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1. Chinese National Standard (GB/T)

Standard Code: GB/T 706-2016 “Hot-Rolled Section Steel”

Key Parameters:

1. Material & Mechanical Properties:
   • Common Grades: Q235B, Q345B.
   • Yield Strength (σₛ):
     • Q235B: ≥235 MPa;
     • Q345B: ≥345 MPa.
   • Tensile Strength (σ_b):
     • Q235B: 375–500 MPa;
     • Q345B: 470–630 MPa.
   • Elongation (δ₅):
     • Q235B: ≥26%;
     • Q345B: ≥21%.
2. Chemical Composition (%):

   Grade	Carbon (C) ≤	Silicon (Si) ≤	Manganese (Mn)	Sulfur (S) ≤	Phosphorus (P) ≤
   Q235B	0.20	0.35	0.30–0.70	0.045	0.045
   Q345B	0.20	0.55	1.00–1.60	0.045	0.045

3. Dimensions & Tolerances:
   • Height (h): 100–630 mm, tolerance ±2.0 mm;
   • Flange Width (b): 68–220 mm, tolerance ±2.0 mm;
   • Web Thickness (d): 4.5–24 mm, tolerance ±0.5 mm;
   • Length: Typically 6–19 m, tolerance +50 mm (positive deviation).
4. Surface Quality:
   • Surfaces shall be free from cracks, folds, scars, and other defects;
   • Minor localized pits or scratches are permitted.

2. International Standard (ASTM)

Standard Code: ASTM A36 “Standard Specification for Carbon Structural Steel”

Key Parameters:

1. Mechanical Properties:
   • Yield Strength: ≥250 MPa (36 ksi);
   • Tensile Strength: 400–550 MPa (58–80 ksi);
   • Elongation: ≥20% (200 mm gauge length).
2. Chemical Composition (%):
   • Carbon (C) ≤0.26, Manganese (Mn) ≥0.80, Phosphorus (P) ≤0.04, Sulfur (S) ≤0.05.

3. European Standard (EN)

Standard Code: EN 10025-2 “Hot-Rolled Products of Structural Steels”

Key Parameters:

1. Common Grades: S235JR, S355JR.
2. Mechanical Properties:
   • S235JR: Yield strength ≥235 MPa, tensile strength 360–510 MPa;
   • S355JR: Yield strength ≥355 MPa, tensile strength 470–630 MPa.
3. Chemical Composition (%):
   • S235JR: C ≤0.17, P ≤0.035, S ≤0.035;
   • S355JR: C ≤0.20, P ≤0.035, S ≤0.035.