High-grade pipeline steel plate and method for manufacturing the same

Abstract

The application discloses a high-steel-grade pipeline steel plate and a preparation method thereof, and relates to the technical field of steel preparation. The chemical components of the high-steel-grade pipeline steel plate comprise the following components in percentage by weight: C: 0.060-0.10%, Si: 0.2-0.4%, Mn: 1.20-1.50%, P: less than or equal to 0.01%, S: less than or equal to 0.0030%, Alt: 0.025-0.035%, Ni: 0.15-0.25%, Cu: 0.20-0.30%, Nb: 0.055-0.085%, V: 0.015-0.035%, and the balance of Fe and inevitable impurities. The method realizes the target that the high-steel-grade pipeline steel plate has excellent low-temperature fracture toughness by further increasing the reduction in the rolling stage and cooperating with the fine control of the cooling stage without adding Cr, Mo and other elements.

Description

Technical Field

[0001] This application relates to the field of steel plate preparation technology, and in particular to a high-grade pipeline steel plate and its preparation method. Background Technology

[0002] With the continuous rise in oil and gas demand, the demand for oil pipeline construction is still in a growth phase. In pipeline construction projects in western my country, Russia, and Central Asia, the extreme temperatures at compressor stations reach -30 to -40°C, which places higher demands on the low-temperature fracture toughness of pipelines, bends, and fittings operating at these stations. This is especially true for the commonly used X80 steel grade, which has a high strength level but also high sensitivity to low-temperature brittle fracture. Furthermore, as the thickness increases, the fracture toughness of the core becomes a critical technical control point. To ensure the safe operation of pipelines, the low-temperature fracture toughness of pipeline steel must maintain sufficient toughness at extreme temperatures.

[0003] Therefore, in view of the above-mentioned problems, it is necessary to develop a high-grade pipeline steel plate that is suitable for thicker pipes and has better and more stable low-temperature fracture toughness, so as to solve one or more of the above problems, improve the fracture toughness of thick-gauge pipeline steel plates, and improve safety during service. Summary of the Invention

[0004] This application provides a high-strength pipeline steel plate and its preparation method to solve the technical problem of insufficient low-temperature fracture toughness of existing pipeline steel.

[0005] In a first aspect, this application provides a high-grade pipeline steel plate, the chemical composition of which, by weight percentage, includes C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities.

[0006] Optionally, the microstructure of the steel plate includes polygonal ferrite, acicular ferrite and MA islands, with an average grain size of 20μm to 29μm and an average size of 1.5μm to 2.5μm for the MA islands.

[0007] Optionally, the steel plate includes an upper part, a core part, and a lower part. The average grain size of the upper and lower parts is 20μm to 25μm, and the average size of the MA islands is 1.5μm to 2.0μm. The average grain size of the core part is 25μm to 29μm, and the average size of the MA islands is 2.0μm to 2.5μm.

[0008] Optionally, the upper part is located from the upper surface of the steel plate to a position of 1 / 4 thickness, and the lower part is located from the lower surface of the steel plate to a position of 1 / 4 thickness; the core is located between the upper part and the lower part.

[0009] Optionally, the steel plate has a thickness of 18mm to 32mm, a yield strength of 555MPa to 705MPa, a tensile strength of 625MPa to 825MPa, a Charpy impact strength of ≥300J at -40℃, and a drop weight DWTT of ≥95% at -15℃.

[0010] In a second aspect, the present invention provides a method for preparing high-grade pipeline steel plates as described in the first aspect, comprising the following steps:

[0011] The molten steel obtained after smelting has the following chemical composition: C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities;

[0012] The molten steel is continuously cast to obtain a billet;

[0013] The billet is heated and held at a constant temperature, and then subjected to rough rolling, fine rolling and cooling processes to obtain high-grade pipeline steel plates.

[0014] Optionally, the billet is heated to a temperature of 1200℃~1250℃, and the holding time is not less than 3 hours.

[0015] Optionally, the rough rolling is performed in the recrystallization zone, with a target initial rolling temperature of 1160℃~1200℃ and a target final rolling temperature of 980℃~1040℃, during which the cumulative deformation reaches more than 45%; the finish rolling is performed in the non-recrystallization zone, with a target initial rolling temperature of 830℃~850℃ and a target final rolling temperature of 790℃~820℃, and the intermediate thickness is controlled at 1.5~2.5 times the finished product thickness, during which the cumulative deformation reaches more than 50%.

[0016] Optionally, the initial cooling temperature is 770℃~790℃, then the upper and lower parts of the steel plate are cooled to 400℃~500℃, while the core of the steel plate is cooled to 490±10℃~560±10℃, and then air-cooled to room temperature.

[0017] Optionally, the cooling rate of the upper and lower parts of the steel plate is ≥30℃ / s; the cooling rate of the core of the steel plate is 18℃ / s~25℃ / s.

