Grade B (ship) vs Grade A (ship)
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
Grade B (ship)
Structural & HSLA Steel
Grade B is the ordinary-strength hull steel with a 0 °C impact guarantee — the default shell and deck plate for vessels in general service under classification-society rules (IACS UR W11 / ASTM A131 / GB/T 712). Its manganese window is set tighter than Grade A to support the toughness requirement.
Standards: AISI A131 B · JIS KB (near) · GB B (GB/T 712)
Grade A (ship)
Structural & HSLA Steel
Grade A is the baseline ordinary-strength hull steel of the classification-society system (IACS UR W11, mirrored by ASTM A131 and GB/T 712). At 235 MPa yield with no impact-test requirement, it covers the least demanding hull zones — internal structure and sheltered areas on classed vessels.
Standards: AISI A131 A · JIS KA (near) · GB A (GB/T 712)
Chemical composition compared (%)
| Element | Grade B (ship) | Grade A (ship) |
|---|---|---|
| C | ≤0.21 | ≤0.21 |
| Si | ≤0.35 | ≤0.50 |
| Mn | 0.80–1.20 | ≥2.5×C |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.035 | ≤0.035 |
| Note | Chemistry per classification-society rules (IACS UR W11) | Chemistry per classification-society rules (IACS UR W11) |
Properties compared
| Property | Grade B (ship) | Grade A (ship) |
|---|---|---|
| Yield strength | ≥235 MPa | ≥235 MPa |
| Tensile strength | 400–520 MPa | 400–520 MPa |
| Impact | 0 °C, ≥27 J longitudinal (≤50 mm) | No impact test required |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: Grade B (ship) · Grade A (ship). Substitution decisions for certified parts stay with the design authority.