A thick-walled high-acid-resistance pipeline steel and a production method thereof

Abstract

The present application relates to the technical field of steel metallurgy, and particularly relates to a thick-wall high-acid-resistance pipeline steel and a production method thereof, chemical components and mass percentages are as follows: C: 0.02%-0.05%, Si: 0.15%-0.35%, Mn: 1.00%-1.20%, P: <=0.015%, S: <=0.0010%, Nb: 0.030-0.050%, V: 0.060-0.070%, Ti: 0.008-0.030%, Cr: 0.10-0.30%, Ni: 0.50%-0.60%, Mo: <=0.050%, Cu: 0.10-0.30%, Al: 0.015%-0.055%, B <=0.00050%, Ca: 0.0006%-0.0030%, N <=0.0060%, H <=0.0002%, and the balance is Fe and inevitable impurities. The present application is based on clean steel smelting, adopts fine-grain strengthening effect, obtains low-carbon bainite structure, and meets product-40 DEG C DWTT, high-concentration HIC resistance and 90% actual yield stress SSCC performance requirements.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a thick-walled high acid-resistant pipeline steel and its production method. Background Technology

[0002] The marine environment is extremely complex and changeable, constantly subjected to extreme weather conditions, including persistently low temperatures, turbulent waves, and occasional strong typhoons. Simultaneously, ocean currents and water pressure place extremely high demands on the transverse and longitudinal mechanical strength of subsea pipelines. In particular, the straight-seam submerged arc welding technology and the welding quality at the pipeline ends directly affect the overall performance of the product.

[0003] In a certain high-acid-resistant, low-temperature crack-arresting subsea acid-resistant pipeline project, the hydrogen sulfide content in the transported medium is extremely high, which places extremely high demands on the corrosion resistance of the pipeline steel. It is necessary to maintain the toughness and strength of the material under extremely cold conditions and meet the strict HIC and SSCC resistance testing standards. Based on this, this invention proposes a thick-walled high-acid-resistant pipeline steel and its production method. Through reasonable composition ratios and production processes, the material's HIC and SSCC resistance performance is improved, ensuring that the material meets the project requirements. Summary of the Invention

[0004] This invention addresses the aforementioned technical problems and overcomes the shortcomings of existing technologies by providing a thick-walled, high-acid-resistant pipeline steel and its production method. This invention employs a low-carbon, fine-grained, strengthened alloy design and achieves a bainitic microstructure through clean steel smelting and rapid cooling after rolling. This meets the product's requirements for transverse and longitudinal tensile properties, low-temperature impact toughness at -40℃, and DWTT performance at -40℃. It also achieves high-concentration HIC and 90% actual yield stress SSCC testing.

[0005] In a first aspect, the present invention provides a thick-walled high acid-resistant pipeline steel, the chemical composition and mass percentage of which are as follows: C: 0.02%~0.05%, Si: 0.15%~0.35%, Mn: 1.00%~1.20%, P: ≤0.015%, S: ≤0.0010%, Nb: 0.030~0.050%, V: 0.060~0.070%, Ti: 0.008~0.030%, Cr: 0.10~0.30%, Ni: 0.50%~0.60%, Mo: ≤0.050%, Cu: 0.10~0.30%, Al: 0.015%~0.055%, B ≤0.00050%, Ca: 0.0006%~0.0030%, N ≤0.0060%, H ≤0.0002%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the chemical composition and mass percentage of the steel for thick-walled high acid-resistant pipelines are as follows: C: 0.02%–0.04%, Si: 0.15%–0.25%, Mn: 1.00%–1.10%, P: ≤0.013%, S: ≤0.0010%, Nb: 0.030–0.040%, V: 0.060–0.065%, Ti: 0.008–0.020%, Cr: 0.10–0.20%, Ni: 0.50%–0.55%, Mo: ≤0.050%, Cu: 0.10–0.20%, Al: 0.015%–0.050%, B ≤0.00050%, Ca: 0.0006%–0.0020%, N ≤0.0060%, H ≤0.0002%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition and mass percentage of the steel for thick-walled high acid-resistant pipelines are as follows: C: 0.03%–0.05%, Si: 0.25%–0.35%, Mn: 1.10%–1.20%, P: ≤0.015%, S: ≤0.0010%, Nb: 0.040–0.050%, V: 0.065–0.070%, Ti: 0.010–0.030%, Cr: 0.20–0.30%, Ni: 0.55%–0.60%, Mo: ≤0.050%, Cu: 0.20–0.30%, Al: 0.020%–0.055%, B ≤0.00050%, Ca: 0.0008%–0.0030%, N ≤0.0060%, H ≤0.0002%, with the balance being Fe and unavoidable impurities.

