Pipeline steel plate and preparation method thereof

Abstract

The invention relates to the technical field of steel preparation, in particular to a pipeline steel plate and a preparation method thereof. The method comprises the following steps: heating a casting blank with set chemical components; performing staged rolling on the heated casting blank to obtain a hot-rolled plate; wherein the step of rolling in stages comprises rough rolling, and technological parameters of the rough rolling are controlled; and cooling the hot-rolled plate to obtain the pipeline steel plate. The technical problem that an existing thick-specification pipeline steel plate is poor in low-temperature fracture toughness is solved. According to the pipeline steel plate, the yield strength is 555-705 MPa, the tensile strength is 625-825 MPa, the Charpy impact at-20 DEG C is larger than or equal to 400 J, and the DWTT at-15 DEG C reaches 95% or above.

Description

Technical Field

[0001] The present application relates to the technical field of steel material preparation, and in particular to a pipeline steel plate and a preparation method thereof. Background Art

[0002] Natural gas has played an effective role in replacing coal in the world's energy transition process and is an important support for the transition period of energy transformation. Under the background of "dual carbon", natural gas will continue to be one of the main carbon reduction forces that cannot be ignored in the next decade. According to the national energy development plan, the proportion of natural gas will increase from 8.8% to 15%. According to the national high-quality development strategic plan, my country's natural gas energy requires further improvement of pipeline safety and transportation efficiency, and pipeline construction will inevitably develop in the direction of high strength, large wall thickness, large diameter and high transportation pressure.

[0003] Low-temperature fracture toughness is the most important technical indicator for gas pipeline steel, and the drop weight tear test (DWTT) performance of the material is a relatively comprehensive and effective indicator for evaluating the low-temperature fracture toughness of pipeline steel. For X80-grade pipeline steel, the thickness is further increased to 33mm. The increase in thickness makes it more difficult to control the deformation penetration of the steel plate during rolling deformation and the uniformity during cooling, which further increases the difficulty of achieving excellent low-temperature toughness. At present, the fracture toughness qualification rate of thick-gauge X80 pipeline steel produced by domestic steel mills is not high, and the production difficulty is extremely great, which has become an industry-wide problem. Summary of the invention

[0004] The present application provides a pipeline steel plate and a preparation method thereof, so as to solve the technical problem that the existing thick-gauge pipeline steel plates have poor low-temperature fracture toughness.

[0005] In a first aspect, the present application provides a method for preparing a pipeline steel plate, the method comprising:

[0006] heating a slab having a set chemical composition;

[0007] The heated ingot is rolled in stages to obtain a hot-rolled plate; wherein the rolling in stages includes rough rolling, and the process parameters of the rough rolling are controlled;

[0008] The hot rolled plate is cooled to obtain a pipeline steel plate.

[0009] Optionally, the process parameters of the rough rolling include: the total deformation of the rough rolling, the deformation of the last pass of the rough rolling, and the interval time between passes of the rough rolling.

[0010] Optionally, the total deformation of the rough rolling is greater than 35%.

[0011] Optionally, the deformation amount of the final rough rolling is not less than 15%.

[0012] Optionally, the interval between passes of the rough rolling is within 20 seconds.

[0013] Optionally, the process parameters of the rough rolling also include:

[0014] The starting rolling temperature of rough rolling and the final rolling temperature of rough rolling;

[0015] The starting rolling temperature of the rough rolling is 1160-1200°C, and / or the finishing rolling temperature of the rough rolling is 980-1040°C.

[0016] Optionally, the heated ingot is rolled in stages to obtain a hot-rolled plate; wherein the staged rolling includes rough rolling, and the process parameters of the rough rolling are controlled, including:

[0017] The heated ingot is rolled in stages to obtain a hot rolled plate; wherein the rolling in stages includes rough rolling and finish rolling, and the process parameters of the rough rolling are controlled.

[0018] The start rolling temperature of the finishing rolling is 830-850°C, and / or the final rolling temperature of the finishing rolling is 790-820°C.

[0019] Optionally, the heating temperature is 1200-1250° C., and the heating time is not less than 180 min;

[0020] The cooling speed is 20-30°C / s, the starting temperature of the cooling is 770-790°C, and the ending temperature of the cooling is 500-600°C.

