Coiled tubing steel covering multiple strength levels and preparation method

Abstract

The invention relates to coiled tubing steel covering multiple strength grades and a preparation method, and belongs to the technical field of steel preparation. The steel for the coiled tubing comprises the following chemical components: C, Si, Mn, P, S, Cr, Ni, Cu, Mo, Ti, Nb, B and a matrix element Fe, the mass part of the Cr is 0.20 to 2.00 parts; the mass part of Mo is 0.05 to 0.10 part; the mass part of Nb is less than or equal to 0.01; the mass part of B is less than or equal to 0.0010. On the one hand, the stability of a quenching process window is ensured by selecting medium-carbon steel component design, and on the other hand, alloy elements such as Cr, Ni, Mo and Ti are added to adapt to the special long-continuity and short-time pipe manufacturing characteristics of a coiled tubing production line, so that the adjustment of the steel grade-process temperature (quenching and tempering) correlation slope is realized, and the steel grade coverage is realized to a greater extent.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a steel for continuous oil pipes covering multiple strength levels and a preparation method thereof. Background Art

[0002] Compared with conventional oil pipes that are threaded downhole, coiled tubing is a long oil pipe that is wound on a reel and can be continuously lowered into or pulled out of the well. With the continuous growth of global energy demand and the continuous advancement of oil and gas field mining technology, coiled tubing, as an indispensable and important tool in the process of oil and gas extraction, has increasingly higher performance requirements. Coiled tubing not only needs to withstand extremely high internal and external pressures, but also needs to maintain sufficient toughness and fatigue resistance in complex geological environments. At the same time, in order to meet the needs of different well depths, different geological conditions and different mining processes, coiled tubing needs to have multiple strength levels to adapt to various harsh service environments.

[0003] However, traditional steel for coiled tubing often has problems such as single strength level, insufficient performance, high cost and complex production process. These problems limit the application of coiled tubing in a wider range of fields and increase the cost and risk of oil and gas production. In order to solve these problems, it is particularly important to develop a steel for coiled tubing covering multiple strength levels and a preparation method. Summary of the invention

[0004] The present application provides a steel for a continuous oil pipe covering multiple strength levels and a preparation method thereof, in order to solve the following technical problem: how to meet the market demand for the use of continuous oil pipes covering multiple strength levels.

[0005] In a first aspect, an embodiment of the present application provides a steel for a coiled tubing covering multiple strength levels, wherein the chemical composition of the steel for a coiled tubing includes: C, Si, Mn, P, S, Cr, Ni, Cu, Mo, Ti, Nb, B, and a matrix element Fe;

[0006] The mass fraction of Cr is 0.20 to 2.00 parts;

[0007] The mass fraction of Mo is 0.05 to 0.10 parts;

[0008] The mass fraction of Nb is ≤0.01 part;

[0009] The mass fraction of B is ≤0.0010 parts.

[0010] Optionally, the chemical composition of the steel for the continuous oil pipe includes, by mass fraction: C: 0.16%~0.25%; Si: 0.05%~0.50%; Mn: 0.70%~1.50%; P≤0.015%; S≤0.005%; Cr: 0.40%~1.50%; Ni: 0.10%~0.50%; Cu: 0.20%~0.60%; Mo: 0.05%~0.10%; Ti: 0.010%~0.050%; Nb≤0.01%; B≤0.0010%.

[0011] Optionally, the chemical composition of the steel for the continuous oil pipe includes, by mass fraction: C: 0.16%~0.20%; Si: 0.05%~0.50%; Mn: 0.70%~1.20%; P≤0.015%; S≤0.005%; Cr: 0.55%~1.00%; Ni: 0.10%~0.50%; Cu: 0.20%~0.60%; Mo: 0.05%~0.10%; Ti: 0.010%~0.030%; Nb≤0.01%; B≤0.0010%.

[0012] Optionally, the strength of the steel pipe made of the continuous oil pipe steel covers CT90 to CT150 steel grades.

[0013] Optionally, the microstructure of the steel for the coiled tubing includes ferrite, pearlite and bainite; in the microstructure, the banded structure is ≤level 2.

