FH36 is a high-strength hull structural steel plate specified under GB/T712-2011 with a minimum yield strength of 355 MPa and guaranteed Charpy impact toughness at -60°C. It is approved by all major classification societies-ABS, DNV, BV, LR, CCS, NK, RINA, and KR-making it the go-to grade for Arctic-grade and cold-water ship structures.
Key Takeaways
- FH36 is the highest impact-toughness grade in the AH36–DH36–EH36–FH36 series, tested at -60°C (vs. 0, -20, and -40°C for the lower grades).
- Yield strength ≥ 355 MPa, tensile strength 490–620 MPa, elongation ≥ 21% (t ≤ 50 mm).
- Key producing mills: Wuyang Iron and Steel (Henan, China), with 4,200 mm and 4,300 mm wide heavy-plate rolling lines.
- Each plate is delivered with a classification society certificate (e.g., ABS, DNV, CCS) and an EN 10204 3.1 or 3.2 mill test certificate (MTC).
- GNEE Steel supplies FH36 plates cut to size, with full documentation and flexible delivery terms.
1. What FH36 Means - Decoding the Grade
China's shipbuilding steel grading system (GB/T712-2011) uses a letter-number convention to communicate strength level and low-temperature toughness in one short code:
- F - the impact test temperature suffix: F = -60°C, E = -40°C, D = -20°C, A = 0°C.
- H - designates "high-strength hull structural steel" (as opposed to general-strength grades A, B, D, E).
- 36 - nominal minimum yield strength of 36 kgf/mm² (approx. 355 MPa).
Put together, FH36 means: high-strength shipbuilding steel that has been Charpy V-notch impact-tested and qualified at -60°C. It is the highest toughness category in the 36-series, one notch above EH36.
2. Chemical Composition (Ladle Analysis) per GB/T712-2011
The table below presents the ladle analysis limits for FH36. Actual mill practice-especially from producers like Wuyang-typically runs tighter than these maxima.
| Element | Symbol | Max % (unless range) |
|---|---|---|
| Carbon | C | ≤ 0.18 |
| Silicon | Si | ≤ 0.50 |
| Manganese | Mn | 0.90 – 1.60 |
| Phosphorus | P | ≤ 0.030 |
| Sulfur | S | ≤ 0.030 |
| Copper | Cu | ≤ 0.35 |
| Nickel | Ni | ≤ 0.40 |
| Chromium | Cr | ≤ 0.20 |
| Molybdenum | Mo | ≤ 0.08 |
| Niobium + Vanadium + Titanium | Nb+V+Ti | ≤ 0.12 |
| Acid-soluble Aluminum | Als | ≥ 0.015 |
Source: GB/T712-2011, Table 7 (High-strength hull structural steel, ladle analysis). Carbon equivalent (CEV) is typically controlled to ≤ 0.38%–0.40% depending on thickness, per IACS UR W11.
3. Mechanical Properties
| Property | Value (t ≤ 50 mm) | Value (50 < t ≤ 70 mm) | Value (70 < t ≤ 100 mm) |
|---|---|---|---|
| Yield Strength ReH, min | 355 MPa | 355 MPa | 355 MPa |
| Tensile Strength Rm | 490–620 MPa | 490–620 MPa | 490–620 MPa |
| Elongation A5, min | 21% | 21% | 21% |
| Charpy Impact at -60°C, min | 34 J (longitudinal) | 34 J (longitudinal) | 34 J (longitudinal) |
Per GB/T712-2011. Actual mill values are typically higher; a study on FH36 plates reported average yield strength of ~420 MPa and tensile strength of ~506 MPa (see Ref. 1). The standard minimum is what classification societies require for design approval.
4. Classification Society Certification - Which Rules Apply
Ship classification is the legal and technical backbone of the marine industry. Each classification society publishes its own rules that incorporate FH36 (or an equivalent grade), and a plate destined for a classified vessel must carry that society's stamp.
| Classification Society | Abbrev. | Country / Region | Equivalent Grade Notation |
|---|---|---|---|
| American Bureau of Shipping | ABS | USA | ABS FH36 |
| DNV (formerly DNV GL) | DNV | Norway / Germany | NV FH36 |
| Bureau Veritas | BV | France | BV FH36 |
| Lloyd's Register | LR | UK | LR FH36 |
| China Classification Society | CCS | China | CCS FH36 |
| ClassNK | NK | Japan | NK FH36 |
| Registro Italiano Navale | RINA | Italy | RINA FH36 |
| Korean Register | KR | South Korea | KR FH36 |
DNV and Germanischer Lloyd (GL) merged in 2013 and rebranded as DNV GL; since 2021 the brand has reverted to simply "DNV." Older certificates may still bear the DNV GL or GL mark.
