ASTM A36 Steel — Properties, Grades, and Structural Applications

ASTM A36 is the most widely used structural carbon steel in North America. It is a low-carbon steel with a minimum yield strength of 36 ksi (250 MPa) and is produced in plate, bar, and shape forms per ASTM A36/A36M. This page covers mechanical properties, chemical composition, equivalent international grades, weldability, and when to specify A36 vs. higher-strength alternatives.

ASTM A36 Mechanical Properties

Note: A36 has a relatively wide Fu range (58–80 ksi). For seismic design, the actual yield-to-tensile ratio and expected yield strength Rye are important — A36 typically has actual Fy significantly above the 36 ksi minimum.

ASTM A36 Chemical Composition

Carbon content varies by product form and thickness:

• Plates ≤ 3/4 in: C max = 0.25%
• Plates 3/4 in to 1-1/2 in: C max = 0.25%
• Plates over 1-1/2 in to 2-1/2 in: C max = 0.27%
• Plates over 2-1/2 in to 4 in: C max = 0.28%
• Shapes: C max = 0.26%

Carbon Equivalent (CE) for weldability: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

For A36 plates: CE ≈ 0.38–0.42 (generally weldable without preheat for t ≤ 3/4 in).

Product Forms Available

ASTM A36 is produced in the following forms:

Important: AISC recommends ASTM A992 for W-shapes and ASTM A572 Grade 50 for plates when higher strength is needed. A36 is now primarily specified for plates and bars rather than structural shapes. Many mills supply A36 shapes that also meet A992 (dual-certified).

A36 vs. Common Alternative Grades

When to choose A36 over A572 Gr50:

• Fabrication simplicity: Lower carbon → easier welding, less preheat concern
• Heavy base plates: For base plates where bending capacity is not the limit
• Anchor rods with ductility requirement: AISC DG1 recommends F1554 Gr36 (similar to A36) over higher-strength grades for ductile yielding
• Cost in large plates: A36 plate can be marginally cheaper for non-critical applications

When A36 is NOT appropriate:

• W-shapes for seismic systems: Use A992 (Fy/Fu ≤ 0.85 required)
• HSS sections: Use A500 Grade C or A1085
• High-strength connection plates where weight reduction matters: Use A572 Gr50

International Equivalent Grades

A36 has approximate equivalents in other standards. Properties are similar but not identical — always verify for design-critical applications.

Design note: When substituting international grades for A36 in calculations, use the specific grade's Fy (not A36's 36 ksi) for capacity calculations. Grade 250 = 250 MPa = 36.3 ksi — essentially identical.

Weldability and Fabrication

Weldability

A36 is classified as readily weldable for thicknesses up to approximately 1 in without preheat. For thicker sections, preheat is required to prevent hydrogen-induced cracking.

Preheat requirements per AWS D1.1:

Matching filler metal per AWS D1.1:

• SMAW: E7018 (70 ksi class — slightly overmatched, acceptable)
• GMAW/FCAW: E70 series
• SAW: F7A2-EM12K or similar

Forming and Cutting

• Shear cutting: Excellent for plates up to ~1 in
• Plasma/flame cutting: Straightforward; preheat for thick plates
• Bending: Minimum inside bend radius ≈ 1.5t for 90° cold bend

Typical A36 Applications

A36 in AISC 360 Design

AISC 360-22 fully covers A36 as a permitted steel under Section A3.1. Key design values:

Seismic note: A36's actual yield strength often exceeds the 36 ksi nominal (due to mill practice). AISC 341 seismic provisions use Ry = 1.5 for A36, meaning expected Fy = 54 ksi. This matters when designing connections to force plastic hinges in members (not connections).

Temperature Effects

A36 carbon steel loses strength at elevated temperature:

For fire design, A36 behaves similarly to other carbon steels. Critical temperature (Tcr) where member capacity = applied demand typically falls between 900–1100°F (480–590°C) for typical utilization ratios.

Frequently Asked Questions

Is A36 the same as "mild steel"? Yes, in common usage. "Mild steel" refers to low-carbon structural steel with Fy around 36–40 ksi. A36 is the ASTM specification that defines the minimum properties for this category in North America. In the UK, S275 is the nearest equivalent; in Australia, Grade 250.

