EN 10025-2 limits phosphorus content in S355JR UB steel to 0.035% max. Phosphorus is a residual impurity from steelmaking, but high levels pose severe risks:
Low-Temperature Brittleness: Phosphorus segregates at grain boundaries, weakening intergranular bonds and making the steel prone to brittle fracture at temperatures below +20°C. For example, an S355JR UB beam with 0.040% phosphorus might crack suddenly in a cold snap.
Weldability Reduction: Excess phosphorus increases the risk of cracking in the heat-affected zone (HAZ) during welding, requiring expensive preheating.To control phosphorus, manufacturers use high-purity iron ore and scrap metal, and employ ladle metallurgy processes (e.g., slagging) to remove impurities. Post-production, each batch is tested via spectroscopic analysis, with phosphorus levels documented in the material certificate. This strict limit ensures S355JR retains toughness and weldability across all service conditions.