A steel for a submarine pipeline and a method for producing the same

Abstract

The application relates to the technical field of steel production, in particular to a steel for submarine pipelines and a preparation method thereof.The method comprises the following steps: heating a casting blank under a set temperature; rolling the heated casting blank and controlling process parameters of the rolling to obtain a hot-rolled plate; under a first set speed, first cooling the hot-rolled plate, and then under a set time, waiting for temperature; wherein the open cooling temperature of the hot-rolled plate and the first final cooling temperature of the hot-rolled plate are controlled; under a second set speed, second cooling the hot-rolled plate after waiting for temperature, so that the hot-rolled plate after waiting for temperature has a second final cooling temperature, and the steel for submarine pipelines is obtained.The application solves the technical problem that the existing steel for submarine pipelines is difficult to simultaneously consider high strength, excellent fracture toughness and high H2S corrosion resistance, thereby improving the service capability and safety of submarine pipelines.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel production, and in particular to a steel for submarine pipelines and a production method thereof. BACKGROUND

[0002] Pipeline transportation of oil and natural gas is considered to be one of the safest, most economical and efficient transportation methods. As onshore oil and gas fields have gradually entered the middle and later stages of exploitation, attention has gradually shifted to the ocean, the polar region and other places with huge potential for oil and gas resources, which have good prospects for exploration. Among them, marine oil and gas resources are mainly distributed on the continental shelf, accounting for about 60% of global marine oil and gas resources, and the oil and gas resources potential in the deep and ultra-deep waters of the continental slope is also considerable, accounting for about 30%. However, due to relatively more severe geological conditions, higher requirements are placed on the comprehensive performance of submarine pipeline steel.

[0003] Submarine pipelines are in a state of motion at any time due to factors such as ocean currents and tides. While bearing the working loads of pipeline self-weight, internal pressure of the pipeline, external water pressure and the like, the pipelines also face the test of environmental loads such as wind, wave, current, surge and even crustal movement, in addition to the complex submarine topography and the scouring action of ocean currents, requiring the submarine pipelines to have high strength and toughness and fracture toughness.

[0004] In addition, wet H2S is one of the common corrosion media in the process of oil and gas exploitation and transportation. The corrosion of steel plates is greatly increased in a service environment containing wet H2S. Land oil and gas resources will be subjected to multiple and deep deacidification and dehydration treatment before concentrated transportation, but even so, it is difficult to completely remove wet H2S. Due to the limitation of operation space, it is difficult to achieve efficient deacidification and dehydration of marine oil and gas before concentrated transportation on land, and in addition to the complexity of marine pipeline working conditions, the submarine pipelines need to have strong H2S corrosion resistance.

[0005] However, with the increase of the diameter and thickness of the steel pipe, great challenges are brought to the production and manufacture of the steel plate. In particular, with the increase of the thickness, the difficulty of uniformity control during the cooling process of the steel plate is further increased, resulting in uneven strain and temperature conduction along the thickness direction of the steel plate, causing uneven structure along the thickness direction, and further causing poor fracture toughness (large fluctuation of low-temperature DWTT drop hammer performance) and H2S corrosion resistance (HIC resistance). SUMMARY

[0006] The present application provides a steel for submarine pipelines and a production method thereof, to solve the technical problem that the existing steel for submarine pipelines cannot simultaneously have high strength, excellent fracture toughness and high H2S corrosion resistance.

[0007] In a first aspect, the present application provides a production method of a steel for submarine pipelines, the method comprising:

[0008] heating the cast slab under a set temperature;

[0009] rolling the heated cast slab and controlling process parameters of the rolling to obtain a hot-rolled plate;

[0010] first cooling the hot-rolled plate under a first set rate, and then tempering under a set time; wherein, the hot-rolled plate is controlled to have a first open cooling temperature and a first final cooling temperature;

[0011] second cooling the tempered hot-rolled plate under a second set rate, so that the tempered hot-rolled plate has a second final cooling temperature, to obtain the steel for submarine pipeline.

[0012] Optionally, the first rate is 10℃ / s-20℃ / s, the hot-rolled plate has a first open cooling temperature of 770℃-790℃, the hot-rolled plate has a first final cooling temperature of 600℃-630℃, and the set time is 8s-12s.

