Australian Steel Grades — AS/NZS 3678 & 3679.1 Complete Reference

Q: What Charpy designation should I specify for a steel building in Sydney?

For standard structural steelwork in Sydney and most of coastal Australia (excluding alpine regions), specify L0 (27 J at 0°C) for primary tension members and fracture-critical elements. For secondary compression members in interior environments, no Charpy testing is typically required. For alpine regions (Snowy Mountains, Victorian Alps, Tasmanian highlands), specify L15 (27 J at -15°C).

Complete Australian structural steel grades reference covering AS/NZS 3678 (plates) and AS/NZS 3679.1 (hot-rolled sections). Grade 250, Grade 300, 300PLUS, Grade 350, and Grade 400 mechanical properties, Charpy impact designations L0 and L15, thickness-dependent yield strength variations, and practical AS 4100 grade selection guidance for Australian steel designers.

Quick access: AS 4100 Steel Design Overview → | AS 4100 Base Plate Design → | Section Properties →

Australian Steel Grade Classification System

Australian structural steel grades are specified under two complementary standards:

AS/NZS 3679.1:2016 — Hot-rolled structural steel bars and sections (UB, UC, PFC, TFB, EA, UA)
AS/NZS 3678:2016 — Hot-rolled structural steel plates (flat products)

Both standards use a grade number indicating the minimum yield strength in MPa at the smallest thickness bracket. The grade designation includes optional Charpy toughness suffixes:

Standard Grade	Fy (t ≤ 12 mm)	Fu Range	Typical Applications
Grade 250	250 MPa	410-540 MPa	Light secondary framing, non-structural components, legacy projects
Grade 300	300 MPa	440-600 MPa	General structural sections (plates and sections)
300PLUS	300 MPa	440-600 MPa	InfraBuild proprietary — default Australian section grade
Grade 350	350 MPa	480-620 MPa	High-strength applications, heavy columns, plates
Grade 400	400 MPa	540-700 MPa	Specialised high-strength, crane runway beams

Charpy Impact Designations

Australian steel grades include optional Charpy V-notch (CVN) impact testing designations:

Suffix	Test Temperature	Min Energy (Longitudinal)	Application
No suffix	Not required	—	Secondary members, interior non-fracture-critical
L0	0°C	27 J	Standard for primary structural members in most Australian climates
L15	-15°C	27 J	Alpine regions, Tasmania, fracture-critical tension members

Most structural engineers in Australia specify 300PLUS as the default section grade, which typically carries Charpy certification equivalent to L0 from InfraBuild's standard production. For plates, Grade 350 with L0 is the most common specification for welded built-up sections and heavy connections.

Complete Grade Table — Yield Strength by Thickness

AS/NZS 3679.1:2016 — Hot-Rolled Sections

Grade	t ≤ 12 mm Fy	12 < t ≤ 20 mm Fy	20 < t ≤ 40 mm Fy	40 < t ≤ 80 mm Fy	Fu min	Fu max
250	250 MPa	250 MPa	240 MPa	230 MPa	410 MPa	540 MPa
300	300 MPa	300 MPa	290 MPa	280 MPa	440 MPa	600 MPa
350	360 MPa	350 MPa	340 MPa	330 MPa	480 MPa	620 MPa
400	400 MPa	390 MPa	380 MPa	360 MPa	540 MPa	700 MPa

Note: Grade 350 in AS/NZS 3679.1 has Fy = 360 MPa for t ≤ 12 mm (higher than the nominal 350), reducing to 350 MPa for 12 < t ≤ 20 mm. This is a unique feature of the Australian section standard.

AS/NZS 3678:2016 — Plates

Grade	t ≤ 12 mm Fy	12 < t ≤ 20 mm Fy	20 < t ≤ 40 mm Fy	40 < t ≤ 80 mm Fy	Fu min	Fu max
250	250 MPa	250 MPa	240 MPa	230 MPa	410 MPa	540 MPa
300	300 MPa	300 MPa	290 MPa	280 MPa	440 MPa	600 MPa
350	340 MPa	330 MPa	320 MPa	310 MPa	480 MPa	620 MPa
400	400 MPa	390 MPa	380 MPa	360 MPa	540 MPa	700 MPa

Note the difference: Plate Grade 350 has lower yield values than section Grade 350 at equivalent thicknesses — 340 MPa vs 360 MPa for t ≤ 12 mm. This reflects the different rolling processes for plates versus sections.

