High-toughness pipeline steel plate and manufacturing method
By optimizing chemical composition and process parameters, high-strength and tough pipeline steel plates with specific microstructure structures were prepared, which solved the problem of poor tissue uniformity along the thickness direction, and achieved good balance between strength and toughness and stable operation under complex stress environments.
Patent Information
- Application Number
- CN202510124753.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-26
- Publication Date
- 2025-05-06
AI Technical Summary
The prior art is difficult to effectively improve the structural uniformity of high-strength grade pipeline steel plates along the thickness direction, affecting their strength and toughness.
By optimizing chemical composition and process parameters, high-strength pipeline steel plates with specific microstructures were prepared. Specific methods include: heating and rolling of the casting billet, controlling the rolling temperature and cooling speed to ensure tissue uniformity along the thickness direction.
The pipeline steel plate is achieved in a good balance between strength and toughness, ensuring its long-term and stable operation under complex stress environments, and meeting the requirements of high yield strength, good low-temperature toughness and hydrogen-induced cracking resistance.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of steel manufacturing, and in particular to a high-strength and toughness pipeline steel plate and a manufacturing method thereof. Background Art
[0002] With the increase in demand for oil and natural gas, it is necessary to improve the transportation efficiency of pipelines, reduce operating costs, and increase transportation pressure, which puts higher requirements on pipeline steel. These demands have led to the development of pipeline steel plates in the direction of thick specifications and high strength. Therefore, it is of great significance to manufacture pipeline steel plates that have both high strength and large thickness and good low-temperature toughness for the safe construction of my country's pipeline projects.
[0003] Microstructure is the decisive factor affecting the strength and toughness of steel plates. However, for thick steel plates, the uniformity of the cross-sectional structure along the thickness direction is difficult to control, which will further affect the strength and toughness of the steel plates, especially for pipeline steel plates with a large demand and a yield strength of 560MPa. Summary of the invention
[0004] The present application provides a high-strength and toughness pipeline steel plate and a manufacturing method to solve the following technical problem: how to improve the structural uniformity of the high-strength grade pipeline steel plate along the thickness direction.
[0005] In a first aspect, an embodiment of the present application provides a high-strength and tough pipeline steel plate, wherein the chemical composition of the pipeline steel plate comprises, by mass fraction: C: 0.060% to 0.10%, Si: 0.2% to 0.4%, Mn: 1.20% to 1.40%, P≤0.01%, S≤0.0030%, Alt: 0.02% to 0.05%, Ni: 0.15% to 0.25%, Nb: 0.015% to 0.035%, Mo: 0.1% to 0.3%, and matrix element Fe;
[0006] Calculated by area fraction, the surface structure of the pipeline steel plate includes: polygonal ferrite: 18% to 24%, granular bainite: 76% to 82%; the core structure of the pipeline steel plate includes: polygonal ferrite: 26% to 32%, granular bainite: 68% to 74%.
[0007] Optionally, the hardness difference of the pipeline steel plate along the thickness direction is <30HV.
[0008] Optionally, the pipeline steel plate meets at least one of the following properties: yield strength>560MPa, DWTT performance at -15°C>95%, and Charpy impact energy at -40°C>350J.
[0009] Optionally, the thickness of the pipeline steel plate is 20 mm to 35 mm.
[0010] In a second aspect, an embodiment of the present application provides a method for preparing the high-strength and toughness pipeline steel plate described in the first aspect, the method comprising:
[0011] Obtaining a casting billet having the chemical composition;
[0012] The ingot is heated and rolled in sequence; wherein the rolling includes rough rolling and finish rolling;
[0013] The rolled ingot is cooled to obtain a target structure type along the thickness direction to obtain a pipeline steel plate.
[0014] Optionally, the heating temperature is 1200° C. to 1250° C., and the heating time is ≥180 min.
[0015] Optionally, the intermediate temperature-waiting thickness of the rolling is 1.5 to 2.5 times the thickness of the pipeline steel plate.
