AS1163 C350(L0)/C450(L0) Cold-Formed Structural Steel Hollow Sections: 
Standard & Scope 
Manufactured to Australian Standard AS 1163: "Structural steel hollow sections".

This standard specifies requirements for cold-formed (welded) structural steel hollow sections (SHS, RHS, CHS) intended for use in structures, mechanical equipment, and general applications.

Material Grade 
Dual Grade Designation (C350/C450): This indicates the steel meets the chemical composition and mechanical property requirements for BOTH grades C350 and C450 as defined in AS 1163. It offers flexibility to designers to utilize either strength level depending on the application requirements.

C350: Specifies a Minimum Yield Strength (ReH) of 350 MPa. 
C450: Specifies a Minimum Yield Strength (ReH) of 450 MPa. 
L0: This suffix signifies the lowest level of impact toughness testing required by AS 1163.

Specifically, it means NO Charpy V-notch (CVN) impact testing is performed at sub-zero temperatures (e.g., -20°C or -40°C).

Section Types & Sizes 
Available in the three main profiles:

CHS (Circular Hollow Sections): Tubes.

SHS (Square Hollow Sections).

RHS (Rectangular Hollow Sections).

A wide range of standard sizes (outside dimensions) and wall thicknesses are defined within the AS 1163 standard.

Manufacturing Process 
Cold-Formed (Cold-Worked): Produced by forming steel strip or plate at ambient temperature (significantly below the recrystallization temperature) into a tubular shape, followed by longitudinal welding.

Implications: Cold-forming increases the yield strength and hardness of the material in the corners compared to the flat faces (cold work hardening). It generally offers tighter dimensional tolerances compared to hot-finished sections. The process can result in residual stresses.

Surface Condition:

Typically supplied with a "mill" surface finish, which may have light scale, light rust, or oil film. Surface imperfections are limited by the standard.

Often hot dip galvanized (after fabrication) for corrosion protection in exposed environments. The cold-formed nature is generally compatible with galvanizing.

Chemical Composition 
Controlled to meet the requirements for both C350 and C450 grades per AS 1163.

Primarily Carbon-Manganese steel. Maximum limits are placed on elements like Carbon (C), Phosphorus (P), Sulfur (S), and sometimes alloying elements to ensure weldability, formability, and achieve the specified mechanical properties.

NOTES :

1 The use of sulphide modification manufacturing techniques for these grades is permitted .

2 The following elements may be present to the limits stated : ( a ) Copper 0.25%. ( b ) Nickel 0.25%.

3 Limits specified are for soluble or total aluminum . 4 Carbon equivalent ( CE ) is calculated from the following equation :

​

5 Applies to niobium and vanadium only . However , niobium greater than 0.010% is not permitted . 
6 Applies to niobium , vanadium and titanium only . However , vanadium greater than 0.10% is not permitted . 
7 For circular hollow sections ( CHS ), the silicon limit shall be 0.45.

Mechanical Properties 

NOTE : These limits apply to the face from which the tensile test is taken . That is , for RHS , the use of b / t or d / t ratio is dependent on which face the test specimen is cut from . For SHS , there is only one ratio ( as b = d ). 
Typical Tensile Strength (Rm): Ranges from approximately 430 MPa to 550 MPa for C350 and 500 MPa to 630 MPa for C450. The specific value depends on the section size and wall thickness. 
Elongation: Minimum elongation requirements apply, typically around 10-20% depending on the tensile strength achieved. 
Impact Toughness Designation (L0): 
L0: This suffix signifies the lowest level of impact toughness testing required by AS 1163.

Specifically, it means NO Charpy V-notch (CVN) impact testing is performed at sub-zero temperatures (e.g., -20°C or -40°C).

Implication: This steel is suitable for applications where the service temperature is not expected to fall below approximately 0°C and where there is no significant risk of brittle fracture under the intended loading conditions. It is NOT suitable for critical structures in cold climates or applications involving high dynamic loading at low temperatures where fracture toughness is paramount.

Hardness testing (e.g., Brinell) is often used as the primary method for routine verification of the tensile strength requirements on the finished hollow section. 
Actual tensile testing on specimens taken from the finished section may be performed according to the standard's sampling rules. 
 

Key Properties Summary 
High Strength: Offers good strength-to-weight ratio (Min YS 350 MPa or 450 MPa).

Stiffness: Hollow sections provide excellent torsional and flexural rigidity.

Aesthetic & Functional: Clean lines, closed sections, easy to fabricate and finish (paint, galvanize).

Economical: Efficient use of material, often cost-effective for many structures.

Common Applications 
Building frames, roof trusses, columns, purlins, girts (especially RHS/SHS). 
Support structures, mezzanines, platforms, handrails, fencing (especially RHS/SHS). 
Machinery frames, conveyors, agricultural equipment (all profiles). 
General fabrication where moderate strength and good formability are needed, and service temperatures remain above freezing. 
Not recommended for: Critical bridges, offshore structures in cold waters, pressure vessels, applications subject to very low temperatures (< 0°C) or severe impact loading where higher toughness grades (like C350L0/C450L0 is inadequate; grades like C350L5/C450L5 or C350L8/C450L8 would be required).

In essence: AS1163 C350(L0)/C450(L0) designates cold-formed structural steel hollow sections (RHS, SHS, CHS) made in Australia to a specific standard. They offer a choice of two minimum yield strengths (350 MPa or 450 MPa) but have no verified impact toughness at sub-zero temperatures (L0), making them suitable for general structural and mechanical applications where temperatures remain above freezing and fracture risk is low.

  
Q And A 
Q1: What Is The Key Difference Between C350(L0) And C450(L0) In AS1163, And How Should Designers Choose Between Them? 
A:

Strength Difference: 
C350(L0) has a minimum yield strength (ReH) of 350 MPa, while C450(L0) guarantees a higher minimum yield strength of 450 MPa.

The tensile strength (Rm) of C450(L0) is also typically higher (500–630 MPa vs. 430–550 MPa for C350(L0)).

Selection Criteria for Designers: 
Higher Load Applications: If a structure requires greater load-bearing capacity with reduced section sizes (e.g., long-span beams, columns under heavy axial loads), C450(L0) is preferred for weight savings and material efficiency.

Cost vs. Performance: C350(L0) is often more economical and sufficient for moderate-load applications (e.g., secondary framing, light-duty supports).

Ductility & Formability: C350(L0) may offer slightly better formability (bending, welding) due to its lower strength, which can be beneficial in complex fabrications.

Note: Both grades share the same L0 toughness rating, meaning neither is suitable for low-temperature or high-impact environments. 
 

Q2: Why Is The "L0" Designation Important? 
A:

L0 means no Charpy V-notch (CVN) impact testing is required at low temperatures.

It indicates the steel is not certified for sub-zero temperature toughness and should only be used in environments above 0°C.

  
Q3:What Are The Typical Applications Where C350(L0)/C450(L0) Should NOT Be Used? 
A:

Low-temperature environments (below 0°C), such as Alaskan bridges, offshore platforms, or refrigeration structures.

High-impact or dynamic load applications (e.g., seismic zones, heavy machinery subjected to shock loads).

Pressure vessels or critical load-bearing structures where higher toughness (L5/L8) is required.