Difference between LR AH40 and LR AH55 steel plate

LR AH40 is a high-strength shipbuilding steel plate certified by Lloyd's Register (LR). The "A" grade signifies it is impact tested at 0°C, ensuring adequate toughness for general marine environments . It has a minimum yield strength of 390 MPa and tensile strength ranging from 510 to 650 MPa, with a minimum elongation of 20% . The chemical composition is strictly controlled with carbon ≤0.18% and manganese 0.90-1.60%, and it may contain microalloying elements such as Nb and V . This grade is typically supplied in normalized or controlled rolling condition and is widely used for hull structures 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 is impact tested at 0°C and has a minimum yield strength of 550 MPa and tensile strength ranging from 670 to 830 MPa, with a minimum elongation of 18% . The chemical composition features carbon ≤0.18%, manganese 0.90-1.60%, and alloying elements such as Cr, Ni, and Cu to enhance strength while maintaining good weldability . This grade is typically supplied in normalized, quenched and tempered (QT), or TMCP conditions and is used for large vessels, offshore platforms, and critical load-bearing components .

Both LR AH40 and LR AH55 are LR-certified high-strength marine steels with impact toughness tested at 0°C, ensuring reliable performance in general marine environments. Their primary difference lies in strength level: AH40 offers a minimum yield strength of 390 MPa with tensile strength of 510-650 MPa, suitable for general high-strength hull construction, while AH55 provides a substantially higher minimum yield strength of 550 MPa with tensile strength reaching 670-830 MPa, designed for more demanding load-bearing applications requiring superior strength-to-weight ratio . Both grades feature controlled chemical composition and maintain good weldability for critical marine service. The selection between them depends on whether the project requires the balanced strength of AH40 or the enhanced performance of AH55 for more extreme structural demands.

Chemical Composition

Mechanical Property