AH, DH, EH, FH — What Do They Mean in Marine Steel Grades?
When buying marine steel plates, many buyers focus on the strength grade first — AH36, DH36, EH36, or FH36. But the first letter is not simply a different strength level.
The "36" in these grades is not what sets them apart. A, D, E and F are the key. These are all high-strength shipbuilding steel grades, but they differ in their impact toughness requirements at different temperatures.
This guide explains the differences between AH36, DH36, EH36 and FH36 — and what buyers should check before ordering.
1. What Do AH36, DH36, EH36 and FH36 Mean?
The table below shows the key difference between these four grades:
Important: The impact test temperatures shown above are based on IACS Unified Requirements and common classification society rules (LR, ABS, DNV, CCS, BV, RINA). However, the exact requirements should always be verified against the specific classification society rules and material standard applicable to your project.[citation:1][citation:7]
2. The "36" in AH36, DH36, EH36 and FH36
The number "36" refers to the minimum yield strength of the steel — 355 MPa (approximately 51,000 psi).[citation:4]
- ✔ AH36, DH36, EH36 and FH36 all have a minimum yield strength of 355 MPa
- ✔ Tensile strength range: 490 – 620 MPa for all four grades[citation:1]
- ✔ The letters A, D, E and F do not indicate different strength levels
💡 Key point: AH36 is not stronger than DH36. DH36 is not stronger than EH36. They share the same strength level. The difference is impact toughness at different temperatures.
3. AH36 vs DH36 vs EH36 vs FH36: What's the Difference?
3.1 Chemical Composition
The chemical composition requirements for AH36, DH36, EH36 and FH36 are generally similar, with the main difference being the grain refinement practice and delivery condition required to achieve the specified impact toughness at lower temperatures.[citation:1]
- ✔ AH36 — typically supplied in control-rolled condition
- ✔ DH36 — control-rolled or normalized condition
- ✔ EH36 — normalized condition required for thicker plates
- ✔ FH36 — normalized or quenched and tempered condition
📌 Note: Chemical composition requirements depend on the applicable marine steel standard and classification society. The grain refinement practice — using elements like Nb, V, Ti, and Al — becomes more important as the required impact test temperature decreases.[citation:1]
3.2 Impact Toughness
This is the key difference between the four grades. Each grade is tested at a different temperature using the Charpy V-notch impact test.[citation:1][citation:4][citation:9]
- ✔ AH36 — impact tested at 0°C
- ✔ DH36 — impact tested at -20°C
- ✔ EH36 — impact tested at -40°C
- ✔ FH36 — impact tested at -60°C
💡 The main difference between AH36, DH36, EH36 and FH36 is their required impact toughness at different temperatures. The strength level is the same.
4. Why Does Impact Toughness Matter for Shipbuilding Steel?
Ship hulls operate in demanding environments:
- ✔ Cold seawater
- ✔ Winter navigation in northern routes
- ✔ Arctic and sub-Arctic conditions
- ✔ Offshore structures and marine equipment
Low temperatures can reduce the toughness of steel, making it more susceptible to brittle fracture. A ship structure cannot be evaluated on yield strength and tensile strength alone — impact toughness is equally important.[citation:4]
⚠️ What we've seen: A shipyard once selected AH36 for a vessel that would operate in North Atlantic winter conditions. The project required -20°C impact toughness. The plates failed the impact test at -20°C — because AH36 is only tested at 0°C. The replacement cost was significant.
5. AH36 vs DH36 vs EH36 vs FH36: Which One Should You Choose?
The choice depends on the vessel's operating environment and the classification society rules.
✅ AH36 — General Shipbuilding
- Cargo ships, general marine structures, temperate climates
- Impact test temperature: 0°C
✅ DH36 — Colder Climates / Offshore
- Ships operating in colder waters, offshore structures
- Impact test temperature: -20°C
✅ EH36 — Low-Temperature / Arctic Regions
- Cold-region vessels, offshore engineering, low-temperature applications
- Impact test temperature: -40°C
✅ FH36 — Extreme Cold / Ice-Class Vessels
- Arctic vessels, icebreakers, extreme cold environments
- Impact test temperature: -60°C
6. Can AH36 Replace DH36, EH36 or FH36?
Not automatically.
- ✔ AH36 and DH36 — similar strength, but different impact toughness requirements
- ✔ EH36 — requires -40°C impact testing, which AH36 cannot meet
- ✔ FH36 — requires -60°C impact testing, the most demanding grade
⚠️ Important: A higher impact toughness requirement cannot be ignored simply because the yield strength is the same. Always check the project specification and classification society rules before substituting grades.
