牌号质量等级化学成分a.b（质量分数）／％CSiMnPSNbVTiCrNiCuNMoBAla不大于不小于Q345A≤0.20≤0.50≤1.700.0350.0350.070.150.200.300.500.300.0120.10－－B0.0350.035C0.0300.0300.015D≤0.180.0300.025E0.0250.020Q390A≤0.20≤0.50≤1.700.0350.0350.070.200.200.300.500.300.0150.10－－B0.0350.035C0.0300.0300.015D0.0300.025E0.0250.020Q420A≤0.20≤0.50≤1.700.0350.0350.070.200.200.300.800.300.0150.20－－B0.0350.035C0.0300.0300.015D0.0300.025E0.0250.020Q460C≤0.20≤0.60≤1.800.0300.0300.110.200.200.300.800.550.0150.200.0040.015D0.0300.025E0.0250.020Q500C≤0.18≤0.60≤1.800.0300.0300.110.120.200.600.800.550.0150.200.0040.015D0.0300.025E0.0250.020牌号质量等级化学成分a.b（质量分数）／％CSiMnPSNbVTiCrNiCuNMoBAla不大于不小于Q550C≤0.18≤0.60≤2.000.0300.0300.110.120.200.800.800.800.0150.300.0040.015D0.0300.025E0.0250.020Q620C≤0.18≤0.60≤2.000.0300.0300.110.120.201.000.800.800.0150.300.0040.015D0.0300.025E0.0250.020Q690C≤0.18≤0.60≤2.000.0300.0300.110.120.201.000.800.800.0150.300.0040.015D0.0300.025E0.0250.020ａ型材及棒材P、S含量可提高0.005%，其中A型钢上限可为0.045%.河南尊信钢铁公司专业定扎ｂ当细化晶粒元素组合加入时，20（Nb+V+Ti）≤0.22%，20（Mo+Cr）≤0.30%.。