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1. Types of marine steel

Marine steel can generally be divided into steel for hull structure and steel for boiler, pressure vessel and mechanical structure.

(1) General strength hull structural steel is the former marine carbon steel, which is divided into four grades: A, B, D, and E. Grade A is boiling steel, B satin is killed steel, grade D and E are fully killed fine grain (aluminum treatment) steel, the manganese content in grade E steel is higher than that of D grade steel and the carbon content is lower than D grade steel steel.

At present, general-strength hull structural steel is widely used in the welding of small and medium-sized ships.

(2) High-strength hull structural steel is also called marine low-alloy steel.

Since high-strength hull structural steel is smelted by adding a small amount of alloying elements such as manganese, niobium, vanadium, aluminum and silicon on the basis of general-strength hull structural steel, its strength, mechanical properties, weldability, corrosion resistance and The ancient items such as wear resistance are better than general strength hull structural steel. Although the price of steel itself is expensive, because of the above-mentioned properties, the amount of steel used in shipbuilding can be reduced, thereby reducing the weight of the hull structure and reducing the cost of shipbuilding. The final economic index is similar to that of general-strength hull structural steel .

2. Application types of marine steel

In order to meet the different needs of the structure of each part of the hull, there are mainly the following types of marine steel in practical application:

(1) Steel plate

Steel plates are the main components of the hull structure, accounting for about 60%-65%, such as hull plates, deck plates and partitions. Generally, steel plates with a thickness of 4mm or less are called thin plates, and those with a thickness of 4mm or more are called thick plates. The size range of marine steel plates is generally: thickness 6-40mm, width 1 200b3 000rDATI, length 6000, 14000mm.

(2) Section steel

The proportion of standard steel section in the hull structure is second only to the steel plate, about 35%-40%, and is mainly used as the hull skeleton. According to its cross-sectional shape, it can be divided into: flat steel, spherical flat steel, angle steel, I-beam, T-shaped steel and channel steel, etc.

(3) Cast steel and forged steel

Fore and stern posts, anchors, fairleads, bollards and stern tubes of ships are often made of cast steel, while simple-shaped components such as rudder stock and shafts of ships are mostly made of forged steel.