Difference between LR B and LR D steel plate

LR B and LR D are standardized shipbuilding steel plates certified by Lloyd's Register (LR), designed for varying levels of structural demand based on service temperature. Both grades commonly feature a minimum yield strength of 235 MPa, but their core distinction lies in the minimum Charpy V-notch impact test temperature and the associated toughness guarantee.

Key Differences

The key difference is the impact toughness requirement and resultant application scope. LR Grade B steel is required to meet Charpy impact energy criteria at 0°C (32°F), providing essential notch toughness for primary hull structures of general oceangoing vessels operating in temperate to cool waters. Conversely, LR Grade D steel must satisfy impact toughness requirements at the lower temperature of -20°C (-4°F), offering superior resistance to brittle fracture. This qualifies Grade D for use in ships intended for cold climate service, such as North Atlantic routes, or for critical structural components where enhanced safety against low-temperature failure is paramount. The production of Grade D typically involves finer grain practice or normalized rolling to achieve this performance. Thus, the selection is governed by the lowest anticipated service temperature: LR B is suitable for most general marine structures, while LR D is specified for vessels and components operating in or exposed to colder environments.

Chemical Composition

Mechanical Property