Q420qE (GB/T 714-2015) is a bridge-specific low-alloy round steel with a composition engineered for durability and load-bearing:
0.16–0.20% carbon (C): Provides base strength without compromising weldability for bridge joints.
1.30–1.60% manganese (Mn): Enhances tensile strength and low-temperature toughness.
0.50–0.80% chromium (Cr): Improves corrosion resistance in humid or coastal bridge environments.
0.02–0.06% niobium (Nb): Refines grain structure to boost fatigue resistance (critical for bridges enduring traffic vibrations).
P ≤0.025%, S ≤0.020%: Strict limits to prevent brittle fracture in cold weather.
This composition delivers 420 MPa minimum yield strength, 540–680 MPa tensile strength, and -40°C impact toughness ≥34 J-making it ideal for long-span bridges like China's Hong Kong-Zhuhai-Macao Bridge. It is equivalent to EN 10025-5 S420ML (EU), with Made-in-China listings highlighting its "Bridge-Grade Durability."