7. AH36, DH36, EH36 and FH36 Under Different Classification Societies
Marine steel plates must be certified by a classification society. Common societies include:
- ✔ ABS — American Bureau of Shipping
- ✔ DNV — Det Norske Veritas
- ✔ LR — Lloyd's Register
- ✔ BV — Bureau Veritas
- ✔ CCS — China Classification Society
- ✔ RINA — Registro Italiano Navale
- ✔ NK — Nippon Kaiji Kyokai
📌 Note: While the impact toughness requirements for AH36, DH36, EH36 and FH36 are generally harmonized across major classification societies through IACS Unified Requirements, buyers should always verify the specific rules of the society applicable to their project.[citation:1][citation:5][citation:7]
8. What Certificates Are Required for Marine Steel Plates?
For marine steel plates, the following documentation is typically required:
- ✔ EN 10204 3.1 — mill-certified inspection certificate
- ✔ EN 10204 3.2 — inspection certificate with independent verification, often required for marine applications
- ✔ Class Certificate — endorsed by the classification society (e.g., ABS, DNV, LR, BV, CCS, RINA)
💡 Important: If a project requires original class endorsement by a classification society surveyor, confirm the specific inspection and signing requirements with the supplier before production.
9. What Should Buyers Check Before Ordering Marine Steel Plates?
Before placing an order, confirm these details:
- ✓ Grade: AH36, DH36, EH36, or FH36
- ✓ Thickness: e.g., 10mm, 20mm, 30mm
- ✓ Width and Length: Standard size, fixed size, or cut-to-size
- ✓ Classification Society: ABS, DNV, LR, BV, CCS, RINA, etc.
- ✓ Impact Test Requirement: Temperature and energy value
- ✓ Delivery Condition: Normalized, TMCP, or controlled rolling
- ✓ Inspection Certificate: EN 10204 3.1 or 3.2, class certificate
10. AH36 vs DH36 vs EH36 vs FH36 — Quick Comparison
11. Frequently Asked Questions
❓ What is AH36 steel?
AH36 is a high-strength marine steel plate with a minimum yield strength of 355 MPa. It is impact tested at 0°C and is suitable for general shipbuilding applications in temperate climates.
❓ What is DH36 steel?
DH36 is a high-strength marine steel plate with the same yield strength as AH36 (355 MPa) but impact tested at -20°C. It is suitable for ships operating in colder climates or offshore structures.
❓ What is EH36 steel?
EH36 is a high-strength marine steel plate with 355 MPa yield strength, impact tested at -40°C. It is used for low-temperature applications, cold-region vessels, and offshore engineering.
❓ What is FH36 steel?
FH36 is a high-strength marine steel plate with 355 MPa yield strength, impact tested at -60°C. It is designed for extreme cold environments, Arctic vessels, and ice-class applications.
❓ What is the difference between AH36 and DH36?
Both have the same strength level (355 MPa yield strength). The difference is the impact test temperature: AH36 is tested at 0°C, DH36 at -20°C. DH36 offers better low-temperature toughness.
❓ Is DH36 stronger than AH36?
No — DH36 and AH36 have the same minimum yield strength (355 MPa) and tensile strength range (490–620 MPa). The difference is not strength but impact toughness at different temperatures.
❓ What temperature is EH36 impact tested at?
EH36 is impact tested at -40°C using the Charpy V-notch test method.[citation:1][citation:6]
❓ Which marine steel grade is suitable for cold climates?
For cold climates, DH36 (-20°C) is suitable. For very low temperatures or Arctic conditions, EH36 (-40°C) or FH36 (-60°C) may be required depending on the design temperature and classification society rules.
❓ What certificates are required for shipbuilding steel plates?
Shipbuilding steel plates typically require an EN 10204 3.1 or 3.2 certificate and a classification society certificate (ABS, DNV, LR, BV, CCS, RINA, etc.). The specific requirements depend on the project and classification society.
12. Final Thoughts
Choosing marine steel is not simply about selecting a higher strength grade. For AH36, DH36, EH36 and FH36, the key question is whether the steel meets the required impact toughness, classification society rules, and project specifications.
The "36" means strength. A, D, E and F mean toughness — at different temperatures. If you're building a vessel for Arctic service, AH36 is not enough. If you're building for temperate waters, EH36 may be unnecessary.
💡 Our view: CEHE STEEL supplies marine steel plates for shipbuilding and offshore applications, including AH36, DH36, EH36, and FH36, with custom sizes and classification certification according to project requirements. If you're not sure which grade you need, send us the design temperature and classification society — we'll recommend the right material.
📚 Further Reading & Related Content
- 🔗 How to Read a Steel Plate Mill Test Certificate (MTC)
- 🔗 Why Do Steel Plates Need Impact Testing? Charpy Impact Test Explained
- 🔗 How to Choose the Right Steel Plate Supplier in China
- 🔗 A Guide to Buying Steel from China – What You Need to Know
- 📄 IACS UR S33, ASTM A131, EN 10025, ABS Rules, DNV Rules, LR Rules, CCS Rules
Need Marine Steel Plates for Shipbuilding?
CEHE STEEL supplies AH36, DH36, EH36, and FH36 marine steel plates with classification society certification. Send us your grade, thickness, and classification society requirement — we'll provide a quotation with full MTC and class documentation.