[0016] Optionally, the starting rolling temperature of the rough rolling is 1160°C to 1200°C, and the finishing rolling temperature of the rough rolling is 980°C to 1040°C.
[0017] Optionally, the start rolling temperature of the finishing rolling is 830°C to 850°C, and the final rolling temperature of the finishing rolling is 790°C to 820°C.
[0018] Optionally, the rolled ingot is cooled to obtain a target structure type along the thickness direction to obtain a pipeline steel plate, comprising:
[0019] The rolled ingot is subjected to a first cooling, a first air cooling and a second cooling;
[0020] When the surface temperature of the ingot after the second cooling is less than 350° C. and the core temperature is less than 450° C., the ingot is subjected to a second air cooling to obtain a target microstructure type along the thickness direction to obtain a pipeline steel plate.
[0021] Optionally, the start temperature of the first cooling is 770°C to 790°C, and the cooling rate of the first cooling is 35°C / s to 45°C / s.
[0022] Optionally, after the first cooling, the core temperature of the ingot is 660°C to 680°C.
[0023] Optionally, the first air cooling time is 15s to 20s.
[0024] Optionally, the cooling rate of the second cooling is 15°C / s to 25°C / s.
[0025] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:
[0026] The embodiment of the present application provides a high-strength and toughness pipeline steel plate. The chemical composition of the pipeline steel plate includes, by mass fraction, C: 0.060% to 0.10%, Si: 0.2% to 0.4%, Mn: 1.20% to 1.40%, P≤0.01%, S≤0.0030%, Alt: 0.02% to 0.05%, Ni: 0.15% to 0.25%, Nb: 0.015% to 0.035%, Mo: 0.1% to 0.3%, and matrix element Fe; by area fraction, the surface structure of the pipeline steel plate includes: polygonal ferrite: 18% to 24%, granular bainite: 76% to 82%; the core structure of the pipeline steel plate includes: polygonal ferrite: 26% to 32%, granular bainite: 68% to 74%. By optimizing the organizational structure, the proportion of polygonal ferrite and granular bainite in the surface and core of the pipeline steel plate is within a reasonable range. This specific microstructural feature ensures the uniformity of the organization of the pipeline steel plate along the thickness direction, so that it achieves a good balance between strength and toughness. This balance is crucial for the long-term stable operation of pipeline steel in complex stress environments. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] 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.
[0028] 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.
[0029] Figure 1 A schematic flow chart of a method for preparing a high-strength and tough pipeline steel plate provided in an embodiment of the present application;
[0030] Figure 2 The surface structure diagram of the pipeline steel plate provided in the embodiment of the present application;
[0031] Figure 3 This is a core structure diagram of the pipeline steel plate provided in an embodiment of the present application. DETAILED DESCRIPTION
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] In a first aspect, an embodiment of the present application provides a high-strength and tough pipeline steel plate, wherein the chemical composition of the pipeline steel plate comprises, by mass fraction: C: 0.060% to 0.10%, Si: 0.2% to 0.4%, Mn: 1.20% to 1.40%, P≤0.01%, S≤0.0030%, Alt: 0.02% to 0.05%, Ni: 0.15% to 0.25%, Nb: 0.015% to 0.035%, Mo: 0.1% to 0.3%, and matrix element Fe;
[0037] The chemical composition design of the high-strength and tough pipeline steel plate provided in the embodiment of the present application aims to obtain the comprehensive performance of high strength and good toughness by accurately controlling the content of each alloying element. High-strength pipeline steel plates can be obtained by reasonably controlling the content of elements such as carbon, silicon, and manganese, and adding appropriate amounts of microalloying elements (such as niobium and molybdenum). Strictly controlling the content of harmful elements such as phosphorus and sulfur, while adding appropriate amounts of beneficial elements such as nickel, helps to improve the toughness of pipeline steel plates.