[0018] The technical solution provided by this invention has the following advantages compared with the prior art:

[0019] This invention provides a high-grade pipeline steel plate and its preparation method. Without adding additional elements such as Cr and Mo, this method achieves the goal of the steel plate having excellent low-temperature fracture toughness by further increasing the reduction in the rolling stage and coordinating with refined control of the cooling stage, making it more suitable for low-temperature service environments. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic flowchart of a method for preparing high-grade pipeline steel plates provided in this application;

[0023] Figure 2 The metallographic structure at 1 / 4 of a high-grade pipeline steel plate provided in Embodiment 1 of this application;

[0024] Figure 3 The metallographic structure of the core of a high-grade pipeline steel plate provided in Embodiment 1 of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0027] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely 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. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" 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 both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0029] In a first aspect, this application provides a high-grade pipeline steel plate, the chemical composition of which, by weight percentage, includes C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities.

[0030] The functions of each element and the main processes in this invention are as follows:

[0031] Carbon (C): Carbon is one of the effective elements for improving the strength of steel plates. This element is inexpensive, which helps reduce production costs; it can also effectively improve the strength of steel plates through solid solution strengthening and other methods. However, higher carbon levels can easily lead to core segregation, which adversely affects the fracture toughness and weldability of the steel plate's core. Therefore, the addition of carbon should be minimized, controlling the carbon content between 0.06% and 0.10%, for example, 0.06%, 0.07%, 0.08%, 0.09%, and 0.10%.

[0032] Silicon (Si): Silicon is a common element added to steel plates and is one of the effective elements for improving the strength of steel plates. However, higher silicon levels can cause grain boundary embrittlement and reduce the fracture toughness of the core. Therefore, the silicon content should be controlled between 0.20% and 0.40%, for example, 0.20%, 0.25%, 0.30%, 0.35%, and 0.40%.

[0033] Manganese (Mn): Manganese can improve the strength of steel plates through solid solution strengthening and other methods. Simultaneously, manganese expands the austenite phase region, lowers the phase transformation temperature, and helps obtain a fine microstructure. However, higher manganese levels can easily lead to core segregation, which can also have a very negative impact on the fracture toughness of the core. Therefore, the manganese content should be controlled between 1.20% and 1.50%, for example, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, and 1.50%.

[0034] Phosphorus (P): Phosphorus is an impurity element and tends to segregate at grain boundaries, which is detrimental to fracture toughness and other properties. Therefore, the lower the phosphorus content, the better. Thus, the phosphorus content should be controlled at 0.01% or below, such as 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, or 0.01%.

[0035] Sulfur (S): Sulfur is an impurity element that is very detrimental to low-temperature toughness and other properties; the lower the content, the better. Therefore, the sulfur content should be reduced as much as possible, controlled at 0.003% or below, such as 0.001%, 0.002%, or 0.003%.

[0036] Nickel (Ni): Nickel can increase the strength of steel without reducing its plasticity, and it can also significantly improve the low-temperature fracture toughness of steel. Furthermore, this element can lower the critical cooling rate of steel, improve its hardenability, and facilitate uniform cooling of the core of thick steel plates. Therefore, the nickel content is controlled between 0.15% and 0.25%, for example, choosing 0.15%, 0.18%, 0.20%, 0.23%, and 0.25%.

[0037] Copper (Cu): Copper is an element that expands the austenite phase region. It can improve the strength of steel plates through precipitation strengthening, but excessive content can have an adverse effect on weldability. Therefore, the copper content should be controlled between 0.20% and 0.30%, for example, 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, and 0.30%.

[0038] Niobium (Nb): Niobium can effectively refine grain size, thereby improving strength and toughness. Therefore, the niobium content is controlled between 0.055% and 0.085%, for example, 0.055%, 0.060%, 0.065%, 0.070%, 0.075%, 0.080%, and 0.085%.

[0039] Vanadium (V): Titanium precipitates can improve the strength of steel plates and refine grain size. Furthermore, V can fix nitrogen in steel, which not only improves strength but also benefits low-temperature impact toughness. Therefore, the vanadium content should be controlled between 0.015% and 0.035%, for example, 0.015%, 0.020%, 0.025%, 0.030%, and 0.035%.

[0040] In some embodiments, the microstructure of the steel plate includes polygonal ferrite, acicular ferrite and MA islands, with an average grain size of 20 μm to 29 μm and an average size of 1.5 μm to 2.5 μm for the MA islands.

[0041] In some embodiments, the steel plate includes an upper part, a core part, and a lower part. The average grain size of the upper and lower parts is 20μm to 25μm, and can be 20μm, 21μm, 22μm, 23μm, 24μm, or 25μm. The average size of the MA islands is 1.5μm to 2.0μm, and can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, or 2.0μm. The average grain size of the core part is 25μm to 29μm, and can be, for example, 25μm, 26μm, 27μm, 28μm, or 29μm. The average size of the MA islands is 2.0μm to 2.5μm, and can be, for example, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, or 2.5μm.

