What Is LR Grade A Marine Steel?

I. Basic Definitions

LR is the abbreviation for Lloyd’s Register.

Grade A is the lowest toughness grade among ordinary-strength shipbuilding structural steels; it is commonly referred to in the industry as LR/A or LRA. This product is manufactured and certified in accordance with Lloyd’s Register material specifications and is suitable for the manufacture of structural components for ships and offshore platforms.

II. Standard Chemical Composition (Mass Fraction)

C ≤ 0.21%

Si ≤ 0.50%

Mn ≥ 2.5 × C (the manganese-to-carbon ratio is strictly controlled to ensure weldability)

P ≤ 0.035%, S ≤ 0.035% (harmful impurities are strictly limited)

Cu, Cr, Ni are limited to trace amounts; aluminate precipitates for grain refinement ≥ 0.035%

III. Core Mechanical Properties

Yield Strength (ReH): ≥ 235 MPa

Tensile Strength (Rm): 400 - 520 MPa

Elongation After Fracture (A): ≥ 22%

Impact Toughness:

- Thickness ≤ 50 mm: Delivered as hot-rolled; impact testing is not mandatory;

- Thickness > 50 mm: When supplied in normalized or TMCP condition, a Charpy V-notch impact test at +20°C must be performed.

- Grade Comparison: Low-temperature toughness increases progressively across grades: LR B (0°C), LR D (-20°C), and LR E (-40°C).

IV. Delivery Conditions and Specifications

Delivery Conditions: Hot-rolled (AR), controlled rolling (TMCP), normalized (N)

Thickness Range: 3 - 300 mm

Width Range: 1,200 - 4,200 mm

Length Range: 3,000 - 18,000 mm

Certification Documents: LR Original 3.1 / 3.2 Ship Inspection Certificates; UT testing and Z-direction properties (Z15 / Z25 / Z35) available upon request

V. Application Scenarios

Applicable Scenarios:

Secondary structures for inland waterway vessels and small-to-medium-sized offshore vessels (under 10,000 metric tons);

secondary supports, pipeline supports, and bases for non-cryogenic equipment on offshore platforms;

vessel maintenance in normal-temperature waters and ice-free zones, as well as simple barge and hopper barges.

Inapplicable Scenarios:

Polar/ice-zone vessels, hull outer plates, bow sides, main decks, and other critical load-bearing components.

VI. Comparison of Grades Within the Same Series