[0013] Optionally, the second set rate is 20℃ / s-30℃ / s, and the second final cooling temperature is 260℃-300℃.

[0014] Optionally, the set temperature is 1200℃-1250℃.

[0015] Optionally, the heated cast slab is rolled, and process parameters of the rolling are controlled to obtain a hot-rolled plate, comprising:

[0016] coarsely rolling the heated cast slab under a first set open rolling temperature and a first set finish rolling temperature;

[0017] finely rolling the coarsely rolled cast slab under a second set open rolling temperature and a second set finish rolling temperature to obtain a hot-rolled plate.

[0018] Optionally, the first set open rolling temperature is 1160℃-1200℃, and / or the first set finish rolling temperature is 980℃-1040℃.

[0019] Optionally, the second set open rolling temperature is 830℃-850℃, and / or the second set finish rolling temperature is 790℃-820℃.

[0020] Optionally, the second set open rolling temperature is 830℃-850℃, and / or the second set finish rolling temperature is 790℃-820℃.

[0021] In a second aspect, the present application provides a steel for submarine pipeline, which is prepared by the method of any one of the first aspect, and the microstructure of the steel comprises:

[0022] polygonal ferrite, acicular ferrite and MA island; wherein,

[0023] The grain size of the structure at the quarter position of the steel is 6-18 mu m, and the grain size of the structure at the core of the steel is 12-30 mu m.

[0024] Optionally, the set chemical composition comprises:

[0025] C, Si, Mn, P, S, Alt, Nb, Ti and Fe; wherein,

[0026] The content of C is 0.08-0.12 wt%, the content of Si is 0.25-0.35 wt%, the content of Mn is 1.25-1.45 wt%, the content of P is ≤0.01 wt%, the content of S is ≤0.003 wt%, the content of Alt is 0.025-0.035 wt%, the content of Nb is 0.045-0.065 wt%, and the content of Ti is 0.035-0.055 wt%.

[0027] Optionally, the performance of the steel plate comprises: the thickness of the steel is ≥30 mm, the yield strength of the steel is 555-705 MPa, the tensile strength of the steel is 625-825 MPa, the Charpy impact at-30℃ of the steel is ≥300 J, the drop weight tear test (DWTT) at-20℃ of the steel is ≥90%, and the hardness difference along the thickness direction of the steel is 20-40 HV.

[0028] The hydrogen-induced cracking resistance of the steel is that the crack length rate (CLR), the crack thickness rate (CTR) and the crack sensitivity rate (CSR) of the steel are all 0.

[0029] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0030] The preparation method of the steel for submarine pipelines provided by the embodiments of the present application controls the hot rolling process of the steel for submarine pipelines, the purpose of which is to make the grain size small and uniform; the cooling process of the steel for submarine pipelines is controlled, the purpose of which is: in the first cooling stage, the temperature is fully conducted from the surface to the core, the temperature distribution is more uniform, the uniformity of the structure along the thickness direction is ensured, the hardness difference along the thickness direction is controlled in a small range, the impact toughness and low-temperature fracture toughness of the core are improved, and the HIC resistance is also improved; the purpose of the second stage cooling is to obtain the target structure type and improve the production efficiency. In summary, the method solves the technical problem that the existing steel for submarine pipelines is difficult to simultaneously have high strength, excellent fracture toughness and high H2S corrosion resistance, thereby improving the service ability and safety of the submarine pipelines. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments consistent with the present application and, together with the description, further serve to explain the principles of the application.

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings required by the embodiments or the prior art description will be briefly introduced as follows. Obviously, those skilled in the art can obtain other drawings from these drawings without any creative effort.

[0033] Figure 1 A flowchart of a preparation method of a steel for a submarine pipeline provided by the embodiments of the present application;

[0034] Figure 2 A typical organization type at a quarter position of a steel for a submarine pipeline provided by the embodiments of the present application;

[0035] Figure 3 A typical organization type at a half position of a steel for a submarine pipeline provided by the embodiments of the present application. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort fall within the scope of the present application.

