Pipeline steel plate for carbon dioxide transportation and preparation method thereof

Abstract

The present invention discloses a carbon dioxide transport pipeline steel plate and its preparation method. In the heating process of the preparation method: the soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min; in the first hot rolling process: including multiple passes, the plate thickness after rolling is (3.2~4.2)t, the starting rolling temperature T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃; in the water cooling process: the final cooling temperature is Ar3-20℃~Ar3+15℃; in the second hot rolling process: including multiple passes, the plate thickness after rolling is t≥38mm, the starting and finishing temperatures are both Ar3-20℃~Ar3+15℃; in the ultra-fast water cooling process: the water inlet temperature is ≥A r3 -30℃, final cooling temperature is B s -(460~300)℃, cooling rate is 9~22℃ / s; in the air cooling and autotempering process: the steel plate is air cooled to room temperature on the cooling bed.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a method for preparing a pipeline steel plate for transporting carbon dioxide. Background Art

[0002] Carbon dioxide exists in solid, gaseous, liquid, dense phase and supercritical states. Based on existing transportation experience and transportation cost comparison, supercritical and dense phase carbon dioxide pipeline transportation is the most economical for long-distance and large-scale carbon dioxide transportation.

[0003] Dry, pure carbon dioxide is non-corrosive to pipelines. However, carbon dioxide transported through pipelines inevitably contains a certain amount of impurities such as H2O, O2, and SO2. Once a free water phase forms in the pipeline, carbon dioxide will dissolve in water to form H2CO3, causing corrosion of the pipeline. The presence of gaseous impurities will especially exacerbate pipeline corrosion, requiring the steel plates used for pipelines to have excellent corrosion resistance.

[0004] Furthermore, when a supercritical / dense-phase CO2 transmission pipeline leaks or vents, the high-pressure CO2 inside the pipeline will create a strong throttling effect at the leaking or venting orifice, resulting in a low temperature at the orifice, for example, the temperature can drop to -40~-60°C, or even up to -78°C. Therefore, CO2 transmission pipeline steel plates are required to have excellent low-temperature fracture resistance.

[0005] Some existing carbon dioxide transmission pipeline steels generally use high-chromium alloy composition systems in their chemical composition. For example, patented technologies such as CN107502823A, CN105132822A, CN104862607A and CN103334055 have Cr contents above 1.5%, even reaching 7.0%. The high alloy content leads to increased production costs.

[0006] There are also some pipeline steels for carbon dioxide transportation that use additional heat treatment technologies in the process. For example, patented technologies such as CN103820714A, CN104451394A, CN102851607A and CN106119727A all use heat treatment processes such as normalizing and tempering. The production process is complex, the production process is long, the cost is high and the efficiency is low.

[0007] There are also some pipeline steels used for transporting carbon dioxide that have problems with corrosion resistance, low-temperature toughness, and even poor mechanical properties. Summary of the Invention

[0008] The object of the present invention is to provide a pipeline steel plate for transporting carbon dioxide and a preparation method thereof.

[0009] To achieve the above-mentioned purpose, one embodiment of the present invention provides a method for preparing steel plates for carbon dioxide transport pipelines. The method comprises heating, first hot rolling, water cooling, second hot rolling, ultra-fast water cooling, and air cooling and self-tempering of the continuous casting billet to produce the finished steel plate.

[0010] The chemical composition of the continuous casting billet comprises, by mass percentage, C 0.026-0.071%, Si 0.11-0.17%, Mn 0.89-1.02%, P 0.0060-0.0099%, Cr 0.31-0.53%, Ni 0.09-0.23%, Mo 0.08-0.22%, Cu 0.15-0.33%, Nb 0.058-0.073%, Ti 0.010-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities;

[0011] During the heating process: the soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min;

[0012] The first hot rolling process includes multiple passes, the plate thickness after rolling is (3.2~4.2)t, and the starting rolling temperature is T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃;

[0013] In the water cooling process: the final cooling temperature is Ar3-20℃~Ar3+15℃;

[0014] The second hot rolling process includes multiple passes, the plate thickness after rolling is t≥38mm, and the starting and finishing temperatures are both Ar3-20℃~Ar3+15℃;

[0015] In the ultra-fast water cooling process: water inlet temperature ≥A r3 -30℃, final cooling temperature is B s -(460~300)℃, cooling rate is 9~22℃ / s;

[0016] In the air-cooling autotempering process: the steel plate is air-cooled to room temperature on the cooling bed.