[0021] Optionally, the setting of chemical composition includes:

[0022] C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti and Fe; among them, in terms of mass fraction,

[0023] The C content is 0.060-0.10%, the Si content is 0.2-0.4%, the Mn content is 1.60-1.80%, the P content is ≤0.01%, the S content is ≤0.0030%, the Alt content is 0.025-0.035%, the Ni content is 0.15-0.25%, the Cu content is 0.20%-0.30%, the Nb content is 0.055-0.085%, and the Ti content is 0.002-0.015%.

[0024] In a second aspect, the present application provides a pipeline steel plate, which is prepared by the method described in any embodiment of the first aspect.

[0025] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0026] The preparation method of the pipeline steel plate provided in the embodiment of the present application is that as the thickness of the steel plate increases, the rolling deformation is difficult to be effectively transmitted to the core, resulting in coarse grains in the core, and thus making it difficult for the strength and fracture toughness of the core to reach the ideal level. By rationally designing the chemical composition and controlling the process parameters of rough rolling to refine the grains, the strength and fracture toughness of the core are improved. This method improves the low-temperature fracture toughness performance of thick-gauge pipeline steel plates, and improves their pass rate and safety during service. 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 embodiments of the present application or the technical solutions in 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 pipeline steel plate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] 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.

[0031] 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, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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 apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0032] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, 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 that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to 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 singular 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, c can be single or plural, respectively.

[0033] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0034] In the first aspect, the present application provides a method for preparing a pipeline steel plate, see Figure 1 , the method comprising:

[0035] S1. heating a casting with a set chemical composition;

[0036] In the embodiment of the present application, a thick specification X80M pipeline steel plate is produced, which involves processes such as smelting, casting into billets, heating of cast billets, rough rolling, finish rolling, and cooling, which are specifically described as follows.

[0037] In some embodiments, the setting of the chemical composition comprises:

[0038] C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti and Fe; among them, in terms of mass fraction,

[0039] The C content is 0.060-0.10%, the Si content is 0.2-0.4%, the Mn content is 1.60-1.80%, the P content is ≤0.01%, the S content is ≤0.0030%, the Alt content is 0.025-0.035%, the Ni content is 0.15-0.25%, the Cu content is 0.20%-0.30%, the Nb content is 0.055-0.085%, and the Ti content is 0.002-0.015%.

[0040] The positive effect of controlling the C content to 0.060-0.10% is that carbon is one of the effective elements for improving the strength of steel plates. This element is low in price and will not bring high production costs; it can also effectively improve the strength of steel plates through solid solution strengthening and other methods. However, higher carbon elements are prone to core segregation, which has an adverse effect on the fracture toughness of the core of the steel plate. Therefore, the addition of carbon elements should be reduced as much as possible to control the carbon content within the above numerical range. Specifically, the C content can be 0.060%, 0.080%, 0.10%, etc.

[0041] The positive effect of controlling the Si content to 0.2-0.4% is that silicon is a common element added to steel plates and is also one of the effective elements for improving the strength of steel plates. However, a higher silicon content will make the grain boundaries embrittled and the fracture toughness of the core worse. Specifically, the Si content can be 0.2%, 0.3%, 0.4%, etc.

[0042] The positive effect of controlling the Mn content to 1.60-1.80% is that the manganese element can improve the strength of the steel plate by solid solution strengthening and other methods. At the same time, the manganese element is an element that expands the austenite phase region, reduces the phase transition temperature, and helps to obtain a fine structure. However, a higher manganese element is prone to core segregation, which will also have a very adverse effect on the fracture toughness of the core. Specifically, the Mn content can be 1.60%, 1.70%, 1.80%, etc.

[0043] The positive effect of controlling the P content to ≤ 0.01% is that phosphorus is an impurity element and is easily segregated at the grain boundary, which is very unfavorable to fracture toughness, etc. The lower the content, the better. Specifically, the P content can be 0.01%, 0.009%, etc.

[0044] The positive effect of controlling the S content to ≤ 0.0030% is that sulfur is an impurity element, which is very unfavorable to low-temperature toughness, etc. The lower the content, the better. Therefore, the sulfur content should be reduced as much as possible. Specifically, the S content can be 0.0030%, 0.0020%, 0.0025%, etc.