[0037] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values in 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 in the described range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0038] In the present application, the orientation words such as "upper" and "lower" are specifically the directions of the drawing surface in the drawings unless otherwise stated. In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but not limited to". In the present text, the 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 the entities or operations. In the present text, the "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent: A exists alone, A and B exist together, and B exists alone. Wherein A, B can be singular or plural. In the present text, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0039] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0040] In a first aspect, the present application provides a method for preparing a steel for submarine pipeline, please refer to Figure 1 , the method comprises:

[0041] S1, heating the casting blank under a set temperature;

[0042] S2, rolling the heated casting blank and controlling the process parameters of the rolling to obtain a hot-rolled plate;

[0043] S3, under the condition of a first set rate, the hot-rolled plate is first cooled, and then under the condition of a set time, it is kept warm; wherein the open cooling temperature of the hot-rolled plate and the first final cooling temperature of the hot-rolled plate are controlled;

[0044] S4, under the condition of a second set rate, the hot-rolled plate after keeping warm is second cooled, so that the hot-rolled plate after keeping warm has a second final cooling temperature, to obtain a steel for submarine pipeline.

[0045] Currently, the increase in the diameter and thickness of steel pipes presents significant challenges to steel plate manufacturing. Especially with increased thickness, the difficulty of controlling uniformity during the cooling process further increases, leading to uneven strain and temperature conduction along the thickness direction. This results in uneven microstructure along the thickness direction, consequently causing poor fracture toughness (large fluctuations in low-temperature DWTT drop hammer test performance) and H2S corrosion resistance (HIC resistance). The method for preparing subsea pipeline steel provided in this application controls the hot rolling process to achieve fine and uniform grain size; it also controls the cooling process. The first cooling stage aims to ensure sufficient temperature conduction from the surface to the core, resulting in a more uniform temperature distribution and ensuring microstructure uniformity along the thickness direction. It also controls the hardness difference along the thickness direction within a small range, thereby improving core impact toughness and low-temperature fracture toughness, and also enhancing HIC resistance. The second cooling stage aims to obtain the target microstructure type and improve production efficiency. In summary, this method solves the technical problem that existing steel for subsea pipelines cannot simultaneously achieve high strength, excellent fracture toughness, and high resistance to H2S corrosion, thereby improving the service capability and safety of subsea pipelines.

[0046] In some embodiments, the first rate is 10°C / s to 20°C / s, and the starting cooling temperature of the hot-rolled plate is...

[0047] The first final cooling temperature of the hot-rolled plate is 600℃~630℃, and the set time is 8s~12s. The temperature ranges from 770℃ to 790℃.

[0048] In this embodiment, "first rate" represents the first cooling rate, and "set time" represents the waiting time for the hot-rolled plate. The positive effects of staged cooling of the hot-rolled plate, controlling the first cooling rate to be 10℃ / s to 20℃ / s, the initial cooling temperature to be 770℃ to 790℃, the first final cooling temperature to be 600℃ to 630℃, and the waiting time to be 8s to 12s, are: to ensure sufficient heat conduction from the surface to the core; to make the temperature distribution more uniform, thereby ensuring the uniformity of the microstructure along the thickness direction; and to control the hardness difference along the thickness direction within a small range, thereby improving the core impact toughness and low-temperature fracture toughness, while also improving HIC resistance. If the above values ​​are too high, a large amount of hard phase microstructure will be generated to some extent, which is detrimental to toughness and HIC resistance; if the above values ​​are too low, it will lead to insufficient strength to some extent. Specifically, the first cooling rate can be 10℃ / s, 12℃ / s, 14℃ / s, 16℃ / s, 18℃ / s, 20℃ / s, etc.; the initial cooling temperature of the hot-rolled plate can be 770℃, 780℃, 790℃, etc.; the first final cooling temperature of the hot-rolled plate can be 600℃, 610℃, 620℃, 630℃, etc.; and the waiting time can be 8s, 9s, 10s, 11s, 12s, etc.

[0049] In some embodiments, the second set rate is 20°C / s to 30°C / s, and the second final cooling temperature is...

[0050] 260℃~300℃.