[0038] In the embodiments of the present application, Alt represents total aluminum, that is, the total content of aluminum, including acid-soluble aluminum and acid-insoluble aluminum.
[0039] 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:
[0040] 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.
[0041] Calculated by area fraction, the surface structure of the pipeline steel plate includes: polygonal ferrite: 18% to 24%, granular bainite: 76% to 82%; the core structure of the pipeline steel plate includes: polygonal ferrite: 26% to 32%, granular bainite: 68% to 74%.
[0042] Polygonal ferrite is a relatively soft and tough phase, and its presence helps to improve the plasticity and toughness of the material. In the surface structure of the pipeline steel plate, the proportion of polygonal ferrite is controlled between 18% and 24%. This proportion can ensure that the surface has sufficient toughness without excessively reducing the strength. Exemplarily, in the surface structure of the pipeline steel plate, the proportion of polygonal ferrite can be 18%, 19%, 20%, 21%, 22%, 23%, 24%, etc. Compared with the surface, the proportion of polygonal ferrite in the core has increased, between 26% and 32%. The increase of polygonal ferrite in the core helps to improve the overall toughness and impact resistance of the material. Exemplarily, in the core structure of the pipeline steel plate, the proportion of polygonal ferrite can be 26%, 27%, 28%, 29%, 30%, 31%, 32%, etc.
[0043] Granular bainite is a structure formed by a mixture of intermediate phase bainite and residual ferrite, with high strength and hardness, as well as good toughness. In pipeline steel, granular bainite is usually used as the main strengthening phase. In the surface structure of the pipeline steel plate, the proportion of granular bainite is controlled between 76% and 82%, which can ensure that the surface has sufficient strength while maintaining good toughness. Exemplarily, in the surface structure of the pipeline steel plate, the proportion of granular bainite can be 76%, 77%, 78%, 79%, 80%, 81%, 82%, etc. Compared with the surface, the proportion of granular bainite in the core is slightly reduced, between 68% and 74%. Nevertheless, granular bainite is still the main component of the core structure, which plays an important role in the strength and hardness of the material. The presence of granular bainite in the core helps to ensure that the pipeline steel has sufficient strength reserve when subjected to internal pressure. For example, in the core structure of the pipeline steel plate, the proportion of granular bainite may be 68%, 69%, 70%, 71%, 72%, 73%, 74%, etc.
[0044] The reasonable ratio of polygonal ferrite and granular bainite enables pipeline steel to achieve a good balance between strength and toughness. This balance is crucial for the long-term stable operation of pipeline steel in complex stress environments.
[0045] In summary, the surface and core structure of the pipeline steel plate embodies specific microstructural characteristics, which have an important influence on the mechanical properties and performance of pipeline steel. By optimizing the structure, a good balance between strength and toughness of pipeline steel can be achieved, and its resistance to hydrogen-induced cracking and welding performance can be improved, thereby ensuring the long-term stable operation of pipeline steel in complex stress environments.
[0046] In some embodiments, the hardness difference of the pipeline steel plate along the thickness direction is <30 HV.
[0047] Hardness is the ability of a material to resist deformation due to local pressure, and hardness difference reflects the uniformity of the mechanical properties of the steel plate in the thickness direction. In the embodiment of the present application, the hardness difference of the pipeline steel plate in the thickness direction <30HV means that the steel plate has more consistent mechanical properties in the thickness direction, which is crucial for the safe operation of the pipeline.
[0048] In some embodiments, the pipeline steel plate meets at least one of the following properties: yield strength>560MPa, DWTT performance at -15°C>95%, and Charpy impact energy at -40°C>350J.
[0049] In the embodiment of the present application, the yield strength of the pipeline steel plate is >560MPa, which means that the steel plate needs to have higher mechanical strength.
