Shipbuilding Steel

Marine Steel Plates: Enhanced Details on Grade Specifications

(Updated as of April 2025)

​Grade Classification & Key Features

Marine steel plates are categorized by ​strength, toughness, and operational temperature, with standardized designations reflecting their performance:

1. ​AH/DH/EH/FH Series
   • ​Letter Codes:
     • ​A: Ambient temperature toughness (e.g., AH36 for 0°C).
     • ​D: Low-temperature toughness (-20°C).
     • ​E: Enhanced low-temperature toughness (-40°C).
     • ​F: Extreme low-temperature toughness (-60°C).
   • ​Number Codes: Indicate minimum yield strength (e.g., FH36 = 355 MPa yield).
   • ​Critical Applications:
     • ​FH40: Polar-class vessels, LNG containment systems.
     • ​EH36: Icebreaker hulls, Arctic offshore platforms.
     • ​DH32: Bulk carriers operating in cold climates.
2. ​Micro-Alloying Elements
   • ​Niobium (Nb) and ​Vanadium (V): Improve grain refinement and weldability.
   • ​Titanium (Ti): Enhances corrosion resistance in saltwater environments.
   • ​Carbon Control: Restricted to ≤0.18% to balance strength and ductility.

​Manufacturing & Processing Standards

1. ​Thermo-Mechanical Controlled Processing (TMCP):
   • Optimizes microstructure for plates up to ​50 mm thick, eliminating preheating requirements.
   • Critical for ​FH-series grades to achieve uniform toughness at -60°C.
2. ​Heat Treatment:
   • ​Normalizing: Applied to plates >50 mm for stress relief and improved impact resistance.
   • ​Quenching & Tempering (Q&T): Used for ultra-thick plates (>100 mm) in offshore rigs.
3. ​Surface Quality:
   • ​SA 2.5 Shot Blasting: Standard for corrosion-prone areas like hull exteriors.
   • ​Zinc Silicate Coatings: Optional for subsea components exposed to microbial corrosion.

​Global Grade Equivalents

While regional standards vary, key cross-references include:

• ​China (CCS):
  • ​AH40 ≈ ASTM A131 FH40 (USA) / EN 10025-6 S390G5M (Europe).
  • ​DH40 aligns with KR D40 (South Korea) but with stricter sulfur/phosphorus limits (≤0.020%).
• ​Europe (DNV/GL):
  • ​EH36 ≈ JIS G3106 KA40 (Japan), optimized for LNG tank membranes.
  • ​FH40 requires additional ​CTOD testing for weld zones, exceeding basic Charpy V-notch requirements.
• ​USA (ABS):
  • ​ABS EH40 incorporates ​API 2W-60 specifications for Arctic offshore structures.

Emerging Trends in Grade Development

1. ​Hybrid Alloys:
   • ​Cr-Mo-Ni Additions: Experimental grades (e.g., FH45) target tensile strengths >700 MPa for deep-sea exploration.
2. ​Digital Twin Integration:
   • Plates embedded with ​IoT sensors monitor real-time stress and corrosion in offshore platforms.
3. ​Recycled Content:
   • ​EH36-R: Contains 30% recycled steel, compliant with EU’s Carbon Border Adjustment Mechanism.

Conclusion
Marine steel grades like ​FH36 and ​EH40 are engineered to meet the dual demands of extreme environments and regulatory rigor. From the micro-alloy innovations in ​Nb/V/Ti to the global harmonization of standards, these plates underpin the safety and efficiency of modern maritime engineering. For project-specific grade selection, consult technical datasheets or certified suppliers.