Steel Grades — Fy & Fu Values for A36, A572, A992, S355 & AS/NZS

Yield strength (Fy) and tensile strength (Fu) for structural steel grades across AISC 360, AS 4100, EN 1993, and CSA S16 design standards. Values are guaranteed minimums per the relevant ASTM, AS/NZS, EN, or CSA specification for the thickness range shown. Confirm with the Mill Test Report (MTR) for project-specific design.

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ASTM Steel Grades — AISC 360 (US)

AS/NZS Steel Grades — AS 4100 (Australia/NZ)

EN Steel Grades — EN 1993 (Europe)

CSA Steel Grades — CSA S16 (Canada)

Why steel grades matter in capacity calculations

Every structural steel capacity equation starts with material strength. Yield strength (Fy) governs most member and connection limit states -- beam bending, column buckling, bolt bearing, weld capacity. Tensile strength (Fu) controls rupture-based checks such as net section tension, bolt shear on the threaded area, and weld metal strength. Getting the grade wrong by even one step (for example, assuming 350 MPa when the material is actually 250 MPa) can inflate calculated capacity by 40% or more.

Steel grades are specified differently across the major design codes. ASTM designations (A36, A992, A572) are used with AISC 360 in the US and Canada. Australian practice references AS/NZS grades (250, 300, 350) under AS 4100. European design to EN 1993 uses S235, S275, S355, and S460. CSA S16 in Canada works with CSA G40.21 grades (300W, 350W, 350WT). While some of these grades have similar yield strengths, they are not interchangeable -- each comes with its own specification for chemistry, toughness, and thickness limits.

A common source of confusion is the relationship between Fy and plate or flange thickness. Most grade specifications reduce the guaranteed minimum yield strength for thicker material. For example, ASTM A992 guarantees Fy = 50 ksi for shapes up to Group 5, but an A36 plate thicker than 8 inches has a lower guaranteed Fy than the 36 ksi commonly assumed. Always check the thickness range when selecting Fy for a calculation.

Grade selection checklist

When entering material properties into any calculator, verify the following:

• Grade designation matches the project specification. Do not default to A992 or Grade 350 unless the spec confirms it.
• Fy corresponds to the actual thickness or shape group. Thicker flanges and heavier groups often have reduced Fy.
• Fu is consistent with the grade. The ratio Fu/Fy varies by grade; for A992 shapes, Fu = 65 ksi and Fy = 50 ksi, but A36 has Fu = 58 ksi and Fy = 36 ksi.
• Dual-certified material is handled correctly. Many W-shapes in the US are dual-certified A36/A992. The higher Fy (50 ksi) applies only if the Mill Test Report (MTR) confirms both certifications.
• The MTR is on file. For stamped design, Fy and Fu should trace back to a specific heat and MTR, not to a handbook assumption.
• Grade equivalence across standards is approximate. A992 (Fy = 345 MPa) and S355 (Fy = 355 MPa) are close but not identical in chemistry, toughness, or specification scope. Do not substitute one for the other without engineering review.

For the full verification and documentation workflow, see How to verify calculator results.

Frequently Asked Questions

What is the difference between Fy and Fu? Fy (yield strength) is the stress at which steel begins to deform permanently. Fu (ultimate tensile strength) is the maximum stress the material can sustain before fracture. Most design equations use Fy for yielding limit states and Fu for rupture limit states. The ratio Fu/Fy is typically between 1.2 and 1.6 depending on the grade.

Why does Fy decrease for thicker plates? Thicker material cools more slowly during rolling, producing a coarser grain structure with lower yield strength. Grade specifications account for this by listing Fy values for specific thickness ranges. Always check the relevant thickness bracket rather than assuming the headline Fy value applies universally.

Are A992 and S355 interchangeable? Not directly. A992 (Fy = 345 MPa, Fu = 450 MPa) and S355 (Fy = 355 MPa, Fu = 470-630 MPa) have different chemistry limits, Charpy toughness requirements, and thickness derating rules. They are close enough for rough comparison, but substitution on a real project requires a formal engineering review against the governing specification.

What does "dual-certified" mean for W-shapes? Many US mills produce W-shapes that satisfy both A36 and A992 simultaneously. The MTR will list both specifications. If dual-certified, the designer can use Fy = 50 ksi (A992). If the MTR only lists A36, Fy = 36 ksi applies. This distinction matters because capacity scales directly with Fy.

