As a cross-sectional dimension and tolerance standard, GB/T 11263 covers hot-rolled H-section steel (wide flange) and T-section steel, providing standardized profiles for structural applications. H-section steel under this standard is characterized by its high section modulus, efficient load-bearing capacity, and uniform cross-sectional dimensions, making it a fundamental component in steel-framed buildings, bridge structures, industrial plants, and heavy equipment support frames. Available in HW (wide flange), HM (medium flange), and HN (narrow flange) series, with materials commonly supplied in Q235B, Q355B, Q390B, and Q420B grades. The standard specifies dimensional tolerances for flange slope, curvature, center deviation, web curvature, and cut-end slope, ensuring consistent quality for engineering applications.
Q235 B/C/D
Q275 B/C/D
Q345 B/C/D/E
Q355 B/C/D/NB/NC/ND/MD/ME
Q390 B/C/D/E/G
Q420B
Q460C
GB-1591-2024(Steel Grades)
As a low-alloy high-strength structural steel, Q355B demonstrates excellent weldability and comprehensive mechanical properties, making it one of the most widely used steel grades in China for structural engineering and construction projects. GB/T 1591 Q355B (formerly Q345B) offers an optimum combination of high yield strength, good ductility, and reliable impact toughness at room temperature. It is commonly used in welded structures, bolted and riveted connections for buildings, bridges, industrial plants, transmission towers, and heavy machinery. Its versatility in various thicknesses and delivery conditions (as-rolled, normalized, TMCP) makes it a preferred grade for both general and critical structural applications.
Number of Standard
Grade
Elongation After Fracture(%)
Impact Test J for KV or J/cm2 for KCU
GB/T 1591-2024
Q355B
A≥22(-20) (t2≤40 mm)
A≥21(-19) (40＜t2≤63 mm)
A≥20(-18) (63＜t2≤100 mm)
A≥18(-18) (100＜t2≤150mm)
A≥17(-17) (150＜t2≤400mm)
20℃ KV2≥34 (horizontal)
20℃ KV2≥27 (vertical)
Q355MB
A≥22
20℃ KV2≥34 (horizontal)
20℃ KV2≥27 (vertical)
Q355NB
A≥22 (t2≤63 mm)
A≥21 (63＜t2≤250 mm)
20℃ KV2≥34 (horizontal)
20℃ KV2≥27 (vertical)
Number of Standard
Grade
Tensile Strength (Rm/Mpa)
GB/T 1591-2024
Q355B
470～630 (t2≤100mm)
450～600 (100＜t2≤150mm)
450～600 (150＜t2≤250mm)
Q355MB
470～630 (t2≤40mm)
450～610 (40＜t2≤63mm)
440～600 (63＜t2≤80mm)
440～600 (80＜t2≤100mm)
430～590 (100＜t2≤120mm)
Q355NB
470～630 (t2≤100mm)
450～600 (100＜t2≤200mm)
450～600 (200＜t2≤250mm)
GB/T 34103
As a marine structural steel, GB/T 34103 covers both normal-strength and high-strength steel grades specifically designed for shipbuilding and offshore engineering applications. These grades demonstrate excellent weldability, toughness, and corrosion resistance in harsh marine environments. The standard includes general-strength grades (A, B, D, E) with a minimum yield strength of 235 MPa, and high-strength grades (AH32–FH500) with yield strengths ranging from 315 to 500 MPa. Grades are designated by strength level (32/36/40/420/460/500) and quality class (A/D/E/F), where higher classes indicate superior low-temperature impact toughness. Commonly used in hull construction, deck structures, bulkheads, offshore platform jackets, and other marine engineering structures requiring guaranteed performance at sub-zero temperatures.As a marine structural steel, GB/T 34103 covers both normal-strength and high-strength steel grades specifically designed for shipbuilding and offshore engineering applications. These grades demonstrate excellent weldability, toughness, and corrosion resistance in harsh marine environments. The standard includes general-strength grades (A, B, D, E) with a minimum yield strength of 235 MPa, and high-strength grades (AH32–FH500) with yield strengths ranging from 315 to 500 MPa. Grades are designated by strength level (32/36/40/420/460/500) and quality class (A/D/E/F), where higher classes indicate superior low-temperature impact toughness. Commonly used in hull construction, deck structures, bulkheads, offshore platform jackets, and other marine engineering structures requiring guaranteed performance at sub-zero temperatures.