[0017] Preferably, the chemical composition of the continuous casting billet further satisfies the following in percentage by mass: 13≤Mn / C≤36.

[0018] Preferably, the chemical composition of the continuous casting billet in terms of mass percentage further satisfies:

[0019] CEV = [C] + [Mn] / 6 + ( [Cr] + [Mo]) / 5 + ( [Cu] + [Ni]) / 15 = 0.294 to 0.403; and / or,

[0020] Pcm=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[Mo] / 15=0.118~0.176.

[0021] Preferably, in the first hot rolling process:

[0022] The reduction of the initial rolling pass of the non-widening pass is ≥42mm, and the minimum reduction of each pass is ≥31mm.

[0023] Preferably, in the second hot rolling process:

[0024] The reduction of the last pass is ≤8mm, and the reduction of the remaining passes is ≥22mm.

[0025] Preferably, during the heating process:

[0026] It includes preheating, first heating, second heating and soaking in sequence;

[0027] The preheating temperature is ≤950℃, the first heating temperature is 1050±15℃, and the second heating temperature is 1150±15℃.

[0028] Preferably, in the second hot rolling process:

[0029] The rolling temperature of each pass is Ar3-20℃~Ar3+15℃.

[0030] Preferably, the preparation method further comprises:

[0031] After the continuous casting billets leave the continuous casting machine, they are directly stacked. The stacking temperature is ≥500℃ and the destacking temperature is 230~280℃.

[0032] Preferably, the chemical composition of the continuous casting billet comprises, by mass percentage, C 0.041-0.071%, Si 0.11-0.17%, Mn 0.89-0.97%, P 0.0060-0.0099%, Cr 0.31-0.39%, Ni 0.15-0.23%, Mo 0.08-0.16%, Cu 0.25-0.33%, Nb 0.058-0.066%, Ti 0.010-0.018%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities;

[0033] In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-20℃~Ar3;

[0034] In the ultra-fast water cooling process: the final cooling temperature is B s -(460~400)℃.

[0035] Preferably, the chemical composition of the continuous casting billet comprises, by mass percentage, C 0.034-0.064%, Si 0.11-0.17%, Mn 0.91-0.99%, P 0.0060-0.0099%, Cr 0.37-0.45%, Ni 0.12-0.20%, Mo 0.11-0.19%, Cu 0.20-0.28%, Nb 0.061-0.069%, Ti 0.012-0.020%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities;

[0036] In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-15℃~Ar3+5℃;

[0037] In the ultra-fast water cooling process: the final cooling temperature is B s -(360~320)℃.

[0038] Preferably, the chemical composition of the continuous casting billet comprises, by mass percentage, C 0.026-0.056%, Si 0.11-0.17%, Mn 0.94-1.02%, P 0.0060-0.0099%, Cr 0.45-0.53%, Ni 0.09-0.17%, Mo 0.14-0.22%, Cu 0.15-0.23%, Nb 0.065-0.073%, Ti 0.014-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities;

[0039] In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-5℃~Ar3+15℃;

[0040] In the ultra-fast water cooling process: the final cooling temperature is B s -(340~300)℃.

[0041] To achieve the above-mentioned objectives, one embodiment of the present invention provides a steel plate for a carbon dioxide transmission pipeline. The chemical composition of the steel plate, in percentage by mass, includes: C 0.026-0.071%, Si 0.11-0.17%, Mn 0.89-1.02%, P 0.0060-0.0099%, Cr 0.31-0.53%, Ni 0.09-0.23%, Mo 0.08-0.22%, Cu 0.15-0.33%, Nb 0.058-0.073%, Ti 0.010-0.022%, Al 0.022-0.049%, with the remainder being iron and unavoidable impurities.

[0042] Preferably, under the conditions of 20° C., carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s, the uniform corrosion rate of the steel plate is ≤0.10 mm / year.

