Q1100D (GB/T 1591) is an ultra-high-strength low-alloy round steel with a chemistry engineered for extreme performance: 0.10–0.20% C, 1.00–1.60% Mn, 1.00–2.00% Cr, 0.30–0.80% Mo, 0.02–0.20% V/Nb/Ti, and ≤0.030% P/S.
This composition delivers 1100 MPa minimum yield strength and 1200–1400 MPa tensile strength, with -40°C impact toughness ≥27 J-making it suitable for armor plating, ballistic shields, and ultra-heavy crane components. Q1100D provides exceptional strength-to-weight ratio, reducing weight by 50% compared to Q690 in equivalent applications. It is China's highest-strength structural steel, used in defense and extreme industrial applications where no compromise on strength is allowed.