Manufacturing method and application of hot-rolled coil for 896MPa grade shale gas well straight seam electric resistance welded casing

Abstract

The present invention discloses a manufacturing method and application of a hot-rolled coil for 896MPa-grade straight-seam resistance-welded casing for shale gas wells, and relates to the technical field of petroleum casing. The present invention defines the required elements and the mass percentage range of each element, as well as the manufacturing process window conditions based on the required performance of the hot-rolled coil for 896MPa-grade straight-seam resistance-welded casing for shale gas wells; based on the defined manufacturing conditions, the composition design of the hot-rolled coil and the mechanical properties of the hot-rolled coil are calculated by material genetic engineering using first principles and molecular dynamics principles; and the hot-rolled coil is manufactured based on the output results. The present invention can quickly run the traditional trial-and-error material development process of optimizing composition and performance in simulation experiments, realize large-system material simulation, fast calculation, improve material screening efficiency and design level, and can quickly predict the composition and mechanical properties of the hot-rolled coil with target performance, shorten the time of material development, and reduce the cost of material development.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum casing, and in particular to a manufacturing method and application of a hot-rolled plate coil for 896MPa-grade shale gas well straight seam electric resistance welded casing. Background Art

[0002] Shale gas development will be a major source of future natural gas production increases. Shale gas extraction is characterized by long horizontal sections, prolonged fracturing operations, and high pressures. Casing is subjected to long, high-pressure, and cyclical combined loads. Multi-stage fracturing in horizontal wells drives uneven sliding within natural fractures and bedding planes, increasing the risk of casing collapse and deformation. Therefore, shale gas well casing requires a high balance of strength and toughness. Currently, high-strength oil casing primarily utilizes seamless steel pipe, which is formed by perforation, making it difficult to precisely control pipe dimensions. Longitudinal resistance welded casing, due to its specialized processing technology, offers excellent uniformity in material and geometric parameters, offering a natural advantage over seamless pipe in terms of high collapse resistance. Hot-rolled coil, the raw material for producing high-grade ERW casing, is crucial for producing high-grade ERW casing for shale gas wells. Developing hot-rolled coil suitable for the narrow process window of high-grade ERW casing and its manufacturing method presents an engineering challenge for high-performance casing in shale gas development. Traditional material research and development uses continuous "trial and error" experimental optimization of components and processes, combined with continuous understanding of structure-performance relationships to obtain materials that meet performance indicators. This method not only consumes high labor and material costs, but also takes a long time and has a relatively low success rate. Summary of the Invention

[0003] In order to meet the requirements for the properties of hot-rolled coils for preparing 896MPa-grade shale gas well casing and reduce resource waste, the present invention proposes a method for manufacturing 896MPa-grade hot-rolled coils for straight seam electric resistance welded casing.

[0004] A method for manufacturing a hot-rolled coil for 896 MPa-grade shale gas well straight seam electric resistance welded casing comprises the following steps:

[0005] First, based on the required properties of hot-rolled coil for 896MPa-grade shale gas well straight seam electric resistance welded casing, the required elements and the mass percentage range of each element, as well as the manufacturing process window conditions, were defined.

[0006] Secondly, based on the limited manufacturing conditions, material genetic engineering is used to calculate the composition design and mechanical properties of the hot-rolled coil. The specific steps are as follows:

[0007] S1: The mass percentage of each element is used as the input for the first-principles calculation and input into the calculation system. The first-principles calculation is applied to pre-calculate the macroscopic properties and obtain the energy band and wave function characteristics of the system.

[0008] S2, using the system energy band and wave function characteristics as input and combining the principles of molecular dynamics to calculate the mechanical properties of hot-rolled coils;

[0009] S3: Determine whether the mechanical properties of the hot-rolled coil obtained in S2 meet the welding performance requirements of the hot-rolled coil for 896 MPa-grade shale gas well straight seam electric resistance welded casing. If so, output the hot-rolled coil composition design and the hot-rolled coil mechanical properties. If not, modify the distribution ratio and return to S1 until the welding performance requirements are met, and output the hot-rolled coil composition design and the hot-rolled coil mechanical properties.