[0014] In a second aspect, an embodiment of the present application provides a method for preparing the steel for a coiled tubing covering multiple strength levels as described in the first aspect, the method comprising:

[0015] Obtaining a slab having the chemical composition;

[0016] Heating the slab to make it reach the furnace discharge temperature;

[0017] The heated slab is rolled, cooled and coiled in sequence to obtain steel for continuous oil pipe.

[0018] Optionally, the heating time is ≥180 min.

[0019] Optionally, the furnace temperature is 1200°C to 1280°C.

[0020] Optionally, the final rolling temperature is 830°C to 920°C.

[0021] Optionally, the coiling temperature is 450°C to 650°C.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a steel for continuous oil pipes covering multiple strength levels, the chemical composition of the steel for continuous oil pipes includes: C, Si, Mn, P, S, Cr, Ni, Cu, Mo, Ti, Nb, B, and matrix element Fe; the mass fraction of Cr is 0.20 parts to 2.00 parts; the mass fraction of Mo is 0.05 parts to 0.10 parts; the mass fraction of Nb is ≤0.01 parts; the mass fraction of B is ≤0.0010 parts. By selecting the medium-carbon steel composition design, the stability of the quenching process window is ensured. On the other hand, alloying elements such as Cr, Ni, Mo, Ti, etc. are added to adapt to the "long continuous, short time" pipe making characteristics unique to the continuous oil pipe production line, so as to achieve the adjustment of the slope of the steel grade-process temperature (quenching, tempering) correlation, thereby achieving a greater degree of coverage of steel grades. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 A schematic flow chart of a method for preparing steel for coiled tubing covering multiple strength levels provided in an embodiment of the present application;

[0027] Figure 2 A microstructure diagram of a steel for a continuous oil pipe covering multiple strength levels provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0029] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0030] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0031] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0032] In a first aspect, an embodiment of the present application provides a steel for a coiled tubing covering multiple strength levels, wherein the chemical composition of the steel for a coiled tubing includes: C, Si, Mn, P, S, Cr, Ni, Cu, Mo, Ti, Nb, B, and a matrix element Fe;

[0033] The mass fraction of Cr is 0.20 to 2.00 parts;

[0034] The mass fraction of Mo is 0.05 to 0.10 parts;

[0035] The mass fraction of Nb is ≤0.01 part;

[0036] The mass fraction of B is ≤0.0010 parts.

[0037] In some embodiments, the chemical composition of the steel for continuous oil pipe includes, by mass fraction: C: 0.16% to 0.25%; Si: 0.05% to 0.50%; Mn: 0.70% to 1.50%; P≤0.015%; S≤0.005%; Cr: 0.40% to 1.50%; Ni: 0.10% to 0.50%; Cu: 0.20% to 0.60%; Mo: 0.05% to 0.10%; Ti: 0.010% to 0.050%; Nb≤0.01%; B≤0.0010%.

[0038] In some embodiments, the chemical composition of the steel for continuous oil pipe includes, by mass fraction: C: 0.16% to 0.20%; Si: 0.05% to 0.50%; Mn: 0.70% to 1.20%; P≤0.015%; S≤0.005%; Cr: 0.55% to 1.00%; Ni: 0.10% to 0.50%; Cu: 0.20% to 0.60%; Mo: 0.05% to 0.10%; Ti: 0.010% to 0.030%; Nb≤0.01%; B≤0.0010%.

[0039] The multi-steel grade coverage of the continuous oil pipe in this application is mainly achieved by the quenching and tempering process, and the adjustment of chemical composition provides the basis for the implementation of the process. It is mainly manifested in that on the one hand, the medium carbon composition design is adopted to ensure the stability of the quenching process window, and on the other hand, the addition of alloy elements is to adapt to the "long continuous, short time" pipe making characteristics unique to the continuous oil pipe production line, so as to adjust the slope of the steel grade-process temperature (quenching, tempering) correlation, so as to achieve greater coverage of steel grades. "Long continuous" means that the length of a steel pipe can reach 8,000 meters, and the pipe making process should be continuous and uninterrupted. "Short time" means that the heat treatment time is very short, and the austenitization and tempering time does not exceed 5 minutes.