[0045] The positive effect of controlling the content of Alt to 0.025-0.035% is that the Alt element is added to the steel as a deoxidizer or alloying element, and its deoxidizing ability is stronger than that of silicon and manganese. Aluminum can combine with N to form AlN, which has the effect of refining grains and can fix nitrogen in steel, thereby significantly improving the impact toughness of steel and reducing cold brittleness and aging tendency; however, too high Al content will have a very adverse effect on welding toughness, etc. Specifically, the content of Alt can be 0.025%, 0.03%, 0.035%, etc.

[0046] The positive effect of controlling the Ni content to 0.15-0.25% is that the nickel element can increase the strength of steel without reducing its plasticity, and can greatly improve the low-temperature fracture toughness of steel. In addition, the element can also reduce the critical cooling rate of steel, improve the hardenability of steel, and facilitate the uniform cooling of the core of thick steel plates. Specifically, the Ni content can be 0.15%, 0.20%, 0.25%, etc.

[0047] The positive effect of controlling the Cu content to 0.20% to 0.30% is that the copper element is an element that expands the austenite phase region, and can improve the strength of the steel plate through precipitation strengthening, etc., but too high a content will have an adverse effect on the welding performance. Specifically, the Cu content can be 0.20%, 0.25%, 0.30%, etc.

[0048] The positive effect of controlling the Nb content to 0.055-0.085% is that niobium can effectively refine the grain size, thereby improving the strength and toughness. Specifically, the Nb content can be 0.055%, 0.070%, 0.085%, etc.

[0049] The positive effect of controlling the Ti content to 0.002-0.015% is that the titanium precipitates can improve the strength of the steel plate and have the effect of refining the grains. Specifically, the Ti content can be 0.002%, 0.01%, 0.015%, etc.

[0050] In some embodiments, the heating temperature is 1200-1250° C., and the heating time is not less than 180 min;

[0051] The positive effect of controlling the heating temperature to 1200-1250°C is: if the heating temperature is too high, it will lead to coarse grains; if the heating temperature is too low, it is not conducive to full austenitization. The positive effect of controlling the heating time to be not less than 180 minutes is: if the heating time is too long, it will also lead to coarse grains, which will have a very adverse effect on the mechanical properties of the steel plate. If the heating time is too short, it will lead to unevenness. Specifically, the heating temperature can be 1200°C, 1230°C, 1250°C, etc., and the heating time can be 180 minutes, 190 minutes, 200 minutes, etc.

[0052] S2, rolling the heated ingot in stages to obtain a hot-rolled plate; wherein the staged rolling includes rough rolling, and controlling the process parameters of the rough rolling;

[0053] In some embodiments, the process parameters of the rough rolling include: a total deformation amount of the rough rolling, a deformation amount of the last pass of the rough rolling, and a pass interval time of the rough rolling.

[0054] In the embodiment of the present application, two-stage rolling is adopted, the first stage is rough rolling, which is also recrystallization zone rolling. Generally, as the thickness of the steel plate increases, the rolling deformation is difficult to be effectively transmitted to the core, resulting in coarse grains in the core, and then making it difficult for the strength and fracture toughness of the core to reach the ideal level. Therefore, the process parameters of the above rough rolling are controlled.

[0055] In some embodiments, the total deformation amount of the rough rolling is greater than 35%.

[0056] The positive effect of controlling the total deformation of rough rolling to be above 35% is that the grains can be effectively refined. If the total deformation of rough rolling is too low, it will cause uneven deformation to a certain extent, which will adversely affect the uniformity of the grain size of the structure. Specifically, the total deformation of rough rolling can be 36%, 37%, 38%, etc.

[0057] In some embodiments, the final deformation amount of the rough rolling is not less than 15%.

[0058] The positive effect of controlling the deformation of the last pass of rough rolling to be not less than 15% is that the last pass of the recrystallization zone is subjected to a large deformation, which is conducive to obtaining a fine austenite structure, providing power for recrystallization, and is conducive to the penetration of deformation into the core and refining the grains. If the deformation of the last pass of the rough rolling is too low, the grain size of the structure along the thickness direction will be uneven to a certain extent, especially the core size will be too large. Specifically, the deformation of the last pass of the rough rolling can be 15%, 16%, 17%, etc.

[0059] In some embodiments, the interval between passes of the rough rolling is within 20 seconds.