[0051] "Second set rate" refers to the second cooling rate. Controlling the second cooling rate to 20℃ / s to 30℃ / s and the second final cooling temperature of the hot-rolled plate to 260℃ to 300℃ has the following positive effects: cooling to the target area at a suitable cooling rate, obtaining the target microstructure, and improving production efficiency. If the above values ​​are too high, the target microstructure may not be obtained to some extent; if the above values ​​are too low, it may lead to excessive internal stress in the steel plate, impairing its HIC resistance. Specifically, the second cooling rate can be 20℃ / s, 22℃ / s, 24℃ / s, 26℃ / s, 28℃ / s, 30℃ / s, etc.; the second final cooling temperature of the hot-rolled plate can be 260℃, 270℃, 280℃, 290℃, 300℃, etc. After the second cooling, the plate is then air-cooled to room temperature.

[0052] In some embodiments, the set temperature is 1200℃~1250℃.

[0053] The "set temperature" refers to the heating temperature of the slab, and the positive effect of controlling the heating temperature to be 1200-1250°C is to reasonably control the austenite grain size. If the heating temperature is too high, the grains will be coarse to some extent; if the heating temperature is too low, the heating will be uneven to some extent. Specifically, the heating temperature can be 1200°C, 1210°C, 1230°C, 1240°C, 1250°C, etc.

[0054] In some embodiments, the heated slab is subjected to rolling, and the process parameters of the rolling are controlled to obtain a hot-rolled plate, comprising:

[0055] The heated slab is subjected to rough rolling under the condition of a first set roughing temperature and a first set finishing temperature;

[0056] The rough-rolled slab is subjected to finish rolling under the condition of a second set roughing temperature and a second set finishing temperature to obtain a hot-rolled plate.

[0057] The "first set roughing temperature" refers to the roughing temperature of rough rolling, the "first set finishing temperature" refers to the finishing temperature of rough rolling, the "second set roughing temperature" refers to the roughing temperature of finish rolling, and the "second set finishing temperature" refers to the finishing temperature of finish rolling. The intermediate thickness to be controlled is 1.5-2.5 times the finished product thickness.

[0058] In some embodiments, the first set roughing temperature is 1160-1200°C, and / or the first set finishing temperature is 980-1040°C.

[0059] The positive effect of controlling the roughing temperature to be 1160-1200°C is that the austenite is fully austenitized without causing grain coarsening; if the temperature is too high, the grains will be coarse to some extent; if the temperature is too low, the uniformity of the structure will be affected to some extent. Specifically, the roughing temperature can be 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, etc.

[0060] The positive effect of controlling the finishing temperature of rough rolling to be 980-1040°C is to fully refine the grains in the recrystallization zone; if the temperature is too high, the grains will be coarse to some extent, and the standby time before finish rolling will be long, affecting the production efficiency; if the temperature is too low, it will be difficult to ensure the finishing temperature of finish rolling to some extent. Specifically, the finishing temperature of rough rolling can be 980°C, 1000°C, 1020°C, 1040°C, etc.

[0061] In some embodiments, the second set roughing temperature is 830-850°C, and / or the second set finishing temperature is 790-820°C.

[0062] The positive effect of controlling the starting temperature of the finish rolling to be 830-850℃ is to ensure that the steel plate is rolled in the unrecrystallization zone; if the temperature is too high, it will lead to uneven grain size to some extent; if the temperature is too low, it will be difficult to ensure the finish rolling temperature to some extent. Specifically, the starting temperature of the finish rolling can be 830℃, 840℃, 850℃, etc.

[0063] The positive effect of controlling the finish rolling temperature to be 790-820℃ is that the austenite grain size can be effectively controlled; if the temperature is too high, it will lead to coarse grains to some extent; if the temperature is too low, it will be difficult to obtain the target microstructure type to some extent. Specifically, the finish rolling temperature can be 790℃, 800℃, 810℃, 820℃, etc.

[0064] In a second aspect, the present application provides a steel for submarine pipelines, which is prepared by the method of any one of the first aspect, and the microstructure of the steel comprises:

[0065] Polygonal ferrite, acicular ferrite and MA islands; wherein,

[0066] The grain size of the microstructure at the quarter position of the steel is 6-18μm, please refer to Figure 2 The grain size of the microstructure at the core of the steel is 12-30μm, please refer to Figure 3 .