[0042] In some embodiments, the upper part is located from the upper surface of the steel plate to a position of 1 / 4 thickness, and the lower part is located from the lower surface of the steel plate to a position of 1 / 4 thickness; the core is located between the upper part and the lower part.

[0043] In some embodiments, the thickness of the steel plate is 18mm to 32mm, such as 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 32mm; the yield strength reaches 555MPa to 705MPa, the tensile strength reaches 625MPa to 825MPa, the Charpy impact at -40℃ is ≥300J, and the drop weight DWTT at -15℃ reaches ≥95%.

[0044] In a second aspect, the present invention provides a method for preparing the high-grade pipeline steel plate described in the first aspect, comprising the following steps:

[0045] The molten steel obtained after smelting has the following chemical composition: C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities;

[0046] The molten steel is continuously cast to obtain a billet;

[0047] The billet is heated and held at a constant temperature, and then subjected to rough rolling, fine rolling and cooling processes to obtain high-grade pipeline steel plates.

[0048] In some embodiments, the temperature for heating the billet is 1200℃~1250℃, for example, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, or 1250℃ can be selected; the holding time is not less than 3 hours.

[0049] In some embodiments, the rough rolling is rolling in the recrystallization zone, with an initial rolling target temperature of 1160℃~1200℃, such as 1160℃, 1170℃, 1180℃, 1190℃, or 1200℃; the final rolling target temperature is 980℃~1040℃, such as 980℃, 1000℃, 1020℃, or 1040℃; the cumulative deformation in this stage reaches more than 45%. The finish rolling is rolling in the non-recrystallization zone, with an initial rolling target temperature of 830℃~850℃, such as 830℃, 835℃, 840℃, 845℃, or 850℃; the final rolling target temperature is 790℃~820℃, such as 790℃, 800℃, 810℃, or 820℃; the intermediate thickness is controlled at 1.5 to 2.5 times the finished product thickness, and the cumulative deformation in this stage reaches more than 50%.

[0050] In some embodiments, the initial cooling temperature is 770°C to 790°C, for example, 770, 775, 780, 785, or 790°C; then the upper and lower parts of the steel plate are cooled to 400°C to 500°C, for example, 400°C, 420°C, 440°C, 460°C, 480°C, or 500°C, while ensuring that the core of the steel plate is cooled to 490±10°C to 560±10°C, and then air-cooled to room temperature.

[0051] In some embodiments, the cooling rate of the upper and lower parts of the steel plate is ≥30℃ / s; the cooling rate of the core of the steel plate is 18℃ / s to 25℃ / s, for example, 18℃ / s, 19℃ / s, 20℃ / s, 21℃ / s, 22℃ / s, 23℃ / s, 24℃ / s, or 25℃ / s.

[0052] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0053] This application provides Examples 1-5 and Comparative Examples 1-5. The smelting composition of the high-grade pipeline steel plates provided in each example and comparative example is shown in Table 1, the rolling process is shown in Table 2, and the cooling process is shown in Table 3.

[0054] Table 1 shows the composition of the high-grade pipeline steel plates provided in Examples 1-5.

[0055]

[0056] Table 2 shows the high-grade pipeline steel plate rolling processes provided in Examples 1-5 and Comparative Examples 1-5.

[0057]

[0058]

[0059] Table 3 shows the cooling processes for high-grade pipeline steel plates provided in Examples 1-5 and Comparative Examples 1-5.

[0060]

[0061] The performance process of the high-grade pipeline steel plate obtained based on the above process data is shown in Table 4 below:

[0062] Table 4 Mechanical properties of high-grade pipeline steel plates in Examples 1-5 and Comparative Examples 1-5

[0063]

[0064] As shown in Table 4, the high-grade pipeline steel plates provided in Examples 1-5 have a yield strength of 555-705 MPa, a tensile strength of 625-825 MPa, a Charpy impact strength of ≥300 J at -40℃, and a drop weight DWTT of over 95% at -15℃. Furthermore, a microstructure scan was performed on the steel plate in Example 1, in which… Figure 2 The microstructure at 1 / 4 of the steel plate is polygonal ferrite + acicular ferrite + MA islands, with an average grain size of 22.5 μm and an average MA island size of 1.8 μm. Figure 3 The microstructure of the steel plate core is polygonal ferrite + acicular ferrite + MA islands, with an average grain size of 28.3 μm and an average MA island size of 2.2 μm.

