ASTM A36 (also written A36/A36M) is the most widely used low-carbon structural steel for plates, shapes, and bars in welded, bolted, and riveted construction. It’s popular because it combines dependable strength, good weldability/formability, broad availability, and reasonable price.
What A36 Covers (and what it doesn’t)
- Scope: Carbon structural steel for plates, shapes, and bars used in general structures (buildings, bridges, machinery bases, tanks, skids). A36 itself is the material grade; general dimensional tolerances for shapes/plates are governed by ASTM A6/A6M.
- Why it’s ubiquitous: It welds readily with common processes (GMAW/SMAW/FCAW/SAW), cold- or hot-forms without fuss, and machines acceptably for non-precision parts.
Chemical Composition (typical limits)
| Element | Max / Range* |
|---|---|
| Carbon (C) | ≤ ~0.25–0.29% |
| Manganese (Mn) | ~0.80–1.20% |
| Phosphorus (P) | ≤ 0.04% |
| Sulfur (S) | ≤ 0.05% |
| Silicon (Si) | ≤ 0.40% |
| Copper (Cu) | ~0.20% (when specified) |
- Exact limits vary with product form and thickness—always confirm on the Mill Test Certificate (MTC). Sources summarizing the typical ranges: Industrial Metal Supply, Octal Steel, Metals USA.
What the chemistry means in practice: Low carbon + modest Mn ⇒ good weldability and ductility, but limited through-hardening by heat treatment; if you need higher strength without adding thickness, you usually step up to HSLA grades (e.g., A572).
Mechanical Properties (reference)
- Yield strength (min): 36 ksi (≈ 250 MPa)
- Tensile strength (typical window): 58–80 ksi (≈ 400–550 MPa)
- Elongation: commonly ~20% (depends on thickness/shape)
Values depend on thickness and product form—plate vs. shapes vs. bar can differ slightly. Always purchase to the governing spec and review the MTC.
Machinability & fabrication
- Machinability index ~72% (vs. 100% for AISI 1112 reference) with typical cutting speeds ~120 ft/min—adequate for general work, but not as easy as 1018.
- Weldability: readily weldable with common processes; preheat usually minimal for thin to medium sections, guided by joint design and carbon equivalent.
Dimensional Tolerances
ASTM A36 gives the grade; ASTM A6/A6M gives the mill tolerances for structural shapes and plates (straightness, camber, twist, thickness, width/length). Designers and buyers typically also apply AISC Manual tables derived from A6 when checking fit-up risk.
Product Forms & Common Supply Conditions
- Plates (HR, often P&O), wide-flange beams, channels, angles, bars (flats, rounds, squares), and flame- or laser-cut blanks. Surface is mill scale in as-rolled condition; pickling, blasting/priming available.
A36 vs. Nearby Structural Grades
A36 vs. A572 Grade 50 (HSLA)
- A572 Gr50 has higher yield strength (50 ksi) and better strength-to-weight; A36 is easier to form and usually cheaper. They serve similar markets (plate, shapes) but are not interchangeable without re-checking design.
For general structural purposes, engineers often cross-reference A36 with “~235–250 MPa yield” steels:
| System | Grade (typical) | Comment |
|---|---|---|
| EN 10025-2 | S235JR | Very close strength window to A36; JR adds a Charpy impact level (27 J @ +20 °C) that A36 itself doesn’t mandate. |
| JIS G3101 | SS400 | Common Asian mild steel; strength ranges overlap A36. |
| GB/T 700 | Q235B | PRC structural steel near 235 MPa yield. (Use local code rules.) |
Substitution caution: “Equivalent” ≠ “identical.” Check impact class (JR/J0/J2), thickness windows, and project code rules before swapping.
Typical Applications
- Buildings & bridges: beams, columns, bracing, base plates
- OEM/industrial: equipment skids, frames, guards, platforms, tanks
- Infrastructure: stairs, handrails, gratings (with proper coating)
- Service centers & fab shops: general‐purpose plate and shape stock due to workability & cost
Sizing & Purchasing Checklist
- Grade & spec: ASTM A36/A36M
- Product form & size: plate/shape/bar, thickness, width, length (or section size)
- Tolerances: per ASTM A6/A6M (note any special straightness/flatness)
- Surface condition: as-rolled, P&O, blasted/primed, or galvanized
- Weld procedure constraints (if any) and NDT requirements
- Test documents: EN 10204 3.1 MTC with chemistry + mechanicals
- Coating/painting/galvanizing notes and packaging
- Quantity, Incoterms, destination port
FAQs
Is A36 heat-treatable for higher strength?
Only to a limited extent: with its low carbon, A36 does not significantly through-harden like alloy steels. If you need strength above A36 without adding thickness, consider A572 or other HSLA grades.
What are the most common A36 plate thicknesses?
Service-center inventories vary by region, but A36 plate commonly spans thin gauges up to heavy thicknesses for structural use; check local stock lists. (Ryerson/Kloeckner overviews.)
How “close” is S235JR to A36?
Very close in yield/tensile windows for general use, but S235JR has a defined impact requirement; many EU projects therefore specify S235JR rather than A36. Always follow the project code.
What standards control shape/plate tolerances?
ASTM A6/A6M for carbon structural shapes and plates; AISC Manual reproduces key tables commonly used by designers/fabricators.
How easy is A36 to machine and weld?
Weldability is excellent with common processes; machinability ~72% with typical speeds around 120 ft/min—fine for general work, but 1018 machines cleaner if precision finish matters.
A36 vs A572: quick chooser
- Pick A36 for cost-effective, easy forming/welding in low-to-moderate stress structures.
- Pick A572 Gr50 when you need higher strength (lighter sections for the same capacity) and better strength-to-weight. Re-check design if substituting.
Gengfei Provides High Quality ASTM A36 Steel
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