[0043] Preferably, the number of inclusions with a size of ≥10 μm on the cross section of the steel plate is ≤10 / cm 2 , the maximum size of inclusions does not exceed 15μm, and the average size of inclusions is 0.1~2μm.

[0044] Preferably, the yield strength R of the steel plate t0.5 ≥420MPa, tensile strength R m ≥560MPa, elongation A 50mm ≥30%, yield strength ratio R t0.5 / R m ≤0.82.

[0045] Preferably, the steel plate has an impact energy KV2 of ≥400J at -20°C, an impact energy KV2 of ≥380J at -40°C, an impact energy KV2 of ≥320J at -60°C, and an impact energy KV2 of ≥250J at -80°C.

[0046] Preferably, the ductile-brittle transition temperature of the steel plate is t50%US ≤-100℃.

[0047] Preferably, the steel plate has a -10°C DWTT drop weight shear area fraction of 100%, a -20°C DWTT drop weight shear area fraction ≥90%, a -30°C DWTT drop weight shear area fraction ≥80%, and a -20°C CTOD crack tip opening displacement ≥1.5 mm.

[0048] Preferably, the hardness of the steel plate is ≤210HV 10 .

[0049] Preferably, the structure of the steel plate is a multiphase structure of quasi-polygonal ferrite + acicular ferrite + bainite;

[0050] The total volume proportion of the quasi-polygonal ferrite structure and the acicular ferrite structure is more than 70%.

[0051] Preferably, the volume proportion of the quasi-polygonal ferrite structure is 15-65%, the volume proportion of the acicular ferrite structure is 15-70%, and the volume proportion of the bainite structure is 5-30%.

[0052] Preferably, the average grain size of the quasi-polygonal ferrite and the acicular ferrite is 3-10 μm.

[0053] Preferably, the chemical composition of the steel plate, in terms of mass percentage, further satisfies:

[0054] 13≤Mn / C≤36; and / or,

[0055] CEV = [C] + [Mn] / 6 + ( [Cr] + [Mo]) / 5 + ( [Cu] + [Ni]) / 15 = 0.294 to 0.403; and / or,

[0056] Pcm=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[Mo] / 15=0.118~0.176.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) Reduce the C content and Cr content in the steel, and add appropriate amounts of carbide-forming elements Nb and Ti to reduce the carbonization of Cr, so that Cr exists in the steel in the form of a solid solution, giving full play to the corrosion resistance of Cr; on the other hand, Cr is added in combination with Ni, Mo, Cu, and P to further improve the corrosion resistance, so that the steel plate has excellent corrosion resistance in the use of carbon dioxide transportation; on the other hand, it does not contain expensive alloys such as V, and the addition content of alloys such as Cr, Ni, and Mo is low. P exists as a corrosion-resistant element without the need for ultra-low content control, which makes steelmaking easy and has low production costs;

[0059] (2) Combining the special controlled rolling and controlled cooling process of "continuous casting billet heating → recrystallization zone + water cooling + two-phase zone special controlled rolling → ultra-fast water cooling + air cooling self-tempering special controlled cooling", the steel plate is improved in terms of strength, yield strength ratio, hardness, low temperature toughness and corrosion resistance; and the alloy content is low, and the alloy cost is low; furthermore, no additional heat treatment process is required, the production process is short, the cost is low and the efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is a metallographic structure diagram of the finished steel plate of Example 1 of the present invention;

[0061] Figure 2 is a metallographic structure diagram of the finished steel plate of Example 3 of the present invention;

[0062] Figure 3 This is a metallographic structure diagram of the finished steel plate of Example 5 of the present invention. DETAILED DESCRIPTION

[0063] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0064] The present invention provides a steel plate and a preparation method thereof. The steel plate is suitable for carbon dioxide transportation engineering, and is therefore called pipeline steel for carbon dioxide transportation.

[0065] More specifically, the steel plate may be suitable for transporting supercritical or dense phase carbon dioxide.

[0066] The preparation method is technically improved in terms of chemical composition and process, which not only ensures the strength, low-temperature toughness and corrosion resistance of the steel plate, but also has the advantages of low cost and short process.

