Shipbuilding Steel Plates
Grade A / Grade B General Strength Marine Steel Plate
Product Overview & Manufacturing Standard
Grade A / Grade B are general-strength hull structural steel plates supplied to GB/T 712-2011 and ASTM A131/A131M. Both grades carry a minimum yield strength of 235 MPa and a tensile range of 400 – 520 MPa. The difference lies in the Charpy impact test condition: Grade A is tested at +20°C and Grade B at 0°C (longitudinal ≥ 34 J, transverse ≥ 24 J).
Plates are supplied as-rolled or normalized, dual certified to the Chinese and American standards on one mill certificate, and endorsed by CCS, DNV, ABS, LR, BV, NK, KR, RINA and RS where required.
Standard & Class Society Requirements
| Standard | Grade | Impact Test Temperature | Charpy V Energy (L / T) | Delivery Condition |
|---|---|---|---|---|
| GB/T 712-2011 | A | +20°C | ≥ 34 J / ≥ 24 J | As-rolled or normalized |
| GB/T 712-2011 | B | 0°C | ≥ 34 J / ≥ 24 J | As-rolled or normalized |
| ASTM A131/A131M | Grade A | +20°C | ≥ 34 J / ≥ 24 J | As-rolled |
| ASTM A131/A131M | Grade B | 0°C | ≥ 34 J / ≥ 24 J | As-rolled |
| Class rules (CCS / DNV / ABS and others) | A / B | Per grade | Per class rule | Mill certificate endorsed |
Chemical Composition (Ladle Analysis, %)
| Grade | C max | Si | Mn | P max | S max | Al (soluble) min | Cr / Ni / Cu max |
|---|---|---|---|---|---|---|---|
| A (GB/T 712 / ASTM A131) | 0.21 | 0.10 – 0.35 | ≥ 2.5 C (0.60 – 1.20) | 0.035 | 0.035 | 0.015 | 0.35 / 0.40 / 0.20 |
| B (GB/T 712 / ASTM A131) | 0.21 | 0.10 – 0.35 | 0.60 – 1.20 (≥ 2.5 C) | 0.035 | 0.035 | 0.015 | 0.35 / 0.40 / 0.20 |
Nitrogen ≤ 0.0090 % when aluminium is used for grain refinement. Residual elements are restricted to the levels above and reported on the mill certificate for every heat.
Mechanical Properties
| Grade | Thickness | Yield ReH | Tensile Rm | Elongation A | Charpy V (L / T) |
|---|---|---|---|---|---|
| A | 5 – 50 mm | ≥ 235 MPa | 400 – 520 MPa | ≥ 23 % | ≥ 34 J / ≥ 24 J at +20°C |
| A | > 50 – 100 mm | ≥ 235 MPa | 400 – 520 MPa | ≥ 22 % | ≥ 34 J / ≥ 24 J at +20°C |
| B | 5 – 50 mm | ≥ 235 MPa | 400 – 520 MPa | ≥ 22 % | ≥ 34 J / ≥ 24 J at 0°C |
| B | > 50 – 100 mm | ≥ 235 MPa | 400 – 520 MPa | ≥ 21 % | ≥ 34 J / ≥ 24 J at 0°C |
Tensile Test Data (Typical Mill Results)
| Grade | Thickness | ReH (MPa) | Rm (MPa) | Elongation A (%) | Yield Ratio | Charpy V at Test Temp |
|---|---|---|---|---|---|---|
| A | 8 mm | 302 | 452 | 28.5 | 0.67 | 118 / 96 / 88 J (avg 101 J) |
| A | 16 mm | 296 | 446 | 27.8 | 0.66 | 104 / 92 / 85 J (avg 94 J) |
| B | 20 mm | 318 | 463 | 26.4 | 0.69 | 86 / 79 / 72 J (avg 79 J) |
| B | 32 mm | 305 | 458 | 25.9 | 0.67 | 74 / 68 / 61 J (avg 68 J) |
Values shown are representative of routine production heats and are always confirmed per heat by the actual mill certificate issued with the shipment.
Surface Preparation: Sa2.5 Shot Blasting & Shop Priming
| Parameter | Specification |
|---|---|
| Surface cleanliness | Sa2.5 (near-white metal) to ISO 8501-1 / GB/T 8923.1 |
| Initial rust grade | A / B (mill scale removed completely; only light shadows permitted) |
| Surface profile | Rz 40 – 75 µm, measured per ISO 8503 |
| Abrasive | Steel grit G18 / G25, oil-free compressed air, chloride-free |
| Salt contamination | ≤ 30 mg/m² (conductivity test per ISO 8502-6/-9) |
| Primer type | Zinc-silicate shop primer (weldable) or epoxy shop primer |
| Dry film thickness | 15 – 25 µm, uniform, verified by magnetic gauge |
| Drying / handling time | Touch dry in 5 – 15 min at 20°C; stackable after full cure per primer datasheet |
Processing Guidance
- Cutting: oxy-fuel, plasma and laser cutting without preheat for standard thicknesses; grinding of the cut edge before welding.
- Welding: E4303 / E4315 electrodes or equivalent wire-flux combinations; no preheat required below 25 mm, 50 °C – 100 °C preheat suggested above 25 mm in cold workshop conditions.
- Forming: cold bending and rolling to a minimum inside radius of 2t with a roll axis transverse to the rolling direction.
- Primer repair: areas damaged by cutting or welding are re-blasted to Sa2.5 and re-primed before final painting.
- Supply range: thickness 5 – 150 mm, width 1,500 – 3,200 mm, length up to 12,000 mm, or cut-to-size per drawing.
Request Grade A / Grade B General Strength Marine Steel Plate Quotation & Mill Certificate
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