Differences Between LR Grades AH36, DH36, and EH36

1. Identical Basic Strength Parameters

LR AH36, DH36, and EH36 have exactly the same core mechanical properties:

The fundamental differences among these three grades lie not in load-bearing capacity, but in low-temperature impact performance, steel purity, microstructural stability, and adaptability to extremely cold environments. These differences determine their respective applicable temperature ranges and engineering safety grades.

2. Key Differences: Low-Temperature Impact Test Temperatures and Suitable Environments

The most significant technical distinction among the three grades lies in the Charpy V-notch impact test temperature:

LR AH36:

a) Requires impact toughness at 0°C;

b) Suitable for non-cold marine projects in tropical, subtropical, and temperate conventional waters (where the annual average temperature is above 0°C).

LR DH36:

a) Requires impact toughness at –20°C;

b) Suitable for cold-temperate waters where winter temperatures frequently drop below zero and for coastal engineering projects in seasonally ice-bound areas.

LR EH36:

a) Requires impact toughness at –40°C;

b) Used exclusively for polar icebreakers and core structures in ultra-low-temperature marine applications.

This temperature hierarchy serves as the primary basis for material selection.

3. Differences in Chemical Composition and Production Processes

Impurity Control:

LR AH36: Adheres to standard impurity limits for high-strength steel;

LR DH36: Further reduces sulfur and phosphorus content to enhance low-temperature toughness;

LR EH36: Achieves the highest purity through ultra-low impurity limits and vacuum secondary refining.

Production Processes:

LR AH36: Uses controlled rolling;

LR DH36: Includes additional low-temperature microstructure stabilization treatment;

LR EH36: Incorporates vacuum degassing secondary refining and gradient tempering processes.

These differences in process and purity directly determine the performance gaps among the three grades in low-temperature environments.

4. Differences in Typical Engineering Applications

LR AH36: Tropical/subtropical ocean-going container ships, large bulk carriers, VLCCs, heavy-duty coastal workboats, and auxiliary and certain primary structures of conventional offshore platforms.

LR DH36: Large vessels in cold-temperate waters, heavy-duty coastal engineering vessels operating in seasonal ice conditions, and heavy-load marine structures requiring low-temperature resistance.

LR EH36: Polar icebreakers, ultra-low-temperature marine load-bearing structures, and core heavy-duty marine engineering projects in extremely cold regions.

5. Differences in Performance and Cost-Balanced Selection Strategies

In terms of market cost and construction efficiency:

LR AH36: Lowest unit price, best value for money, simple production and construction processes, avoiding the high costs associated with the low-temperature treatment and complex processing required for DH36/EH36.

LR DH36: Moderate cost, suitable for projects in cold and temperate waters.

LR EH36: Due to complex processes, it has the highest production cost and is suitable only for extremely cold environments.