Shipbuilding mainly purchases ship plate, flat steel, spherical flat steel, equal angle steel, unequal angle steel, round steel, pipe rivets, fasteners, paint, etc.

Marine steel can generally be divided into hull structure steel, boiler, pressure vessel and mechanical structure steel. All steel used for hull structure shall be produced by a steel factory approved by the classification society, and the qualified products shall be stamped by the classification society. The smelting method of marine castings can be open hearth furnace, electric furnace or basic oxygen blowing converter. If other methods are adopted, it shall be specially approved by the classification society.

The finished steel shall also be tested according to regulations. The test contents include chemical composition analysis and physical test. The physical test items mainly include tensile test, cold bending test and impact test.

According to chemical composition and properties, hull structural steels can be divided into general strength hull structural steels and high strength hull structural steels.

1) General strength hull structural steel

The general strength hull structural steel, i.e. the previous marine carbon steel, is divided into four grades A, B, D and E. Grade A is boiling steel, grade B is killed steel, grade D and grade e are fully ballasted fine grain (aluminum treated) steel. The manganese content of Grade E steel is higher than that of grade D steel and the carbon content is lower than that of grade D 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

High strength hull structural steel is also called marine low alloy steel. Since the high-strength hull structural steel is smelted by adding a small amount of alloy elements such as manganese, niobium, vanadium, aluminum and silicon on the basis of the general strength hull structural steel, its strength, mechanical properties, weldability, corrosion resistance and wear resistance are superior to the general strength hull structural steel.

Although the steel itself is expensive, due to its various properties, it can reduce the amount of steel used in shipbuilding, thereby reducing the weight of the hull structure and reducing the shipbuilding cost. The final economic index is similar to that of the general strength hull structural steel.