无缝方矩管材质 Q345A：C≤0.20，Mn ≤1.70，Si≤0.50，P≤0.035，S≤0.035;Q345B：C≤0.20，Mn ≤1.70，Si≤0.50，P≤0.035，S≤0.035;Q345C：C≤0.20，Mn ≤1.70，Si≤0.50，P≤0.030，S≤0.030，Al≥0.015;Q345D：C≤0.18，Mn ≤1.70，Si≤0.50，P≤0.030，S≤0.025，Al≥0.015;Q345E：C≤0.18，Mn ≤1.70，Si≤0.50，P≤0.025，S≤0.020，Al≥0.015;Q345A、B、C、D、E均含Nb≤0.07，V≤0.15，Ti≤0.20，Cr≤0.30，N≤0.012，Mo≤0.10。20#、Q235B