[0010] Finally, the hot rolled coil is manufactured according to the output composition design and mechanical properties of the hot rolled coil.

[0011] In the calculation system of material genetic engineering, the process flow is set as: coil forming-welding-quenching and tempering heat treatment.

[0012] When applying the first principle calculation to pre-calculate the macroscopic properties, the input of the first principle calculation is the mass percentage of C, Mn, Cr, Mo, Si and B; the carbon equivalent composition is used as the boundary condition, and the carbon equivalent is less than 0.5.

[0013] Mechanical properties include room temperature yield strength and toughness after hot rolling, weldability, and room temperature yield strength and toughness after quenching and tempering.

[0014] The required elements and the mass percentage range of each element are defined as follows: C: 0.12% to 0.22%, Mn: 1.0% to 1.6%, Cr: 0.4% to 0.6%, Mo: 0.3% to 0.5%, Si: 0.05% to 0.6%, B: 5 to 60PPM, and the rest is Fe and unavoidable impurities in the steel billet.

[0015] The process window conditions for manufacturing hot-rolled coils for 896MPa-grade straight seam electric resistance welded casing for shale gas wells are as follows: during the high-temperature hot rolling process, the heating temperature of the heating furnace is 1170-1210°C, the final rolling temperature is controlled at 830-870°C, and a steel plate with a thickness of 10-13mm is obtained; after rolling, the steel plate is controlled to cool and then coiled, with the coiling temperature being 550-650°C.

[0016] The welding performance requirements for hot-rolled coils for 896MPa grade shale gas well straight seam resistance welded casing are as follows:

[0017] The yield strength is 300-600 MPa, the elongation is ≥20%, the transverse impact energy is ≥40J at 0°C, the grain size complies with ASTM E112 NO.9 or finer, and the banded structure is ≤3.0 grade.

[0018] The production process includes converter rough refining, refining outside the furnace, slab continuous casting, high-temperature hot rolling and controlled cooling after rolling.

[0019] The production process includes converter roughing, refining outside the furnace, slab continuous casting, high-temperature hot rolling and controlled cooling after rolling. The specific operations are as follows:

[0020] Step 1: Iron and steel materials are put into the furnace, and argon is used for low-pressure blowing in the converter and ladle. During the refining process, ferrosilicon, metallic manganese, and low-carbon ferrochrome are used to fine-tune the composition. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate. The molten steel enters the crystallizer through the tundish and is cooled by the fan-shaped section to form a cast slab.

[0021] Step 2: The cast slab containing the calculated chemical composition mass percentage is used as a hot-rolled slab. The initial continuous casting slab thickness is 230 mm. During heating, the continuous casting slab is placed in a heating furnace for heating. The temperature of the continuous casting slab out of the furnace is controlled to be 1170-1210° C., and the holding time is 1 hour.

[0022] Step 3: The continuous casting slab obtained in step 2 is subjected to seven-stand continuous rolling, with a cumulative deformation of ≥ 60%, and the final rolling temperature is controlled at 830-870°C to obtain a steel plate with a thickness of 10-13 mm;

[0023] Step 4: After the rolled steel plate is cooled, it is coiled. The coiling temperature is 550-650°C. Gradient cooling is used to ensure the toughness of the coil while reducing the formation of banded structure, thereby ensuring good processing performance of the coil.

[0024] A hot-rolled coil prepared by the above method is used for welding 896MPa-grade shale gas well casing. After the pipe is made by the straight seam electric resistance welding process, the 896MPa-grade shale gas well casing with a yield strength of 900-960MPa and a Charpy impact energy of 130-220J can be obtained through tempering treatment.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses material genetic engineering, first principles and molecular dynamics principles to quickly run the traditional trial-and-error material development process of optimizing composition and performance in simulation experiments, realize large-system material simulation, fast calculation, improve material screening efficiency and design level, and can quickly predict the composition and mechanical properties of target performance hot-rolled coils, shortening the time and reducing the cost of material development. It also defines manufacturing conditions according to needs and narrows the scope of simulation experiments. After processing through the process flow, 896MPa-grade hot-rolled coils for straight seam electric resistance welding casing of shale gas wells that meet welding performance are obtained.