[0067] The role of polygonal ferrite is to effectively improve the hydrogen-induced cracking resistance as a soft phase structure, the role of acicular ferrite is to have good crack arrest, and the role of MA islands is to effectively improve the strength. The positive effect of controlling the grain size of the microstructure at the quarter position of the steel to be 6-18μm is to ensure the strength, toughness and hydrogen-induced cracking resistance. If the grain size is too large, it will reduce the strength and toughness to some extent; if the grain size is too small, it will lead to high steel plate strength to some extent. Specifically, the grain size can be 6μm, 10μm, 14μm, 18μm, etc., and the average grain size at the position is 11μm.

[0068] The positive effect of controlling the grain size of the core microstructure of the steel to be between 12 μm and 30 μm is that it effectively improves resistance to hydrogen-induced cracking. If the grain size is too large, it will impair strength and toughness to some extent, and also have an adverse effect on resistance to hydrogen-induced cracking; if the grain size is too small, it will lead to increased internal stress in the steel plate to some extent, and the hardness difference between the core and other parts of the steel plate will also increase, thus having a very negative impact on resistance to hydrogen-induced cracking. Specifically, the grain size can be 12 μm, 16 μm, 20 μm, 24 μm, 28 μm, 30 μm, etc., with an average grain size of 18 μm at this location.

[0069] In some embodiments, the specified chemical composition includes:

[0070] C, Si, Mn, P, S, Alt, Nb, Ti, and Fe; among which,

[0071] The C content is 0.08 wt% to 0.12 wt%, the Si content is 0.25 wt% to 0.35 wt%, the Mn content is 1.25 wt% to 1.45 wt%, the P content is ≤0.01 wt%, the S content is ≤0.003 wt%, the Alt content is 0.025 wt% to 0.035 wt%, the Nb content is 0.045 wt% to 0.065 wt%, and the Ti content is 0.035 wt% to 0.055 wt%.

[0072] The positive effects of controlling the carbon content to 0.08 wt% to 0.12 wt%: Carbon is one of the effective elements for improving the strength of steel plates. Its addition not only increases the strength of the steel plate but also reduces production costs. However, higher carbon content can easily lead to segregation, which can adversely affect the steel plate's resistance to hydrogen-induced cracking and its hydrogen compatibility. Furthermore, higher carbon content can also negatively impact the weldability, ductility, and impact resistance of the steel plate. Specifically, the carbon content can be 0.08 wt%, 0.09 wt%, 0.10 wt%, 0.11 wt%, 0.12 wt%, etc.

[0073] The positive effects of controlling the Si content to 0.25 wt% to 0.35 wt%: Silicon is also one of the effective elements for improving the strength of steel plates. However, higher silicon content can cause grain boundary embrittlement and deteriorate low-temperature toughness and resistance to hydrogen-induced cracking. Specifically, the Si content can be 0.25 wt%, 0.30 wt%, 0.35 wt%, etc.

[0074] The positive effect of controlling the content of Mn to be 1.25wt%-1.45wt%: Manganese can improve the strength of the steel plate, but higher manganese is prone to segregation and embrittlement, which is not conducive to improving the hydrogen-induced cracking resistance. Specifically, the content of Mn can be 1.25wt%, 1.30wt%, 1.35wt%, 1.40wt%, 1.45wt% and the like.

[0075] The positive effect of controlling the content of P to be ≤0.01wt%: Phosphorus is an impurity element, and is prone to segregation at grain boundaries, which is very detrimental to low-temperature toughness, hydrogen-induced cracking resistance and the like. Specifically, the content of P can be 0.01wt%, 0.009wt%, 0.008wt% and the like.

[0076] The positive effect of controlling the content of S to be ≤0.003wt%: Sulfur is an impurity element, which is easy to combine with Mn to form non-metallic inclusions MnS, which becomes the initiation position of hydrogen-induced cracking, which is very detrimental to low-temperature toughness, hydrogen-induced cracking resistance and the like. Specifically, the content of S can be 0.003wt%, 0.0025wt%, 0.002wt% and the like.

