Differences in Delivery Conditions for BV Grade B Shipbuilding Steel Plates

1. Hot Rolled (HR)

Process: The steel billet is heated to the austenitic range, rolled, and then allowed to cool naturally.

Applications: Thin-gauge steel plates with a thickness of ≤40 mm.

Advantages: High production efficiency and relatively low cost, but the grain size is relatively coarse.

2. Controlled Rolled (CR)

Process: The final rolling temperature and pass reduction ratio are strictly controlled to refine the austenite grain size.

Applications: Thin steel plates with a thickness of ≤40 mm.

Advantages: Achieves higher strength and toughness than hot-rolled steel without the need for heat treatment. Commonly used for plates with a thickness of ≤40 mm.

3. Normalized (N)

Process: After rolling, the steel is reheated to a temperature above the Ac3 point (typically 850–950°C), held at that temperature, and then air-cooled.

Applications: Steel plates with a thickness greater than 40 mm or thick plates requiring guaranteed core properties.

Advantages: Thoroughly refines the grain structure, eliminates internal stresses, stabilizes the microstructure, and significantly improves low-temperature impact toughness (0°C).

4. Thermo-mechanical Controlled Processed (TMCP)

Process: Multiple passes of controlled rolling are performed in both the recrystallization zone and the non-recrystallization zone, combined with accelerated post-rolling cooling.

Advantages: Achieves a combination of high strength and high toughness without significantly increasing alloying costs; particularly suitable for thick plate specifications.

5. Selection Recommendations:

If a project involves low-temperature impact testing or the welding of thick plates, prioritize steel plates supplied in the normalized (N) or TMCP condition to ensure uniform and stable base metal properties.