Difference between LR AH42 and LR AH55 steel plate

LR AH42 is an extra-high-strength shipbuilding steel plate certified by Lloyd's Register (LR). It is a fine-grain, weldable structural steel intended for marine and offshore applications. It has a minimum yield strength of 420 MPa and tensile strength ranging from 530 to 680 MPa, with a minimum elongation of 20% . The chemical composition is strictly controlled, with carbon ≤0.21% and manganese ≤1.70% . This grade is typically supplied in normalized (N), thermo-mechanically controlled rolled (TM), or quenched and tempered (QT) conditions .

LR AH55 is an ultra-high-strength marine steel plate also certified by Lloyd's Register (LR), designed for more demanding structural applications. It has a minimum yield strength of 550 MPa and tensile strength ranging from 670 to 830 MPa . The chemical composition features carbon ≤0.18% and manganese 0.90-1.60% . This grade is typically supplied in TM or QT conditions and is used for critical components in large vessels, offshore platforms, and other marine structures requiring superior strength .

Both LR AH42 and LR AH55 are LR-certified high-strength marine steels with guaranteed impact toughness and excellent weldability for shipbuilding and offshore applications. Their primary difference lies in strength level: AH42 offers a minimum yield strength of 420 MPa, suitable for extra-high-strength hull construction, while AH55 provides a substantially higher minimum yield strength of 550 MPa, designed for more demanding load-bearing applications requiring superior strength-to-weight ratio. Both grades feature controlled chemical composition and are available in various delivery conditions, including TMCP and QT, to achieve their enhanced mechanical properties while maintaining good weldability for critical marine service.

Chemical Composition

Mechanical Property