Why should I always check the Mill Test Report (MTR)? The MTR is the certified record of actual material properties for a specific heat of steel. Handbook values are guaranteed minimums, but real Fy often exceeds the minimum by 10-20%. For capacity calculations, use the specified minimum (conservative). For connection compatibility checks or seismic design, actual yield from the MTR may be needed to avoid over-strength issues.

Run This Calculation

→ Beam Capacity Calculator — check beam capacity using the Fy and Fu values confirmed from this grade reference.

→ Bolted Connections Calculator — net section rupture and bearing checks depend directly on the Fu of the connected material.

→ Base Plate & Anchors Calculator — base plate bending uses Fy; anchor bolt design requires confirming steel grade for both plate and rods.

Comprehensive ASTM Structural Steel Designation Table

The table below covers every commonly specified structural steel grade under ASTM standards used in US construction. Fy and Fu are specified minimum values for the typical thickness range. Elongation is the minimum percent in 2 inches (50 mm) unless noted. Weldability is rated by carbon equivalent and typical preheat requirements.

Notes: A913 uses the Quenching and Self-Tempering (QST) process, which produces a lower carbon equivalent than conventionally rolled grades at the same strength level. A514 and A709 Gr 100 are quenched and tempered (Q&T) plates requiring controlled welding procedures. A242 and A588 develop a protective oxide patina when exposed to weather; they should not be used in buried or continuously wet conditions without coating.

Chemical Composition Summary

Carbon equivalent and key alloying elements control weldability, toughness, and atmospheric corrosion resistance. Values below are maximum percentages from the respective ASTM specification for the most common thickness range. Actual chemistry varies by producer and should be confirmed via the Mill Test Report.

CE formula (IIW): CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

The IIW carbon equivalent formula is the most widely used predictor of weldability for structural steels. Steels with CE below 0.40 generally require no preheat for moderate thicknesses. Steels with CE between 0.40 and 0.48 typically require low preheat (50-150°F) for thicker sections. Steels with CE above 0.48 require controlled preheat, interpass temperature management, and low-hydrogen welding consumables per AWS D1.1.

Application Matrix by Industry

Different industries prioritize different combinations of strength, toughness, weldability, and corrosion resistance. This matrix shows which grades dominate each sector and why.

Reading the matrix: "Primary" means the grade is the default first choice for that sector. "Common" means it is frequently specified but not the dominant grade. Cells left blank indicate the grade is rarely or never used in that sector. Selection depends on project-specific requirements for strength, ductility, corrosion resistance, and cost.

Cost Tier Comparison

Material cost is driven by alloy content, production volume, and processing route (hot-rolled vs. QST vs. Q&T). The table below groups grades into cost tiers with a rough multiplier relative to A36 as the baseline. These are indicative ranges based on US mill pricing for standard sections; actual prices vary by producer, order quantity, and market conditions.

Cost selection guidance: For most building structures, the Standard tier (A992 for W-shapes, A500 Gr C or A1085 for HSS) provides the best strength-to-cost ratio. Specifying A36 when A992 is available at the same price wastes capacity. Premium and Specialty grades are justified when corrosion resistance eliminates coating costs (A588), or when higher strength reduces member sizes enough to offset the material premium (A514, A913 Gr 65).

International Grade Equivalents

Structural steel grades across different national standards are approximately equivalent but never identical. The table below matches grades with comparable yield strength ranges. Chemistry, toughness testing, and dimensional tolerances differ between standards. Substitution requires engineering review against the governing specification.

Key differences that matter:

• EN 10025 designates toughness grades with JR (27J at 20°C), J0 (27J at 0°C), J2 (27J at -20°C), K2 (40J at -20°C). The ASTM grade alone does not convey toughness class.
• JIS standards use separate designations for hot-rolled (SM) and general structural (SS) steel. SM grades have tighter chemistry control and are preferred for welded structures.
• Chinese GB/T standards specify quality levels (B, C, D) indicating impact testing temperature. Q345B is the most common general structural grade; Q345C or D is required for seismic or low-temperature service.
• Australian AS/NZS grades are designated by Fy directly (250, 300, 350) rather than by ASTM-style alphanumeric codes.

Weldability and Fabrication Notes

Carbon Equivalent and Preheat Requirements

Weldability of structural steel is governed primarily by the carbon equivalent (CE). AWS D1.1 Table 3.2 provides preheat and interpass temperature requirements based on the base metal grade, thickness, and welding process.