[0067] The preparation method prepares the continuous casting billet into a finished steel plate through heating, first hot rolling, water cooling, second hot rolling, ultra-fast water cooling, air cooling and self-tempering.

[0068] In terms of chemical composition, the chemical composition of the continuous casting billet includes, by mass percentage, C 0.026~0.071%, Si 0.11~0.17%, Mn 0.89~1.02%, P 0.0060~0.0099%, Cr 0.31~0.53%, Ni 0.09~0.23%, Mo0.08~0.22%, Cu 0.15~0.33%, Nb 0.058~0.073%, Ti 0.010~0.022%, Al 0.022~0.049%, and the rest is iron and unavoidable impurities.

[0069] It can be understood that the chemical composition of the continuous casting billet is also the chemical composition of the final steel plate product.

[0070] The following is a detailed analysis of the main functions of each element and the selection of its dosage.

[0071] C: Carbon is the most economical strengthening element in steel, providing solid solution strengthening and forming carbides with niobium, titanium, chromium, molybdenum, and other elements, which contribute to precipitation strengthening. Increasing carbon content significantly improves the strength and hardness of steel plates, but excessive carbon content can lead to poor low-temperature toughness and weldability, reducing the steel plate's low-temperature drop hammer performance. Reducing carbon content promotes homogenization of composition and structure, increases the transformation temperature of acicular ferrite, expands the cooling rate range for acicular ferrite transformation, facilitates the formation of acicular ferrite, and minimizes the difference in electrode potential between microstructures, enhancing corrosion resistance. In the present invention, the carbon content is controlled to 0.026-0.071%.

[0072] Si: Silicon acts as a solid solution strengthener in steel. When used in combination with copper, it improves corrosion resistance. However, high silicon content can increase grain boundary segregation of elements like phosphorus and sulfur, reducing low-temperature toughness and weldability. Excessive silicon can also easily form Fe2SiO4 on the surface of the continuous casting ingot, compromising surface quality control of the steel plate. In one embodiment, the silicon content is controlled to 0.11-0.17%.

[0073] Mn: Manganese plays a role in solid solution strengthening in steel, improving strength and hardness. A reasonable manganese content can ensure the strength of the steel plate at a low cost. As the manganese content increases, the strength of the steel plate increases significantly, while the ductile-brittle transition temperature hardly changes. Excessive manganese will cause segregation in the center of the ingot, which is detrimental to toughness. At the same time, it will increase the level of banded structure. The higher the level of banded structure, the more uneven the tissue distribution, and the more prone to localized corrosion. In one embodiment, taking into account corrosion performance, low-temperature toughness, and strength, the manganese content is controlled to be 0.89~1.02%.

[0074] Phosphorus (P) is used in this application to improve corrosion resistance. Excessive phosphorus levels can lead to segregation and significantly reduce the steel's low-temperature toughness. Considering both corrosion resistance and low-temperature toughness, the phosphorus content should be controlled between 0.0060% and 0.0099%.

[0075] Cr: Chromium acts as a solid solution strengthener in steel and is the most effective element in steel against CO2 corrosion. As a ferrite-forming element, chromium produces a more acicular ferrite structure in high-niobium steel. Increasing chromium content significantly enhances CO2 corrosion resistance. However, excessive chromium content increases the microhardness of the steel plate and reduces low-temperature toughness. In one embodiment, the chromium content is controlled to 0.31-0.53%.

[0076] Nickel: Nickel acts as a solid solution strengthener in steel, increasing its strength without significantly increasing its hardness. It also improves the steel's low-temperature toughness and weldability, shifts the steel's self-corrosion potential toward the positive side, promotes the formation of the α-FeOOH phase in the rust layer, and improves its stability. However, excessive nickel content increases alloy cost. Therefore, considering corrosion resistance, low-temperature toughness, weldability, and alloy cost, the nickel content is controlled between 0.09% and 0.23%.

