CSA G40.21 Steel Grades — 260W, 300W, 350W, 400W, 480W

Quick Reference: 350W (fy = 350 MPa) is the standard structural grade in Canada. 300W (fy = 300 MPa) for general use. 400W (fy = 400 MPa) for high-strength. 350WT for low-temperature toughness. All per CSA G40.20/G40.21.

G40.21 Grade Overview

CSA G40.21 is the Canadian standard for structural quality steel. The designation system encodes yield strength (in MPa) and material characteristics in a compact format:

350W is the default specification for all primary structural members in Canadian building construction. It replaces the older G40.21 44W designation (fy = 300 MPa / 44 ksi) that was common before metrication.

Grade Designation System

The G40.21 designation has three parts:

Example: 350WT

• 350 — Minimum yield strength in MPa
• W — Weldable (guaranteed weldability, CEV limits apply). "A" = Atmospheric corrosion-resistant (weathering steel)
• T — Toughness (Charpy V-notch tested at specified temperature). Absence of T means no Charpy requirement beyond the base material standard

Suffix Combinations

The "T" grades are critical for Canadian conditions. Most of Canada experiences winter temperatures below -20°C, and northern regions routinely see -40°C. Standard 350W without the "T" suffix has no guaranteed low-temperature toughness.

Yield Strength by Thickness

Per CSA G40.21, yield strength reduces for thicker sections. The following reductions apply (fy in MPa):

The threshold thicknesses mirror ASTM A6/A6M reductions. A 50 mm plate in 350W has fy = 340 MPa — a 10 MPa reduction that matters for heavy column and base plate design.

Tensile Strength

The fu/fy ratio for 350W is approximately 450/350 = 1.29. This is slightly higher than A992's fu/fy = 450/345 = 1.30 minimum — both provide good strain-hardening capacity for tension-controlled connections.

Chemical Composition (Ladle Analysis, %)

CSA G40.21 specifies maximum limits for key elements. Typical values for 350W plates and shapes:

For 350WT and 350AT, phosphorus and sulphur limits are tighter (typically P <= 0.030, S <= 0.030) to ensure low-temperature toughness.

Carbon Equivalent Value (CEV)

The CEV formula per CSA G40.21:

CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

For 350W sections up to 40 mm, CEV typically ranges from 0.38 to 0.43. This is well within the commonly accepted 0.45 threshold for good weldability without preheat. For thicker sections (>40 mm) in 350W, CEV may reach 0.45.

Preheat requirements per CSA W59 (Welded Steel Construction) are based on CEV, section thickness, and hydrogen level of the welding consumable, not on the grade alone.

Charpy Impact Requirements

Charpy V-notch testing per CSA G40.21 is the defining difference between standard and "T" grades. Canadian climate zones demand more rigorous toughness than any other national standard except possibly for Scandinavian specifications.

Base Requirements (Non-T grades)

Toughness (T) Grades

The -45°C test temperature for 350WT reflects the Canadian climate reality. With design metal temperatures reaching -40°C in northern Alberta, Manitoba, and the territories, the Charpy test temperature must be well below the minimum service temperature per CSA S16-19 Cl. 27.

CSA S16-19 Material Selection (Cl. 27)

CSA S16-19 provides a material selection procedure based on:

1. Minimum service temperature (from NBCC Appendix C climatic data)
2. Member thickness (thicker = more brittle fracture risk)
3. Stress level (tension vs compression, fatigue vs static)
4. Consequence category (failure consequence)

Practical selection rules for Canadian construction:

South of the 49th parallel in Ontario and Quebec, 350W without Charpy supplement may be adequate for interior steelwork. Above 55°N latitude, 350WT is the minimum for all structural steel regardless of exposure.

Weathering Steels (350A, 350AT)

CSA G40.21 Grade 350A and 350AT are atmospheric corrosion-resistant (weathering) steels. They contain small additions of copper, chromium, and nickel that form a dense, adherent oxide patina when exposed to the atmosphere:

Weathering steel requires alternating wet/dry cycles to form the protective patina. It is NOT suitable for:

• Permanently submerged conditions
• Buried applications
• Marine splash zones (continuous salt spray)
• Environments with persistent high humidity and no drying cycle (e.g., inside a constantly wet tunnel)

In Canadian practice, 350A is specified for exposed bridge girders in southern climates (Vancouver, Toronto). 350AT is specified for exposed steelwork in Quebec, the prairies, and northern locations where both weathering and toughness are required.

Delivery Conditions

CSA G40.20/G40.21 specifies the product standard including delivery conditions:

For 480W (quenched and tempered), the delivery condition is +QT — quenched from the austenitizing temperature and tempered. This produces the high strength with adequate toughness.

CSA G40.21 vs ASTM — Detailed Cross-Reference

Canadian W shapes are rolled to the same ASTM A6 dimensional tolerances as US shapes, but the material certification differs:

Key practical difference: The 350W minimum yield is 350 MPa while A992's minimum is 345 MPa — a 5 MPa (1.4%) difference. For design purposes this is negligible: a CSA S16 design with 350W can be considered equivalent to an AISC design with A992 for member sizing, though the resistance factors differ (phi = 0.90 in both cases, fortunately).

The fu/fy ratio of both grades comfortably exceeds the 1.20 minimum that AISC requires for connection design. Both provide adequate strain-hardening for net section fracture and block tearing capacity.

Canadian vs US Steel — Practical Procurement

In Canadian practice, structural steel is often dual-certified to both CSA G40.21 and ASTM specifications. A W310x39 may arrive with a mill certificate showing:

• CSA G40.21 350W (for Canadian code compliance)
• ASTM A992 (for US code compliance, if exported)

This is common because the steel chemistry and rolling practice are identical — only the certification paperwork differs. When dual-certified:

• Use fy = 350 MPa for CSA S16 design (the higher of the two)
• Use fy = 345 MPa for AISC 360 design (the guaranteed ASTM minimum)
• Charpy values from the mill certificate apply regardless of which code you're designing to

For projects near the US-Canada border (e.g., Detroit-Windsor, Buffalo-Niagara), dual-certified steel is routinely specified and available.

CSA G40.21 vs EN 10025 vs AS/NZS 3679

Canadian 350WT is the only grade in this comparison that guarantees Charpy toughness at -45°C. This reflects the uniquely severe Canadian climate requirements — Scandinavia uses similar toughness levels, but European EN 10025 does not provide a -45°C subgrade.

Related Pages

• Canadian Steel Beam Sizes — W Shapes, HSS, G40.21 — Complete section tables
• CSA S16 Beam Design — Flexure, LTB & Shear — Canadian beam design guide
• Steel Grades — A36, A572, A992, 350 Grade — Cross-standard grade comparison
• EN 10025 Steel Grades — S235-S460 — European steel grades
• CSA S16 Code Overview — Canadian design code reference
• Beam Capacity Calculator — Multi-code beam calculator

This page is for educational reference. All grade data per CSA G40.20/G40.21. Verify material properties against mill certificates before procurement or design. For fracture-critical members, follow CSA S16-19 Cl. 27 and CSA W59 for welding procedure qualification. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.