 — defined by minimum yield strength only, with no upper UTS limit. A572 Gr50 can generally substitute for A36 at a cost premium, but requires documentation of compliance with both standards or a substitution letter.
ASTM A36/A36M and ASTM A572/A572M are the two most widely specified structural steel standards in North American construction and fabrication. A36 is a carbon-steel standard governing plates, shapes, and bars for general structural use. A572 is a columbium-vanadium high-strength low-alloy (HSLA) standard offering five strength levels for weight-efficient structural design. Both are issued by ASTM International; the M suffix denotes the SI-unit edition.
Scope and Applicability
ASTM A36 applies to:
- Carbon-steel plates up to 200 mm (8 in.) thick
- Structural shapes (W, S, C, L, HP, MC sections)
- Bars — flat, round, and square
ASTM A572 applies to:
- High-strength low-alloy columbium-vanadium steel plates, sheets, piling, and structural shapes
- Plates: thickness limits vary by grade (see table below)
- Hot-rolled structural shapes and sheet piling
Both standards are used primarily for building frames, bridges, tanks, machinery bases, and general fabricated structures.
Grade Coverage
| Standard | Grade | Strength Basis | Common Product Forms |
|---|---|---|---|
| A36 | A36 | Carbon steel, single grade | Plate, shapes, bars |
| A572 | Gr42 | HSLA, 42 ksi (290 MPa) min YS | Plate, shapes, sheet piling |
| A572 | Gr50 | HSLA, 50 ksi (345 MPa) min YS | Plate, shapes, sheet piling |
| A572 | Gr55 | HSLA, 55 ksi (380 MPa) min YS | Plate, shapes |
| A572 | Gr60 | HSLA, 60 ksi (415 MPa) min YS | Plate |
| A572 | Gr65 | HSLA, 65 ksi (450 MPa) min YS | Plate ≤ 32 mm |
A572 Gr65 thickness limit: Plates are restricted to a maximum of 32 mm (1¼ in.) thick. Gr60 plates are limited to 32 mm for shapes and 19 mm for certain applications; confirm current edition limits for project use.
Chemical Composition Requirements
ASTM A36 — Chemical Composition (wt%, ladle analysis)
| Element | ≤ 19 mm thick | 19–38 mm thick | 38–57 mm thick | > 57 mm thick |
|---|---|---|---|---|
| C max | 0.25 | 0.25 | 0.26 | 0.27 |
| Mn | — | 0.80–1.20 | 0.80–1.20 | 0.85–1.20 |
| P max | 0.04 | 0.04 | 0.04 | 0.04 |
| S max | 0.05 | 0.05 | 0.05 | 0.05 |
| Si | 0.40 max | 0.15–0.40 | 0.15–0.40 | 0.15–0.40 |
| Cu min (when specified) | 0.20 | 0.20 | 0.20 | 0.20 |
For shapes and bars ≤ 19 mm: Mn is not specified when C ≥ 0.24%; Si 0.40% max. Refer to current A36 edition for shape-specific requirements.
ASTM A572 — Chemical Composition by Grade (wt%, ladle analysis)
| Element | Gr42 | Gr50 | Gr55 | Gr60 | Gr65 |
|---|---|---|---|---|---|
| C max (plates ≤ 40 mm) | 0.21 | 0.23 | 0.25 | 0.26 | 0.26 |
| C max (plates > 40 mm) | 0.21 | 0.23 | 0.25 | — | — |
| Mn max | 1.35 | 1.35 | 1.35 | 1.35 | 1.35 |
| P max | 0.04 | 0.04 | 0.04 | 0.04 | 0.04 |
| S max | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 |
| Si max | 0.40 | 0.40 | 0.40 | 0.40 | 0.40 |
| Nb (Columbium) | 0.005–0.05 | 0.005–0.05 | 0.005–0.05 | 0.005–0.05 | 0.005–0.05 |
| V max | 0.11 | 0.11 | 0.11 | 0.11 | 0.11 |
| Ti max | 0.04 | 0.04 | 0.04 | 0.04 | 0.04 |
| Nb+V+Ti max | — | — | 0.15 | 0.15 | 0.15 |
A572 requires that at least one of Nb, V, or Ti be present. The exact combination is at the producer's option.
Mechanical Properties
ASTM A36 — Mechanical Properties (all thicknesses, plates and shapes)
| Property | Requirement |
|---|---|
| Yield Strength min | 250 MPa (36 ksi) |
| Tensile Strength | 400–550 MPa (58–80 ksi) |
| Elongation in 200 mm (8 in.) min | 20% |
| Elongation in 50 mm (2 in.) min | 23% |
A36 is one of the few structural steel standards specifying an upper tensile limit (550 MPa), which constrains weldability by preventing excessively high carbon equivalents.
ASTM A572 — Mechanical Properties by Grade
| Grade | Min Yield Strength MPa (ksi) | Min Tensile Strength MPa (ksi) | Elongation in 200 mm min % | Elongation in 50 mm min % |
|---|---|---|---|---|
| Gr42 | 290 (42) | 415 (60) | 20 | 24 |
| Gr50 | 345 (50) | 450 (65) | 18 | 21 |
| Gr55 | 380 (55) | 485 (70) | 17 | 20 |
| Gr60 | 415 (60) | 520 (75) | 16 | 18 |
| Gr65 | 450 (65) | 550 (80) | 15 | 17 |
A572 has no upper UTS limit. The designer may specify Charpy impact testing (supplementary requirement S91) for low-temperature applications.