[0050] The drop weight tear test (DWTT) is an important method for detecting the toughness of materials, and is particularly suitable for studying the low-temperature brittleness of metal materials. In DWTT, a specimen of a certain size is pressed with a special tool steel blade-shaped indenter to form a sharp notch so that a crack source can be formed during impact. Then, the specimen is cooled to a specific temperature (such as -15°C), and is broken at one time with a pendulum or a drop hammer to evaluate the percentage of the shear fracture area of the fracture surface (SA%), and the brittle-toughness properties of the material are judged according to the value of SA%. The higher the value of SA%, the better the toughness of the material, and the more it can resist brittle cracking in a low-temperature environment. The embodiment of the present application performs DWTT at a relatively low temperature of -15°C, aiming to simulate the fracture behavior of the material in an extremely cold environment to evaluate the low-temperature toughness of the material. Exemplarily, the DWTT performance of pipeline steel plates at -15°C can be 95%, 96%, 97%, 98%, 99%, 100%, etc.
[0051] The Charpy impact test is a test method for evaluating the ability of metal materials to resist notch damage under impact loads. The method prepares a metal specimen with a specific shape and size, and makes it have a U-shaped or V-shaped notch, and then impacts the specimen once on a Charpy impact tester to measure the energy absorbed. A large absorbed energy value indicates that the material has good toughness and is insensitive to notches or stress concentration. In a low temperature environment of -40°C, the toughness of the material will be challenged because as the temperature decreases, the brittleness of the material increases and it is more likely to break. In the embodiment of the present application, a Charpy impact test is performed on the material under a low temperature environment of -40°C to evaluate the toughness of the material at low temperatures, that is, its ability to resist fracture. Exemplarily, the -40°C Charpy impact energy of the pipeline steel plate can be 350J, 360J, 370J, 380J, 390J, 400J, etc.
[0052] In some embodiments, the pipeline steel plate has a thickness of 20 mm to 35 mm.
[0053] Figure 1 A schematic flow chart of a method for preparing a high-strength and tough pipeline steel plate provided in an embodiment of the present application.
[0054] See also Figure 1 In a second aspect, an embodiment of the present application provides a method for preparing the high-strength and toughness pipeline steel plate described in the first aspect, the method comprising:
[0055] S1, obtaining a casting billet having the chemical composition;
[0056] Chemical composition design: Ensure that the chemical composition meets the requirements of high-strength and tough pipeline steel plates, including appropriate carbon content, manganese content, and the addition of micro-alloying elements (such as niobium, vanadium, titanium, etc.). Strictly control the content of harmful elements (such as sulfur, phosphorus, etc.) to improve the purity and uniformity of the steel.
[0057] Ingot preparation: Use advanced smelting and continuous casting technology to ensure uniform quality of the ingot, without obvious segregation and inclusions. Control the cooling rate of the ingot to avoid uneven structure caused by too fast or too slow cooling.
[0058] S2, heating and rolling the ingot in sequence; wherein the rolling includes rough rolling and finish rolling;
[0059] Heating: The heating temperature should be moderate, ensuring uniform temperature inside the ingot while avoiding excessively high temperature that causes grain coarsening. The heating rate should be reasonably controlled to avoid excessive temperature gradients that lead to uneven organization. The holding time should be sufficient to ensure uniform temperature distribution inside the ingot.
[0060] Rough rolling: The shape and size of the ingot are adjusted through rough rolling to prepare for the subsequent finishing rolling; the rolling temperature and deformation should be controlled during the rough rolling process to avoid excessive internal stress and uneven structure. Finishing rolling: Finishing rolling is a key step in obtaining high-quality pipeline steel plates; the process parameters of finishing rolling should be accurately controlled to refine the grains and improve the uniformity of the structure; at the same time, the plate shape should be ensured to be good during the finishing rolling process to avoid defects such as waves and bends.
[0061] In some embodiments, the heating temperature is 1200° C. to 1250° C., and the heating time is ≥180 min.
[0062] This step is to ensure that the temperature inside the ingot is uniform and reaches the temperature range required for rolling. For example, the heating temperature can be 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, etc.; the heating time can be 180min, 182min, 184min, 186min, 188min, 190min, etc.
