Production method of anti-acid pipeline steel X70MS

Abstract

The invention discloses a production method of anti-acid pipeline steel X70MS. The technological process comprises converter smelting, refining, continuous casting, heating rolling, cooling and inspection warehousing, the produced anti-acid pipeline steel has high strength, good toughness, excellent low-temperature toughness, excellent HIC and SSCC resistance and excellent machining performance and welding performance, the yield strength of the steel is 485-560 Mpa, the tensile strength is 580-680 Mpa, the yield ratio is smaller than or equal to 0.88, and the yield ratio is smaller than or equal to 0.88. The plate thickness low-temperature impact toughness Akv is greater than or equal to 230J, the crack-arrest drop hammer temperature is-30 DEG C, the toughness area is greater than or equal to 88%, and the HIC resistance CLR is less than or equal to 5%, CTR is less than or equal to 1%, and CSR is less than or equal to 1%. And the 90% yield strength load SSCC is qualified.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a production method of X70MS pipeline steel with good performance in acidic environments. Background Technology

[0002] With changes in energy structure and increasing energy demand, energy extraction has gradually extended from inland areas to the ocean and polar regions, greatly promoting the development of long-distance pipelines. As extracted resources continue to dwindle, the extraction of natural gas resources rich in H2S / CO2 corrosive media is increasing. H2S is one of the most corrosive and harmful media in oil and gas. Hydrogen atoms generated in corrosive environments continuously penetrate and accumulate at defect sites in pipeline steel, leading to corrosion and cracking even at relatively low gas transmission pressures. To ensure the safety of oil and gas transportation, steel used in oil and gas pipelines must possess excellent H2S resistance, creating a demand for steel designed for use in acidic environments.

[0003] Acid-resistant pipeline steel, in addition to high yield strength and tensile strength, also possesses good elongation, cold bending performance, weldability, and low-temperature crack arrest properties, as well as excellent resistance to H2S corrosion. It is primarily used in the natural gas and oil transportation industry to adapt to the service environment of transporting acidic media, effectively resist H2S corrosion, reduce carbon emissions, increase engineering safety, and conserve resources. Summary of the Invention

[0004] This invention aims to provide a production method for X70MS, a high-strength, low-temperature toughness, and acid-resistant pipeline steel for oil and gas. The produced pipeline steel exhibits high strength, good toughness, excellent low-temperature toughness, excellent resistance to HIC and SSCC, and excellent processing and welding properties. The steel has a yield strength of 485~560 MPa, tensile strength of 580~680 MPa, yield-to-tensile ratio ≤0.88, low-temperature impact toughness at -40℃, Akv ≥230 J, crack arresting drop hammer temperature of -30℃, toughness area ≥88%, and HIC resistance properties: CLR ≤5%, CTR ≤1%, CSR ≤1%. It also meets the SSCC requirement at 90% yield strength.