[0040] Cr is one of the main alloying elements in stainless steel, which can increase the corrosion resistance of steel. In coiled tubing steel, 0.20 to 2.00 parts by mass of Cr helps to increase the service life of steel in harsh environments. In high temperature environments, Cr can stabilize the austenite structure of steel, prevent grain boundary weakening or creep, and thus improve the high temperature strength of steel.

[0041] The element Mo can increase the strength and creep resistance of steel at high temperatures, thereby extending the service life of steel in high temperature environments. This is particularly important for the manufacture of coiled tubing that needs to withstand high temperature stress. In addition, Mo can improve the corrosion resistance of steel in certain media, especially the resistance to pitting and crevice corrosion. This is an important performance requirement for coiled tubing that needs to work in harsh environments.

[0042] The positive effect of limiting the mass fraction of Nb to ≤0.01 parts is that by reducing the addition of element Nb, the formation of strong carbide structure is reduced, thereby making it easier to adjust the strength level and broaden the process window.

[0043] The positive effect of limiting the mass fraction of B to ≤0.0010 parts: B can improve the hardenability, but improper use of element B can easily reduce the toughness of steel and increase the risk of cracks. In addition, the coiled tubing is of relatively thin specifications, and the guarantee of hardenability can be fully achieved by adding other alloys.

[0044] C is the most important alloying element in steel materials, which can improve the strength and hardness of steel. As the mass fraction of C increases, the tensile strength and yield strength of steel will increase accordingly. However, the increase in the mass fraction of carbon will also reduce the plasticity and toughness of steel. When the mass fraction of carbon is too high, the steel is prone to brittle fracture when subjected to stress. Too high a mass fraction of carbon will also reduce the welding performance of steel, because defects such as cracks and pores are easily generated during the welding process.

[0045] Elemental Si can dissolve in ferrite and austenite, and improve the strength and hardness of steel through solid solution strengthening. As the silicon content increases, the tensile strength and yield strength of steel will increase accordingly. Si can improve the corrosion resistance of steel, especially in some corrosive media, it can form a dense oxide protective film on the surface of steel to prevent the corrosive medium from corroding the steel.

[0046] Mn is one of the important alloying elements in steel materials, which can significantly improve the strength and hardness of steel. Mn can form a solid solution with iron, and improve the tensile strength and yield strength of steel through solid solution strengthening. The mass fraction of Mn is 0.70% to 1.50%, which is determined according to the specific needs of steel for continuous oil pipes. When the mass fraction of Mn is lower than 0.70%, although the cost of steel can be reduced, the effect of manganese on improving the performance of steel may not be fully exerted. When the mass fraction of Mn exceeds 1.50%, although the strength and hardness of steel can be further improved, it may also cause the toughness of steel to decrease and increase the risk of brittle fracture. In addition, too high a mass fraction of Mn may also affect the welding and processing properties of steel.

[0047] Ni is one of the important elements to improve the corrosion resistance of steel. It can enhance the resistance of steel to a variety of corrosive media, such as acid, alkali, salt, etc. In an environment containing chloride, the element Ni can form a dense oxide protective film, which effectively prevents the corrosion of corrosive media on steel. In addition, the element Ni can increase the strength and creep resistance of steel at high temperatures, thereby extending the service life of steel in high temperature environments, which is particularly important for coiled tubing that needs to withstand high temperature stress. The mass fraction of Ni of 0.10% to 0.50% is determined according to the specific needs of steel for coiled tubing. When the mass fraction of Ni is lower than 0.10%, although the cost of steel can be reduced, the improvement effect of nickel on the performance of steel may not be fully exerted. When the mass fraction of Ni exceeds 0.50%, although the corrosion resistance and high temperature strength of steel can be further improved, the cost will also increase, and the toughness of steel may decrease (although Ni itself can improve toughness, too high a mass fraction of Ni may have adverse interactions with other elements or change the overall microstructure of steel). In addition, too high a mass fraction of Ni may also affect the welding and processing properties of steel.

[0048] The element Cu can enhance the strength and toughness of steel, making it more able to withstand the impact of various external forces. The addition of Cu can make the grains in steel smaller and increase the grain boundary area, thereby improving the hardness and strength of steel. At the same time, Cu can also make the fiber structure in steel denser, further improving the strength of steel.