[0027] Furthermore, under specific limited manufacturing conditions, the hot-rolled coil for 896MPa grade shale gas well straight seam electric resistance welded casing needs to have lower yield strength and higher toughness, good cold formability and welding performance, and higher yield strength and toughness matching after quenching and tempering treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments:

[0029] Figure 1 Flowchart of the method for manufacturing hot-rolled coil of the present invention;

[0030] Figure 2 Flowchart of genetic engineering of materials used in the present invention;

[0031] Figure 3 The metallographic structure diagram of the hot-rolled coil prepared in Example 1 of the present invention;

[0032] Figure 4 This is the metallographic structure diagram of the hot-rolled coil prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0034] like Figure 1 As shown, a method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing comprises the following steps:

[0035] First, based on the required performance of the hot-rolled coil for 896MPa grade shale gas well straight seam electric resistance welded casing, the mass percentage of each required element is limited to the following range:

[0036] Including C: 0.12%~0.22%, Mn: 1.0%~1.6%, Cr: 0.4%~0.6%, Mo: 0.3%~0.5%, Si: 0.05%~0.6%, B: 5~60PPM, and the rest is Fe and unavoidable inclusions.

[0037] Carbon equivalent is the equivalent amount of carbon in metal materials recommended by the International Welding Institute. Controlling it within a smaller range is beneficial to reducing the heat affected zone of welding, improving the crack resistance and impact resistance of the weld, and ensuring the stability of weld quality and performance. The calculation method of carbon equivalent is as follows:

[0038] CE(IIW)=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15

[0039] The carbon equivalent is controlled within 0.5 according to the design of alloy elements and their mass percentage.

[0040] The design principles of each alloy element and its mass percentage are as follows:

[0041] C is the most economical strengthening element. Adding C can significantly improve the strength of steel. However, for 896MPa grade hot-rolled coils for shale gas well casing, in order to ensure excellent toughness and welding performance, the C content is controlled at 0.12% to 0.22%.

[0042] Si plays a role of solid solution strengthening in steel, thereby improving the strength of hot-rolled coils. However, too high Si content will affect the surface quality of the steel and impair its performance. Therefore, the Si content is controlled at 0.05% to 0.6% to meet the use requirements.

[0043] Mn can improve the strength of steel through solid solution strengthening, but too high Mn content will cause central segregation of the material, which is not conducive to the processing performance of hot-rolled coils. Therefore, the Mn content is controlled within 1.00-1.50%.

[0044] The addition of Cr improves the atmospheric corrosion resistance of the material. In steel, a Cr addition of >0.3% by mass is generally beneficial. However, when the Cr content exceeds 0.6%, the effect on the atmospheric corrosion resistance of the material is not significant. Therefore, the Cr content is controlled between 0.4% and 0.6%.

[0045] Mo provides solid solution strengthening and promotes the formation of bainite, thereby achieving bainite transformation strengthening. Adding up to 5% Mo increases the bainite content and improves the material's high-temperature yield strength. Mo precipitation typically occurs when the content exceeds 5%, so the Mo content is controlled between 0.3% and 0.5%.

[0046] The B element plays a role in increasing hardenability, improving density and hot rolling performance, and increasing strength. When the B element content exceeds 70PPM, the steel will easily become brittle, so the B element content is controlled at about 5-60PPM.

[0047] The process window conditions for manufacturing hot-rolled coils for 896MPa-grade straight seam resistance welded casing for shale gas wells are as follows: during the high-temperature hot rolling process, the heating furnace is heated to 1170-1210°C and the holding time is 1 hour to ensure uniform heating, promote austenite homogenization and sufficient solid solution of micro-alloying elements such as MO and Si in the austenite, while also avoiding excessive coarsening of austenite grains; the final rolling temperature is 830-870°C to avoid coarsening of austenite grains caused by excessively high final rolling temperature; the rolled steel plate is cooled under controlled conditions before coiling, and the coiling temperature is 550-650°C. A gradient controlled cooling method is adopted to ensure the processing performance of the coiled plate.