[0063] In some embodiments, the starting rolling temperature of the rough rolling is 1160°C to 1200°C, and the finishing rolling temperature of the rough rolling is 980°C to 1040°C.
[0064] Rough rolling is the initial stage in the steel plate rolling process. Its main purpose is to break the original structure of the ingot by large reduction and prepare the appropriate organizational morphology for the subsequent finishing rolling stage. In this temperature range, the ingot has good plasticity and is easy to deform. It also helps to form ideal structures such as polygonal ferrite and granular bainite. Exemplarily, the starting rolling temperature of rough rolling can be 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, etc.; the final rolling temperature of rough rolling can be 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, etc.
[0065] In some embodiments, the start rolling temperature of the finish rolling is 830°C to 850°C, and the final rolling temperature of the finish rolling is 790°C to 820°C.
[0066] The finishing rolling stage focuses more on the control of the dimensional accuracy and surface quality of the steel plate. Rolling in this lower temperature range helps to further refine the grains of the steel plate and improve the density and uniformity of the organization. At the same time, this temperature range also helps to reduce heat loss during rolling and maintain the temperature stability of the steel plate during rolling. For example, the start rolling temperature of the finishing rolling can be 830°C, 835°C, 840°C, 845°C, 850°C, etc.; the final rolling temperature of the finishing rolling can be 790°C, 795°C, 800°C, 805°C, 810°C, 815°C, 820°C, etc.
[0067] In some embodiments, the intermediate temperature-waiting thickness of the rolling is 1.5 to 2.5 times the thickness of the pipeline steel plate.
[0068] The intermediate warm thickness refers to the thickness of the steel plate maintained after rough rolling and before finishing rolling in the rolling process of metal materials.
[0069] S3, cooling the rolled ingot to obtain a target structure type along the thickness direction to obtain a pipeline steel plate.
[0070] Cooling rate: Selecting the appropriate cooling rate is crucial to obtaining the target tissue type along the thickness direction. Too fast a cooling rate may lead to tissue hardening and embrittlement, while too slow a cooling rate may lead to coarsening and uneven tissue. Cooling method: Depending on the specific material and performance requirements of the pipeline steel plate, you can choose a variety of cooling methods such as water cooling, air cooling, and oil cooling. Water cooling is usually used in situations where rapid cooling is required to obtain hard tissues such as martensite; air cooling is suitable for situations where slower cooling is required to obtain soft tissues such as ferrite + pearlite; oil cooling is between the two. Cooling uniformity: Ensure that the cooling rate of the pipeline steel plate along the thickness direction during the cooling process is uniform to avoid uneven tissue and performance differences.
[0071] In some embodiments, the rolling of the ingot is cooled to obtain a target structure type along the thickness direction to obtain a pipeline steel plate, comprising:
[0072] The rolled ingot is subjected to a first cooling, a first air cooling and a second cooling;
[0073] When the surface temperature of the ingot after the second cooling is less than 350° C. and the core temperature is less than 450° C., the ingot is subjected to a second air cooling to obtain a target microstructure type along the thickness direction to obtain a pipeline steel plate.
[0074] Cooling process is an important link in the heat treatment of steel, especially in the production and processing of steel plates, it directly affects the mechanical properties, organizational structure and final application performance of steel.
[0075] In some embodiments, the first cooling start temperature is 770° C. to 790° C., and the first cooling speed is 35° C. / s to 45° C. / s.
[0076] Cooling at a high temperature of 770°C to 790°C at a cooling rate of 35°C / s to 45°C / s helps to form the desired organizational structure.
[0077] In some embodiments, after the first cooling, the core temperature of the ingot is 660°C to 680°C.
[0078] In some embodiments, the first air cooling time is 15s to 20s.
[0079] When the core temperature of the steel plate drops to 660℃~680℃, a short air cooling is carried out. The purpose of this stage is to slow down the cooling rate so that the internal structure of the steel plate has a "buffer" process, which helps to reduce internal stress and prevent cracks. At the same time, this also helps to control the material structure more evenly and avoid uneven phase change caused by too fast cooling rate.