Grade Details and Selection Guidance

Grade 250

Grade 250 is the lowest-strength structural grade in the Australian system, with Fy = 250 MPa for t ≤ 20 mm. It is comparable to ASTM A36 and EN 10025 S235JR. Grade 250 is rarely specified for primary structural members in modern Australian construction but remains available for:

Light secondary bracing and handrails
Stair stringers and landings
Legacy restoration projects matching existing steelwork
Non-structural steel components

The steel calculator supports Grade 250 for compatibility with existing structures, but 300PLUS is recommended for all new structural work.

Grade 300 and 300PLUS

Grade 300 (Fy = 300 MPa for t ≤ 20 mm) is the default structural steel grade in Australia, with 300PLUS being InfraBuild's proprietary brand. 300PLUS is chemically equivalent to Grade 300 but includes guaranteed weldability and Charpy properties. Key characteristics:

Fy = 300 MPa for sections up to 20 mm thickness
Fu = 440-600 MPa providing good ductility
Elongation ≥ 22% (50 mm gauge length)
Excellent weldability with E48XX electrodes without preheat for most thicknesses
CEV (carbon equivalent value) typically 0.38-0.43, controlled for welding

Practically all UB, UC, PFC, TFB, EA, and UA sections from Australian mills (InfraBuild, formerly OneSteel) are supplied as 300PLUS. Over 85% of structural steel in Australian buildings and industrial structures is 300PLUS.

Grade 350

Grade 350 sections (Fy = 360 MPa for t ≤ 12 mm) provide approximately 17% higher yield strength than Grade 300. In AS/NZS 3679.1, Grade 350 sections are available but less commonly stocked than 300PLUS. Plate Grade 350 to AS/NZS 3678 (Fy = 340 MPa for t ≤ 12 mm) is commonly specified for:

Heavy welded plate girders and built-up columns
Base plates and stiffener plates
High-capacity transfer structures
Crane runway girders requiring higher strength

Grade 350 is comparable to ASTM A572 Grade 50 and EN 10025 S355JR. Weldability is good using E48XX electrodes with minimal preheat for most thicknesses.

Grade 400

Grade 400 (Fy = 400 MPa for t ≤ 12 mm) is the highest-strength standard grade in AS/NZS 3678/3679.1. Applications include:

Heavy columns in lower storeys of high-rise buildings
Highly stressed crane beams
Mobile equipment and mining structures
Specialised long-span lightweight structures

Grade 400 requires careful welding procedure control, including preheat (typically 75-150°C depending on thickness) and low-hydrogen welding processes. It compares to ASTM A572 Grade 60.

Hollow Sections — AS/NZS 1163

Cold-formed hollow sections to AS/NZS 1163 use a separate grade system:

Grade	Fy min	Fu min	Typical Application
C250L0	250 MPa	320 MPa	Light structural, handrails
C350L0	350 MPa	430 MPa	General structural CHS/SHS/RHS
C450L0	450 MPa	500 MPa	High-strength structural hollow sections

C450L0 is now the dominant grade for structural hollow sections in Australia, offering 50% higher yield than Grade 300 at comparable cost. CHS, SHS, and RHS in C450L0 are standard for trusses, columns, and bracing in all types of steel structures.

Grade Selection by Application

Building Framing

Structural Element	Recommended Grade	Sections	Notes
Beams and rafters	300PLUS	UB, WB	Default — widely available, economical
Columns	300PLUS or Grade 350	UC, SHS	Grade 350 for heavy loads
Bracing	C450L0 or 300PLUS	SHS, CHS, PFC, UA	C450L0 for efficiency
Roof purlins	C450L0	RHS, C-section	Cold-formed lightweight
Base plates	Grade 350 plate	PLT	Higher bearing strength