[0048] The 896MPa-grade hot-rolled coil for straight seam resistance welded casing of shale gas wells meets the yield strength of 300-600MPa, elongation ≥20%, and transverse impact energy ≥40J at 0°C, meeting the requirements for room-temperature asymptotic forming control of the coil; the grain size complies with ASTME112NO.9 or finer, and the banded structure ≤3.0, meeting the requirements for welding stability and quality control.

[0049] The SEW process is adopted for pipe making, and the pipe is quenched by internal spraying at a heating temperature of 860-920℃ and holding time of 25-50 minutes, and then tempered by heating temperature of 510-570℃ and holding time of 50-100 minutes. This ensures that the performance requirements of shale gas well casing pipe are met, such as yield strength of 900-960MPa and Charpy impact energy of 130-220J.

[0050] Secondly, according to the limited manufacturing conditions, after optimizing the composition through material genetic engineering, the composition design and mechanical properties of the hot-rolled coil were obtained by calculation, thus achieving the welding performance of the hot-rolled coil for 896MPa-grade shale gas well straight seam electric resistance welding casing.

[0051] The calculation steps of material genetic engineering are as follows:

[0052] Step 1: Apply first principles (KS-DFT) to predict and calculate macroscopic properties. According to the basic idea of ​​KS-DFT, the solution of density functional principle based on the numerical expression of carbon equivalent can be given by the following equation:

[0053]

[0054] in, is the Hamiltonian of the system, ψ is the wave function of the system, represents the reduced Planck constant, m is the mass of the system, is the Laplace gradient operator of the system in the rectangular coordinate system, is a commonly used central system potential function expression. For this calculation system, the process flow is: coil forming - welding - quenching and tempering heat treatment. The input of the first-principles calculation is the content of each element (C, Mn, Cr, Mo, Si, B), with the carbon equivalent composition as a boundary condition and a carbon equivalent constraint of less than 0.5. The Hamiltonian can be constructed based on the elemental composition, and then the energy band and wave function characteristics can be calculated using first-principles calculations, thereby predicting its mechanical properties.

[0055] Step 2: Combined with the principles of molecular dynamics, further calculate its macroscopic mechanical properties. For this calculation system, the input values ​​can be the system energy band and wave function characteristics obtained by the first principles. Through a large number of step simulations, the software can output macroscopic mechanical properties such as strength-toughness and tensile strength. The basic principle of the molecular dynamics algorithm can be given by the following formula:

[0056]

[0057] Where m is the mass of the system, a is the acceleration of the system, and F(x(t)) represents the function of the force acting on the system relative to the displacement. The Laplace operator represents potential energy. The core algorithm of molecular dynamics is to solve multiple differential equations like this and perform iterative operations to obtain the macroscopic mechanical properties of the system.

[0058] Step 3: Determine whether the calculation results of material genetic engineering meet the welding performance requirements of 896MPa-grade hot-rolled coil for straight seam electric resistance welded casing of shale gas wells. If so, process treatment is performed; if not, the distribution ratio is modified for calculation until the welding performance requirements are met and process treatment is performed.

[0059] like Figure 2 As shown, through material genetic engineering simulation calculations, the hot-rolled coil composition design, room-temperature yield strength and toughness after hot rolling, weldability, quenching and tempering heat treatment process, and room-temperature yield strength and toughness after quenching and tempering are obtained, which serve the optimization and verification of the hot-rolled coil composition and manufacturing process, so that the component ratio matches the strength and toughness of the hot-rolled coil for 896MPa-grade shale gas well straight seam electric resistance welded casing and the narrow process window of the plastic toughness of the welded pipe.

[0060] Finally, based on the output hot-rolled coil composition design and mechanical properties of the hot-rolled coil, the process flow for manufacturing 896MPa grade hot-rolled coil for shale gas well straight seam electric resistance welded casing is as follows:

[0061] The process adopts a series of operations including converter rough refining, refining outside the furnace, slab continuous casting, high temperature hot rolling, and controlled cooling after rolling. The specific steps are as follows:

[0062] Step 1: Iron and steel materials are put into the furnace, and argon is used for low-pressure blowing in the converter and ladle. During the refining process, ferrosilicon, metallic manganese, and low-carbon ferrochrome are used to fine-tune the composition. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate. The molten steel enters the crystallizer through the tundish and is cooled by the fan-shaped section to form a cast slab.