[0080] In some embodiments, the cooling rate of the second cooling is 15° C. / s to 25° C. / s.
[0081] After intermediate air cooling, the steel plate is cooled again at a slower cooling rate (15℃ / s~25℃ / s). The cooling rate in this stage is slower than that in the initial stage, which helps to further adjust and control the microstructure of the steel plate. Exemplarily, the cooling rate of the second cooling can be 15℃ / s, 17℃ / s, 19℃ / s, 21℃ / s, 23℃ / s, 25℃ / s, etc. When the surface temperature drops below 350℃ and the core temperature drops below 450℃, it means that the steel plate has reached the desired microstructure state, and the cooling rate at this time will not have a significant effect on the performance of the material. At this point, the steel plate is finally air-cooled to room temperature. This stage is mainly to allow the steel plate to slowly cool to room temperature in a natural environment to further release internal stress and ensure the stability of the steel plate performance.
[0082] 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.
[0083] The ingots of Examples 1 to 4 and Comparative Examples 1 to 4 were obtained, and the chemical compositions of the ingots are shown in Table 1.
[0084] Table 1 Chemical composition of the ingot (wt%)
[0085] C Si Mn P S Alt Ni Nb Mo Example 1 0.06 0.25 1.25 0.006 0.003 0.030 0.22 0.015 0.15 Example 2 0.08 0.30 1.35 0.007 0.002 0.030 0.15 0.020 0.1 Example 3 0.08 0.32 1.40 0.008 0.002 0.035 0.17 0.045 0.27 Example 4 0.07 0.37 1.25 0.006 0.002 0.025 0.25 0.025 0.3 Comparative Example 1 0.06 0.25 1.25 0.006 0.003 0.030 0.22 0.015 0.15 Comparative Example 2 0.08 0.30 1.35 0.007 0.002 0.030 0.15 0.020 0.1 Comparative Example 3 0.08 0.32 1.40 0.008 0.002 0.035 0.17 0.045 0.27 Comparative Example 4 0.07 0.37 1.25 0.006 0.002 0.025 0.25 0.025 0.3
[0086] Based on the chemical composition of the ingots in the embodiment and the comparative example, this embodiment also provides a method for preparing a high-strength and tough pipeline steel plate, comprising the following steps:
[0087] Obtaining a casting billet having the chemical composition;
[0088] The ingot is heated and rolled in sequence; wherein the rolling includes rough rolling and finish rolling;
[0089] The rolled ingot is cooled to obtain the target structure type along the thickness direction to obtain a pipeline steel plate. The process parameters of the preparation are shown in Tables 2 and 3.
[0090] Table 2
[0091]
[0092] Table 3
[0093]
[0094] In the comparative example, the rolled ingot is cooled, comprising:
[0095] The initial cooling temperature is 770°C to 790°C, the cooling rate is 20°C / s to 30°C / s, and when the final cooling temperature is 350°C to 450°C, the ingot is air-cooled to room temperature. For specific process parameters, please refer to Table 4.
[0096] Table 4 Cooling process parameters of comparative example
[0097]
[0098]
[0099] The mechanical properties of the pipeline steel plates prepared in the examples and comparative examples were tested. Please see Table 5 for the results.
[0100] Table 5
[0101] Yield strength / MPa Tensile strength / MPa -40℃ Charpy impact energy / J DWTT / % at -15℃ Example 1 577 692 367 98 Example 2 585 705 388 100 Example 3 572 688 398 100 Example 4 583 698 379 97 Comparative Example 1 568 685 115 72 Comparative Example 2 579 708 128 60 Comparative Example 3 581 701 116 55 Comparative Example 4 572 688 135 45
[0102] It can be seen from Tables 1 to 5 that the embodiments have excellent strength-toughness matching, while the comparative example has a Charpy impact energy of less than 200 J at -40°C and a DWTT of less than 75% at -15°C, and does not have an excellent matching of strength and toughness.