[0077] Mo: Molybdenum significantly improves the hardenability of steel, increasing its strength and toughness. It also refines grains and enhances corrosion resistance. Molybdenum is a medium-strong carbide-forming element that combines with carbon, allowing more chromium to exist in the steel as a solid solution. This maximizes chromium's corrosion resistance and improves the utilization efficiency of the matrix alloying elements. Molybdenum delays ferrite transformation, resulting in an acicular ferrite structure, which contributes to the strength and toughness of the steel plate. However, excessive molybdenum content significantly increases alloy cost. Therefore, considering corrosion resistance, strength, low-temperature toughness, and alloy cost, the molybdenum content is controlled between 0.08% and 0.22%.

[0078] Cu: Copper promotes niobium precipitation and compensates for the strength loss caused by the decrease in carbon content. Adding a certain amount of nickel along with copper can effectively suppress surface cracking. Copper complements the corrosion resistance of chromium, hindering the crystallization of the rust layer, promoting the formation of α-FeOOH and amorphous Fe₃O₄, and improving pitting resistance. However, high copper content can negatively impact weldability. In one embodiment, the copper content is controlled to 0.15-0.33%.

[0079] Nb: Niobium is a key grain-refining element in steel. During hot rolling, niobium strongly inhibits austenite recrystallization and its precipitation within the austenite, pinning austenite grain boundaries and refining the recrystallized grains. During cooling, dissolved niobium can continue to precipitate as niobium carbonitrides, significantly refining the resulting microstructure after phase transformation and further improving the steel's strength and toughness. Niobium is a strong carbide-forming element, preventing carbon from combining with chromium, which can affect corrosion resistance. However, high niobium levels increase alloy cost and reduce the low-temperature toughness of the heat-affected zone (HAZ) of welded joints. Therefore, considering all factors, the niobium content is controlled between 0.058% and 0.073%.

[0080] Titanium: Titanium is a nitrogen-fixing element in steel. It forms dispersed titanium nitride particles, which inhibit austenite grain coarsening during billet heating and rolling. However, excessive addition can easily lead to the formation of coarse carbon / nitride precipitation in the core of the billet, affecting the low-temperature toughness of the steel plate. Therefore, the titanium content is controlled between 0.010% and 0.022%.

[0081] Al: Aluminum is a deoxidizing element in steel. Excessive aluminum can easily increase Al2O3 inclusions in the steel, affecting the steel's low-temperature toughness. While ensuring the deoxidation effect, the aluminum content should be minimized. Therefore, the aluminum content is controlled at 0.022-0.049%.

[0082] Thus, in terms of chemical composition, the present invention adopts a low-alloy component system design with low carbon, low manganese, high niobium and a composite addition of corrosion-resistant elements Cr+Ni+Mo+Cu+P. On the one hand, the C content and Cr content in the steel are reduced, and carbide-forming elements Nb and Ti are added in appropriate amounts to reduce the carburization of Cr, so that Cr exists in the steel in the form of a solid solution, and the corrosion-resistant effect of Cr is fully exerted; on the other hand, Cr is compositely added with Ni, Mo, Cu, and P to further improve the corrosion resistance, thereby making the steel plate have excellent corrosion resistance in carbon dioxide transportation applications; on the other hand, it does not contain expensive alloys such as V, and the content of alloy additions such as Cr, Ni, and Mo is relatively low. P exists as a corrosion-resistant element without the need for ultra-low content control, which facilitates steelmaking production and has a low production cost.

[0083] The process is as follows:

[0084] During the heating process: the soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min;

[0085] The first hot rolling process includes multiple passes, the plate thickness after rolling is (3.2~4.2)t, and the starting rolling temperature is T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃;

[0086] In the water cooling process: the final cooling temperature is Ar3-20℃~Ar3+15℃;

[0087] The second hot rolling process includes multiple passes, the plate thickness after rolling is t≥38mm, and the starting and finishing temperatures are both Ar3-20℃~Ar3+15℃;

[0088] In the ultra-fast water cooling process: water inlet temperature ≥A r3 -30℃, final cooling temperature is B s -(460~300)℃, cooling rate is 9~22℃ / s;

[0089] In the air-cooling autotempering process: the steel plate is air-cooled to room temperature on the cooling bed.

