What are the selection principles for Q355 steel plates in large-span steel structures?
Prioritize Q355D/E grade to ensure low-temperature toughness and fatigue resistance; use Z25/Z35 grade for thicker plates; control the width-to-thickness ratio of the cross-section to meet stability requirements.
What are the cutting methods for Q355 plates, and what are the precautions?
Cutting methods: flame cutting, plasma cutting, laser cutting.
Note: Remove surface oil and rust before cutting; control cutting speed and temperature to reduce the heat-affected zone; thick plates need to bevel and remove oxide scale after cutting.
18. What are the process requirements for cold working (bending, shearing) of Q355 plates?
Cold bending: 180° cold bending, the bending mandrel diameter is adjusted according to the plate thickness (t≤16mm, d=3t; t>16mm, d=4t), no cracks after bending.
Shearing: Avoid excessive cold working to prevent work hardening and micro-cracks; thick plates need edge grinding after shearing.
19. What are the matching welding consumables for welding Q355 plates?
Electrodes: E50 series (E5015, E5016); Welding wire: ER50-6; Flux: HJ431, matching the strength grade of Q355.
20. Preheating and interpass temperature control standards for welding Q355 plates?
Plate thickness ≤25mm: Preheating not required; 25-40mm: Preheat to 80-120℃; >40mm: Preheat to 100-150℃.
Interpass temperature: 100-200℃. Avoid overheating or undercooling to reduce welding stress and cracking.