[0060] The positive effect of controlling the interval time of rough rolling to within 20s: a shorter interval time can increase the deformation between passes, thereby improving deformation energy storage and further achieving the purpose of grain refinement. If the interval time of rough rolling is too long, the grains will grow and coarsen to a certain extent, which is not conducive to the control of grain size. Specifically, the interval time of rough rolling can be 18s, 16s, etc.

[0061] In some embodiments, the process parameters of the rough rolling further include:

[0062] The starting rolling temperature of rough rolling and the final rolling temperature of rough rolling;

[0063] The starting rolling temperature of the rough rolling is 1160-1200°C, and / or the finishing rolling temperature of the rough rolling is 980-1040°C.

[0064] The positive effect of controlling the starting rolling temperature of the rough rolling to 1160-1200°C is that the rough rolling starts at the time of complete austenitization, and the temperature difference with the initial holding temperature is not large, so as to avoid excessively long waiting time due to cooling. Specifically, the starting rolling temperature of the rough rolling can be 1160°C, 1180°C, 1200°C, etc.

[0065] The positive effect of controlling the final rolling temperature of the rough rolling to 980-1040°C is that the rough rolling stage is completed in the complete austenite region to avoid mixed crystals. Specifically, the final rolling temperature of the rough rolling is 980°C, 1000°C, 1020°C, 1040°C, etc.

[0066] In some embodiments, the heated ingot is rolled in stages to obtain a hot-rolled plate; wherein the staged rolling includes rough rolling, and the process parameters of the rough rolling are controlled, including:

[0067] The heated ingot is rolled in stages to obtain a hot rolled plate; wherein the rolling in stages includes rough rolling and finish rolling, and the process parameters of the rough rolling are controlled.

[0068] The start rolling temperature of the finishing rolling is 830-850°C, and / or the final rolling temperature of the finishing rolling is 790-820°C.

[0069] The second stage is finishing rolling, which is also rolling in the non-recrystallization zone. In this two-stage rolling, the intermediate waiting thickness is controlled at 1.5 to 2.5 times the thickness of the finished product, and the cumulative deformation in this stage reaches more than 60%. The positive effect of controlling the start rolling temperature of finishing rolling to 830 to 850°C is that finishing rolling in the non-recrystallization zone of the steel plate can effectively refine the grains and avoid grain growth and coarsening. Specifically, the start rolling temperature of the rough rolling can be 830°C, 8401°C, 850°C, etc.

[0070] The positive effect of controlling the final rolling temperature of the fine rolling to 790-820°C is that a too high final rolling temperature will cause problems such as insufficient strength, and a too low final rolling temperature will reduce the toughness of the steel plate. Specifically, the final rolling temperature of the rough rolling is 790°C, 820°C, 800°C, 810°C, etc.

[0071] S3. Cooling the hot-rolled plate to obtain a pipeline steel plate.

[0072] The cooling speed is 20-30°C / s, the starting temperature of the cooling is 770-790°C, and the ending temperature of the cooling is 500-600°C.

[0073] The positive effect of controlling the cooling speed to 20-30℃ / s is that the target microstructure type can be obtained; the positive effect of controlling the starting temperature of cooling to 770-790℃ is that the temperature difference with the final rolling temperature is not large, and the waiting time can be shortened; in addition, the strength of the steel plate can be effectively controlled; the positive effect of controlling the ending temperature of cooling to 500-600℃ is that the strength of the steel plate is further controlled to meet the requirements and avoid being too high or too low. Specifically, the cooling speed can be 20℃ / s, 25℃ / s, 30℃ / s, etc., the starting temperature of cooling can be 770℃, 780℃, 790℃, etc., and the ending temperature of cooling can be 500℃, 550℃, 600℃, etc. After cooling, continue air cooling to room temperature.

[0074] In a second aspect, the present application provides a pipeline steel plate, which is prepared by the method described in any embodiment of the first aspect.

[0075] The pipeline steel plate is realized based on the preparation method of the pipeline steel plate mentioned above. The specific steps of the preparation method of the pipeline steel plate can refer to the above embodiment. Since the pipeline steel plate adopts part or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be repeated here one by one.