[0103] Attached Figure 2-3 Detailed description:
[0104] Figure 2 The surface microstructure of the pipeline steel plate provided in the embodiment of the present application comprises 20% polygonal ferrite and 80% granular bainite; Figure 3 The core structure diagram of the pipeline steel plate provided in the embodiment of the present application includes 29% polygonal ferrite and 71% granular bainite; Figure 2-3 It can be seen that the structure of the pipeline steel plate provided in the embodiment is uniform along the thickness direction.
[0105] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
[0106] The pipeline steel plate in the embodiment of the present invention satisfies at least one of the following properties: yield strength>560MPa, DWTT performance at -15°C>95%, and Charpy impact energy at -40°C>350J.
[0107] The above description 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 the embodiments shown in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.
Claims
1. A high-strength and tough pipeline steel plate, wherein the chemical composition of the pipeline steel plate comprises, by mass fraction: C: 0.060% to 0.10%, Si: 0.2% to 0.4%, Mn: 1.20% to 1.40%, P≤0.01%, S≤0.0030%, Alt: 0.02% to 0.05%, Ni: 0.15% to 0.25%, Nb: 0.015% to 0.035%, Mo: 0.1% to 0.3%, and matrix element Fe; Calculated by area fraction, the surface structure of the pipeline steel plate includes: polygonal ferrite: 18% to 24%, granular bainite: 76% to 82%; the core structure of the pipeline steel plate includes: polygonal ferrite: 26% to 32%, granular bainite: 68% to 74%.
2. The pipeline steel plate according to claim 1, characterized in that: The hardness difference of the pipeline steel plate along the thickness direction is less than 30HV.
3. The pipeline steel plate according to claim 1, characterized in that: The pipeline steel plate meets at least one of the following properties: yield strength>560MPa, DWTT performance at -15°C>95%, and Charpy impact energy at -40°C>350J.
4. The pipeline steel plate according to claim 1, characterized in that: The thickness of the pipeline steel plate is 20 mm to 35 mm.
5. A method for preparing the pipeline steel plate according to any one of claims 1 to 4, the method comprising: Obtaining a casting billet having the chemical composition; The ingot is heated and rolled in sequence; wherein the rolling includes rough rolling and finish rolling; The rolled ingot is cooled to obtain a target structure type along the thickness direction to obtain a pipeline steel plate.
6. The method according to claim 5, characterized in that The heating temperature is 1200° C. to 1250° C., and the heating time is ≥180 min.
7. The method according to claim 5, characterized in that The intermediate temperature-waiting thickness of the rolling is 1.5 to 2.5 times the thickness of the pipeline steel plate.
8. The method according to claim 5, characterized in that The starting rolling temperature of the rough rolling is 1160° C. to 1200° C., and the finishing rolling temperature of the rough rolling is 980° C. to 1040° C.; and / or, The start rolling temperature of the finishing rolling is 830°C to 850°C, and the final rolling temperature of the finishing rolling is 790°C to 820°C.
9. The method according to claim 5, characterized in that The rolled ingot is cooled to obtain a target structure type along the thickness direction to obtain a pipeline steel plate, comprising: The rolled ingot is subjected to a first cooling, a first air cooling and a second cooling; When the surface temperature of the ingot after the second cooling is less than 350° C. and the core temperature is less than 450° C., the ingot is subjected to a second air cooling to obtain a target microstructure type along the thickness direction to obtain a pipeline steel plate.
10. The method according to claim 9, characterized in that The first cooling start temperature is 770° C. to 790° C., and the first cooling speed is 35° C. / s to 45° C. / s; and / or, After the first cooling, the core temperature of the ingot is 660° C. to 680° C.; and / or, The first air cooling time is 15s to 20s; and / or, The cooling rate of the second cooling is 15°C / s to 25°C / s.