A pipeline steel plate and a method of manufacturing the same

Abstract

The application relates to a pipeline steel plate and a preparation method thereof. The method comprises the following steps: obtaining a casting blank with a set chemical composition; heating the casting blank, and then rolling to obtain a hot-rolled plate; under the condition of a first cooling speed, first cooling the surface to 1 / 4 of the hot-rolled plate to a first temperature, and under the condition of a second cooling speed, second cooling the core position of the hot-rolled plate to a second temperature to obtain the pipeline steel plate. The application solves the technical problem that the low-temperature fracture toughness of the existing pipeline steel plate is poor.

Description

Technical Field

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

[0002] In recent years, with the continuous increase in global demand for oil and natural gas, there is a need to further improve pipeline transportation efficiency. This has led to the development of steel plates for natural gas pipelines towards higher strength, higher transportation pressure, and larger diameters. However, pipelines often pass through high-altitude and frigid regions, which are characterized by extremely cold climates due to their high altitude or latitude. This presents numerous technical challenges for oil and gas pipeline construction. Low-temperature fracture toughness is one of the key considerations for steel used in pipelines in these high-altitude and frigid regions.

[0003] Currently, the most in-demand pipeline steel on the market is X80M, with thicknesses ranging from 20mm to 33mm. However, increased thickness leads to poor low-temperature fracture toughness in the core. Improving the fracture toughness of the core has become a common challenge for domestic steel mills. Summary of the Invention

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

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

[0006] A cast billet with a set chemical composition is obtained;

[0007] The billet is heated and then rolled to obtain a hot-rolled plate;

[0008] Under a first cooling rate, the surface of the hot-rolled plate is cooled to a first temperature at a position of 1 / 4, and simultaneously, under a second cooling rate, the core of the hot-rolled plate is cooled to a second temperature to obtain a pipeline steel plate.

[0009] Optionally, the specified chemical composition includes: C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti, Cr, Mo, and Fe; wherein, by mass fraction,

[0010] The Cr content is 0.1% to 0.3%, and the Mo content is 0.1% to 0.3%.

[0011] Optionally, the C content is 0.03% to 0.07%, the Si content is 0.2% to 0.4%, and the Mn content is...

[0012] The content of P is 1.60% to 1.80%, the content of S is ≤0.01%, the content of Alt is 0.025% to 0.035%, the content of Ni is 0.1% to 0.2%, the content of Cu is 0.10% to 0.20%, the content of Nb is 0.035% to 0.055%, and the content of Ti is 0.002% to 0.015%.

[0013] Optionally, the first cooling rate is 20℃ / s to 25℃ / s.

[0014] Optionally, the first temperature is 450℃~550℃.

[0015] Optionally, the second cooling rate is 15°C / s to 20°C / s.

[0016] Optionally, the second temperature is 540℃~610℃.

[0017] Optionally, the rolling process includes roughing and finishing; wherein,

[0018] The initial rolling temperature of the roughing mill is 1160–1200℃, and the final rolling temperature of the roughing mill is 980℃–1040℃; and / or

[0019] or,

[0020] The initial rolling temperature of the finishing mill is 830–850°C, and the final rolling temperature of the finishing mill is 790–820°C.

[0021] Optionally, the heating temperature is 1200℃~1250℃.

[0022] Secondly, this application provides a pipeline steel plate, which is prepared by the method described in any embodiment of the first aspect.

[0023] The technical solutions provided in this application have the following advantages compared with the prior art:

[0024] The pipeline steel plate preparation method provided in this application uses a cast billet with a set chemical composition to improve the hardenability of the steel plate and enhance the cooling conduction capacity of the core. A suitable cooling process is employed to obtain the target microstructure. Precise control of different final cooling temperatures and cooling rates along the thickness direction (from the surface to 1 / 4 of the steel plate and the core) further ensures the uniformity of the microstructure along the thickness direction and the degree of cooling in the core. This makes the microstructure uniform in the core area, the weakest point in low-temperature fracture toughness, thereby improving the overall low-temperature fracture toughness of the steel plate along the thickness direction. This solves the technical problem of poor low-temperature fracture toughness in existing pipeline steel plates. Attached Figure Description

[0025] 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.

[0026] 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.

