DH40

DH40 is a high-strength steel plate used for ship hull structures, with its designation following the steel grading system of the American Bureau of Shipping (ABS) and other major international classification societies (such as DNV, LR, and NK). It is widely used in the construction of ships and offshore engineering structures. The letter "D" stands for "Quality Grade D," indicating that the steel is a fully killed, fine-grain steel with guaranteed impact toughness at low temperatures. Specifically, it must meet a minimum average absorbed energy of 27 J in Charpy V-notch impact testing at -20°C, making it suitable for vessels operating in cold sea areas. "H" denotes "High-strength steel," distinguishing it from ordinary-strength steels (e.g., Grades A or B) and indicating its use in critical hull areas requiring higher load-bearing capacity. The number "40" refers to the specified minimum yield strength of 40 ksi (approximately 275 MPa) at room temperature. Therefore, DH40 is a high-strength structural steel for shipbuilding with a yield strength of no less than 275 MPa and reliable toughness at -20°C. It is an important grade within the ABS high-strength series (AH40, DH40, EH40, FH40), suitable for ship structures operating in moderate low-temperature environments.

The main characteristics of DH40 steel plate include high strength, excellent low-temperature toughness, and superior weldability. Its chemical composition is strictly controlled, with a low carbon content (typically ≤0.18%) to ensure a low carbon equivalent (CEV) and good weldability. It also contains moderate amounts of microalloying elements such as manganese, niobium, and vanadium, which significantly enhance both strength and toughness through solid-solution strengthening, grain refinement, and precipitation hardening. The tensile strength ranges from 78 to 94 ksi (540–650 MPa), with elongation meeting specification requirements, offering outstanding fatigue resistance and the ability to withstand dynamic loads. Due to its ability to maintain sufficient toughness at -20°C, DH40 is particularly suitable for ships operating in cold climates or navigating high-latitude waters during winter, effectively preventing brittle fracture under low-temperature conditions. It exhibits excellent weldability and is compatible with various welding processes such as submerged arc welding (SAW) and gas metal arc welding (GMAW). Welded joints are stable and high-quality, generally requiring no preheating or only minimal preheating, making it ideal for automated welding in large-scale shipbuilding. Additionally, the steel offers good cold-forming and bending capabilities, facilitating the fabrication of complex hull components.

DH40 steel plate is widely used in primary hull structures of commercial vessels operating in cold regions, such as large cargo ships, tankers, container ships, bulk carriers, and offshore vessels. It is commonly applied to critical load-bearing components including decks, side shell plating, keels, frames, bulkheads, and girders. Compared to ordinary-strength steels or AH40 steel, DH40 not only offers higher strength but also superior low-temperature toughness, allowing for reduced hull weight while maintaining structural integrity, thereby improving vessel payload capacity and economic efficiency.

The current standard for DH40 steel plate is the Rules for Materials and Welding published by the American Bureau of Shipping, specifically Part 2: "Steels" and Part 3: "Hull Structures." The latest edition is the 2025 version, which provides detailed technical requirements for chemical composition, mechanical properties, impact toughness (-20°C), manufacturing processes, inspection methods, and classification approval. It is an authoritative and internationally recognized technical standard widely adopted in the global shipbuilding industry. Due to its excellent overall performance, DH40 has become an indispensable key material in modern shipbuilding.