Bridge and Infrastructure

Application	Recommended Grade	Standard	Notes
Main plate girders	Grade 350 L0	AS/NZS 3678	Welded fabrication
Cross-beams	300PLUS	AS/NZS 3679.1	Standard sections
Truss chords	C450L0	AS/NZS 1163	CHS/SHS compression
Bearings and stiffeners	Grade 400 L15	AS/NZS 3678	High bearing stress

Industrial and Mining

Application	Recommended Grade	Notes
Crane runway beams	Grade 350 to Grade 400	Fatigue-critical — specify Charpy L0
Equipment supports	300PLUS or C450L0	Cost-effective standard
Conveyor structures	C450L0 CHS/SHS	Lightweight, corrosion-resistant options
Heavy haulage bridges	Grade 350 plate	Welded plate girders

International Grade Comparisons

Australian	AISC (US)	EN 10025 (Europe)	CSA G40.21 (Canada)
Grade 250	A36	S235JR	260W
Grade 300	A572 Grade 42	S275JR	300W
300PLUS	A572 Grade 42	S275JR	300W
Grade 350	A572 Grade 50	S355JR	350W
Grade 400	A572 Grade 60	S420JR	400W
C450L0	—	S460MH	—

While these grades are broadly comparable, designers should verify specific ductility, Charpy, and weldability requirements for their project jurisdiction. Australian 300PLUS has slightly lower yield (300 MPa) than A992 (345 MPa), so equivalent substitution requires a 13% increase in area for the same axial capacity if designing to AISC 360.

Chemical Composition and Weldability

Australian structural steels have carefully controlled carbon equivalent values (CEV) to ensure weldability:

Grade	CEV (typical max)	Preheat Requirement	Welding Electrode
250	0.38	None for t ≤ 25 mm	E48XX
300/300PLUS	0.40	None for t ≤ 20 mm	E48XX
350	0.43	50°C for t > 25 mm	E48XX
400	0.45	75-100°C for t > 20 mm	E48XX or E55XX

Weldability of Australian grades is excellent. The controlled CEV limits ensure that most welding can be performed without preheat for thicknesses up to 20-25 mm, making site welding straightforward. For thicker elements or highly restrained connections, follow AS/NZS 1554.1 (structural steel welding) for preheat and interpass temperature requirements.

Frequently Asked Questions

What is the most common steel grade used in Australian structural steel design?

300PLUS (Fy = 300 MPa for t ≤ 20 mm) is by far the most common grade, accounting for over 85% of hot-rolled sections in Australian buildings. It is the standard grade supplied by InfraBuild for Universal Beams, Universal Columns, Parallel Flange Channels, and angles. Grade 350 is specified for heavy columns and plates where higher strength is needed. Grade 400 is reserved for specialised high-strength applications.

What is the difference between Grade 300 and 300PLUS steel?

Grade 300 is the AS/NZS 3679.1 standard designation with a minimum yield of 300 MPa. 300PLUS is InfraBuild's proprietary brand name for sections that meet Grade 300 requirements with additional quality assurances. In practice, 300PLUS is chemically equivalent to Grade 300 but includes tighter controls on carbon equivalent, guaranteed Charpy properties (typically L0 equivalent), and traceability. Most Australian stockists supply 300PLUS for all Universal Beam and Column orders.

Can Australian Grade 350 be welded without preheat?

Grade 350 sections (AS/NZS 3679.1) can generally be welded without preheat for thicknesses up to 25 mm using E48XX electrodes per AS/NZS 1554.1. Grade 350 plates (AS/NZS 3678) have a higher CEV and may require 50°C preheat for thicknesses exceeding 20 mm, particularly in highly restrained connections during cold weather. Standard practice is to apply 50°C preheat for any Grade 350 plate over 25 mm thick regardless of ambient temperature.

What is the Australian equivalent of ASTM A992 steel?

The closest Australian equivalent to A992 (Fy = 345-450 MPa) is Grade 350 section (Fy = 360 MPa for t ≤ 12 mm, reducing to 350 MPa for 12 < t ≤ 20 mm). However, 300PLUS (Fy = 300 MPa) is more commonly used for the same applications where A992 would be specified in the US. For a direct strength match, Grade 350 sections are the appropriate Australian specification.

What Charpy designation should I specify for a steel building in Sydney?