What is the maximum phosphorus content allowed in S355JR channel steel?

EN 10025-2:2004 limits the maximum phosphorus content in S355JR channel steel to 0.035%. Phosphorus is a naturally occurring impurity in steel, but high levels have severe negative effects: it increases brittleness (especially at low temperatures), reduces ductility, and impairs weldability. At concentrations above 0.035%, phosphorus segregates at grain boundaries, weakening the bonds between grains and making the steel prone to brittle fracture under impact or cyclic loads. For example, a channel with 0.040% phosphorus might break suddenly in cold weather, even under moderate loads. To control phosphorus, manufacturers use high-quality iron ore and scrap metal with low phosphorus content, and they employ refining processes (e.g., ladle metallurgy) to remove excess phosphorus from the molten steel. Post-production, each batch is tested for chemical composition, with phosphorus levels documented in the material certificate. This strict limit ensures S355JR maintains its toughness and ductility, even in challenging environments.