Overview
Higher-strength hull steel designations are controlled by strength family, toughness class, thickness, delivery condition and classification approval. Selecting a higher strength notation does not itself prove weld procedure, fracture performance or suitability for every hull member.
Designation and acceptance
IACS Unified Requirements are minimum classification-society requirements. Grade notation, thickness, delivery condition, test temperature, plate approval and the ship’s class rules must be read together; notation alone does not create an interchangeable material approval.
Members and selection
| Designation | Selection context |
|---|---|
| FH36 | Higher-strength notation requiring project-specific toughness, thickness and delivery-condition confirmation. |
| DH40 | Higher-strength notation; verify the approved strength/toughness combination instead of comparing only the number. |
| EH40 | Higher-strength notation that needs class-approved product, testing and fabrication controls. |
Comparison framework
| Criterion | Decision context |
|---|---|
| Selection basis | Higher-strength groups need deliberate welding and fracture-control review, particularly as thickness and structural consequence increase. |
Performance
- FH36, DH40 and EH40 illustrate that toughness letters and strength numbers are separate selection axes; higher-strength use needs explicit fracture and structural-consequence review.
Orderable product scope
- Shipbuilding plate, wide flat and sections must be quoted with class approval, grade notation, thickness, delivery condition, inspection and material certificates.
Processing
- Higher-strength fabrication needs class-approved welding procedures, heat-input windows, consumable matching, hardness/toughness evidence, forming limits, repair controls and field-fabrication traceability.
Applications
- Hull structural members and marine structures where the design, classification and fabrication documents approve the ordered steel.
Selection
- Do not select FH36, DH40, EH40 or another higher-strength designation for weight saving until buckling, fatigue, fracture, weldability and available product thickness have been recalculated.
Procurement
- Require the exact strength/toughness designation, IACS/class basis, approved mill and thickness, delivery condition, through-thickness property if ordered, toughness/NDT evidence and fabrication qualification package.