[0005] This invention is achieved through the following technical solution: A production method for acid-resistant pipeline steel X70MS, the process flow includes converter smelting, refining, continuous casting, hot rolling, cooling, inspection and warehousing. The chemical composition of the steel (mass percentage) is: carbon = 0.03~0.04%, silicon = 0.10~0.20%, manganese = 1.30~1.40%, phosphorus ≤0.012%, sulfur ≤0.0010%, niobium = 0.038~0.044%, titanium = 0.012~0.018%, aluminum ≤0.015%, nickel = 0.1%. 0~0.13, chromium=0.15~0.18, molybdenum=0.08~0.10, copper=0.15~0.18, V=0.03~0.04, the rest is Fe and unavoidable impurities; key process steps include: (1) converter: the converter controls oxygen ≥450ppm, COE=0.0023%, uses a sliding plate device to block slag and tap steel, lime and modifier are added after the furnace for slag treatment, no aluminum deoxidation; no Al wire is fed after the furnace and alloying operation is performed; (2) Refining: The LF is turned on with a large flow of Ar stirring, and the electrodes heat the molten steel. The oxygen and carbon in the converter molten steel are used to further react with carbon and oxygen to reduce the oxygen content of the molten steel. After the carbon-oxygen reaction endpoint, the measured value of carbon is ≤0.025%. After the decarburization reaction, alloys are added to control the oxygen content of the molten steel to ≤30ppm. Lime and refining slag are added to the molten steel for deoxidation and desulfurization. The basicity of the refining slag CaO / SiO2 is ≤4.2~5.5. The aluminum content in the molten steel is controlled throughout the process to reduce the formation of Al2O3 inclusions. The inclusions in the molten steel are controlled. The vacuum is maintained at a working vacuum of 0.5tor for more than 18 minutes. The molten steel is denitrified, dehydrogenated and deoxygenated, and the oxygen content is ≤15ppm. (3) Continuous casting: casting with low superheat protection throughout the process, controlling the superheat to 8~12℃, using dynamic water ratio for secondary cooling, and dynamic light pressure technology to reduce the center segregation and porosity of the billet. After the billet exits the secondary cooling flame cutting, it is quenched to ≤600℃ by a billet quenching device. The billet is then placed in a heat preservation device for slow cooling to ≤350℃ before being loaded into the furnace for rolling. (4) Rolling: Heating temperature 1150~1180℃, heating time 280~320min, waiting billet thickness >3h, initial rolling temperature 840~930℃, final rolling temperature 770~810℃, water cooling is adopted, initial cooling temperature 780~820℃, final cooling temperature 480~570℃, cooling rate 10~20℃ / s.

[0006] The resulting steel plates exhibit a yield strength of 485~560 MPa, a tensile strength of 580~680 MPa, a yield-to-tensile ratio ≤0.88, low-temperature impact toughness at -40℃, Akv ≥230 J, crack arresting drop hammer temperature -30℃, toughness area ≥88%, and HIC resistance properties: CLR ≤5%, CTR ≤1%, CSR ≤1%. The SSCC (Self-Standardized Crush Test) for 90% yield strength is qualified.

[0007] The principle of this invention: Regarding step (1) of the converter, a large oxygen jet is used to stir the molten pool and create high-basicity slag, so that the oxygen content of the tapped steel is ≥450ppm, the carbon-oxygen product (COE) is 0.0023%, and P is ≤0.010%. A sliding plate is used to block slag during tapping to reduce the mixing of high-oxidation slag. No deoxidation or alloying is performed to maintain the high oxygen content of the molten steel. After the furnace, lime and modifiers are added to modify the steel slag. The molten steel is not deoxidized or alloyed to maintain the oxygen content in the molten steel, reduce the temperature loss, and facilitate the occurrence of subsequent decarburization reactions.

[0008] Regarding step (2) refining, after entering the LF, a large argon flow rate is turned on for stirring, and the electrode heats the molten steel to raise the temperature, so that the carbon-oxygen reaction occurs further, generating CO2 which is discharged, further reducing the carbon content of the molten steel, reducing the precipitation of carbides, eliminating the generation of abnormal structures, and stabilizing the carbon content to ≤0.025%. Non-aluminum element deoxidation alloying is used to reduce the generation of inclusions Al2O3. After the deoxidation reaction, alloy deoxidation alloying is added. Lime and refining slag are used for deoxidation and desulfurization to create high alkali. The slag is highly fluid, and the basicity of the refining slag (CaO / SiO2) is 4.2~5.5. The aluminum content in the molten steel is controlled throughout the process to reduce the formation of Al2O3 inclusions, which facilitates the transformation of CaO-Al2O3 into low-melting-point CaO-Al2O3-MgO composite inclusions. This also facilitates the flotation and removal of inclusions. The inclusion stability is controlled as follows: Category A: coarse / fine ratio ≤ 0.5; Category B: coarse / fine ratio ≤ 1.0; Category C: coarse / fine ratio ≤ 0.5; Category D: coarse / fine ratio ≤ 1.0.