[0049] Ti is a strong deoxidizer in steel, which can make the internal structure of steel dense, refine grains, reduce aging sensitivity and cold brittleness, and thus improve the welding performance of steel. In addition, Ti easily forms carbides TiC with carbon in steel, and these carbides affect the properties of steel, such as improving hardness and wear resistance.

[0050] P is one of the harmful elements in steel. It will make steel more brittle at low temperatures, which is called cold brittleness. Cold brittleness will cause steel to easily fracture when subjected to stress, which will seriously affect the safety and service life of the steel. In addition, the presence of P will also reduce the welding performance of steel, causing defects such as cracks and pores to easily appear in the weld. This is an important consideration for continuous oil pipes that need to be welded.

[0051] Sulfur usually exists in the form of sulfides in steel. These sulfides easily form low-melting eutectics during the hot working of steel, which leads to hot brittleness of steel during hot working. Hot brittleness reduces the plasticity and toughness of steel, making it prone to fracture. Sulfur also increases the tendency of steel to crack during welding, especially in the heat-affected zone of the weld.

[0052] Fe is a matrix element. The specific content / content range of Fe can be obtained by the upper and lower limit formula of the component, that is:

[0053] The sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit value of other components ≤ 100; the lower limit value of a component + the upper limit value of other components ≥ 100.

[0054] In summary, the coiled tubing steel provided in the embodiment of the present application has the ability to cover multiple strength levels, and its chemical composition has been carefully designed and optimized to meet the needs of different application scenarios. By adjusting the content range of the chemical composition, the mechanical properties of the steel pipe can be accurately controlled to meet different strength levels and performance requirements.

[0055] In some embodiments, the strength of the steel pipe made of the coiled tubing steel covers steel grades of CT90 to CT150.

[0056] CT90 represents the minimum yield strength grade of the continuous tubing, usually expressed in the American strength unit psi (pounds per square inch). Specifically, the minimum yield strength of the CT90 continuous tubing is 90,000 psi, which is equivalent to about 620 MPa. The CT150 steel grade is a high-strength grade in the continuous tubing, representing one of the highest strength grades of continuous tubing products on the market. The strength grade of the CT150 continuous tubing exceeds 1100 MPa, and it has good anti-buckling, anti-torsion and pressure-bearing capabilities, as well as many advantages such as high strength, high pressure bearing and long service life. This high-strength, high-performance continuous tubing is crucial for the exploitation of unconventional oil and gas resources, especially in complex operating environments such as deep wells, ultra-deep wells and horizontal wells. The steel pipe made of the steel for continuous tubing provided in the embodiment of the present application can cover CT90 to CT150 steel grades, which represents that the steel pipe has a wide range of strengths and applications.

[0057] In some embodiments, the microstructure of the steel for coiled tubing includes ferrite, pearlite and bainite; in the microstructure, the banded structure is ≤ level 2.

[0058] Banded structure is a common structural defect in steel, which is usually caused by factors such as component segregation and uneven cooling rate during the rolling or heat treatment of steel. The presence of banded structure will affect the strength and toughness of steel, especially reduce the longitudinal impact toughness, and may produce quenching cracks during heat treatment. Therefore, in steel used for continuous oil pipes, the level of banded structure needs to be strictly controlled. In the embodiment of the present application, according to the standard rating chart, the level of banded structure is ≤ level 2, which means that the degree of banded structure in the steel is relatively light and the impact on the performance of the steel is relatively small.

[0059] In summary, the microstructural characteristics of coiled tubing steel include the presence of ferrite, pearlite and bainite and strict control of banded structure. The optimized combination of these microstructures helps to improve the overall performance of the steel pipe, including strength, toughness, impact resistance and welding performance.

[0060] Figure 1 A schematic flow chart of a method for preparing steel for continuous oil pipes covering multiple strength levels provided in an embodiment of the present application.

[0061] See also Figure 1 In a second aspect, an embodiment of the present application provides a method for preparing the steel for a coiled tubing covering multiple strength levels as described in the first aspect, the method comprising:

[0062] S1, obtaining a slab having the chemical composition;

[0063] The chemical composition of the slab needs to be precisely controlled to meet the multiple strength grade requirements of coiled tubing steel. This includes the content of C (carbon), Si (silicon), Mn (manganese), P (phosphorus), S (sulfur), Cr (chromium), Ni (nickel), Cu (copper), Mo (molybdenum), Ti (titanium), Nb (niobium), B (boron) and the matrix element Fe (iron).