Can I use A36 for seismic moment frames? No, not for W-shape beams in AISC 341 special moment frames (SMF) or intermediate moment frames (IMF). AISC 341 Section A3.1 requires A992 for W-shapes in seismic systems due to its Fy/Fu ≤ 0.85 requirement and maximum Fy cap of 65 ksi. A36 can be used for connection plates where ductility is the governing requirement.

Why has A572 Gr50 largely replaced A36 for plates? A572 Grade 50 provides 39% higher yield strength at essentially the same cost. For connection plates, gusset plates, and column base plates where area is determined by capacity, Grade 50 results in lighter and smaller components. The difference in weldability is minor for typical thicknesses (CE is similar for Grade 50 at the same thickness).

What is the difference between A36 and A36M? A36M is the metric companion specification. Yield strength is 250 MPa min (vs. 36 ksi = 248 MPa — essentially identical). The specifications are dual-unit certified; most mill test reports report both units.

How do I verify A36 steel on a project? Request a Certified Mill Test Report (CMTR) showing chemical analysis and mechanical properties (yield, tensile, elongation) for each heat of steel. AISC quality requirements (per RCSC and AISC Code of Standard Practice) require CMTRs for all structural steel. Verify the grade designation, heat number, and that all values meet A36 minimums.

What preheat temperature does A36 require for welding? Per AWS D1.1 Table 4.5, A36 requires no preheat for material under 3/4 in thickness (ambient above 32°F). For 3/4 in to 1-1/2 in: preheat to 50°F minimum. For 1-1/2 in to 2-1/2 in: 150°F minimum. For material over 2-1/2 in: 225°F minimum. The E70 electrode series (E7018 for SMAW, ER70S-6 for GMAW, E70T-1 for FCAW) is the standard matching filler for A36 in structural applications.

What is the net tensile strength of an A36 plate with bolt holes? For net section fracture, use Fu = 58 ksi (A36 minimum tensile strength) applied to the net area. The AISC 360 fracture limit state is φPn = φ × Fu × Ae, where φ = 0.75 and Ae = U × An (effective net area, accounting for the shear lag factor U). For a directly connected plate with all elements connected, U = 1.0. Example: a 3/8 × 4 in A36 plate with two 3/4 in bolts in standard holes → An = (4 − 2 × 13/16) × 3/8 = 0.938 in²; φPn = 0.75 × 58 × 0.938 = 40.8 kips.

What is the Ry factor for A36 and why does it matter? AISC 341 assigns Ry = 1.5 to A36 steel. This means the expected yield strength is Rye × Fy = 1.5 × 36 = 54 ksi — substantially above the nominal 36 ksi minimum. Ry matters in seismic design when calculating the capacity-design demand on connections and adjacent elements: if a beam is expected to yield at Mp = Ry × Fy × Z, the connections must be designed for this amplified force to ensure yielding occurs in the member, not the connection.

Related pages

• Steel Grades Reference Table — compare A36, A572, A992, A588 side by side
• Steel Material Properties — Fy, Fu, E, G for all structural steel grades
• Beam Capacity Calculator — verify moment and shear capacity using A36 Fy = 36 ksi
• Column Capacity Calculator — axial compression design for A36 sections
• Steel Beam Span Guide — span ranges and preliminary sizing
• Wide Flange Beam Sizes — W-shape dimensions and properties
• Bolted Connections Calculator — bolt shear, bearing, and block shear for A36 plates (Fu = 58 ksi)
• Welded Connections Calculator — fillet weld capacity for A36 with E70 electrode
• Fillet Weld Size Chart — minimum and maximum weld sizes for A36 base metal
• structural steel weight per foot table
• ASCE 7 Load Combinations
• Steel Fy and Fu reference table

Material properties are nominal (ASTM minimum) values for design use. Actual mill properties typically exceed these minimums. Always confirm material compliance via Certified Mill Test Reports for structural applications.

Run This Calculation

→ Beam Capacity Calculator — verify moment, shear, and LTB capacity for A36 sections per AISC 360, AS 4100, EN 1993, or CSA S16.

→ Bolted Connections Calculator — bolt shear, bearing, and block shear for A36 connection plates using the correct Fu = 58 ksi.

→ Welded Connections Calculator — fillet and groove weld capacity matched to A36 base metal with E70 electrode.

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