[0027] Figure 1 This is a schematic flowchart illustrating a method for preparing a pipeline steel plate according to an embodiment of this application. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] 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, 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 existing alone, A and B existing simultaneously, or B existing alone. Here, A and B can be singular or plural.

[0031] 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.

[0032] Figure 1 A schematic flowchart illustrating a method for preparing a pipeline steel plate according to an embodiment of this application; please refer to... Figure 1 This application provides a method for preparing pipeline steel plates, the method comprising:

[0033] S1. Obtain a cast billet with a set chemical composition;

[0034] In some embodiments, the specified chemical composition includes: C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti, Cr, Mo, and Fe; wherein, by mass fraction,

[0035] The Cr content is 0.1% to 0.3%, and the Mo content is 0.1% to 0.3%.

[0036] In this embodiment, by adding appropriate amounts of Cr and Mo elements, the hardenability of the steel plate is improved, laying the foundation for enhancing the cooling capacity of the core during the cooling process. The chromium (Cr) content is limited. Chromium increases the hardenability of steel and has a secondary hardening effect, enabling the steel plate to effectively conduct cooling capacity during cooling. Excessive Cr content may reduce elongation and reduction of area, and is also detrimental to weldability and low-temperature fracture toughness. Insufficient Cr content may affect the hardenability of the steel plate and may also lead to lower steel plate strength. The molybdenum (Mo) content is also limited. Molybdenum significantly improves the hardenability of the steel plate, especially for larger cross-sections. Excessive Mo may lead to an excessively high carbon equivalent in the steel plate, negatively impacting weldability and toughness. Insufficient Mo may result in insufficient hardenability of the steel plate, leading to insufficient cooling conduction capacity in the core and affecting core quality. The addition of Cr and Mo in combination not only gives the steel plate strong hardenability but also excellent secondary hardening properties, allowing deformation to be better conducted centripetally; while Mo has a better hardenability effect on large-sized cross-sections. The combined addition of these two elements can achieve a synergistic effect of enhancing hardenability and effectively conducting deformation centripetally. For example, the Cr content can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc., and the Mo content can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0037] In some embodiments, the content of C is 0.03% to 0.07%, the content of Si is 0.2% to 0.4%, the content of Mn is 1.60% to 1.80%, the content of P is ≤0.01%, the content of S is ≤0.0030%, the content of Alt is 0.025% to 0.035%, the content of Ni is 0.1% to 0.2%, the content of Cu is 0.10% to 0.20%, the content of Nb is 0.035% to 0.055%, and the content of Ti is 0.002% to 0.015%.

[0038] In this embodiment, carbon (C) is one of the effective elements for improving the strength of steel plates. However, higher carbon content can easily lead to core segregation, which has an adverse effect on the fracture toughness and weldability of the steel plate core. Therefore, the amount of carbon added should be reasonably controlled. For example, the C content can be 0.06%, 0.07%, 0.05%, 0.04%, 0.03%, etc.

[0039] Silicon (Si): Silicon is soluble in ferrite and austenite, which can significantly improve the hardness and strength of steel sheets. However, a high silicon content can reduce the plasticity and toughness of steel and cause grain boundary embrittlement. For example, the Si content can be 0.2%, 0.3%, 0.4%, etc.

[0040] Manganese (Mn): Manganese is a good deoxidizer and desulfurizer. It is a common additive element in steel, which can eliminate or reduce the thermal brittleness of steel caused by sulfur, while improving the strength and hardness of steel plates. However, manganese increases the tendency of steel grain coarsening and temper brittleness, which has a very adverse effect on toughness. For example, the Mn content can be 1.60%, 1.65%, 1.70%, 1.75%, 1.80%, etc.

[0041] Aluminum (Alt): Al is added to steel as a deoxidizer or alloying element, exhibiting stronger deoxidizing ability than silicon and manganese. Furthermore, aluminum can combine with nitrogen to form AlN, refining the grain size and fixing nitrogen in the steel, thereby significantly improving the steel's impact toughness and reducing its tendency for cold brittleness and aging. For example, the Al content can be 0.025%, 0.030%, 0.035%, etc.

[0042] Phosphorus (P): Phosphorus is an impurity element and tends to segregate at grain boundaries, increasing temper brittleness and negatively impacting weldability and fracture toughness. Therefore, a lower content is better. For example, the P content can be 0.01%, 0.009%, or 0.095%.