[0064] S2, heating the slab to make the slab reach the furnace discharge temperature;

[0065] The slab is sent into the heating furnace for uniform heating. By accurately controlling the temperature out of the furnace, it can ensure that the steel obtains the ideal heating effect, providing a good foundation for subsequent processes.

[0066] In some embodiments, the heating time is ≥ 180 min.

[0067] In some embodiments, the furnace temperature is 1200°C to 1280°C.

[0068] The temperature out of the furnace is 1200℃~1280℃ to ensure uniform temperature distribution inside the slab. This helps to reduce the temperature gradient during rolling and avoid cracks or deformation of the steel due to uneven heating. The temperature out of the furnace cannot be too high to prevent overheating and overburning of the steel. Overheating will cause the grain boundaries in the steel to become fragile, while overburning will completely destroy the grain structure in the steel, seriously affecting its mechanical properties and service life.

[0069] S3. The heated slab is rolled, cooled and coiled in sequence to obtain steel for continuous oil pipe.

[0070] The heated slab is rolled through a rolling mill to change its shape and size. After rolling, the steel needs to be cooled quickly to inhibit grain growth and improve the strength and toughness of the steel. The cooling method can be selected according to actual needs, such as water cooling, air cooling, etc. The cooled steel is coiled by a coiler to obtain steel for continuous oil pipes.

[0071] In some embodiments, the final rolling temperature of the rolling is 830°C to 920°C.

[0072] During the rolling process, the final rolling temperature must be strictly controlled and maintained within the range of 830℃ ~ 920℃ to ensure that the finishing rolling process is rolled in the non-recrystallization zone and prepare the organization for the subsequent laminar cooling process.

[0073] In some embodiments, the coiling temperature is 450°C to 650°C.

[0074] The positive effect of limiting the coiling temperature to 450℃~650℃ is to ensure the hardness and mechanical property range of the finished strip. If the temperature is too high, there is a risk that the mechanical properties of the strip will exceed the lower limit requirements. If the temperature is too low, there is a risk that the mechanical properties of the strip will exceed the upper limit requirements.

[0075] The preparation method of the steel for continuous oil pipe includes the steps of heating, rolling, cooling and coiling of the slab, and the quality and performance of the steel are ensured by accurately controlling the furnace temperature, the final rolling temperature and the coiling temperature. This steel has a wide range of application prospects in the oil industry, especially in the manufacture of oil pipes that require high strength and good corrosion resistance.

[0076] The product prepared by the method for preparing steel for continuous oil pipes covering multiple strength levels is the above-mentioned steel for continuous oil pipes covering multiple strength levels. Since the method for preparing steel for continuous oil pipes covering multiple strength levels adopts part or all of the technical solutions of the embodiment of steel for continuous oil pipes covering multiple strength levels, it at least has all the beneficial effects brought by the technical solutions of the embodiment of steel for continuous oil pipes covering multiple strength levels, which will not be described one by one here.

[0077] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions or conditions recommended by the manufacturer.

[0078] The molten iron is smelted in a converter or an electric furnace to obtain molten steel, and then the molten steel is continuously cast to obtain a slab with a set chemical composition. The chemical composition of the slab is shown in Table 1.

[0079] Table 1 Chemical composition of slab (wt%), the balance is Fe and unavoidable impurities

[0080] Group C Si Mn Cr Ni Cu Mo Ti P S Nb B Example 1 0.14 0.15 1.30 1.00 0.20 0.30 0.10 0.030 0.0080 0.0010 0.01 0.0006 Example 2 0.20 0.15 0.90 0.70 0.15 0.30 0.08 0.020 0.0095 0.0007 0.005 0.0003 Example 3 0.30 0.15 0.70 0.55 0.20 0.40 0.05 0.010 0.0088 0.0009 0.003 0.0009

[0081] Based on the chemical composition of the slab in the embodiment, this embodiment also provides a method for preparing steel for a coiled tubing covering multiple strength levels, comprising the following steps:

[0082] Obtaining a slab having the chemical composition;

[0083] Heating the slab to make it reach the furnace discharge temperature;

[0084] The heated slab is rolled, cooled and coiled in sequence to obtain steel for continuous oil pipe. Please refer to Table 2 for the preparation process parameters.

