Australian Steel Chemical Composition — AS/NZS 3679.1 Guide
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Complete reference for chemical composition limits of Australian structural steel per AS/NZS 3679.1:2016 and AS/NZS 3678:2016. Carbon equivalent (CEV) values, elemental limits by grade, and weldability implications for AS 4100:2020 design.
Carbon Equivalent Formula (CEV)
AS/NZS 3679.1 specifies: CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
| Element | Effect | Typical Limit |
|---|---|---|
| C | Strength, hardenability | 0.22% max (t ≤ 12 mm) |
| Mn | Strength, toughness | 1.40% max |
| Si | Deoxidiser | 0.50% max |
| P | Impurity | 0.040% max |
| S | Impurity | 0.040% max |
Maximum CEV by Grade and Thickness
| Grade | t ≤ 12 | 12-20 | 20-40 | >40 |
|---|---|---|---|---|
| Gr 300 (section) | 0.44 | 0.46 | 0.48 | 0.48 |
| Gr 300 (plate) | 0.42 | 0.44 | 0.46 | 0.48 |
| Gr 350 (section) | 0.46 | 0.48 | 0.50 | 0.52 |
| Gr 400 (section) | — | 0.48 | 0.50 | 0.52 |
Worked Example
Problem: Grade 300 plate 16 mm, C=0.18%, Mn=1.25%, Si=0.35%, Cr=0.12%, Ni=0.10%, Mo=0.04%, V=0.06%, Cu=0.12%.
Solution: CEV = 0.18 + 1.25/6 + (0.12+0.04+0.06)/5 + (0.10+0.12)/15 = 0.18 + 0.208 + 0.044 + 0.015 = 0.447. Limit for 16 mm = 0.46. Acceptable. Welding without preheat permitted per AS/NZS 1554.1.
Design Resources
- [[Australian Steel Grades|/reference/australian-steel-grades/]] | [[Australian Steel Properties|/reference/australian-steel-properties/]] | [[Australian Beam Sizes|/reference/au-beam-sizes/]] | [[Australian Bolt Capacity|/reference/australian-bolt-capacity/]] | [[AS 4100 Beam Design|/reference/as4100-beam-design-example/]] | [[All Australian References|/reference/]]
FAQ
What is the CEV formula for Australian structural steel? AS/NZS 3679.1 specifies CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. For Grade 300 sections ≤12 mm, max CEV is 0.44%.
What is the maximum carbon content for Grade 300 steel? Max carbon is 0.22% for t≤12 mm and 0.25% for thicker sections. Grade 300PLUS controls below 0.20%.
Does Grade 400 steel require preheat? CEV 0.45-0.52%, 50-100°C preheat per AS/NZS 1554.1 for t>16 mm in restrained conditions.
Educational Use Only — This reference is for educational and preliminary design purposes only. All structural designs must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) in accordance with AS 4100:2020 and all applicable Australian Standards. Results are not for construction.