Difference between LR AH55 and LR AH69 steel plate

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

LR AH69 is an ultra-high-strength marine steel plate also certified by Lloyd's Register (LR), designed for the most demanding structural applications. Its chemical composition includes carbon ≤0.21%, manganese ≤1.70%, and microalloying elements such as Nb, V, Ti, Cr, Ni, and Mo . It has a minimum yield strength of 690 MPa and tensile strength ranging from 770 to 940 MPa, with a minimum elongation of 16-18% . Impact toughness is tested at -60°C, requiring ≥46J (transverse) and ≥69J (longitudinal) . This grade is delivered in normalized, quenched and tempered (QT), or TMCP conditions and is used for hull structures, offshore platforms, and critical marine engineering projects requiring maximum strength-to-weight ratio .

Both LR AH55 and LR AH69 are LR-certified ultra-high-strength marine steels designed for demanding shipbuilding and offshore applications. Their primary difference lies in strength level and low-temperature performance: AH55 offers a minimum yield strength of 355 MPa with tensile strength of 550-700 MPa and impact testing at -40°C, making it suitable for Arctic offshore platforms and general high-strength marine structures, while AH69 provides a substantially higher minimum yield strength of 690 MPa with tensile strength reaching 770-940 MPa and superior low-temperature toughness tested at -60°C, designed for the most demanding load-bearing applications requiring maximum strength-to-weight ratio in extreme environments. Both grades feature strictly controlled chemical composition and maintain good weldability for critical marine service. 

Chemical Composition

Mechanical Property