Q345 Structural Steel Overview
Q345 is a high-strength low-alloy structural steel defined in the earlier edition of GB/T 1591, with a minimum yield strength of 345 MPa for thickness up to 16 mm and tensile strength of 470-630 MPa. It was the standard Chinese high-strength grade for decades and remains widely specified; its direct successor in the current standard is Q355B. Q345 offers roughly 40% more design strength than Q235 at a modest cost premium.
Custom Size H Beam Production
When the required section is not in the hot rolled programme, H beams can be manufactured as custom built-up sections: a web plate welded between two flange plates by automated submerged arc welding. Custom production allows any combination of depth, flange width and thickness, plus long continuous lengths up to 18 m or more. The section is then straightened, inspected and, if specified, cut and drilled to the fabrication drawing.
Hot-Dip Galvanizing for Corrosion Protection
After fabrication, the beam is hot-dip galvanized to ISO 1461:
Surface preparation by degreasing, pickling and fluxing ensures a clean metallurgical bond.
Immersion in molten zinc at about 440-460 °C forms a durable zinc-iron alloy coating.
Typical average coating thickness for sections above 6 mm is 85 µm or more, with local minimums per the standard.
The coating protects the steel for decades in atmospheric, industrial and coastal environments.
Why Galvanized Q345 for Industrial Use
The combination is engineered for industrial environments:
High strength - Q345 supports heavier loads with lighter sections, reducing steel tonnage and foundations.
Corrosion resistance - the zinc coating eliminates painting cycles in plants where maintenance access is difficult.
Impact and fatigue - the fine-grained low-alloy structure gives good toughness for crane and equipment support duty.
Long service life - galvanized members typically outlast painted steel in the same environment.
Typical Applications
Industrial plant frames - equipment platforms, pipe racks and process building structures.
Outdoor steelwork - gantries, jetties, walkways and solar mounting structures.
Material handling - conveyor supports, transfer towers and hopper frames.
Marine and coastal - jetties and structures exposed to salt-laden air.
Specification Checklist
When ordering custom galvanized H beams, specify the section dimensions and grade, the coating thickness or mass per ISO 1461, the surface preparation class, fabrication details such as holes and cut-outs, and the inspection and certificate requirements. Vent and drainage holes must be arranged for hollow or boxed sections before galvanizing.
Frequently Asked Questions
Q: Is Q345 still available?
Yes, Q345 remains in wide use and is supplied alongside its successor Q355B; both have 345-355 MPa minimum yield in thin sections.
Q: What custom sizes are possible?
Built-up sections can be produced from about 200 mm to 2000 mm depth with flange widths to 800 mm and lengths to 18 m or more.
Q: Does galvanizing weaken the welded joints?
No, the zinc coating does not affect the base metal strength; weld quality is controlled before galvanizing by the applicable standard.
Q: Can I order beams with holes already drilled?
Yes, holes and cut-outs are made before galvanizing, and vent or drain holes are added where required.
Q: What coating thickness should I specify?
For sections over 6 mm thick, specify an average coating thickness of 85 µm per ISO 1461, or a higher value for aggressive coastal service.
Q: What certificates are provided?
Mill certificates for the Q345 plate and galvanizing reports with measured coating thickness are supplied with each delivery.