16Mn round steel (GB/T 1591, now part of Q345 series) is a low-alloy steel with a chemistry optimized for low-temperature service: 0.12–0.20% C, 1.20–1.60% Mn, 0.20–0.55% Si, and trace Nb/V/Ti for grain refinement.
This composition provides good toughness at -40°C (impact energy ≥34 J) while maintaining 345 MPa yield strength and 470–630 MPa tensile strength-ideal for low-temperature pressure vessels storing LPG and liquid nitrogen. Manganese enhances low-temperature toughness, while microalloys prevent grain growth during welding. 16Mn is equivalent to ASTM A537 Class 1 and EN 10025-2 S355NL, with Chinese production focused on cryogenic storage equipment.