[0008] Secondly, the present invention also provides a method for producing steel for thick-walled, high-acid-resistant pipelines, comprising the following steps:

[0009] S1. After desulfurization, the steel is smelted in a smelting furnace. Nickel iron and copper plates are added to the smelting furnace along with scrap steel. After the molten steel is qualified, it is sent to LF / RH for refining.

[0010] S2. Add ferrovanadium in the later stage of alloying. After the ferrovanadium alloying is completed, perform calcium treatment and stir statically for 15-20 minutes after calcium treatment.

[0011] S3. Continuous casting adopts dynamic light reduction and electromagnetic stirring technology, with a casting speed of 0.6 to 1.3 m / min. After the billet is cast, it is stacked and cooled for 48 hours before surface inspection.

[0012] S4. The billet that passes the surface inspection is subjected to austenitizing heating, with a tapping temperature of 1200-1260 degrees Celsius. Two-stage rolling is adopted, with a reduction rate of not less than 22% and a reduction of not less than 26mm in the last pass of roughing rolling, and even-pass rolling is adopted for finishing rolling.

[0013] S5. The rolled steel plate is rapidly cooled with a water immersion temperature of 780-820 degrees Celsius, a cooling rate of 20-30 degrees Celsius / min, and a reddening temperature of 400-500 degrees Celsius.

[0014] S6. After cooling, the steel plates are stacked, sheared, marked, and put into storage.

[0015] Furthermore, the thickness of the steel plate described in S6 is 20–50 mm.

[0016] Furthermore, the steel plate described in S6 has a yield strength greater than 452 MPa and a tensile strength greater than 568 MPa.

[0017] Furthermore, the steel plate described in S6 has an impact energy greater than 360J at a low temperature of -40℃.

[0018] Furthermore, the steel plate described in S6 has an SA% ≥ 86 at -40°C under DWTT conditions.

[0019] The beneficial effects of this invention are:

[0020] (1) The present invention adopts a low carbon design to effectively increase the ferrite content, reduce the potential difference formed by carbides in the microstructure, and improve the HIC and SSCC qualification rate. The low manganese design can reduce the harm of manganese sulfide, ensure the core quality of thick-walled pipelines, and improve the performance stability of HIC and SSCC. Chromium can improve the hardenability of thick-walled pipelines and improve the microstructure uniformity in the thickness direction of thick-walled pipelines. Nickel can improve the adverse effects of low carbon and stabilize the strength of steel. The simultaneous use of nickel and chromium can improve the strength and toughness of thick-walled pipelines and improve the comprehensive mechanical properties after welding. Nickel can promote the nucleation of austenite grains, refine the microstructure grain size, strengthen the intergranular structure, and improve the low temperature toughness of steel.

[0021] (2) In this invention, vanadium ferrovanadium is added after refining and complete deoxidation, which can promote the production of vanadium nitrides and reduce the harm of nitrogen in steel. At the same time, vanadium in the solid solution steel can enhance the strength of steel through precipitation strengthening. In the austenitization process, it can organize the growth of austenite grains, promote the nucleation of ferrite in the grains, refine the ferrite grains, and effectively improve the low temperature toughness of the product and the stability of HIC and SSCC performance.

[0022] (3) This invention produces solid inclusions mainly composed of CaS-CaO by calcium treatment after deoxidation. Solid inclusions are more likely to float on molten steel, improving the purity of molten steel. Clean molten steel smelting is conducive to the stability of HIC and SSCC performance.

[0023] (4) The present invention can improve the melting of segregated structure in the core of the billet into the austenite region by using an austenite temperature of 1200-1260 degrees, reduce the adverse effects of banded structure, and at the same time, the high temperature austenitization technology can enhance the precipitation strengthening of nickel, chromium, copper, niobium, vanadium and titanium elements, improve the metallurgical effect of alloying elements, and improve the stability of transverse and longitudinal mechanical properties.

