The Q345B square steel tube is a low-alloy steel tube. Q345B is a type of material in steel.

Q345B is a B-grade low-carbon alloy steel material. It boasts excellent comprehensive properties, good low-temperature performance, cold stamping capabilities, excellent welding and machinability. Moreover, as the material thickness increases, the yield strength decreases. This steel is primarily used in the manufacturing of bridges, vehicles, ships, buildings, pressure vessels, and more.

Q345B Introduction
Q345B is a B-grade low-carbon alloy steel material.
In the Q345B steel grade, "Q" indicates the yield strength of the steel; the number following "Q" denotes the yield strength value of the steel, measured in MPa. The number 345 signifies that the yield value of this material is approximately 345MPa, which decreases with the increase in material thickness. "B" denotes that the steel grade is of the B quality level.
The Q345B steel features excellent comprehensive properties, good low-temperature performance, cold-forming capabilities, good welding and machinability. It is widely used in bridges, vehicles, ships, buildings, pressure vessels, and more.
The Q345B steel is a low-carbon alloy steel with a carbon content less than the marked 0.2%. Carbon steel with specific applications, such as bridge steel and ship steel, generally follows the representation method of carbon structural steel but adds a letter to indicate the purpose after the steel number.