Offshore platform steel with CTOD being greater than or equal to 2 millimeters at minus 40 DEG C and production method thereof

Abstract

An offshore platform steel with CTOD being greater than or equal to 2 millimeters at minus 40 DEG C comprises the following chemical components of: by weight, 0.065-0.15% of C, 0.16-0.55% of Si, 0.05-0.50% of Ni, 0.0002-0.002% of B, Ti being less than or equal to 0.005%, 0.0008-0.008% of La, P being less than or equal to 0.010%, S being less than or equal to 0.005%, Mn being less than or equal to 0.08%, Als being less than or equal to 0.008%, O being less than or equal to 0.0015%, N being less than or equal to 0.001%, H being less than or equal to 0.0001%, and the balance Fe and unavoidable impurities. The technology comprises the following steps of: deep desulphurization of molten iron; converter smelting; vacuum treatment in PH furnace; continuous casting and heating of casting blank; subsection rolling; cooling; and standby. On the basis of guaranteeing mechanical properties of the steel plate for usage and preventing corrosion performance of seawater, CTOD of the steel plate is greater than or equal to 2 millimeters at the environment of minus 40 DEG C, operational reliability of the steel can be guaranteed, life cycle can be raised by no less than 30 years, and the components and the technology are simple such that relative manufacturing cost is low.

Description

technical field [0001] The invention relates to low-carbon, low-alloy, high-strength engineering steel and a production method thereof, in particular to steel for offshore platforms with a CTOD of -40°C ≥ 2 mm and a production method thereof. Background technique [0002] The steel structure of the offshore platform is in the dynamic load state of sea waves and sea wind. The micro-cracks in the steel expand under the action of dynamic load. The ability of the steel plate to resist the expansion of cracks is called the fracture toughness of the material, which is measured by the opening displacement CTOD of the crack tip. The higher the CTOD value, the better the fracture toughness of the material. Offshore platform steel The higher the quality of the structure, the longer the service life. At present, the commonly used steel for offshore platforms does not require the fracture toughness of the steel plate, but only requires the design service life of the offshore platform t...

AI Technical Summary

Problems solved by technology

Its shortcomings are: the high content of harmful gas elements N and O in the steel reduces the fracture toughness and processability of the steel, and the Alt content is high, the irregular shape of Al formed in the steel 2 o 3 Violently destroys the fracture toughness of steel

[0006] The above two patent technologies are insufficient: Mn with a high content is added to the steel, which is easy to react with the S that cannot be removed in the steel to form easily deformable inclusions of MnS. Such inclusions are equivalent to cracks, which significantly reduce the fracture toughness of the steel. The second is that the alloying element Nb is also added to the steel. According to a large number of actual production data, there are unmelted elemental Nb blocks in the low-alloy structural steel with Nb added, which not only leads to poor quality of the steel plate, but also deteriorates the fracture toughness of the steel.

The disadvantage is that the steel contains Cu, Cr, Mo, Ni, V and other alloying elements, and the added alloying elements are many and complex, which increases the difficulty of production, reduces production efficiency, and increases production costs

The disadvantage of this patent document is that 1.0-1.6% of Mn is added to the steel, and it is easy to form MnS inclusions with the residual S in the steel, which reduces the fracture toughness of the steel. Adding Nb: 0.020-0.050%, V: 0.050-0.100%, Ti: 0.005-0.020%, in the production process, it is easy to form large particle inclusions such as Nb(NC), VC, Ti(NC), which seriously reduces the fracture toughness of steel

[0009] The above-mentioned existing patent documents have the common deficiency that there are many elements in the steel, and the Mn content is higher than 1.0%, because Mn is easy to form MnS inclusions with S in the structural steel, which reduces the mechanical properties of the steel, especially the low temperature of the steel. Impact toughness, so the presence of MnS is very unfavorable for steels that require low-temperature impact toughness at -80°C

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