[0024] (5) The present invention adopts a two-stage rolling technology and a rapid cooling process after rolling, which can improve the adverse effects of the band structure, refine the grain size and stability of the structure transformation, and improve the stability of product performance. Attached Figure Description

[0025] Figure 1 This is a metallographic diagram of the steel used for thick-walled, high-acid-resistant pipelines in Embodiment 1 of the present invention. Detailed Implementation

[0026] Example 1

[0027] The chemical composition and mass percentage of the steel used for thick-walled high acid-resistant pipelines in this embodiment are as follows: C: 0.03%, Si: 0.23%, Mn: 1.06%, P: 0.011%, S: 0.0009%, Nb: 0.037%, V: 0.063%, Ti: 0.009%, Cr: 0.17%, Ni: 0.53%, Mo: 0.030%, Cu: 0.17%, Al: 0.023%, B: 0.00030%, Ca: 0.00180%, N: 0.0051%, H: 0.00012%, with the balance being Fe and unavoidable impurities.

[0028] The specific production method of thick-walled, high-acid-resistant pipeline steel in this embodiment includes:

[0029] S1. After desulfurization, the steel is smelted in a smelting furnace. Nickel iron and copper plates are added to the smelting furnace along with scrap steel. After the molten steel is qualified, it is sent to LF / RH for refining.

[0030] S2. Add ferrovanadium in the later stage of alloying. After the ferrovanadium alloying is completed, perform calcium treatment and stir statically for 15-20 minutes after calcium treatment.

[0031] S3. Continuous casting adopts dynamic light reduction and electromagnetic stirring technology, with a casting speed of 0.6 to 1.3 m / min. After the billet is cast, it is stacked and cooled for 48 hours before surface inspection.

[0032] S4. The billet that passes the surface inspection is subjected to austenitizing heating, with a tapping temperature of 1200-1260 degrees Celsius. Two-stage rolling is adopted, with a reduction rate of not less than 22% and a reduction of not less than 26mm in the last pass of roughing rolling, and even-pass rolling is adopted for finishing rolling.

[0033] S5. The rolled steel plate is rapidly cooled with a water immersion temperature of 780-820 degrees Celsius, a cooling rate of 20-30 degrees Celsius / min, and a reddening temperature of 400-500 degrees Celsius.

[0034] S6. After cooling, the steel plates are stacked, sheared, marked, and put into storage.

[0035] Example 2

[0036] The chemical composition and mass percentage of the steel used for thick-walled high acid-resistant pipelines in this embodiment are as follows: C: 0.041%, Si: 0.31%, Mn: 1.19%, P: 0.011%, S: 0.0008%, Nb: 0.043%, V: 0.069%, Ti: 0.017%, Cr: 0.26%, Ni: 0.57%, Mo: 0.020%, Cu: 0.27%, Al: 0.032%, B: 0.00030%, Ca: 0.0021%, N: 0.0046%, H: 0.00013%, with the balance being Fe and unavoidable impurities.

[0037] The specific production method of thick-walled, high-acid-resistant pipeline steel in this embodiment includes:

[0038] S1. After desulfurization, the steel is smelted in a smelting furnace. Nickel iron and copper plates are added to the smelting furnace along with scrap steel. After the molten steel is qualified, it is sent to LF / RH for refining.

[0039] S2. Add ferrovanadium in the later stage of alloying. After the ferrovanadium alloying is completed, perform calcium treatment and stir statically for 15-20 minutes after calcium treatment.

[0040] S3. Continuous casting adopts dynamic light reduction and electromagnetic stirring technology, with a casting speed of 0.6 to 1.3 m / min. After the billet is cast, it is stacked and cooled for 48 hours before surface inspection.

[0041] S4. The billet that passes the surface inspection is subjected to austenitizing heating, with a tapping temperature of 1200-1260 degrees Celsius. Two-stage rolling is adopted, with a reduction rate of not less than 22% and a reduction of not less than 26mm in the last pass of roughing rolling, and even-pass rolling is adopted for finishing rolling.

[0042] S5. The rolled steel plate is rapidly cooled with a water immersion temperature of 780-820 degrees Celsius, a cooling rate of 20-30 degrees Celsius / min, and a reddening temperature of 400-500 degrees Celsius.

[0043] S6. After cooling, the steel plates are stacked, sheared, marked, and put into storage.

[0044] in, Figure 1 The metallographic structure of the steel for thick-walled high acid-resistant pipelines obtained in Example 1 is shown in Tables 1 and 2. The performance test results of the aforementioned examples are shown in Tables 1 and 2.