[0077] The positive effect of controlling the content of Alt to be 0.025wt%-0.035wt%: As a deoxidizing element, the dispersed AlN particles formed by combining with nitrogen can prevent austenite grain growth. Specifically, the content of Alt can be 0.025wt%, 0.030wt%, 0.035wt% and the like.

[0078] The positive effect of controlling the content of Nb to be 0.045wt%-0.065wt%: Niobium can effectively refine the grain size, thereby improving the strength and toughness; the precipitation strengthening effect of niobium precipitates can also effectively improve the strength of the steel plate. In addition, the niobium precipitates can also act as hydrogen traps, uniformly distributed on the matrix, which can effectively improve the hydrogen-induced cracking resistance. Specifically, the content of Nb can be 0.045wt%, 0.050wt%, 0.060wt%, 0.065wt% and the like.

[0079] The positive effect of controlling the content of Ti to be 0.035wt%-0.055wt%: Titanium precipitates can improve the strength of the steel plate, and can act as hydrogen traps to capture hydrogen elements, which helps to improve the hydrogen-induced cracking resistance. Specifically, the content of Ti can be 0.035wt%, 0.040wt%, 0.045wt%, 0.050wt%, 0.055wt% and the like.

[0080] In some embodiments, the performance of the steel plate comprises: thickness of the steel ≥ 30 mm, yield strength of the steel 555 MPa-705 MPa, tensile strength of the steel 625 MPa-825 MPa, Charpy impact at -30℃ of the steel ≥ 300 J, -20℃ drop hammer DWTT of the steel ≥ 90%, hardness difference along the thickness direction of the steel 20 HV-40 HV.

[0081] The hydrogen-induced cracking resistance of the steel is that the crack length rate (CLR), crack thickness rate (CTR) and crack sensitivity rate (CSR) of the steel are all 0.

[0082] The above-mentioned steel for submarine pipeline has excellent mechanical properties and hydrogen-induced cracking resistance.

[0083] The steel for submarine pipeline is realized based on the preparation method of the above-mentioned steel for submarine pipeline. The specific steps of the preparation method of the steel for submarine pipeline can refer to the above-mentioned embodiments. Since the steel for submarine pipeline adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here.

[0084] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods not specified in the following examples are generally determined according to the national standards. If there is no corresponding national standard, the international standard, the conventional condition or the condition suggested by the manufacturer is used.

[0085] Table 1 Chemical composition of steel for submarine pipeline

[0086] No. C Si Mn P S Alt Nb Ti Example 1 0.10 0.27 1.25 0.008 0.003 0.032 0.055 0.035 Example 2 0.12 0.29 1.30 0.007 0.002 0.030 0.050 0.040 Example 3 0.09 0.3 1.40 0.008 0.002 0.035 0.05 0.042 Example 4 0.11 0.32 1.43 0.007 0.002 0.025 0.06 0.050 Example 5 0.08 0.27 1.37 0.007 0.002 0.030 0.065 0.055 Example 6 0.08 0.27 1.37 0.007 0.002 0.030 0.065 0.055 Comparative Example 1 0.10 0.25 1.35 0.008 0.003 0.032 0.045 0.035 Comparative Example 2 0.12 0.27 1.25 0.007 0.002 0.030 0.055 0.048 Comparative Example 3 0.11 0.32 1.3 0.008 0.003 0.035 0.049 0.037 Comparative Example 4 0.09 0.28 1.4 0.007 0.002 0.025 0.057 0.050 Comparative Example 5 0.08 0.29 1.45 0.007 0.003 0.030 0.053 0.055

[0087] Table 2 Microstructure and grain size of steel for submarine pipeline

[0088] No. Grain size at 1 / 4 / pm Grain size at core / pm Difference in hardness / HV Example 1 12 16 20 Example 2 15 21 25 Example 3 16 22 23 Example 4 8 13 35 Example 5 14 28 23 Example 6 18 28 20 Comparative Example 1 5 35 65 Comparative Example 2 20 35 38 Comparative Example 3 4 40 48 Comparative Example 4 4 35 42 Comparative Example 5 22 32 18

[0089] Table 3 Hot rolling process parameters of steel for submarine pipeline

[0090]

[0091]

[0092] Table 4 Cooling process parameters of steel for submarine pipeline

[0093]

