Both European (EN 10025-2) and Chinese (GB/T 1591) H-beam standards strictly control four key impurities to ensure material equivalence and structural safety:
Phosphorus (P): Max 0.035% (S355JR/Q355B) and 0.045% (S235JR/Q235B). Phosphorus segregates at grain boundaries, increasing brittleness-especially at low temperatures. Controlling it prevents sudden fracture in cold climates or under impact loads.
Sulfur (S): Max 0.035% (S355JR/Q355B) and 0.045% (S235JR/Q235B). Sulfur forms iron sulfides, which melt at low temperatures and cause "hot shortness" (cracking during rolling or welding). Limiting sulfur ensures the beam can be fabricated without defects.
Nitrogen (N): Max 0.012% (S355JR) and 0.014% (Q355B). Excess nitrogen forms brittle nitrides, reducing ductility. Both standards cap nitrogen to maintain weldability and toughness.
Titanium (Ti)/Niobium (Nb): Optional microalloys (max 0.15% combined) added to refine grain structure. European and GB standards allow these elements to boost strength without compromising ductility, ensuring consistent performance across grades.
By controlling these impurities to nearly identical levels, European and GB H-beams exhibit the same resistance to brittleness, cracking, and fabrication defects. This chemical consistency is a cornerstone of their equivalence, as it ensures predictable behavior in service.