Difference between LR AH50 and LR AH55 steel plate

LR AH50 is an extra-high-strength marine steel plate certified by Lloyd's Register (LR). It has a minimum yield strength of 500 MPa and tensile strength ranging from 610 to 770 MPa, with a minimum elongation of 18% . The chemical composition is strictly controlled with carbon ≤0.21% and manganese ≤1.70%, along with microalloying elements such as Nb and V . Impact toughness is tested at 0°C, requiring minimum 33J (transverse) and 50J (longitudinal) . This grade is typically supplied in normalized or TMCP conditions and is used for critical components in large vessels and offshore platforms .

LR AH55 is an ultra-high-strength marine steel plate also certified by Lloyd's Register (LR), designed for demanding structural applications. It has a minimum yield strength of 550 MPa and tensile strength ranging from 550 to 700 MPa . The chemical composition features carbon ≤0.18% and manganese 0.90-1.60%, with alloying elements such as Cr, Ni, and Cu to enhance strength while maintaining good weldability . Impact toughness is tested at -40°C, requiring minimum 47J . This grade is delivered in normalized, quenched and tempered (QT), or TMCP conditions and is used for offshore drilling platforms, ship hulls, and other marine structures .

Both LR AH50 and LR AH55 are LR-certified high-strength marine steels designed for shipbuilding and offshore applications. Their primary difference lies in strength level and impact test temperature: AH50 offers a minimum yield strength of 500 MPa with impact testing at 0°C, suitable for high-strength hull construction, while AH55 provides a higher minimum yield strength of 550 MPa with superior low-temperature toughness tested at -40°C, making it ideal for more demanding applications such as Arctic offshore platforms and critical load-bearing structures. Both grades feature controlled chemical composition and maintain good weldability for critical marine service. 

Chemical Composition

Mechanical Property