A3是过去的叫法，现在叫Q235了
Q235分A、B、C、D四级(GB/T 700-2006)
Q235A级含 C ≤0.22% Mn ≤1.4% Si ≤0.35% S ≤0.050 P ≤0.045
Q235B级含 C ≤0.20% Mn ≤1.4% Si ≤0.35% S ≤0.045 P ≤0.045
Q235C级含 C ≤0.17% Mn ≤1.4% Si ≤0.35% S ≤0.040 P ≤0.040
Q235D级含 C ≤0.17% Mn ≤1.4% Si ≤0.35% S ≤0.035 P ≤0.035
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