GB/T 1591-1994 Specification of Low Alloy High Strength Structural Steels
This standard GB/T 1591-1994, “Low Alloy High Strength Structural Steels” specifies technical requirements, inspection rules and permissible tolerances for seven grades of steel used in the manufacture of structural steel parts.
The seven grades include: Q345, Q345G, Q345G.S, Q345G.L, Q390, Q390G, and Q390G.L.
The chemical composition of each grade of steel is as follows:
Q345: C:0.12- 0.20, Si<=0.35, Mn:1.00-1.60, P<=0.045, S<=0.035, Nb<=0.06;
Q345G: C:0.12- 0.20, Si<=1.00, Mn:1.00-1.60, P<=0.055, S<=0.035, Nb<=0.06;
Q345G.S: C:0.12- 0.20, Si<=0.35, Mn:1.00-1.60, P<=0.055, S<=0.035, Nb<=0.06;
Q345G.L: C:0.12- 0.20, Si<=0.35, Mn:1.00-1.60, P<=0.045, S<=0.035, Nb<=0.06;
Q390: C:0.12- 0.20, Si<=1.00, Mn:1.00-1.60, P<=0.045, S<=0.035, Nb/V<=0.06;
Q390G: C:0.12- 0.20, Si<=1.00, Mn:1.00-1.60, P<=0.055, S<=0.035, Nb/V<=0.06;
Q390G.L: C:0.12- 0.20, Si<=0.35, Mn:1.00-1.60, P<=0.045, S<=0.035, Nb/V<=0.06.
The technical requirements of each grade of steel include requirements for primary chemical composition and mechanical properties as measured in the tensile strength, yield strength and elongation.
Tensile strength requirements vary depending on the grade of steel. Q345 steel must demonstrate a minimum tensile strength of 390MPa, while Q390 steel must demonstrate a minimum tensile strength of 440MPa. Q390G.L must demonstrate a minimum tensile strength of 500MPa.
Yield strength also varies depending on the grade of steel. Q345 must demonstrate a minimum yield strength of 345MPa, while Q390 must demonstrate a minimum yield strength of 390MPa. Q390G.L must demonstrate a minimum yield strength of 450MPa.
Elongation requirements vary depending on the grade of steel. Q345 and Q345G must demonstrate an elongation of 22%, while Q390 must demonstrate an elongation of 16%. Q390G.L must demonstrate an elongation of 14%.
In addition to the above mentioned technical requirements, inspection rules and permitting tolerances are also specified for each grade of steel. These include rules for determining structural dimensions and for assessing surface quality and cosmetic appearances. There are additional requirements for verifying the physical and chemical properties of the steel. A range of permissible tolerances is determined to ensure the quality of the steel product.
This standard GB/T 1591-1994 is an important industry standard that provides guidance to ensure that the low alloy high strength structural steel components used in many applications such as bridges, towers and other structural components meet required specifications and quality standards. This standard sets out requirements for the manufacture of low alloy high strength structural steel in China and it provides an important guidance to manufacturers and suppliers to ensure that the steel they produce meets the required technical, inspection and quality requirements.
