Difference between LR EH50 and LR EH55 steel plate

LR EH50 and LR EH55 are ultra-high-strength shipbuilding steel plates certified by Lloyd's Register (LR). The "EH" designation stands for Extra High-strength with High toughness. They are engineered for highly stressed structural components in large vessels, such as the upper deck and sheer strake of very large container ships, ice-strengthened vessels, and offshore installations. These grades provide an exceptional combination of high strength, excellent low-temperature toughness (down to -40°C or lower), and good weldability, enabling the design of lighter and more efficient structures.

Key Differences:

The primary distinction lies in their specified minimum yield strength. LR EH50 has a minimum yield strength of 390 MPa (corresponding to a minimum tensile strength of 500 MPa, or 50 kgf/mm²). LR EH55 offers a higher yield strength of 420 MPa (with a minimum tensile strength of 550 MPa, or 55 kgf/mm²). This makes EH55 the stronger grade, allowing for further weight reduction or increased load capacity in structural design.

To achieve this incremental strength increase while maintaining the stringent toughness requirements, EH55 typically requires a more refined chemical composition and precise control during the thermo-mechanically controlled processing (TMCP). This results in a marginally higher carbon equivalent and Pcm value for EH55 compared to EH50. Consequently, the welding of EH55 may demand slightly more stringent procedures regarding preheating, interpass temperature control, and heat input management to mitigate the risk of hydrogen-induced cracking and preserve the toughness in the weld heat-affected zone. 

Chemical Composition

Mechanical Property