GB/T1591 standard specifies the grades and technical requirements, test methods, inspection rules, packaging, marking and quality specifications of low alloy high strength structural steels.GB/T1591 standard applies to hot rolling, controlled rolling, normalizing, normalizing tempering and quenching and tempering supply of engineering steel and general structure with thickness of not less than 3mm steel, steel and steel, steel bar, generally in the supply State use.GB/T1591 standard stipulates that the chemical composition of low-alloy high-strength structural steel is also applicable to steel ingot, continuous casting billet, billet and its products.GB/T1591 Standard main steel grade:Q345A,Q345B,Q345D,Q390A,Q390B,Q390D,Q420A,Q420B,Q460D and so on.