GNEE Steel can supply FH36 plates with the specific classification society certificate your project requires. Each plate is stamped with the society's mark, heat number, and grade identification.
5. Thickness Ranges and Common Applications
FH36 plates are typically ordered in thicknesses of 6 mm to 100 mm, with the most common commercial range being 8–50 mm. Widths up to 4,000 mm and lengths up to 12,000 mm are routine.
Where you will find FH36:
- Arctic-class vessel hulls and decks - the -60°C toughness is mandatory for ice-class notation.
- Offshore platform structural members - jack-up rig legs, flare booms, and helideck substructures.
- LNG carrier containment system supports - where low-temperature ductility is non-negotiable.
- Icebreaker shells and frames - plates must remain tough at the waterline in freezing conditions.
If your service temperature is warmer, EH36 (-40°C) or DH36 (-20°C) can reduce cost without sacrificing strength. Consult GNEE Steel's technical team for a grade recommendation specific to your design temperature and classification society.
7. Delivery Condition and Inspection Documentation
FH36 is typically delivered in the normalized (N) or thermo-mechanical controlled processed (TMCP) condition. TMCP is increasingly preferred because it achieves the required strength and toughness with a leaner chemistry, which improves weldability.
Every shipment from GNEE Steel includes:
- Mill Test Certificate (EN 10204 3.1 or 3.2) showing actual chemical analysis, tensile results, and Charpy values.
- Classification society certificate (ABS, DNV, BV, etc.) stamped and signed by the attending surveyor.
- Dimensional inspection report confirming thickness, width, length, flatness, and surface condition.
- Ultrasonic testing (UT) report per EN 10160 S2E2 or equivalent, when specified.
Frequently Asked Questions
What is the difference between FH36 and EH36?
The only difference mandated by GB/T712-2011 is impact test temperature: FH36 at -60°C, EH36 at -40°C. Yield and tensile requirements are identical. In practice, mills achieve the lower temperature rating through tighter chemistry control (slightly higher Ni and microalloying) and by adjusting the rolling and cooling schedule. Choose FH36 when the design temperature calls for it; for most temperate-water vessels, EH36 is sufficient.
Which classification societies certify FH36 steel?
All nine IACS member societies: ABS, DNV, BV, LR, CCS, ClassNK (NK), RINA, KR, and the Chile Maritime Register of Shipping (RS). GNEE Steel has supplied FH36 with certificates from ABS, DNV, BV, LR, and CCS. The plate is stamped with the classification society's mark during the surveyor's inspection at the mill.
What standard governs FH36 shipbuilding steel?
FH36 is specified under GB/T712-2011 Hull Structural Steel (China). Equivalent requirements appear in each classification society's own rules (e.g., ABS Rules for Materials and Welding Part 2, DNV Rules Pt.2 Ch.2). The underlying technical requirements are harmonized through IACS Unified Requirement W11 on normal and higher-strength hull structural steels.
What thicknesses and sizes can GNEE Steel supply?
Standard supply range: thickness 6–100 mm, width up to 4,000 mm, length up to 12,000 mm. Custom cutting (CNC plasma, oxy-fuel, waterjet) is available. For dimensions outside these ranges, contact our team-we can source from multiple qualified mills.
Does FH36 require preheating before welding?
For thin sections (< 25 mm) at ambient temperature, FH36 generally does not require preheat. For thicker plates or shop-floor temperatures below 5°C, a preheat of 50–100°C is recommended. Always follow the approved welding procedure specification (WPS) for your classification society. GNEE Steel provides the base-material data (CEV, mill chemistry) needed to write the WPS.
References
- Wuyang Iron and Steel Co., Ltd. - Official website.
- GB/T712-2011 Hull Structural Steel - National Standard of the People's Republic of China. Issued by SAC/TC 183.
- IACS UR W11 Rev.8 (2021). "Normal and Higher Strength Hull Structural Steels." International Association of Classification Societies.
- ABS (2025). Rules for Materials and Welding (Part 2). American Bureau of Shipping.
All data were verified against cited standards and public sources as of the update date. If you find an error or omission, contact GNEE Steel so we can correct it.
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Disclaimer: This article is provided for general technical information and does not constitute engineering advice or a product warranty. Technical data reflects the cited standards at the time of writing; always confirm final properties and compliance with the applicable project specification and classification society rules. Gnee Steel (Tianjin) Co., Ltd. makes no representation regarding the accuracy of third-party references.