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

Preheat guidance by CE range (low-hydrogen SMAW or GMAW):

Grade-Specific Welding Considerations

A36 — The most forgiving structural steel to weld. No preheat required for thicknesses up to 3/4 inch with low-hydrogen processes. Standard E70XX fillers are adequate.

A572 Gr 50 and A992 — Slightly higher CE than A36. Preheat 50°F for thicknesses above 3/4 inch. E7018 (SMAW) or ER70S-6 (GMAW) are standard filler choices. These two grades weld similarly; many WPS documents cover both under the same procedure.

A572 Gr 60 and Gr 65 — Higher carbon and manganese content increases crack sensitivity. Preheat is mandatory for thicknesses above 1/2 inch. Use low-hydrogen consumables exclusively (E7018-H4R or equivalent). Consider undermatching filler (E70XX rather than E80XX) for fillet welds unless the design requires matching strength.

A500 Gr B and Gr C (HSS) — Cold forming during HSS manufacturing creates a heat-affected zone (HAZ) at the seam weld and corners. The corner HAZ can have reduced toughness. Avoid placing full-penetration groove welds at HSS corners when possible. Preheat is generally not required for HSS connections with wall thicknesses under 1/2 inch.

A588 (weathering steel) — Requires weathering-grade filler metals (E8018-W, ER80S-W) when the weld will be exposed and the patina is the final finish. Using standard carbon steel filler creates a rust-prone weld that defeats the weathering system. When the structure will be painted, standard E70XX fillers are acceptable. The higher alloy content (Cr, Cu) pushes CE to approximately 0.52, requiring preheat for thicker sections.

A514 and A709 Gr 100 (Q&T plate) — These are the most demanding grades to weld in common structural use. The quenched and tempered microstructure is degraded if interpass temperatures exceed the tempering temperature (typically 600-700°F). Strict control of heat input (typically 15-50 kJ/in) and interpass temperature is mandatory. Preheat is always required. A qualified Welding Procedure Specification (WPS) with Procedure Qualification Records (PQR) is essential. Undermatching filler (E100XX or E110XX depending on joint configuration) is often used for fillet welds.

A913 Gr 50 and Gr 65 — Despite the higher strength of Gr 65, the QST process keeps the carbon equivalent low (approximately 0.38 for Gr 50, 0.47 for Gr 65). This makes A913 more weldable than conventionally rolled grades at the same Fy. Standard E70XX fillers are used even for Gr 65. Preheat requirements are similar to A572 Gr 50 for Gr 50, and similar to A572 Gr 65 for Gr 65.

A1085 — Welding characteristics are similar to A500 Gr C, but the tighter wall tolerance means less variability in fit-up. The consistent wall thickness produces more predictable weld joint geometries. Standard E70XX fillers apply.

Fabrication Best Practices

• Interpass temperature control — Use tempilstiks or infrared thermometers to verify interpass temperature between passes, especially on thick sections and high-CE steels.
• Low-hydrogen practice — For any steel with CE above 0.40, use only low-hydrogen consumables. Store electrodes per AWS D5.0 (heated rod ovens for SMAW). GMAW and FCAW are inherently low-hydrogen.
• Tack weld considerations — Small tack welds cool rapidly and are crack-prone on high-CE steels. Use sufficient tack size (minimum 2x the weld size or 1/4 inch, whichever is greater) and maintain preheat during tacking.
• Restraint and joint design — Highly restrained joints (e.g., repairs, heavy stiffener welds) increase cracking risk regardless of grade. Sequence welds to minimize restraint and consider buttering passes on high-CE base metals.

Related pages

• Beam capacity calculator
• Column capacity calculator
• Welded connections calculator
• Bolted connections calculator
• Unit converter
• Tools directory
• Reference tables directory
• Guides and checklists
• How to verify calculator results
• Disclaimer (educational use only)
• EN 1993-1-8 Steel Connection Design
• AISC 360 Notes
• AS 4100 Notes

Related Tools & References

• Steel Beam Capacity Calculator — check beam capacity with these grades
• Welded Connection Calculator — FEXX and base metal compatibility
• Steel Fy & Fu Reference — Yield and Tensile Strength by Grade
• Structural Steel Weight Per Foot — W, HSS, Angle, Channel
• ASTM A36 Steel — Properties and Equivalents
• Bolt Capacity Table — A325 & A490 Shear and Tension

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

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