[0043] Sulfur (S): Sulfur is an impurity element that segregates severely in steel. It is a harmful element that is detrimental to the plasticity and low-temperature toughness of steel plates. The lower the content, the better. For example, the S content can be 0.003%, 0.0028%, 0.0026%, etc.

[0044] Nickel (Ni): Nickel can improve the strength of steel. Statistics show that every 1% increase in nickel content can increase strength by approximately 30 MPa, with minimal impact on toughness, ductility, and other processing properties. Furthermore, nickel can lower the low-temperature ductile-brittle transition temperature of steel, which is highly beneficial for low-temperature toughness. In addition, this element can reduce the critical cooling rate of steel, improve hardenability, and facilitate uniform cooling of the core of thick steel plates. For example, the Ni content can be 0.15%, 0.20%, 0.10%, etc.

[0045] Copper (Cu): Copper can improve the strength of steel plates through precipitation strengthening, etc.; however, excessively high content can be detrimental to hot deformation processing, easily causing copper brittleness during hot working, and also adversely affecting weldability. For example, the Cu content can be 0.10%, 0.15%, 0.20%, etc.

[0046] Niobium (Nb): Niobium can effectively refine grain size, thereby improving strength without affecting the toughness and ductility of steel. Furthermore, due to its grain-refining effect, it can improve the impact toughness of steel and lower its ductile-brittle transition temperature. It also increases the tempering stability of steel and has a secondary hardening effect. However, excessive Nb content can cause the strength of the steel plate to exceed a certain range. For example, the Nb content can be 0.035%, 0.04%, 0.045%, 0.050%, 0.055%, etc.

[0047] Titanium (Ti): Titanium readily combines with carbon to form stable, non-decomposing composite compounds. This not only improves strength but also inhibits grain growth. For example, the Ti content can be 0.002%, 0.004%, 0.006%, 0.008%, 0.010%, 0.012%, 0.015%, etc.

[0048] S2. The billet is heated and then rolled to obtain a hot-rolled plate;

[0049] In some embodiments, the rolling process includes roughing and finishing; wherein,

[0050] The initial rolling temperature of the roughing mill is 1160–1200℃, and the final rolling temperature of the roughing mill is 980℃–1040℃; and / or

[0051] or,

[0052] The initial rolling temperature of the finishing mill is 830–850°C, and the final rolling temperature of the finishing mill is 790–820°C.

[0053] In this embodiment, limiting the starting and ending rolling temperatures of the roughing mill improves the efficiency of deformation transfer to the centripetal region and allows for sufficient recrystallization of austenite, which is beneficial for grain refinement. Limiting the starting and ending rolling temperatures of the finishing mill further refines the grains and allows them to be as close as possible to Ar3, thus facilitating efficient connection between the rolling and cooling processes and shortening the process time. For example, the starting rolling temperature of the roughing mill can be 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, etc.; the ending rolling temperature of the roughing mill can be 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, etc.; the starting rolling temperature of the finishing mill can be 830℃, 840℃, 850℃, etc.; and the ending rolling temperature of the finishing mill can be 790℃, 800℃, 810℃, 820℃, etc. In addition, the rough rolling mentioned above is rolling in the recrystallization zone, and the cumulative deformation in this rough rolling stage reaches more than 40%; the second stage of finishing rolling is rolling in the non-recrystallization zone, and the intermediate thickness is controlled at 1.5 to 2.5 times the thickness of the finished product, and the cumulative deformation in this finishing rolling stage reaches more than 50%.

[0054] In some embodiments, the heating temperature is 1200°C to 1250°C.

[0055] In this embodiment, the heating temperature is limited to ensure sufficient austenitization and control the grain size within a reasonable range, while also ensuring uniform heating of the billet. The heating time is no less than 3 hours. For example, the heating temperature can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, etc.

[0056] S3. Under the condition of the first cooling rate, the surface of the hot-rolled plate to 1 / 4 position is cooled to the first temperature, and under the condition of the second cooling rate, the core position of the hot-rolled plate is cooled to the second temperature to obtain the pipeline steel plate.

[0057] In some embodiments, the first cooling rate is 20°C / s to 25°C / s.

