55Si2Mn (GB/T 1222) is a high-silicon spring steel with mechanical properties optimized for automotive suspension systems:
Tensile strength: 1225–1520 MPa after quenching (870°C) and tempering (410°C), ensuring it can support vehicle weight while absorbing road shocks.
Yield strength: ≥1080 MPa, providing the "spring rate" needed for consistent ride quality-too low, and the spring sags; too high, and it becomes rigid.
Fatigue strength: ≥500 MPa for 10⁶ cycles, enabling 100,000+ km service life without failure.
Hardness: 40–45 HRC, balancing elasticity and resistance to permanent deformation (set) under heavy loads.
Its chemistry (0.52–0.60% C, 1.50–2.00% Si, 0.60–0.90% Mn) promotes fine pearlite formation, enhancing fatigue resistance. 55Si2Mn is equivalent to ASTM 9254 (USA) and DIN 1.7102 (Germany), dominating Chinese automotive spring production for trucks and passenger cars.