Complete Differences Between LR AH32, DH32, and EH32 Marine Steels

I. Grade Designations

H: High Strength

32: Minimum yield strength ≥ 315 MPa

A / D / E: Low-temperature toughness quality grades:

AH32: Impact test at 0°C

DH32: Impact test at -20°C

EH32: Impact test at -40°C

II. Comparison of Mechanical Properties

The three grades are identical in yield strength, tensile strength, elongation, and bending properties; the only difference is the impact test temperature.

1) The strength, tensile, and bending properties are identical across all three grades;

2) Only the low-temperature impact test temperatures differ in a graded manner.

III. Differences in Chemical Composition

1) The basic composition ranges are similar;

2) Differences lie in impurity control and grain refinement requirements: the lower the grade, the more lenient the limits for carbon content and impurities;

3) EH32 requires the highest steel purity and the strictest grain refinement control.

IV. Production, Delivery Conditions, and Plate Thickness Limits

V. Applicable Vessels and Environments

AH32 (0°C)

Applications: General cargo ships, container ships, bulk carriers, and inland waterway/coastal vessels operating on temperate routes.

Environment: Water temperatures generally above 0°C year-round; no prolonged freezing or extremely cold waters. Application Areas: General-purpose primary materials for decks, bulkheads, superstructures, etc.; offers the best cost-effectiveness.

DH32 (-20°C)

Applicable to: Winter routes in the North Atlantic, northern coastal waters, winter ice-covered waters, and small offshore platforms.

Environment: Air temperatures can drop to -10°C to -20°C; decks and ship sides are prone to freezing and cracking in winter. Application Areas: Preferred for hull plating, high-strength decks, and primary structural ribs.

EH32 (-40°C)

Applications: Polar vessels, icebreakers, vessels operating on Arctic routes, LNG carriers, offshore equipment in extremely cold waters, and ice-class vessels.

Environment: Temperatures consistently below -20°C, with a risk of brittle fracture due to extreme cold. Application Areas: Mandatory use in the hull’s ice-load zone, bow outer plates, and support structures for cryogenic storage tanks.

VI. Welding and Construction Guidelines

AH32: When plate thickness is <30 mm, welding may be performed at ambient temperature; in low-temperature environments, only simple preheating is required.

DH32: For thick plates and low-temperature construction, preheating temperatures must be increased, and control of welding heat input is more stringent.

EH32: Sensitive to low-temperature toughness; has the most stringent requirements for preheating, interpass temperatures, and post-weld heat treatment; welding procedures must be strictly controlled to avoid cold cracks and a decrease in low-temperature impact toughness.

All three grades have similar carbon equivalents and excellent overall weldability; however, EH32 has the most restrictive welding process window.