[0009] Regarding step (3) continuous casting, low superheat protection casting is adopted. Full protection casting can effectively reduce the generation of secondary oxides and control the superheat to 8~12℃. The continuous casting uses dynamic water distribution technology for secondary cooling and three-stage dynamic light reduction technology at the end of solidification. The reduction is 7~9mm, which reduces the formation of central bridges and alleviates central segregation and porosity. The central segregation is ≤0.5 grade. After the billet is flame-cut, the billet is quenched to ≤600℃ by the billet quenching device to achieve uniform billet structure. After cooling to ≤350℃ in the line protection cover, it is loaded into the furnace for rolling. The billet structure is further stabilized to obtain a fine equiaxed grain structure.

[0010] Regarding step (4) rolling, the initial austenite is fine due to low-temperature heating at 1150~1180℃. Combined with high-reduction rolling, the grains are further broken down, and the high cooling rate results in a mixed structure of a large number of needle-like ferrites on the surface and bainite in the middle. The ferrite structure is intertwined, which prevents the extension of fracture, improves the crack arrest performance of the material, and enhances its acid resistance.

[0011] Advantages of this invention: (1) Controlling the micro-aluminum composition can effectively reduce the generation of Al2O3 inclusions, reduce the amount of large inclusions in steel, and improve the performance of steel.

[0012] (2) The unique LF decarburization technology using residual oxygen in molten steel eliminates the traditional RH vacuum decarburization process, reduces production steps, saves energy, reduces CO2 emissions, lowers production costs, reduces the blowing pressure on the converter, protects the converter lining, and extends the converter life. Through the further occurrence of the carbon-oxygen reaction by LF heating and blowing argon, the carbon content can be stably controlled at 0.03%~0.04%.

[0013] (3) The heat preservation technology of continuous casting billet quenching and cooling + heat preservation cover makes the billet obtain as many fine equiaxed crystal structures as possible.

[0014] (4) The steel has a ferrite and bainite winding structure, which gives the pipeline steel excellent resistance to HIC and SSCC.

[0015] (5) The acid-resistant pipeline steel X65MS produced by this invention has a billet segregation C≤0.5, uniform and stable steel plate properties, excellent resistance to HIC and SSCC, yield strength 450~550Mpa, tensile strength 550~650Mpa, yield ratio ≤0.86, impact strength at -40℃ 260~450J, drop shear area at -30℃ ≥88%; inclusions A coarse series / fine series ≤0.5 grade, B coarse series / fine series ≤1.0 grade, C coarse series / fine series ≤0.5 grade, D coarse series / fine series ≤1.0 grade, HIC resistance performance CLR≤5%, CTR≤1%, CSR≤1%; 90% strength load SSCC qualified. Attached Figure Description

[0016] Figure 1 The image shows the metallographic structure of the steel plate produced in Example 1. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments.

[0018] Example 1: Production method of 9.5mm x 70MS acid-resistant pipeline steel The chemical composition (by weight percentage) of the alloying elements is: C=0.035, Si=0.18, Mn=1.35, P=0.011, S=0.0008, Nb=0.042, Ti=0.01, Al=0.012, Ni=0.13, Gr=0.16, Mo=0.09, Cu=0.16, V=0.037, with the balance being iron and unavoidable impurities. Key process steps: Converter smelting: The oxygen content of the steel produced from the converter is 480ppm and the carbon content is 0.049%. Argon stirring is controlled after the furnace is turned on, and 600kg of lime and 300kg of modifier are added.

[0019] (2) LF furnace refining: In the early stage, start stirring with a large argon flow rate of 600~1000 standard L / H and a refining temperature of 1500~1650℃; power on for 30 minutes, carbon and oxygen reaction is sufficient, and the final carbon content C=0.022% is reduced. Reduce the addition of argon to alloy deoxidation and alloying treatment, deoxidation and decarburization refining treatment, control the aluminum content in the molten steel throughout the process, reduce the generation of Al2O3 inclusions, facilitate the transformation of CaO-Al2O3 into low melting point CaO-Al2O3-MgO composite inclusions, and facilitate the floating and removal of inclusions. Class A coarse / fine series 0 grade; Class B coarse / fine series 0.5 grade; Class C coarse / fine series 0 grade; Class D coarse / fine series 0.5 grade. Under a vacuum of 0.5tor, maintain the vacuum time for 18 minutes; denitrify, hydrogen and oxygen treat the molten steel, with an oxygen content of 12ppm, which greatly improves the purity of the molten steel.