[0063] Step 2: The cast slab containing the calculated chemical composition mass percentage is converted into a hot-rolled slab, wherein during heating, the continuous casting slab is placed in a heating furnace for heating, and the temperature of the continuous casting slab out of the furnace is controlled to be 1170-1210° C., and the initial continuous casting slab thickness is 230 mm;

[0064] Step 3: The continuous casting slab obtained in step 2 is subjected to seven-stand continuous rolling with a cumulative deformation of ≥ 60%. The cumulative large deformation increases the deformation band and dislocation density in the deformed austenite, increases the phase deformation nucleus points, and refines the grains. The finishing rolling temperature is controlled at 830-870°C to obtain a steel plate with a thickness of 10-13 mm.

[0065] The heating temperature of the heating furnace in the rolling process is 1170-1210° C., and the holding time is 1 hour to ensure uniform heating, promote austenite homogenization and sufficient solid solution of micro-alloying elements such as MO and Si in the austenite, while also avoiding excessive coarsening of the austenite grains; the final rolling temperature is 830-870° C. to avoid coarsening of the austenite grains caused by too high a final rolling temperature.

[0066] Step 4: After the rolled steel plate is cooled, it is coiled. The coiling temperature is 550-650°C. Gradient cooling is used to ensure the toughness of the coil while reducing the formation of banded structure, thereby ensuring good processing performance of the coil.

[0067] A hot-rolled coil for 896MPa-grade straight seam electric resistance welded casing for shale gas wells has a carbon equivalent of less than 0.5 and excellent weldability. After being manufactured using the SEW process, the 896MPa-grade shale gas well casing can be obtained through appropriate quenching and tempering treatment to achieve a yield strength of 900-960MPa and a Charpy impact energy of 130-220J.

[0068] Through the quenching treatment of heating temperature to 860-920℃, holding time for 25-50 minutes by internal spraying, and tempering treatment by heating temperature to 510-570℃, holding time for 50-100 minutes, the performance requirements of shale gas well casing material yield strength of 900-960MPa and Charpy impact energy of 130-220J are guaranteed.

[0069] The corresponding relationship between quenching time and tempering time ensures the feasibility of the actual working conditions of the production line; the lower limit of the tempering temperature of 510℃ is adopted to ensure the online smoothness of the actual production process from the tempering process to the hot straightening process, and meet the temperature drop control requirements of the final minimum temperature of hot straightening (400℃).

[0070] This 896MPa-grade hot-rolled coil for straight-seam electric resistance welded casing in shale gas wells is composed of the following components by mass: C: 0.12%-0.22%, Mn: 1.0%-1.6%, Cr: 0.4%-0.6%, Mo: 0.3%-0.5%, Si: 0.05%-0.6%, with approximately 5-60 parts per million (ppm) of added boron. The carbon equivalent is less than 0.5, with the remainder consisting of Fe and unavoidable inclusions. The process involves a series of operations: converter refining, external refining, slab continuous casting, high-temperature hot rolling, and controlled cooling after rolling.

[0071] Example 1: Rolling 11.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells

[0072] A steel billet composed of the following components in percentage by mass: C: 0.17%, Si: 0.065%, Mn: 1.21%, Cr: 0.34%, Mo: 0.39%, B: 0.0020%, with the remainder being Fe and inevitable impurities;

[0073] The rationality of the component design is verified by calculation. First, the mass of the system of each component is calculated according to the percentage coefficient, and the wave function characteristics of the system are obtained using the first principles. Then, through molecular dynamics, the differential equation is solved according to the onlooker force of the system to predict the deformation resistance of the material within the elastic deformation range and the plastic deformation range. The yield strength and tensile strength of the material of the component system are obtained, which meet the design requirements.

