Hot-Dip Galvanizing S235JR and SS400 Plate: What to Check Before You Order
Watch silicon content first. Steels with silicon between roughly 0.04% and 0.3% react strongly with molten zinc and come out with thick, grey, sometimes brittle coatings. Ordinary S235JR and SS400 are usually safe, but if appearance or paintability matters, ask for the mill certificate and check the Si value before ordering.
Second, expect distortion on thin or asymmetric parts. A 5 mm plate dipped at about 450°C expands and relaxes, and long flat parts can leave the kettle with waves. If flatness is critical, order thicker sections, add stiffeners, or plan a straightening allowance after galvanizing.
Third, specify the coating thickness, not just the word galvanized. A common requirement for outdoor structural work is an average of 70 to 85 μm of zinc, in line with ISO 1461. Vent and drain holes on closed sections must also be agreed in advance, otherwise the galvanizer decides for you.
We supply S235JR, SS400 and Q235B steel plate and cut parts, and we can arrange hot-dip galvanizing to ISO 1461 with coating thickness reports before shipment.