Marine steel

Marine steel refers to the steel used to manufacture the hull structure of sea-going ships and inland ships, usually high-quality carbon steel and high-quality low-alloy steel.

Marine steel is required to have certain strength, toughness and hardness, certain low temperature resistance and corrosion resistance, and requires good welding performance.

Marine steel types:
Commonly used hull structural steels are:
General strength steel (A, B, D, E grade) steel plate specified in GB712,
High strength steel (AH32, DH32, EH32, AH36, DH36, EH36 grade) steel plate;
High-quality carbon steel (CIO, C20) steel pipes for ships specified in GB5312;
Grade A and B steel bulbs for shipbuilding specified in GB9945.

The general strength steel for hull structure is divided into four grades: A, B, C and D. The yield strength (not less than 235N/mm^2) of these four grades of steel is the same as the tensile strength (400～520N/mm^2). , but the impact power at different temperatures is different;

High-strength hull structural steel is divided into strength grades according to its minimum yield strength, and each strength grade is divided into A, D, E, F4 grades according to its impact toughness.

The yield strength of A32, D32, E32, and F32 is not less than 315N/mm^2, and the tensile strength is 440-570N/mm^2. Impact toughness that can be achieved at -40°, -60°;

The yield strength of A36, D36, E36 and F36 is not less than 355N/mm^2, and the tensile strength is 490～620N/mm^2. Impact toughness that can be achieved at -40°, -60°;

The yield strength of A40, D40, E40, and F40 is not less than 390N/mm^2, and the tensile strength is 510~660N/mm^2. The impact toughness that can be achieved at -40° and -60°.

Due to the harsh working environment of the ship, the hull shell is subject to chemical corrosion, electrochemical corrosion of seawater and corrosion of marine organisms and microorganisms; the hull is subjected to large wind and wave shocks and alternating loads; The steel requirements for hull structure are strict.

High-strength quenched and tempered steel for welded structure: A420, D420, E420, F420; A460, D460, E460, F460; A500, D500, E500, F500; A550, D550, E550, F550; A620, D620, E620, F620; A690, D690, E690, F690;

Steel for boilers and pressure vessels: 360A, 360B; 410A, 410B; 460A, 460B; 490A, 490B; 1Cr0.5Mo, 2.25Cr1Mo
Steel for mechanical structure: Generally, the above steel can be used;

Low temperature toughness steel: 0.5NiA, 0.5NiB, 1.5Ni, 3.5Ni, 5Ni, 9Ni;

Austenitic stainless steel: 00Cr18Ni10, 00Cr18Ni10N, 00Cr17Ni14Mo2, 00Cr17Ni13Mo2N, 00Cr19Ni13Mo3, 00Cr19Ni13Mo3N, 0Cr18Ni11Nb;

Duplex stainless steel: 00Cr22Ni5Mo3N, 00Cr25Ni6Mo3Cu, 00Cr25Ni7Mo4N3.

First of all, good toughness is the most critical requirement. In addition, high strength, good corrosion resistance, welding performance, processability and surface quality are required.

In order to maintain the quality and ensure sufficient toughness, the Mn/C of the chemical composition is required to be above 2.5, and the carbon equivalent is also strictly required, and it is produced by a steel mill approved by the ship inspection department.

Structural steel for hull is divided into strength grades according to its minimum yield point:
general-strength structural steel and high-strength structural steel.
General strength steel is divided into four grades A, B, D and E according to quality;
High-strength steel is divided into two strength levels and three quality levels; AH32, DH32, EH32, AH36, DH36, EH36.

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