EN 10025-2 limits carbon content in S355JR UPE/UPN channels to 0.24% max. Carbon enhances strength but poses risks at higher levels:
Brittleness: Excess carbon increases the likelihood of brittle fracture, especially at low temperatures or under impact.
Weldability Loss: Carbon forms hard, crack-prone microstructures (e.g., martensite) in the heat-affected zone (HAZ) during welding, requiring costly preheating.The 0.24% cap balances strength and workability, allowing UPE/UPN channels to be welded via standard methods (MIG, TIG) without preheating. Manufacturers use spectroscopic analysis to monitor carbon levels during steelmaking, with post-production testing documented in material certificates. This control ensures S355JR retains fabrication flexibility while meeting structural demands.