ASTM A588 Gr.B is a high-strength, low-alloy weathering structural steel defined by ASTM A588/A588M, with mechanical properties that vary by thickness. Below are the standard minimum values for the relevant thickness ranges.
1. Yield Strength (Rp0.2, min)
The minimum yield strength of ASTM A588 Gr.B decreases with increasing plate thickness:
≤ 100 mm thickness: ≥ 345 MPa (50 ksi)
100–125 mm thickness: ≥ 315 MPa (46 ksi)
125–200 mm thickness: ≥ 290 MPa (42 ksi)
These thickness-dependent values should be considered when selecting ASTM A588 Gr.B for load-bearing structural applications.
2. Tensile Strength (Rm, min)
The minimum tensile strength also varies according to plate thickness:
≤ 100 mm: ≥ 485 MPa (70 ksi)
100–125 mm: ≥ 460 MPa (67 ksi)
125–200 mm: ≥ 435 MPa (63 ksi)
The combination of yield strength and tensile strength provides ASTM A588 Gr.B with the mechanical capacity required for weathering structural steel applications.
3. Elongation (A, min)
For ASTM A588 Gr.B, elongation requirements depend on the gauge length used for the tensile test:
50-mm gauge length: ≥ 21%
200-mm (8-in) gauge length: ≥ 18%
The two values should not be treated as interchangeable because elongation depends on the specified gauge length. For plates within the applicable thickness range, the 50-mm and 200-mm gauge-length requirements provide different standard measurement bases for ductility.
4. Impact Toughness (Charpy V-Notch, CVN)
A minimum impact toughness value of ≥ 21 J at −23°C may be specified for applications requiring additional Charpy V-Notch impact performance, particularly for applicable thicknesses.
However, this impact value should be treated as a project or purchase supplementary requirement, rather than a universal mandatory Charpy requirement of ASTM A588/A588M itself. Where low-temperature impact performance is required, the purchaser should specify the applicable supplementary requirements or testing standard in the purchase specification.
Typical performance is often described as providing good toughness at temperatures down to approximately −40°C, but actual impact performance should be verified against the applicable test requirements rather than assumed from the grade designation alone.
5. Hardness
Brinell hardness: Typically 157 HB max.
This value should be understood as a typical reference value, rather than a guaranteed maximum hardness requirement of ASTM A588/A588M unless specifically stated in the applicable material or purchase specification.
6. Formability & Weldability
Excellent cold bendability: ASTM A588 Gr.B can be subjected to a 180° bend test, with the required bend diameter depending on plate thickness:
t ≤ 19 mm: d = 2t
t > 19 mm: d = 3t
where d is the inside bend diameter and t is the plate thickness.
Therefore, the commonly stated d = 2t bending requirement should not be applied to every ASTM A588 Gr.B plate thickness.
Excellent weldability: ASTM A588 Gr.B has good weldability when appropriate welding procedures are used. The weathering characteristics of welded areas also need to be considered when selecting welding consumables and fabrication procedures, particularly for structures where uniform weathering appearance and corrosion protection are important.
7. Fatigue & Structural Performance
ASTM A588 Gr.B offers:
High fatigue strength for structural components subjected to cyclic loading
Good toughness and ductility to help resist brittle fracture
High yield and tensile strength for load-bearing structural applications
Weathering characteristics that support long-term outdoor structural use
Overall, the key mechanical properties of ASTM A588 Gr.B are its thickness-dependent yield and tensile strength, defined elongation requirements, good toughness and weldability, and suitability for weathering structural applications. When specifying the material, users should pay particular attention to plate thickness, tensile-test gauge length, bend-test thickness limits, and any project-specific Charpy impact requirements.
