DH40 is a high-strength structural steel specifically engineered to deliver superior toughness in moderately cold marine environments, classified under esteemed standards like LR, ABS, and DNV. As an HSLA grade, it builds upon the properties of AH40 with enhanced microalloying, particularly incorporating niobium and titanium in precise proportions. These additions further refine the grain structure, improving low-temperature performance without compromising the steel's weldability, a critical attribute in structural applications.
The chemical composition of DH40 is nearly identical to that of AH40, with a maximum carbon content of 0.18%, manganese ranging from 0.90% to 1.60%, and tight controls on phosphorus and sulfur (each ≤0.035%). This similarity ensures that DH40 retains many of the favorable characteristics of AH40, including good formability.
In terms of mechanical properties, DH40 achieves a minimum yield strength of 390 MPa and a tensile strength of 510–650 MPa, matching the strength levels of AH40. Its defining feature, however, is its exceptional impact resistance. It maintains 34J of energy absorption at -20°C, a significant improvement over AH40, making it highly resilient against brittle fracture in icy or subzero conditions that are common in regions with seasonal freezing.
The primary advantage of DH40 lies in its ability to balance strength and cold-weather durability, outperforming AH40 in environments where temperatures regularly drop below freezing. This makes it widely used in ice-strengthened vessels, offshore supply ships that operate in colder waters, and coastal infrastructure exposed to moderate cold. Its weldability remains excellent, though for thicker sections, preheating to 100–150°C is recommended to ensure optimal weld quality. This allows for reliable fabrication of critical components such as cargo holds, structural frames, and other parts that need to withstand the rigors of cold marine environments.
