A36 Steel: Properties, Composition & Applications of ASTM A36 Carbon Steel
ASTM A36/A36M · Published: 2026-07-25 · Updated: July 2026
A36 steel (ASTM A36/A36M) is the most widely used structural carbon steel in North America and the default specification for beams, channels, angles, plates, and bars in building construction, bridges, and general fabrication. The '36'...
A36 steel (ASTM A36/A36M) is the most widely used structural carbon steel in North America and the default specification for beams, channels, angles, plates, and bars in building construction, bridges, and general fabrication. The '36' designation refers to its 36 ksi (250 MPa) minimum yield strength—the baseline structural strength against which all other structural grades are measured. A36 contains 0.25-0.29% carbon, 0.80-1.20% manganese, ≤0.04% phosphorus, and ≥0.05% sulfur, providing an optimal balance of strength, weldability, machinability, and low cost. It is produced in every standard section size by all U.S. steel mills (Nucor, Gerdau, Steel Dynamics) and stocked by every steel service center with the shortest lead times and lowest prices of any structural grade. A36 is the default material for building frameworks, transmission towers, bridge components, machinery frames, base plates, gussets, and stiffeners. Not recommended for: cryogenic service (brittle transition below -20°C), high-temperature pressure vessels (use SA-516 Gr 70), or applications requiring hardenability (use AISI 1045 or 4140 for heat-treated wear resistance). For higher-strength structural applications, a572-steel/">A572 steel (345 MPa yield) or European s355-steel/">S355 steel (355 MPa yield) are common upgrades. For the full ASTM A36 data sheet with detailed mechanical, physical, and welding properties, see astm-a36/">ASTM A36 Carbon Steel.
Quick Facts
| Category | Carbon Steel |
| Standard | ASTM A36/A36M |
| Density | 7.85 g/cm³ |
| Yield Strength | 250 MPa (36 ksi) |
| Tensile Strength | 400-550 MPa (58-80 ksi) |
Detailed Mechanical Properties
| Elongation | 20% (in 200mm) |
| Hardness | 119-159 HB |
| Charpy V Notch | 27J at 0°C (longitudinal) |
| Shear Modulus | 79.3 GPa |
Physical Properties
| Melting Point | 1425-1540 °C |
| Thermal Conductivity | 52 W/m·K at 20°C |
| Electrical Resistivity | 0.0000174 Ω·cm |
| Specific Heat | 486 J/kg·K |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| ASTM A36 | Compare |
| Q235B | Compare |
| S275JR | Compare |
| SS400 | Compare |
| E250 | Compare |
| St37-2 | Compare |
Heat Treatment & Processing
| Normalizing | 890-940°C, air cool |
| Annealing | 840-880°C, furnace cool |
| Stress Relieving | 595-650°C, 1h per 25mm, air cool |
| Note | A36 is typically used in as-rolled condition; heat treatment is uncommon for structural applications |
Welding & Fabrication
| Preheat | Not required for thicknesses under 20mm; 50-100°C for 20-40mm; 100-150°C for >40mm |
| Filler Metal | E7018 (SMAW), ER70S-6 (GMAW), E71T-1 (FCAW) |
| Interpass Temp | Max 315°C |
| Weldability Rating | Excellent — one of the most weldable carbon steels |
Related Materials
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Frequently Asked Questions
What is A36 steel used for?
A36 is the default structural steel for buildings (beams, columns, base plates), bridges, transmission towers, machinery frames, automotive frames, agricultural equipment, sign posts, and general fabrication. It is the most available and cheapest structural grade in North America.
Is A36 steel the same as mild steel?
A36 is a specific ASTM-grade mild (low-carbon) structural steel. 'Mild steel' is a general term for any low-carbon steel (0.05-0.25% C), which includes A36 but also AISI 1018, 1020, and others. A36 has tighter chemistry and mechanical requirements than generic mild steel, with guaranteed 36 ksi minimum yield.
Can A36 steel be welded?
Yes—A36 is one of the most weldable carbon steels. With carbon equivalent typically below 0.40, A36 requires no preheat for thicknesses under 20 mm using E7018 (SMAW), ER70S-6 (GMAW), or E71T-1 (FCAW). For thicker sections (>20 mm), 50-100°C preheat is recommended. No post-weld heat treatment is required for structural applications.
Can A36 be hardened by heat treatment?
Limited hardenability. A36's low carbon content (0.25-0.29%) gives low response to quenching—through-hardening is impractical for sections over 12 mm. Surface hardening (carburizing, induction hardening) is possible but uncommon. For wear-resistant or hardened components, use AISI 1045 (medium carbon) or 4140 (alloy steel) instead.
What is the difference between A36 and A572 steel?
A36 has 250 MPa (36 ksi) minimum yield; A572 Grade 50 has 345 MPa (50 ksi)—38% stronger. A572 Gr 50 achieves higher strength through micro-alloying (vanadium, niobium) without increasing carbon, preserving good weldability. A572 Gr 50 is increasingly the default for new construction; A36 remains common for repair, simple structures, and projects valuing weldability.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Structural & Carbon Steel — Engineering Reference
Structural steels are the backbone of construction and heavy industry. Grades in this category are specified primarily by their yield strength, tensile strength, and weldability — the three properties that determine whether a building stands or a bridge holds.
ASTM A36/A572/A516, EN 10025, JIS G3101/G3106, GB/T 700/1591
Building frames, bridges, pressure vessels, shipbuilding, offshore platforms, pipelines
When selecting a structural grade, match the required yield strength to the design load, but also verify Charpy impact values if the structure will operate below freezing — many structural steels undergo a ductile-to-brittle transition at low temperatures.