[0058] In some embodiments, the first temperature is 450°C to 550°C.

[0059] In some embodiments, the second cooling rate is 15°C / s to 20°C / s.

[0060] In some embodiments, the second temperature is 540°C to 610°C.

[0061] In this embodiment, the "first cooling rate" refers to the cooling rate at the 1 / 4 position of the steel plate surface. Limiting the cooling rate at this position serves two purposes: firstly, it determines the target microstructure; secondly, a suitable microstructure can further increase the efficiency of deformation propagation towards the center. Excessive cooling rate may result in excessively high steel plate strength and internal stress, affecting impact performance and negatively impacting plate shape control. Conversely, insufficient cooling rate may lead to lower hardness at this point, hindering effective deformation propagation towards the center and impeding fracture toughness improvement. For example, the first cooling rate can be 20℃ / s, 21℃ / s, 22℃ / s, 23℃ / s, 24℃ / s, 25℃ / s, etc.

[0062] "First temperature" refers to the final cooling temperature at one-quarter of the steel plate's surface. This temperature, matched with the cooling rate at this position, works together to achieve the target microstructure, thereby further improving deformation conduction efficiency. If the final cooling temperature is too high or too low, it will be difficult to achieve the target microstructure, thus affecting further grain refinement at the core. For example, this first temperature can be 450℃, 470℃, 490℃, 510℃, 530℃, 550℃, etc.

[0063] "Second cooling rate" refers to the cooling rate at the core of the steel plate, which determines the fine target microstructure. An excessively high cooling rate may lead to excessively high core hardness and stress, adversely affecting toughness; furthermore, it will make plate shape control more difficult. An excessively low cooling rate will result in lower strength. For example, this second cooling rate can be 15℃ / s, 16℃ / s, 17℃ / s, 18℃ / s, 19℃ / s, 20℃ / s, etc.

[0064] The "second temperature" refers to the final cooling temperature of the core area, which, in conjunction with the aforementioned core cooling rate, determines the target microstructure. An excessively high final cooling temperature may result in a coarse core microstructure, poor fracture toughness, and low strength; conversely, an excessively low final cooling temperature may lead to excessive internal stress in the steel plate, hindering the improvement of fracture toughness. For example, this second temperature could be 540℃, 560℃, 580℃, 600℃, or 610℃. The initial cooling temperature of the hot-rolled plate is 770℃~790℃, which, on the one hand, is as close as possible to the phase transformation temperature to obtain the target microstructure; on the other hand, it shortens the waiting time between the cooling and rolling stages, improving production efficiency. After step S3, the hot-rolled plate is air-cooled to room temperature.

[0065] Using the above-mentioned method for preparing pipeline steel plates, the following performance indicators are achieved: thickness 18mm~32mm, yield strength 555~705MPa, tensile strength 625~825MPa, Charpy impact at -40℃ ≥350J, and drop weight DWTT at -15℃ reaching over 95%.

[0066] Based on a general inventive concept, this application provides a pipeline steel plate, which is prepared by the method described in any embodiment of the first aspect.

[0067] The pipeline steel plate is made based on the above-described pipeline steel plate preparation method. The specific steps of the pipeline steel plate preparation method can be referred to the above embodiments. Since the pipeline steel plate adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0068] 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.

[0069] Example

[0070] Producing pipeline steel plates with excellent fracture toughness in 31.5mm diameter. Converter smelting is employed. Table 1 shows the smelting composition, Table 2 shows the rolling process, Table 3 shows the cooling process, and Table 4 shows the mechanical properties.

[0071] Table 1 Smelting composition (wt / %)

[0072] C Si Mn P S Alt Ni Cu Nb Ti Cr Mo Example 1 0.04 0.35 1.60 0.008 0.003 0.030 0.12 0.12 0.035 0.005 0.15 0.20 Example 2 0.07 0.24 1.75 0.007 0.002 0.030 0.20 0.11 0.050 0.010 0.20 0.15 Example 3 0.03 0.3 1.60 0.008 0.002 0.035 0.20 0.14 0.045 0.015 0.15 0.20 Example 4 0.05 0.32 1.65 0.007 0.002 0.025 0.15 0.16 0.035 0.010 0.30 0.30 Example 5 0.06 0.29 1.80 0.007 0.002 0.030 0.17 0.20 0.055 0.007 0.10 0.10