[0076] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0077] The present application provides a method for preparing a pipeline steel plate, the method comprising:

[0078] S1. heating a casting with a set chemical composition;

[0079] S2, rolling the heated ingot in stages to obtain a hot-rolled plate; wherein the staged rolling includes rough rolling, and controlling the process parameters of the rough rolling;

[0080] S3, cooling the hot rolled plate to obtain a pipeline steel plate. Specific process parameters are shown in Tables 1 to 3, and mechanical properties of pipeline steel are shown in Table 4.

[0081] Table 1 Chemical composition of pipeline steel plate (wt%)

[0082]

[0083]

[0084] Table 2 Rolling process parameters of pipeline steel plate

[0085]

[0086]

[0087] Table 3 Cooling process parameters of pipeline steel plate

[0088] Serial number Start cooling temperature / ℃ Cooling speed / ℃ / s Final cooling temperature / ℃ Example 1 780 22 525 Example 2 790 20 517 Example 3 775 25 553 Example 4 790 24 600 Example 5 785 30 550 Comparative Example 1 780 21 523 Comparative Example 2 790 24 540 Comparative Example 3 775 25 576 Comparative Example 4 790 24 580 Comparative Example 5 785 30 555

[0089] Table 4 Mechanical properties of pipeline steel plates

[0090]

[0091]

[0092] Through the scheme of the embodiment of the present application, a 34mm specification X80M pipeline steel plate is prepared, with a yield strength of 555-705MPa, a tensile strength of 625-825MPa, a -20℃ Charpy impact of ≥400J, and a -15℃ drop hammer DWTT of more than 95%. In the comparative example, the total deformation of rough rolling did not reach more than 35%, and the deformation of the last pass in this stage was less than 15%, and the pass interval time was controlled to exceed 20s; the yield strength was 555-705MPa, and the tensile strength was 625-825MPa, but the -20℃ Charpy impact did not reach 400J, and the -15℃ drop hammer DWTT did not reach 95%.

[0093] 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. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein 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 herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing a pipeline steel plate, characterized in that: The method comprises: heating a slab having a set chemical composition; The heated ingot is rolled in stages to obtain a hot-rolled plate; wherein the rolling in stages includes rough rolling, and the process parameters of the rough rolling are controlled; The hot rolled plate is cooled to obtain a pipeline steel plate.

2. The method according to claim 1, characterized in that The process parameters of the rough rolling include: the total deformation of the rough rolling, the deformation of the last pass of the rough rolling, and the interval time between passes of the rough rolling.

3. The method according to claim 2, characterized in that The total deformation amount of the rough rolling is more than 35%.

4. The method according to claim 2, characterized in that: The final deformation amount of the rough rolling is not less than 15%.

5. The method according to claim 2, characterized in that: The interval between passes of the rough rolling is within 20 seconds.

6. The method according to claim 2, characterized in that The process parameters of the rough rolling also include: The starting rolling temperature of rough rolling and the final rolling temperature of rough rolling; The starting rolling temperature of the rough rolling is 1160-1200°C, and / or the finishing rolling temperature of the rough rolling is 980-1040°C.

7. The method according to claim 1, characterized in that The heated ingot is rolled in stages to obtain a hot rolled plate; wherein the staged rolling includes rough rolling, and the process parameters of the rough rolling are controlled, including: The heated ingot is rolled in stages to obtain a hot rolled plate; wherein the rolling in stages includes rough rolling and finish rolling, and the process parameters of the rough rolling are controlled. The start rolling temperature of the finishing rolling is 830-850°C, and / or the final rolling temperature of the finishing rolling is 790-820°C.

8. The method according to claim 1, characterized in that The heating temperature is 1200-1250°C, and the heating time is not less than 180 minutes; The cooling speed is 20-30°C / s, the starting temperature of the cooling is 770-790°C, and the ending temperature of the cooling is 500-600°C.

9. The method according to claim 1, characterized in that: The set chemical composition includes: C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti and Fe; among them, in terms of mass fraction, The C content is 0.060-0.10%, the Si content is 0.2-0.4%, the Mn content is 1.60-1.80%, the P content is ≤0.01%, the S content is ≤0.0030%, the Alt content is 0.025-0.035%, the Ni content is 0.15-0.25%, the Cu content is 0.20%-0.30%, the Nb content is 0.055-0.085%, and the Ti content is 0.002-0.015%.

10. A pipeline steel plate, characterized in that: The pipeline steel plate is prepared by the method according to any one of claims 1 to 9.

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