Additional Tests and Requirements
- Bend test: Required for plates and bars per A36; specimen width and bend radius vary by thickness.
- Heat analysis: One ladle analysis per heat; product analysis by the purchaser at product analysis tolerances per A6/A6M.
- Marking: Each piece must be marked with the standard, grade, heat number, and mill identification.
- Flatness and straightness: Governed by ASTM A6/A6M general requirements for structural steel, which applies to both standards.
- Supplementary Requirements (A572): S1 (Charpy V-Notch impact), S4 (Ultrasonic examination of plates), S91 (fracture toughness for seismic applications) may be invoked on the purchase order.
ASME Equivalents
| ASTM Standard | ASME Equivalent | Code Section |
|---|---|---|
| A36 | SA-36 | ASME Sec II Part A |
| A572 Gr42 | SA-572 Gr42 | ASME Sec II Part A |
| A572 Gr50 | SA-572 Gr50 | ASME Sec II Part A |
| A572 Gr55 | SA-572 Gr55 | ASME Sec II Part A |
| A572 Gr60 | SA-572 Gr60 | ASME Sec II Part A |
| A572 Gr65 | SA-572 Gr65 | ASME Sec II Part A |
SA-36 and SA-572 are technically identical to their ASTM counterparts. Pressure-vessel and boiler fabrication subject to ASME Boiler and Pressure Vessel Code (BPVC) must invoke the SA- designation.
Cross-Standard Equivalents
ASTM A36 Equivalents
| Standard | Grade | YS min MPa | Notes |
|---|---|---|---|
| EN 10025-2 | S235JR | 235 | Slightly lower YS; Si and C differ |
| IS 2062 | E250 Gr A | 250 | Near-identical YS; Indian standard |
| JIS G3101 | SS400 | 245 | Comparable general structural grade |
| GB/T 700 | Q235B | 235 | Chinese equivalent; Mn and Si limits differ |
ASTM A572 Equivalents
| A572 Grade | EN 10025-2 | IS 2062 | JIS G3106 | GB/T 1591 |
|---|---|---|---|---|
| Gr42 | S275JR | E275 | SM400B | Q345B (partial) |
| Gr50 | S355JR | E350 | SM490B | Q345B |
| Gr55 | S380 / S420 (approx) | E410 | SM520B | Q390B |
| Gr60 | S420M | E450 | SM570 | Q420B |
| Gr65 | S460M | — | — | Q460C |
Cross-standard equivalents are approximate. Chemistry limits and testing requirements differ between standards; direct substitution requires review of applicable code provisions.
Substitution Rules: A572 Gr50 for A36
A572 Gr50 is frequently substituted for A36 because its minimum yield strength (345 MPa) exceeds A36's (250 MPa). Before substituting:
- Verify UTS compatibility: A36 has UTS max 550 MPa; A572 Gr50 has no UTS upper limit. Some connection designs using A36's upper UTS bound require specific attention.
- Obtain a substitution letter: The mill or supplier must confirm the material meets A36 in addition to A572 Gr50, or the design engineer must accept the substitution in writing.
- Check weld procedure: Higher yield strength may require re-qualification of WPS/PQR per AWS D1.1.
- ASME pressure vessels: Substitution is only permitted if both SA-36 and SA-572 Gr50 are listed in the applicable code case.
MTC Verification Checklist
When verifying a mill test certificate for A36 or A572 material, confirm:
- Standard designation and grade match the purchase order exactly
- Heat number is traceable to physical markings on the plate or shape
- Carbon content complies with the thickness-dependent limits (A36) or grade limits (A572)
- For A572: at least one of Nb, V, or Ti is reported
- Yield strength, tensile strength, and elongation meet the minimums in the tables above
- A36 UTS does not exceed 550 MPa
- Certificate is signed by the mill's authorized representative with date
- Product analysis tolerances (if product analysis was performed) are within A6/A6M limits
Frequently Asked Questions
What is the main difference between ASTM A36 and ASTM A572 Grade 50?
The key difference is strength level and specification approach. A36 has a minimum yield strength of 250 MPa and a UTS range of 400–550 MPa (with an upper limit). A572 Gr50 has a minimum yield strength of 345 MPa with no upper UTS limit. A572 also uses columbium (niobium) and/or vanadium microalloying to achieve higher strength at similar thickness, while A36 is a plain carbon steel.
Why does ASTM A36 specify an upper tensile strength limit but A572 does not?
A36's upper UTS limit of 550 MPa was historically important for ensuring adequate ductility and weldability in plain carbon steel. A572 uses controlled microalloying (Nb, V, Ti) to achieve high strength without excessive carbon, so the upper limit is unnecessary — the alloy design inherently controls toughness and weldability.
What are the maximum plate thicknesses for ASTM A572 Grade 65?
A572 Gr65 is limited to plates up to 32 mm (1¼ in.) thick. Grades 42, 50, and 55 are available up to 150 mm (6 in.) thick for plates, subject to the latest edition of the standard.
Is SA-36 the same as ASTM A36?
Yes, technically. ASME SA-36 adopts ASTM A36 into the ASME Boiler and Pressure Vessel Code Section II Part A with no technical changes. For any pressure-vessel application governed by ASME BPVC, the purchase order must reference SA-36, not A36.
Can I use ASTM A572 Gr50 instead of A36 without engineering approval?
Generally no. Even though A572 Gr50 exceeds A36's minimum yield strength, substitution requires engineering approval because the two standards differ in UTS range, chemistry, and supplementary requirements. The substitution should be documented in writing by the engineer of record or approved via a formal substitution letter from the supplier confirming dual compliance.
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