[0073] Table 2 Rolling Process

[0074]

[0075]

[0076] Table 3 Cooling Process

[0077]

[0078] Table 4 Mechanical Properties of Steel Plates

[0079] Yield strength / MPa Tensile strength / MPa Charpy impact energy at -40℃ / J -15℃ Drop Weight DWTT / % Example 1 571 761 385 100 Example 2 593 760 420 100 Example 3 617 775 407 98 Example 4 598 788 429 99 Example 5 635 785 396 100

[0080] Comparative Example

[0081] 31.5mm steel plates were produced using converter smelting. Table 5 shows the smelting composition, without the addition of Cr and Mo elements. Table 6 shows the rolling process. Table 7 shows the post-rolling cooling process. The core cooling process (including final cooling temperature and cooling rate) was not precisely controlled, and the actual measured cooling rate of the steel plate core was less than 15℃ / s, while the final cooling temperature of the core was higher than 600℃. Table 8 shows the mechanical properties.

[0082] Table 5 Smelting composition (wt / %)

[0083]

[0084]

[0085] Table 6 Rolling Process

[0086]

[0087] Table 7 Cooling Process

[0088]

[0089] Table 8 Mechanical Properties of Steel Plates

[0090]

[0091]

[0092] Through Examples 1-5 and in conjunction with Tables 1-4, the pipeline steel plate preparation method of this application achieves the following performance indicators: thickness 18mm-32mm, yield strength 555-705MPa, tensile strength 625-825MPa, Charpy impact strength ≥350J at -40℃, and drop weight DWTT exceeding 95% at -15℃. In contrast, Comparative Examples 1-5, in conjunction with Tables 5-8, did not include Cr or Mo elements, and did not have refined control over the core cooling process (including final cooling temperature and cooling rate). While Comparative Examples 1-5 achieved a yield strength of 555-705MPa and a tensile strength of 625-825MPa, the Charpy impact strength at -40℃ did not reach 350J, and the drop weight DWTT at -15℃ did not reach 95%.

[0093] 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 method for preparing pipeline steel plates, characterized in that, The method includes: A cast billet with a set chemical composition is obtained; The billet is heated and then rolled to obtain a hot-rolled plate; At a cooling rate of 20℃ / s to 25℃ / s, the surface of the hot-rolled plate is cooled to 450℃ to 550℃ at 1 / 4 of its length, while at a cooling rate of 15℃ / s to 20℃ / s, the core of the hot-rolled plate is cooled to 540℃ to 610℃ to obtain a pipeline steel plate. The specified chemical composition includes Cr and Mo, wherein, by mass fraction, the content of Cr is 0.1%~0.25% and the content of Mo is 0.1%~0.25%; The pipeline steel plate has a thickness of 18mm~32mm, a Charpy impact strength of ≥350J at -40℃, and a drop weight DWTT of ≥95% at -15℃.

2. The method according to claim 1, characterized in that, The specified chemical components include: C, Si, Mn, P, S, Alt, Ni, Cu, Nb, Ti, Cr, Mo, and Fe.

3. The method according to claim 2, characterized in that, The content of C is 0.03% to 0.07%, the content of Si is 0.2% to 0.4%, the content of Mn is 1.60% to 1.80%, the content of P is ≤0.01%, the content of S is ≤0.0030%, the content of Alt is 0.025% to 0.035%, the content of Ni is 0.1% to 0.2%, the content of Cu is 0.10% to 0.20%, the content of Nb is 0.035% to 0.055%, and the content of Ti is 0.002% to 0.015%.

4. The method according to claim 1, characterized in that, The rolling process includes roughing and finishing; wherein... The initial rolling temperature of the roughing mill is 1160~1200℃, and the final rolling temperature of the roughing mill is 980℃~1040℃; and / or, The initial rolling temperature of the finishing mill is 830~850℃, and the final rolling temperature of the finishing mill is 790~820℃.

5. The method according to claim 1, characterized in that, The heating temperature is 1200℃~1250℃.

6. A pipeline steel plate, characterized in that, The pipeline steel plate is prepared by the method described in any one of claims 1 to 5.

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