[0045] Table 1. Transverse and longitudinal tensile properties of steel plates

[0046] Example direction Yield strength / MPa Tensile strength / MPa Elongation / % Yield ratio / % Example 1 Horizontal 460 570 45 81 Example 1 Vertical 455 569 42 80 Example 2 Horizontal 480 606 38 79 Example 2 Vertical 469 593 37 79

[0047] Table 2 Low-temperature impact, DWTT performance, HIC and 90% actual yield stress SSCC test results

[0048] Example Impact average (-40℃) / J DWTT (-40℃) / % HIC SSCC Example 1 363 88 qualified qualified Example 2 386 90 qualified qualified .

[0049] As shown in Tables 1 and 2, the thick-walled high acid-resistant pipeline steel and its production method provided by this invention have successfully developed high acid-resistant pipeline steel, achieving a bainite-dominant microstructure, effectively improving the low-temperature toughness and stability of HIC and SSCC properties of the product. The product meets the requirements for transverse and longitudinal tensile properties, low-temperature impact toughness at -40℃, and DWTT performance at -40℃. It has achieved high-concentration HIC and 90% actual yield stress SSCC testing, meeting the requirements of third-party testing recognized by DNV.

[0050] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A type of thick-walled, high-acid-resistant pipeline steel, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.02%~0.05%, Si: 0.15%~0.35%, Mn: 1.00%~1.20%, P: ≤0.015%, S: ≤0.0010%, Nb: 0.030~0.050%, V: 0.060~0.070%, Ti: 0.008~0.030%, Cr: 0.10~0.30%, Ni: 0.50%~0.60%, Mo: ≤0.050%, Cu: 0.10~0.30%, Al: 0.015%~0.055%, B≤0.00050%, Ca: 0.0006%~0.0030%, N≤0.0060%, H≤0.0002%, with the balance being Fe and unavoidable impurities; The production method of the thick-walled, high-acid-resistant pipeline steel includes the following steps: S1. After desulfurization, the steel is smelted in a smelting furnace. Nickel iron and copper plates are added to the smelting furnace along with scrap steel. After the molten steel is qualified, it is sent to LF / RH for refining. S2. Add ferrovanadium in the later stage of alloying. After the ferrovanadium alloying is completed, perform calcium treatment and stir statically for 15-20 minutes after calcium treatment. S3. Continuous casting adopts dynamic light reduction and electromagnetic stirring technology, with a casting speed of 0.6 to 1.3 m / min. After the billet is cast, it is stacked and cooled for 48 hours before surface inspection. S4. The billet that passes the surface inspection is subjected to austenitizing heating, with a tapping temperature of 1200-1260 degrees Celsius. Two-stage rolling is adopted, with a reduction rate of not less than 22% and a reduction of not less than 26mm in the last pass of roughing rolling, and even-pass rolling is adopted for finishing rolling. S5. The rolled steel plate is rapidly cooled with a water immersion temperature of 780-820 degrees Celsius, a cooling rate of 20-30 degrees Celsius / min, and a reddening temperature of 400-500 degrees Celsius. S6. After cooling, the steel plates are stacked for cooling, sheared, marked, and put into storage. The steel plate described in S6 has a yield strength greater than 452 MPa, a tensile strength greater than 568 MPa, an impact energy greater than 360 J at -40℃, and an SA% ≥ 86% under DWTT at -40℃.

2. The steel for thick-walled, high-acid-resistant pipelines according to claim 1, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.02%~0.04%, Si: 0.15%~0.25%, Mn: 1.00%~1.10%, P: ≤0.013%, S: ≤0.0010%, Nb: 0.030~0.040%, V: 0.060~0.065%, Ti: 0.008~0.020%, Cr: 0.10~0.20%, Ni: 0.50%~0.55%, Mo: ≤0.050%, Cu: 0.10~0.20%, Al: 0.015%~0.050%, B≤0.00050%, Ca: 0.0006%~0.0020%, N≤0.0060%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

3. The steel for thick-walled, high-acid-resistant pipelines according to claim 1, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.03%~0.05%, Si: 0.25%~0.35%, Mn: 1.10%~1.20%, P: ≤0.015%, S: ≤0.0010%, Nb: 0.040~0.050%, V: 0.065~0.070%, Ti: 0.010~0.030%, Cr: 0.20~0.30%, Ni: 0.55%~0.60%, Mo: ≤0.050%, Cu: 0.20~0.30%, Al: 0.020%~0.055%, B≤0.00050%, Ca: 0.0008%~0.0030%, N≤0.0060%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

4. The steel for thick-walled, high-acid-resistant pipelines according to claim 1, characterized in that, The thickness of the steel plate described in S6 is 20-50 mm.

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