[0074] The preparation steps are as follows:

[0075] Argon is used for low-pressure blowing in the converter and ladle. Ferrosilicon, metallic manganese, and low-carbon ferrochrome are used during the refining process to fine-tune the composition. Ferrosilicon powder and aluminum pellets are then deoxidized, and the steel is tapped after reaching the desired temperature and composition. The molten steel enters the crystallizer through the tundish and is cooled in the sectors to form a cast slab.

[0076] The ingot slab containing the calculated chemical composition mass percentage was charged into a heating furnace for heating at 1200°C. After being kept warm in the equalizing section for 1 hour, the ingot was taken out of the furnace for rolling. The starting rolling temperature was 1200°C, the finishing rolling temperature was 850°C, the coiling temperature was 630°C, and the ingot was cooled after rolling at a cooling rate of 10°C / s to obtain an 11.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells.

[0077] Figure 3 This is a metallographic photograph of the coil prepared in Example 1. The test method is based on GB / T 13298-2015.

[0078] The microstructure of the above-mentioned 11.5 mm 896 MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells is ferrite + pearlite.

[0079] The mechanical properties of the 11.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells are: at room temperature, Rm is 350MPa, elongation is 35%, transverse impact energy (0℃) is 60J, and banded structure is level 3.0.

[0080] Example 2: Rolling 12.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells:

[0081] A steel billet composed of the following components in percentage by mass: C: 0.16%, Si: 0.064%, Mn: 1.5%, Cr: 0.45%, Mo: 0.42%, B: 0.0013%, with the remainder being Fe and inevitable impurities;

[0082] The rationality of the component design is verified by calculation. First, the mass of the system of each component is calculated according to the percentage coefficient, and the wave function characteristics of the system are obtained using the first principles. Then, through molecular dynamics, the differential equation is solved according to the onlooker force of the system to predict the deformation resistance of the material within the elastic deformation range and the plastic deformation range. The yield strength and tensile strength of the material of the component system are obtained, which meet the design requirements.

[0083] The preparation steps are as follows:

[0084] Argon is used for low-pressure blowing in the converter and ladle. Ferrosilicon, metallic manganese, and low-carbon ferrochrome are used during the refining process to fine-tune the composition. Ferrosilicon powder and aluminum pellets are then deoxidized, and the steel is tapped after reaching the desired temperature and composition. The molten steel enters the crystallizer through the tundish and is cooled in the sectors to form a cast slab.

[0085] The ingot slab containing the calculated chemical composition mass percentage was charged into a heating furnace for heating at 1150°C. After being kept in the equalizing section for 1 hour, the ingot was taken out of the furnace for rolling. The starting rolling temperature was 1150°C, the finishing rolling temperature was 840°C, the coiling temperature was 580°C, and controlled cooling was performed after rolling at a cooling rate of 15°C / s to obtain a 12.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing of shale gas wells.

[0086] Figure 4 This is a metallographic photograph of the coil prepared in Example 2. The test method is based on GB / T 13298-2015.

[0087] The microstructure of the 12.5 mm 896 MPa grade hot-rolled coil for straight seam electric resistance welded casing for shale gas wells is ferrite + granular bainite, with a bainite content of approximately 43%.

[0088] The mechanical properties of the above-mentioned 12.5mm 896MPa grade hot-rolled coil for straight seam electric resistance welded casing of shale gas wells are: at room temperature, Rm is 550MPa, elongation is 21%, transverse impact energy (0°C) is 45J, and banded structure is level 2.5.

[0089] At room temperature, the mechanical properties of Example 1 and Example 2 are tested as shown in Table 1.

[0090] Table 1 Mechanical properties test results of examples at room temperature

[0091]