[0065] In the comparative example, the cumulative deformation during the rough rolling stage did not reach more than 45%, and the cooling rate at the core position during the cooling process did not reach 18℃ / s~25℃ / s, and the final cooling temperature did not reach 490±10℃~560±10℃; the yield strength of the obtained steel plate was 555~705MPa, the tensile strength was 625~825MPa, but the Charpy impact at -40℃ did not reach 300J, and the drop hammer DWTT at -15℃ did not reach 95%.

[0066] The unique aspect of the production process of the high-grade pipeline steel plate in this invention lies in achieving excellent low-temperature fracture toughness of the steel plate without adding additional elements such as Cr and Mo. This is achieved by further increasing the reduction during the rolling stage and combining it with refined control of the cooling stage. The refined control process for the cooling stage is as follows: the initial cooling temperature of the steel plate is 770℃~790℃, then the upper and lower parts are cooled to 400~500℃ at a cooling rate of ≥30℃ / s, while the core area is cooled to 490±10℃~560±10℃ at a cooling rate of 18℃ / s~25℃ / s, and then air-cooled to room temperature. The purpose of this process control is that, under normal circumstances, after the steel plate thickness reaches a certain level, the water cooling effect along the thickness direction is not uniform, especially the cooling capacity conducted to the core is limited, resulting in the core microstructure not reaching the expected microstructure type, thus leading to poor low-temperature fracture toughness. The refined control of the cooling stage focuses on strictly controlling the cooling process of the core, so that the cooling rate and final cooling temperature of the core are consistent with the corresponding process for generating the target tissue type, thus avoiding the phenomenon of poor low-temperature fracture toughness of the core due to an undesirable tissue type.

[0067] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A high-grade pipeline steel plate, characterized in that, Its chemical composition, by weight percentage, includes C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities; the high-strength steel... The preparation method of the pipeline steel plate includes rough rolling, finish rolling, and cooling processes. The cumulative deformation in the rough rolling stage is more than 45%, and the cumulative deformation in the finish rolling stage is more than 50%. The initial cooling temperature is 770℃~790℃, then the upper and lower parts of the steel plate are cooled to 400℃~500℃, while the core of the steel plate is cooled to 490±10℃~560±10℃, and then air-cooled to room temperature. The cooling rate of the upper and lower parts of the steel plate is ≥30℃ / s, and the cooling rate of the core of the steel plate is 18℃ / s~25℃ / s.

2. The high-grade pipeline steel plate according to claim 1, characterized in that, The microstructure of the steel plate includes polygonal ferrite, acicular ferrite and MA islands, with an average grain size of 20μm to 29μm and an average MA island size of 1.5μm to 2.5μm.

3. The high-grade pipeline steel plate according to claim 2, characterized in that, The steel plate comprises an upper part, a core part, and a lower part. The average grain size of the upper and lower parts is 20μm to 25μm, and the average size of the MA islands is 1.5μm to 2.0μm. The average grain size of the core part is 25μm to 29μm, and the average size of the MA islands is 2.0μm to 2.5μm.

4. The high-grade pipeline steel plate according to claim 3, characterized in that, The upper part is the area from the upper surface of the steel plate to 1 / 4 of its thickness, and the lower part is the area from the lower surface of the steel plate to 1 / 4 of its thickness; the core is located between the upper part and the lower part.

5. The high-grade pipeline steel plate according to claim 1, characterized in that, The steel plate has a thickness of 18mm to 32mm, a yield strength of 555 MPa to 705 MPa, a tensile strength of 625 MPa to 825 MPa, a Charpy impact strength of ≥300J at -40℃, and a drop weight DWTT of over 95% at -15℃.

6. The method for preparing high-grade pipeline steel plates according to any one of claims 1-5, characterized in that, Includes the following steps: The molten steel obtained after smelting has the following chemical composition: C: 0.060%–0.10%, Si: 0.2%–0.4%, Mn: 1.20%–1.50%, P ≤ 0.01%, S ≤ 0.0030%, Alt: 0.025%–0.035%, Ni: 0.15%–0.25%, Cu: 0.20%–0.30%, Nb: 0.055%–0.085%, V: 0.015%–0.035%, with the balance being Fe and unavoidable impurities; The molten steel is continuously cast to obtain a billet; The billet is heated and held at a constant temperature, and then subjected to rough rolling, finish rolling and cooling processes to obtain high-grade pipeline steel plates.

7. The preparation method according to claim 6, characterized in that, The billet is heated to a temperature of 1200℃~1250℃, and the holding time is not less than 3 hours.

8. The preparation method according to claim 6, characterized in that, The rough rolling is performed in the recrystallization zone, with a target initial rolling temperature of 1160℃~1200℃ and a target final rolling temperature of 980℃~1040℃; the finish rolling is performed in the non-recrystallization zone, with a target initial rolling temperature of 830℃~850℃ and a target final rolling temperature of 790℃~820℃, and the intermediate thickness is controlled at 1.5~2.5 times the finished product thickness.

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