Technical Specifications and Certification Requirements for LR Grade D Shipbuilding Steel Plates

1. Chemical Composition

LR Grade D is a fully quenched and tempered steel, designed with low carbon content and strictly controlled impurity elements to optimize low-temperature toughness and structural stability. Its chemical composition (by mass) complies with LR specifications:

Carbon (C) ≤ 0.21%

Silicon (Si): 0.10% - 0.35%

Manganese (Mn): 0.90% - 1.25%

Phosphorus (P) ≤ 0.030%

Sulfur (S) ≤ 0.030%

Compared to LR Grade B steel, the carbon, sulfur, and phosphorus contents have been further reduced, effectively minimizing the risk of low-temperature brittle fracture. Carbon equivalent (CEV) is strictly controlled at ≤ 0.38% to ensure the material possesses excellent weldability, cold formability, and low-temperature toughness.

2. Mechanical Properties and Low-Temperature Impact Performance

2.1 Mechanical Properties

All LR Grade D steel plates must pass official LR inspection. Their mechanical properties are stable and reliable, meeting the service requirements for cold-water regions:

2.2 Low-Temperature Impact Properties

Key indicator: In the -20°C Charpy V-notch impact test, the impact energy must meet the values specified in LR regulations to ensure there is no risk of brittle fracture in low-temperature environments; this is a critical criterion for selecting materials for ship structures in cold regions.

3. Dimensional Range and Tolerance Standards

3.1 LR Grade D steel plates are available in a variety of specifications to meet the needs of shipbuilding and offshore engineering in cold regions:

Thickness range: 5 mm - 100 mm

Maximum width: 4,000 mm

Maximum length: 18,000 mm

3.2 Dimensional tolerances comply with LR high-precision standards:

Thickness tolerance: ± 0.25 mm

Flatness error: ≤ 1.8 mm/m

Edge flatness deviation is zero

Precise dimensional control helps reduce on-site machining errors and improves structural assembly accuracy, making it suitable for the mass production of cargo ships, offshore platforms, and coastal low-temperature facilities in cold regions.

4. Full-Process LR Certification Requirements

LR Grade D shipbuilding steel plates are subject to the most stringent full-process production and inspection specifications among LR’s general-strength steels. From smelting, controlled rolling, and heat treatment to finishing, every stage must comply with LR Shipbuilding Rules.

Each batch of products must undergo sampling tests for chemical composition, mechanical properties, and low-temperature impact toughness. Upon passing these tests, an EN 10204 Class 3.2 certificate and an official LR inspection report are issued, serving as the basic qualification documents for LR-class vessels in cold regions and low-temperature offshore engineering projects.