[0020] (3) Continuous casting: control the superheat to 10℃, the water ratio of the secondary cooling water in continuous casting is 0.18L / kg, and the three-stage dynamic light reduction technology at the end of solidification is used to reduce the formation of central bridges and reduce central segregation and porosity. The central segregation is grade 0.5. After the billet is flame-cut, the billet is quenched at 580℃ by the billet quenching device, and then cooled to 330℃ in the line protection cover before being loaded into the furnace for rolling. The billet structure is further stabilized and a fine equiaxed grain structure is obtained.

[0021] (4) Rolling: Heating temperature 1150~1180℃, heating time 290min, billet thickness 68mm, initial rolling temperature 930℃, final rolling temperature 770~810℃, online quenching, initial cooling temperature 825℃, final cooling temperature 240~320℃, cooling rate 15.6℃ / s.

[0022] The properties of the 9.5mm acid-resistant pipeline steel X70MS produced in Example 1 are shown in Table 1.

[0023] Table 1. Performance of 9.5mm acid-resistant pipeline steel X70MS produced in Example 1 .

[0024] The metallographic structure of the steel plate produced in Example 1 is as follows: Figure 1 SSC was tested using ASTM G39 with a 4-point bending test in NACE TM0177-2016 standard A solution. The applied stress was 90% of the actual yield strength of the steel plate, and no cracks appeared on the surface. HIC was tested according to NACE TM0284 standard A solution, and CLR, CTR, and CSR all met the standard requirements.

[0025] Example 2: Production method of 25.4mm x 70MS acid-resistant pipeline steel The chemical composition of the alloying elements by weight percentage is C=0.035, Si=0.18, Mn=1.36, P=0.011, S=0.0008, Nb=0.042, Ti=0.01, Al=0.012, Ni=0.13, Gr=0.16, Mo=0.09, Cu=0.16, V=0.037, with the balance being iron and unavoidable impurities; Key process steps: (1) Converter smelting: The oxygen content of the steel produced by the converter is 480ppm and the carbon content is 0.049%. Argon stirring is controlled after the furnace is used, and 600kg of lime and 300kg of modifier are added.

[0026] (2) LF furnace refining: In the early stage, start stirring with a large argon flow rate of 600~1000 standard L / H and a refining temperature of 1500~1650℃; power on for 30 minutes, carbon and oxygen reaction is sufficient, and the final carbon content C=0.022% is achieved. Reduce the addition of argon to the alloy deoxidation and alloying treatment, deoxidation and decarburization refining treatment, control the aluminum content in the molten steel throughout the process, reduce the generation of Al2O3 inclusions, facilitate the transformation of CaO-Al2O3 into low melting point CaO-Al2O3-MgO composite inclusions, and facilitate the floating and removal of inclusions. Class A coarse / fine series 0 grade; Class B coarse / fine series 0.5 grade; Class C coarse / fine series 0 grade; Class D coarse / fine series 0.5 grade. Under a vacuum of 0.5tor, maintain the vacuum time for 18 minutes; denitrify, dehydrogenate and oxygenate the molten steel, with an oxygen content of 12ppm, which greatly improves the purity of the molten steel.

[0027] (3) Continuous casting: control the superheat to 10℃, the water ratio of the secondary cooling water in continuous casting is 0.18L / kg, and the three-stage dynamic light reduction technology at the end of solidification is used to reduce the formation of central bridges and reduce central segregation and porosity. The central segregation is grade 0.5. After the billet is flame-cut, the billet is quenched at 580℃ by the billet quenching device, and then cooled to 330℃ in the line protection cover before being loaded into the furnace for rolling. The billet structure is further stabilized and a fine equiaxed grain structure is obtained.

