The production of Q355B I-beams in China is governed by a hierarchy of interrelated national standards, primarily managed by the Standardization Administration of China (SAC). The two most critical standards are:
1. GB/T 1591-2018 "High strength low alloy structural steels": This is the fundamental material standard. It defines the chemical composition, mechanical properties (yield strength, tensile strength, elongation, impact toughness), test methods (tensile, impact, bend), inspection rules, and marking requirements for the steel grade itself, irrespective of its final product form (plate, section, etc.).
2. GB/T 706-2016 "Dimensions, shape, weight and tolerances for hot-rolled section steel": This is the product-specific standard for hot-rolled steel sections like I-beams, channels, and angles. It specifies the exact dimensional series (e.g., HN 400x200, HW 300x300), cross-sectional tolerances (height, width, web/flange thickness, deviation from verticality, camber, twist), weight tolerances, and straightness requirements for the rolled sections. For I-beams, it distinguishes between "H-beams" (wide or parallel flange beams, series HW, HM, HN) and traditional "I-beams" (with tapered inner flange surfaces, series I). The actual production process in a steel mill must comply with both standards. Additionally, the testing procedures refer to other standards like GB/T 228.1 (tensile testing), GB/T 229 (Charpy impact testing), and GB/T 232 (bend testing). For export or international projects, equivalent standards like EN 10025-2 (S355JR/J0/J2) or ASTM A6/A6M and A992/A992M (for W-shapes, Grade 50) may be specified, though chemical and mechanical details are not identical.