What are the heat treatment requirements after welding Q355 plates?
Thick plates (>40mm) and important components require stress-relief annealing after welding at 600-650℃, with holding time calculated based on plate thickness (1-2 min/mm).
General components can cool naturally without heat treatment, but welding deformation must be controlled.
22. How to avoid cold cracking in Q355 plate welding?
Control carbon equivalent ≤0.43%; reasonable preheating and layer temperature; use low-hydrogen welding materials; slow cooling or heat treatment after welding; optimize welding sequence to reduce stress concentration.
What are the anti-corrosion treatment methods for Q355 plates?
Surface treatment: Sandblasting to Sa2.5 grade to remove oxide scale and rust.
Coating: Epoxy zinc-rich primer + epoxy micaceous iron oxide intermediate paint + fluorocarbon topcoat, dry film thickness ≥120μm.
Special environments: Use weathering steel Q355NH in severely corrosive areas, or hot-dip galvanized steel with heavy-duty anti-corrosion coating.
24. What are the application advantages of Q355 weathering steel (Q355NH)?
Its atmospheric corrosion resistance index I≥6.0 is 2-3 times higher than ordinary Q355, reducing coating maintenance and making it suitable for outdoor bridges and factory steel structures.
25. What are the fire protection design requirements for Q355 steel structures?
According to the "Technical Specification for Fire Protection of Steel Structures," fire-retardant coatings should be selected based on the fire resistance rating (1.5h/2.0h/3.0h). The thickness of thick coatings should be adjusted according to the section modulus of the structural members.