16mn方管的含磷、硫量分别是多少 Q345A 含磷和硫都小于等于0.045% Q345B 含磷和硫都小于等于0.040% Q345C 含磷和硫都小于等于0.035% Q345D 含磷和硫都小于等于0.030% Q345E 含磷和硫都小于等于0.025% 而磷和硫杂质元素在钢中越多其冲击韧性就越差