[0085] Table 2 Preparation process parameters of coiled tubing steel

[0086]

[0087] It can be seen from Tables 1 to 2 that the chemical composition and preparation process parameters of the examples are within the required range of the present invention, and the strength of the prepared coiled tubing steel meets the CT90 to CT150 steel grade after tubing.

[0088] By comparing the corrosion tests on the finished steel pipes, the average corrosion rate of the steel pipes in the embodiments of the present application is significantly lower than that of the TMCP products of the same steel grade.

[0089] Attached Figure 2 Detailed description:

[0090] Figure 2 A microstructure diagram of a steel for a coiled tubing covering multiple strength levels provided in an embodiment of the present application, such as Figure 2 As shown, the microstructure of coiled tubing steel includes ferrite, pearlite and bainite.

[0091] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0092] After the steel for continuous oil pipe provided in the embodiment of the present invention is processed through the pipe making process, the strength meets the steel grade of CT90 to CT150. The pipe reaches a higher standard in terms of strength performance and can withstand higher pressure and tension, thereby improving mining efficiency.

[0093] The steel pipe for the coiled tubing provided in the embodiment of the present invention has a long service life due to its high strength and good corrosion resistance. Due to the long service life, the frequency of replacing the pipe is reduced, thereby reducing the operating cost.

[0094] The coiled tubing steel provided by the embodiment of the present invention can easily meet the requirements of high strength level while using lower alloy to ensure corrosion resistance, thereby realizing the development of low-cost, corrosion-resistant and high-level coiled tubing products.

[0095] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features applied for by the present application.

Claims

1. A steel for a coiled tubing covering multiple strength levels, the chemical composition of the steel for a coiled tubing comprising: C, Si, Mn, P, S, Cr, Ni, Cu, Mo, Ti, Nb, B, and matrix element Fe; The mass fraction of Cr is 0.20 to 2.00 parts; The mass fraction of Mo is 0.05 to 0.10 parts; The mass fraction of Nb is ≤0.01 part; The mass fraction of B is ≤0.0010 parts.

2. The steel for coiled tubing according to claim 1, characterized in that: The chemical composition of the steel for continuous oil pipe includes, by mass fraction, C: 0.16% to 0.25%; Si: 0.05% to 0.50%; Mn: 0.70% to 1.50%; P≤0.015%; S≤0.005%; Cr: 0.40% to 1.50%; Ni: 0.10% to 0.50%; Cu: 0.20% to 0.60%; Mo: 0.05% to 0.10%; Ti: 0.010% to 0.050%; Nb≤0.01%; B≤0.0010%.

3. The steel for coiled tubing according to claim 1, characterized in that: The chemical composition of the steel for continuous oil pipe includes, by mass fraction, C: 0.16% to 0.20%; Si: 0.05% to 0.50%; Mn: 0.70% to 1.20%; P≤0.015%; S≤0.005%; Cr: 0.55% to 1.00%; Ni: 0.10% to 0.50%; Cu: 0.20% to 0.60%; Mo: 0.05% to 0.10%; Ti: 0.010% to 0.030%; Nb≤0.01%; B≤0.0010%.

4. The steel for coiled tubing according to claim 1, characterized in that: The strength of the steel pipe made of the coiled tubing steel covers steel grades CT90 to CT150.

5. The steel for coiled tubing according to claim 1, characterized in that: The microstructure of the steel for coiled tubing includes ferrite, pearlite and bainite; in the microstructure, the banded structure is ≤level 2.

6. A method for preparing the steel for coiled tubing according to any one of claims 1 to 5, the method comprising: Obtaining a slab having the chemical composition; Heating the slab to make it reach the furnace discharge temperature; The heated slab is rolled, cooled and coiled in sequence to obtain steel for continuous oil pipe.

7. The method according to claim 6, characterized in that The heating time is ≥180 min.

8. The method according to claim 6, characterized in that The furnace temperature is 1200°C to 1280°C.

9. The method according to claim 6, characterized in that The final rolling temperature of the rolling is 830°C to 920°C.

10. The method according to claim 6, characterized in that The coiling temperature is 450°C to 650°C.

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