Difference between LR AH55 and LR AH62 steel plate

LR AH55 is an ultra-high-strength marine steel plate certified by Lloyd's Register (LR) for demanding shipbuilding and offshore applications. It has a minimum yield strength of 355 MPa and tensile strength ranging from 550 to 700 MPa, with a minimum elongation of 21% . The chemical composition features carbon ≤0.18%, manganese 0.90-1.60%, and includes alloying elements such as chromium (0.20-0.40%), nickel (0.20-0.80%), and copper (0.35%) . Impact toughness is tested at -40°C, requiring minimum 47J . This grade is typically supplied in normalized, quenched and tempered (QT), or TMCP conditions and is used for offshore drilling platforms and ship hulls.

LR AH62 is an ultra-high-strength marine steel plate also certified by Lloyd's Register (LR), designed for the most demanding structural applications. It has a minimum yield strength of 620 MPa (or 440 MPa depending on standard) and tensile strength ranging from 620 to 800 MPa, with a minimum elongation of 17-19% . The chemical composition is more complex than AH55, with carbon ≤0.18-0.21%, manganese 0.90-1.70%, and additional alloying elements including nickel (0.70-1.80%), chromium (0.40-1.60%), and molybdenum (≤0.70%) to achieve superior mechanical properties . Impact toughness is tested at 0°C, requiring minimum 41J (transverse) and 62J (longitudinal) . This grade is delivered in normalized or quenched and tempered (QT) conditions.

Both LR AH55 and LR AH62 are LR-certified ultra-high-strength marine steels designed for shipbuilding and offshore applications. Their primary differences lie in strength level and low-temperature performance: AH55 offers a tensile strength range of 550-700 MPa with superior low-temperature toughness tested at -40°C, making it ideal for Arctic offshore platforms; while AH62 provides substantially higher strength (up to 800 MPa tensile) and employs a more complex alloying design with Ni, Cr, and Mo additions to achieve its enhanced mechanical properties. Both grades feature controlled chemical composition and maintain good weldability for critical marine service.

Chemical Composition

Mechanical Property