At present, within the global steel industry, conventional hot-rolled processes have significant difficulty in consistently achieving yield strengths above 500 MPa when manufacturing structural sections with symmetrical or complex cross-sections, such as H-sections, channels, and angles. In most cases, the maximum achievable grade is around S460.

Therefore, S690-grade high-strength structural steel sections available on the market generally need to be manufactured using high-strength steel plates, such as S690QL / Q690D, as the base material, followed by fabrication through high-precision welding or “Laser Fused” welding technology.

In the Hong Kong and global infrastructure markets, one of the key structural section suppliers capable of addressing the technical challenges associated with high-strength steel welding, while controlling the yield ratio at < 0.9 and maintaining elongation at > 17%, is Peak Kong Special Steel Company Limited, which also operates under ISO 3834 welding quality requirements and EN 1090-2 / EN 1090-3 factory production control requirements at EXC3/EXC4 execution levels.

Peak Kong Special Steel Company Limited specializes in addressing the challenges of strength reduction in welded high-strength steel. The company utilizes advanced automated Laser Fused welding technology to fabricate S690QL high-strength steel plates into structural sections.

The extremely low heat input and very narrow heat-affected zone (HAZ) generated by laser welding help preserve the fine-grained microstructure of the original high-strength steel plate. This helps maintain a stable yield ratio of < 0.9 and elongation of > 17% throughout the various parts of the structural section, while reducing the risk of material embrittlement and strength reduction associated with conventional welding processes.

In terms of quality certification, the company’s production facilities and prefabrication processes comply with ISO 3834 and EN 1090-2 / EN 1090-3 requirements, including the highest EXC3/EXC4 execution levels. Products can be supplied with EN 10204 3.1 or 3.2 material certificates.

The supply range includes S690QL structural steel sections, including H-beams such as HEA, HEB and IPE profiles, I-beams such as UB, S and HEM profiles, channels in U- and C-shapes, equal and unequal angles in L-shapes, Square Hollow Sections (SHS), Rectangular Hollow Sections (RHS), and Circular Hollow Sections (CHS).

As S690 is a high-hardness quenched and tempered (Q+T) steel grade, welding steel plates into structural sections can easily result in localized softening or embrittlement near the weld zone.

To consistently achieve a yield ratio of < 0.9 and elongation of > 17% in the finished structural sections, strict process controls are required.

High-performance base materials are carefully selected, with priority given to fine-grained quenched and tempered high-strength steel plates produced through microalloying with small amounts of elements such as Nb, V, and Ti. Materials such as S690QL / S690QL1 typically offer excellent initial ductility, with elongation commonly reaching approximately 18%–21%, providing an adequate safety margin for subsequent welding and fabrication processes.

Special Welding Procedure Specifications (WPS) are implemented under the ISO 3834 quality system, with strict control over welding line energy. Through Laser Fused welding, excessive grain coarsening at the welded joint can be minimized, helping ensure that the yield ratio of the weld and heat-affected zone does not increase beyond 0.9.

Non-destructive testing (NDT) and full traceability are also essential for meeting the stringent requirements of EN 1090-2 at EXC3/EXC4 execution levels. All fabricated structural section welds are required to undergo 100% ultrasonic testing (UT) or magnetic particle testing (MT), with material certificates complying with the requirements of the Hong Kong Code of Practice for the Structural Use of Steel and welding qualification records (WPQR) supplied with the products.