Q345B is a material for steel pipes. Q represents the yield of this material, and the back 345 refers to the yield value of this material. The Q345B steel pipe is a 16Mn steel pipe, which is one of the seamless steel pipe products. 16Mn is a material in steel. A name for steel in the past. Now called the law:Q345B. 16Mn is a low-alloy steel series.