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art may still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing, characterized in that: The following steps are involved: First, based on the required properties of hot-rolled coil for 896MPa-grade shale gas well straight seam electric resistance welded casing, the required elements and the mass percentage range of each element, as well as the manufacturing process window conditions, were defined. Welding performance requirements are as follows: yield strength of 300~600MPa, elongation ≥20%, transverse impact energy ≥40J at 0℃, grain size conforming to ASTM E112 NO.9 or finer, and banded structure ≤3.0 grade; The required elements and the mass percentage ranges of each element are defined as follows: C: 0.12%~0.22%, Mn: 1.0%~1.6%, Cr: 0.4%~0.6%, Mo: 0.3%~0.5%, Si: 0.05%~0.6%, B: 5~60PPM, and the rest is Fe and unavoidable impurities; Process window conditions: During the high-temperature hot rolling process, the heating furnace temperature is 1170-1210°C, and the final rolling temperature is controlled at 830-870°C, resulting in a steel plate thickness of 10-13mm. After rolling, the steel plate is cooled and then coiled, with the coiling temperature being 550-650°C. Secondly, based on the limited manufacturing conditions, material genetic engineering is used to calculate the composition design and mechanical properties of the hot-rolled coil. The specific steps are as follows: S1: The mass percentage of each element is used as the input of the first-principles calculation. The input of the first-principles calculation is the mass percentage of C, Mn, Cr, Mo, Si and B. The carbon equivalent composition is used as the boundary condition, and the carbon equivalent is less than 0.

5. It is input into the calculation system, and the macroscopic characteristics are pre-calculated by applying the first-principles calculation to obtain the system energy band and wave function characteristics. S2, using the system energy band and wave function characteristics as input and combining the principles of molecular dynamics to calculate the mechanical properties of hot-rolled coils; S3: Determine whether the mechanical properties of the hot-rolled coil obtained in S2 meet the welding performance requirements of the hot-rolled coil for 896 MPa-grade shale gas well straight seam electric resistance welded casing. If so, output the hot-rolled coil composition design and the hot-rolled coil mechanical properties. If not, modify the distribution ratio and return to S1 until the welding performance requirements are met, and output the hot-rolled coil composition design and the hot-rolled coil mechanical properties. Finally, the hot rolled coil is manufactured according to the output composition design and mechanical properties of the hot rolled coil.

2. The method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing according to claim 1, characterized in that: In the calculation system of material genetic engineering, the process flow is set as: coil forming-welding-quenching and tempering heat treatment.

3. The method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing according to claim 1, characterized in that: Mechanical properties include room temperature yield strength and toughness after hot rolling, weldability, and room temperature yield strength and toughness after quenching and tempering.

4. The method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing according to claim 1, characterized in that: The production process includes converter rough refining, refining outside the furnace, slab continuous casting, high-temperature hot rolling and controlled cooling after rolling.

5. The method for manufacturing a hot-rolled coil for 896 MPa grade shale gas well straight seam electric resistance welded casing according to claim 4, characterized in that: The production process includes converter roughing, refining outside the furnace, slab continuous casting, high-temperature hot rolling and controlled cooling after rolling. The specific operations are as follows: Step 1: Iron and steel materials are put into the furnace, and argon is used for low-pressure blowing in the converter and ladle. During the refining process, ferrosilicon, metallic manganese, and low-carbon ferrochrome are used to fine-tune the composition. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate. The molten steel enters the crystallizer through the tundish and is cooled by the fan-shaped section to form a cast slab. Step 2: The cast slab containing the calculated chemical composition mass percentage is used as a hot-rolled slab. The initial continuous casting slab thickness is 230 mm. During heating, the continuous casting slab is placed in a heating furnace for heating. The temperature of the continuous casting slab out of the furnace is controlled to be between 1170°C and 1210°C, and the holding time is 1 hour. Step 3: The continuously cast slab obtained in step 2 is subjected to seven-stand continuous rolling, with a cumulative deformation of ≥ 60% and a final rolling temperature controlled at 830-870°C to obtain a steel plate with a thickness of 10-13 mm; Step 4: After the rolled steel plate is cooled, it is coiled. The coiling temperature is 550 ~ 650 ℃. Gradient cooling is used to ensure the toughness of the coil while reducing the formation of banded structure, thereby ensuring good processing performance of the coil.

6. A hot-rolled coil prepared according to the method according to any one of claims 1 to 5 for welding 896 MPa grade shale gas well casing, characterized in that: After pipe making using the straight seam electric resistance welding process, 896 MPa-grade shale gas well casing with a yield strength of 900-960 MPa and a Charpy impact energy of 130-220 J can be obtained through tempering treatment.

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