Extra-thick wall X70-grade ocean acid-resistant pipeline steel and preparation method thereof

Abstract

The invention discloses extra-thick wall X70-grade ocean acid-resistant pipeline steel. Chemical components of the extra-thick wall X70-grade ocean acid-resistant pipeline steel comprise, by mass percent, 0.03%-0.05% of C, 0.10%-0.30% of Si, 1.0-1.3% of Mn, 0.2%-0.3% of Cr, 0.2%-0.4% of Ni, 0.10%-0.20% of Mo, 0.04%-0.07% of Nb, 0.03%-0.05% of V, 0.01%-0.02% of Ti, 0.01%-0.045% of Al and the balance Fe. The matrix structure of the obtained steel is granular bainite / acicular ferrite and a small quantity of small-size quasi-polygonal ferrite, high strength, high toughness, hydrogen sulfide corrosion resistance and stress corrosion resistance are all achieved well, and the technical index requirements of X70 MOSs with the thickness being 25 mm or above are met; and the involved preparation process is simple, energy consumption is low, and the steel is suitable for application and popularization.

Description

technical field [0001] The invention belongs to the technical field of low-carbon micro-alloy steel materials, and in particular relates to an extra-thick wall X70 grade marine acid-resistant pipeline steel and a preparation method thereof. Background technique [0002] Offshore oil and gas resources account for 70% of the world's total oil and gas resources. With the gradual depletion of land oil resources, the ocean has become the main battlefield for future oil and gas resources. As a pipeline steel for marine service, it needs to withstand the service environment such as low temperature, high pressure, ocean current movement, external / internal corrosive media, etc., and puts forward strict requirements on the low temperature toughness, strength, corrosion resistance and large wall thickness of the material. At present, the pipeline steel used in my country's marine service engineering is mainly steel grades below X70, and X65 and X70 submarine pipeline steels with thickn...

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Problems solved by technology

[0003] Patent CN 106566991 A discloses a X65MOS acid-resistant submarine pipeline steel and its preparation method. The compression ratio of the steel plate is ≥ 11, and the thickness of the obtained steel plate is 34-48mm, but the yield strength cannot reach 485MPa; CN 105132807 A discloses a submarine acid-resistant corrosion-resistant For pipeline steel with excellent performance, the cumulative reduction rate of rough rolling and finish rolling is not less than 70%. Continuous casting slabs with a thickness of 250mm and below can only be used to produce seabed acid-resistant pipelines below 23mm, and cannot be used for 25mm and below. Production of the above extra-thick submarine acid-resistant pipelines; CN 108624811 A discloses a large thick-walled acid-resistant corrosion-resistant pipeline steel and its production method. It is rolled by TMCP technology and cooled to 280-300°C by ultra-fast cooling to obtain a core of 30 μm. Polygonal and bainite structure, which can meet the requirements of acid corrosion resistance, but the mechanical properties and steel plate thickness specifications have not been published. Considering that the content of strengthening element C is low, the size of polygonal ferrite is relatively large, and the strength level is not expected to be high; CN 105132833 A Disclosed is an economical high-strength submarine pipeline steel and its production method. The high-carbon composition system is prone to cause H due to carbon composition and structure segregation 2 The S test is unacceptable, and it is not suitable for the composition of the thick-sized submarine acid-resistant pipeline; CN 105648327 A discloses a pipeline steel plate with a small compression ratio that is resistant to HIC and SSC and its preparation method. The obtained steel plate has excellent resistance to HIC and SSC, and less alloy addition , low production cost, effective compression ratio ≤ 10, good structure uniformity, and small restrictions on the thickness of the slab. It is suitable for the manufacture of oil and natural gas pipelines containing acidic media, but it can only be prepared with thickness specifications below 25mm. steel

[0004] Based on the difficulties and characteristics of the existing ultra-thick and high-strength submarine acid-resistant pipelines, there are four main problems: 1) The purity of molten steel is extremely high. During the hydrogen sulfide corrosion process, hydrogen atoms are easy to accumulate on the two-phase interface and Cracks are formed, so the higher the purity of the molten steel, the better; 2) For thick-gauge pipeline steel plates, in order to ensure that the grains are sufficiently refined, a large thickness of high-homogeneity continuous casting slab is required, but the greater the thickness of the continuous casting slab, the greater the thickness of the continuous casting slab. The more serious the segregation, the worse the wet hydrogen sulfide corrosion resistance will be. The two contradict each other, and it is extremely difficult to take into account; 3) For the pipeline steel with a thickness of more than 25mm, there is a large difference in the deformation in the thickness direction during the rolling process, and the deformation It is difficult to penetrate into the center, and the temperature gradient and cooling rate during the cooling process are also very different, and the uniformity of the tissue is difficult to control; 4) High-strength submarine acid-resistant pipelines require a lower yield ratio on the basis of high strength And high impact drop hammer toughness, for this reason, it is necessary to take into account the requirements of high strength, high toughness and low yield ratio, which puts higher demands on the composition, structure design and precise control of the process in terms of matching the mechanical properties of the material. technical challenges

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