The global demand for high strength shipbuilding steel continues to rise, and among the most widely used materials in marine engineering are AH36, DH36, and EH36 steel plates. These grades play a crucial role in offshore structures, hull fabrication, and critical marine components where strength, durability, and toughness are essential. As leading suppliers such as sakysteel focus on quality-driven production, understanding the manufacturing process behind these steels provides deeper insight into their reliability and performance.
Introduction to AH36, DH36, and EH36 Steel Grades
AH36, DH36, and EH36 belong to the high-strength structural steel family defined by classification societies such as ABS, DNV, Lloyds, BV, and CCS. Although they share similar chemical compositions and base mechanical properties, their impact toughness requirements differ significantly.
AH36 exhibits good toughness at 0°C, DH36 reaches higher impact energy levels at -20°C, while EH36 is engineered for even more demanding conditions at -40°C. These variations make the materials suitable for different marine applications, including mid decks, hull structures, offshore cranes, jack-up rigs, and subsea equipment.
Each grade is produced following strict procedures involving steelmaking, rolling, heat treatment, and final inspection to meet international standards.
Steelmaking and Refining Stage
The manufacturing process starts with steelmaking using high-quality raw materials with controlled levels of carbon, manganese, sulfur, and phosphorus. Modern facilities apply BOF or EAF technology followed by secondary refining to adjust chemical composition and remove impurities.
Key refining processes include:
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Argon oxygen decarburization for carbon control
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Ladle furnace adjustment for alloying elements
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Vacuum degassing to reduce hydrogen and nitrogen
These refining steps are essential to ensure the steel achieves both high strength and excellent toughness, which are critical for marine applications.
Continuous Casting and Slab Preparation
After refining, the molten steel is poured into the continuous casting machine. It solidifies into slabs of controlled thickness, typically between 150 mm and 250 mm. The slabs undergo surface conditioning to remove scale and eliminate surface defects that may affect rolling performance.
Slab reheating follows, allowing the steel to reach optimal temperature for hot rolling. This stage ensures uniform grain structure and prepares the material for deformation in the rolling mill.
Hot Rolling Process for AH36, DH36, and EH36
Hot rolling is one of the most important steps in producing shipbuilding steel plates. The slab is passed through multiple roughing and finishing stands to achieve the required thickness and width.
Key benefits of controlled hot rolling include:
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Improved surface finish
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Enhanced mechanical strength
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Uniform plate thickness
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Better grain refinement
Temperature control during rolling is vital. If rolled too hot, grain growth may reduce toughness; too cold, and the material may crack. Rolling schedules for AH36, DH36, and EH36 are carefully optimized to balance strength and ductility.
Controlled Cooling Technology
After hot rolling, controlled cooling plays a critical role in determining final properties. Techniques such as accelerated cooling and laminar flow cooling are used to regulate cooling speed.
Controlled cooling enhances:
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Fine-grained microstructure
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High yield strength
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Uniform impact toughness
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Improved lamellar tearing resistance
Shipbuilding steel must maintain stable properties across the entire plate, making cooling control a key factor in production quality.
Heat Treatment Options: Normalizing, TMCP, and Quenching Tempering
Depending on customer requirements and classification society standards, AH36, DH36, and EH36 plates may undergo different heat treatment processes.
Normalizing
Normalizing involves heating the steel above its critical temperature and air cooling it to refine the grain structure. This improves toughness and homogenizes the mechanical properties.
TMCP (Thermo Mechanical Controlled Process)
TMCP combines controlled rolling with accelerated cooling to achieve high strength without adding excessive alloy content. It also enhances weldability, making TMCP plates widely used in modern shipbuilding.
Quenching and Tempering QT
For applications requiring higher strength and toughness, QT plates are produced by:
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Heating to austenitizing temperature
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Rapid water quenching
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Tempering at controlled temperatures
EH36 plates with demanding performance requirements often use this process to ensure superior impact resistance in low temperature environments.
Dimensional Accuracy and Surface Quality Control
Throughout rolling and heat treatment, several quality control steps ensure consistency and compliance, including:
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Automatic thickness measurement
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Non destructive testing UT inspection
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Hardness measurement
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Surface defect detection
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Mechanical testing per standards
Producers like sakysteel maintain strict quality assurance systems to meet the expectations of global shipyards and offshore engineering companies.
Mechanical Properties Achieved After Treatment
AH36, DH36, and EH36 steel plates must meet classification society specifications. Typical mechanical properties include:
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Yield strength minimum 355 MPa
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Tensile strength between 490 to 620 MPa
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Good elongation for bending and forming
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High impact toughness at required temperatures
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Excellent weldability with low carbon equivalent
These performance characteristics are achieved through optimized rolling and heat treatment routes.
Applications in Marine and Offshore Engineering
Because of their reliability and strength, these steel plates are used in a wide range of critical structures:
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Hull plates for large commercial vessels
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Offshore platform decks and support structures
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FPSO topside modules
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Subsea equipment
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Jack up legs and crane booms
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Icebreakers and cold climate ships
Their combination of toughness, weldability, and corrosion resistance makes them indispensable in demanding marine environments.
Conclusion
The manufacturing process of AH36, DH36, and EH36 steel plates involves precise rolling schedules, advanced heat treatment methods, and stringent quality control. Each stage contributes to the steel’s strength, toughness, and reliability under harsh marine conditions. Through optimized steelmaking and controlled processing, these shipbuilding steels continue to support global maritime and offshore projects.
High quality manufacturers like sakysteel ensure that every plate meets international standards, delivering consistent performance for shipyards around the world.
Post time: Nov-13-2025