Difference between LR AH42 and LR AH69 steel plate

LR AH42 is an extra-high-strength shipbuilding steel plate certified by Lloyd's Register (LR) . 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, controlled rolled, or TMCP conditions and is widely used for hull structures and offshore platforms.

LR AH69 is an ultra-high-strength marine steel plate also certified by LR, designed for the most demanding structural applications . It has a minimum yield strength of 690 MPa and tensile strength ranging from 770 to 940 MPa, with a minimum elongation of 16% . The chemical composition is similar to AH42 with carbon ≤0.21% and manganese ≤1.70% . This grade requires advanced processing like TMCP or quenching and tempering (QT) to achieve its superior mechanical properties .

Both LR AH42 and LR AH69 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: AH42 offers a minimum yield strength of 420 MPa, suitable for extra-high-strength hull construction, while AH69 provides a substantially higher minimum yield strength of 690 MPa, designed for the most demanding load-bearing applications requiring superior strength-to-weight ratio . Both grades feature controlled chemical composition and maintain good weldability for critical marine service, though AH69 requires more complex alloying and advanced processing to achieve its enhanced properties.

Chemical Composition

Mechanical Property