[0094] Table 5 Mechanical properties of steel for submarine pipeline

[0095]

[0096]

[0097] Table 6 Test results of hydrogen induced cracking resistance of the steel for submarine pipeline

[0098] No. Crack length rate / % Crack thickness rate / % Crack sensitivity rate / % Example 1 0 0 0 Example 2 0 0 0 Example 3 0 0 0 Example 4 0 0 0 Example 5 0 0 0 Example 6 0 0 0 Comparative Example 1 12.3 0 0 Comparative Example 2 22.8 0 0 Comparative Example 3 15.5 6.5 1.77 Comparative Example 4 16.0 0 0 Comparative Example 5 18 7.85 2.05

[0099] By the preparation method of the steel for submarine pipeline of the embodiments of the present application, please refer to Tables 1-6, the prepared steel for submarine pipeline has excellent mechanical properties and excellent hydrogen induced cracking resistance. The comparative examples use the traditional cooling process, resulting in poor mechanical properties and poor hydrogen induced cracking resistance.

[0100] The above description is merely that of the embodiments of the present application, to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing steel for submarine pipelines, characterized in that, The method includes: The billet is heated under a set temperature condition; The heated billet is rolled, and the rolling process parameters are controlled to obtain a hot-rolled plate; Under a first set rate, the hot-rolled plate is subjected to a first cooling, and then under a set time... The process involves waiting for the hot-rolled plate to cool down; wherein, the initial cooling temperature and the first final cooling temperature of the hot-rolled plate are controlled. Under a second set rate, the hot-rolled plate, after being heated, is subjected to a second cooling process to ensure that the heated plate is cooled to a suitable temperature. The hot-rolled plate has a second final cooling temperature to obtain steel for submarine pipelines; The first set rate is 10℃ / s~20℃ / s, the initial cooling temperature of the hot-rolled plate is 770℃~790℃, the first final cooling temperature is 600℃~630℃, and the set time is 8s~12s. The second set rate is 20℃ / s~30℃ / s, and the second final cooling temperature is 260℃~300℃. The chemical composition of the steel used for the pipeline is: C, Si, Mn, P, S, Alt, Nb, Ti, and Fe; among which, The steel contains 0.08 wt% to 0.12 wt% of carbon, 0.25 wt% to 0.35 wt% of silicon, 1.25 wt% to 1.45 wt% of manganese, ≤0.01 wt% of phosphorus, ≤0.003 wt% of sulfur, 0.025 wt% to 0.035 wt% of alumina, 0.045 wt% to 0.065 wt% of nitrogen, and 0.035 wt% to 0.055 wt% of titanium. The steel has a thickness ≥30 mm. The hardness difference along the thickness direction is 20 HV to 40 HV. The steel's resistance to hydrogen-induced cracking is 0 for crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR).

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

3. The method according to claim 1, characterized in that, The heated billet is rolled, and the rolling process parameters are controlled to obtain a hot-rolled plate, including: Under the conditions of a first set initial rolling temperature and a first set final rolling temperature, the heated billet is subjected to rough rolling. Rolling; Under the conditions of a second set initial rolling temperature and a second set final rolling temperature, the rough-rolled billet is subjected to a finishing process. Rolling produces hot-rolled plates.

4. The method according to claim 3, characterized in that, The first set initial rolling temperature is 1160℃~1200℃, and / or the first set final rolling temperature is 980℃~1040℃.

5. The method according to claim 3, characterized in that, The second set initial rolling temperature is 830℃~850℃, and / or the second set final rolling temperature is 790℃~820℃.

6. A type of steel for submarine pipelines, characterized in that, The steel used for the subsea pipeline is prepared by the method described in any one of claims 1-5, and the microstructure of the steel comprises: Polygonal ferrite, acicular ferrite, and MA islands; among them... The grain size of the microstructure at the quarter position of the steel is 6μm to 18μm, and the grain size of the microstructure in the core of the steel is 12μm to 30μm.

7. The steel according to claim 6, characterized in that, The properties of the steel include: yield strength of 555MPa~705MPa, tensile strength of 625MPa~825MPa, Charpy impact strength of ≥300J at -30℃, and drop weight drop weight DWTT of ≥90% at -20℃.

Images