These steel plates are high strength, high toughness, good welding performance of low alloy high strength steel plates, often used in the manufacture of ships, Bridges, buildings and other structural parts. To be specific:

Q205HD: High-strength steel plate with yield strength of 205MPa, with good plasticity and weldability, suitable for structures and components with high strength requirements.
Q230HD: high strength steel plate with yield strength of 230MPa, with good plasticity and welding properties, suitable for the manufacture of ships, Bridges, buildings and other structural parts.
Q250HD: High-strength steel plate with yield strength of 250MPa, with higher strength and better plasticity and weldability, suitable for structures and components with higher strength requirements.
Q275HD: High strength steel plate with yield strength of 275MPa, with higher strength and better plasticity and welding properties, suitable for the manufacture of heavy machinery, construction and other structural parts.
Q345HD: high-strength steel plate with yield strength of 345MPa, is a widely used steel plate for construction and Bridges, with good plasticity, toughness, welding and corrosion resistance.
Q420HD: High strength steel plate with yield strength of 420MPa, with higher strength and better plasticity, toughness, welding and corrosion resistance, suitable for manufacturing heavy machinery, construction and other structural parts.

These steel plates have undergone strict heat treatment and quality control during the manufacturing process to ensure that they have excellent mechanical properties and weldability to meet the needs of a variety of different engineering applications.

These steel plates are types of steel, specifically, they are steel plates with specific chemical compositions and mechanical properties. Here are some explanations for these steel plates:

0MnHR: This steel plate may be a high-strength, high-toughness low-alloy steel plate, often used in the manufacture of Bridges, buildings, ships and other structural parts.
16MnHR: This steel plate is a kind of low alloy steel plate with high strength, high toughness and good welding performance, which is often used in the manufacture of ships, Bridges, buildings and other structural parts.
20HR: This steel plate is a low carbon, high toughness, good welding performance of the steel plate, often used in the manufacture of automobiles, ships, buildings and other structural parts.
16MnD5: This steel plate is a kind of low alloy steel plate with high strength, high toughness and good low temperature impact performance, which is often used in the manufacture of petrochemical, ships, buildings and other structural parts.
18MnD5: This steel plate is a kind of low alloy steel plate with high strength, high toughness and good low temperature impact performance, which is often used in the manufacture of petrochemical, ships, buildings and other structural parts.
20MnD5: This steel plate is a low alloy steel plate with high strength, high toughness and good low temperature impact performance, which is often used in the manufacture of petrochemical, ships, buildings and other structural parts.

The chemical composition and mechanical properties of these steel plates are strictly regulated to ensure that they can meet the needs of a wide variety of engineering applications.