[0028] (4) Rolling: Heating temperature 1150~1180℃, heating time 290min, billet thickness 90mm, initial rolling temperature 840℃, final rolling temperature 770~810℃, online quenching, initial cooling temperature 805℃, final cooling temperature 240~320℃, cooling rate 18.2℃ / s.

[0029] The performance of the 25.4mm acid-resistant pipeline steel X70MS produced in Example 2 is shown in Table 2.

[0030] Table 2 Performance of 25.4mm acid-resistant pipeline steel X70MS produced in Example 2 .

[0031] SSC was tested using ASTM G39 with a 4-point bending test in NACE TM0177-2016 standard A solution. The applied stress was 90% of the actual yield strength of the steel plate, and no cracks appeared on the surface. HIC was tested according to NACE TM0284 standard A solution, and CLR, CTR, and CSR all met the standard requirements.

Claims

1. A method for producing acid-resistant pipeline steel X70MS, the process flow including converter smelting, refining, continuous casting, heating and rolling, cooling, inspection and warehousing, characterized in that: The chemical composition of the steel (by mass percentage) is C=0.03~0.04, Si=0.10~0.20, Mn=1.30~1.40, p≤0.012, s≤0.0010, Nb=0.038~0.044, Ti=0.012~0.018, Al≤0.015, Ni=0.10~0.13, Gr=0.15~0.18, Mo=0.08~0.10, Cu=0.15~0.18, V=0.03~0.04, with the remainder being Fe and unavoidable impurities; Key process steps include: (1) Converter: O is controlled at ≥450ppm and COE = 0.0023%. Slag is blocked and steel is tapped using a sliding plate device. Lime and modifier are added after the furnace for slag treatment. Aluminum deoxidation is not performed. Al wire is not fed after the furnace and alloying operations are not performed. (2) Refining: The LF is turned on with a large flow of Ar stirring, and the electrodes heat the molten steel. The oxygen and carbon in the converter molten steel are used to further react with carbon and oxygen to reduce the oxygen content of the molten steel. After the carbon-oxygen reaction endpoint, the measured value of carbon C ≤ 0.025%. After the decarburization reaction, alloys are added to control the oxygen content of the molten steel O ≤ 30ppm. Lime and refining slag are added to the molten steel for deoxidation and desulfurization. The basicity of the refining slag CaO / SiO2 ≤ 4.2~5.

5. The aluminum content in the molten steel is controlled throughout the process to reduce the formation of Al2O3 inclusions. The inclusions in the molten steel are controlled. The vacuum is maintained at a working vacuum of 0.5tor for more than 18 minutes. The molten steel is denitrified, dehydrogenated and deoxygenated, and the oxygen content O ≤ 15ppm. (3) Continuous casting: casting with low superheat protection throughout the process, controlling the superheat to 8~12℃, using dynamic water ratio for secondary cooling, and dynamic light pressure technology to reduce the center segregation and porosity of the billet. After the billet exits the secondary cooling flame cutting, it is quenched to ≤600℃ by a billet quenching device. The billet is then placed in a heat preservation device for slow cooling to ≤350℃ before being loaded into the furnace for rolling. (4) Rolling: Heating temperature 1150~1180℃, heating time 280~320min, waiting billet thickness >3h, initial rolling temperature 840~930℃, final rolling temperature 770~810℃, water cooling is adopted, initial cooling temperature 780~820℃, final cooling temperature 480~570℃, cooling rate 10~20℃ / s.

2. The production method of acid-resistant pipeline steel X70MS according to claim 1, characterized in that: The resulting steel plates exhibit a yield strength of 485~560 MPa, a tensile strength of 580~680 MPa, a yield-to-tensile ratio ≤0.88, low-temperature impact toughness at -40℃, Akv ≥230 J, crack arresting drop hammer temperature -30℃, toughness area ≥88%, and HIC resistance properties: CLR ≤5%, CTR ≤1%, CSR ≤1%. The SSCC (Self-Standardized Crush Test) for 90% yield strength is qualified.

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