[0090] Among them, T NbC is the precipitation start temperature of NbC, which can be analyzed by thermodynamic calculation software (such as Thermo-Calc) or laboratory measurement (such as thermal simulation test) combined with the chemical composition of the specific continuous casting billet.

[0091] For example, T NbC The formula lg([Nb]×[C] 0.875 )=3.11-7520 / (T NbC +273.15) is calculated, but T NbC The value of is not limited to this.

[0092] T nr It indicates the lowest temperature of austenite recrystallization, which can be obtained through various methods such as theoretical calculation, experimental measurement and empirical formula.

[0093] For example, in one embodiment, T can be calculated according to the following formula: nr :T nr =887+464[C]+(6445[Nb]-644 )+890[Ti]+363[Al]–357[Si]. But T nr The value of is not limited to this. nr Other value-taking methods that can be known based on the concept can all be applied to the present invention.

[0094] Ar3 is the temperature at which austenite (γ-Fe) begins to precipitate ferrite (α-Fe) during cooling. It can be obtained by testing and measuring using a differential scanning calorimeter (DSC) or thermogravimetric analysis (TG), or by an empirical formula.

[0095] For example, in one embodiment, Ar3 can be calculated according to the following formula: Ar3 = 910-203[C] + 44.7[Si] + 30[Mn] + 70[Cr]. However, the value of Ar3 is not limited to this. Other values ​​of Ar3 known to those skilled in the art based on the concept of Ar3 can be applied to the present invention.

[0096] B s It is the temperature at which the bainite phase transformation begins, which can be measured from the continuous cooling transformation curve of supercooled austenite, namely the CCT curve, or obtained through an empirical formula.

[0097] For example, B s =830-270[C]-90[Mn]-37[Ni]-70[Cr]-83[Mo]. But B s The value of is not limited to this. s Other value-taking methods that can be known based on the concept can all be applied to the present invention.

[0098] The beneficial effects of the process are introduced below.

[0099] During the heating process, the alloy elements are effectively dissolved by controlling the soaking temperature and duration, ensuring that the Nb precipitates in the steel are completely dissolved and the austenite grains do not grow excessively, preparing for precipitation in the subsequent first hot rolling process.

[0100] In the first hot rolling process, rolling is carried out in a higher temperature range, which can reduce the rolling deformation resistance, increase the rolling reduction, and facilitate the deformation penetration into the core of the billet, thereby improving defects such as segregation and looseness in the core, and at the same time, reducing banded structure; furthermore, the billet is rolled in the recrystallization zone to avoid mixed crystals, and at the same time, the precipitation of Nb compounds during the rolling process can prevent the growth of recrystallized grains and refine the recrystallized grains.

[0101] After the first hot rolling, fine recrystallized grains are obtained. After a water cooling process, they are quickly cooled to below the recrystallization temperature through a water cooling device. On the one hand, this prevents the recrystallized grains from growing rapidly during the waiting process, which leads to the deterioration of the low-temperature toughness of the final steel plate; on the other hand, it reduces the waiting time and improves the rolling efficiency.

[0102] In the second hot rolling process, on the one hand, a large amount of deformation is carried out in the non-recrystallization zone to obtain a deformed structure, so that a large number of deformation bands are accumulated in the structure, and a fine structure is obtained in the subsequent cooling process, thereby improving the low-temperature toughness of the steel plate; on the other hand, the steel plate is always rolled at the two-phase critical point, that is, the rolling deformation is always carried out within a range of 30°C near the starting point of the two-phase phase transformation, which can ensure that the deformation-induced ferrite content is not too high, resulting in a low yield strength, and can also ensure that the deformation-induced ferrite content is not too low, resulting in an excessively high yield strength ratio, so that the deformation-induced ferrite content is within an optimal range; on the other hand, if the final rolling temperature is too high, the subsequent cooling temperature drop is large, resulting in high yield and tensile strength and low toughness, while if the final rolling temperature is too low, the subsequent cooling temperature drop is small, and the deformation-induced ferrite content is high, resulting in low yield and tensile strength. The final rolling temperature control of the present application ensures low yield strength, high tensile strength, and high toughness.

[0103] In the ultra-fast water cooling process, higher tensile strength and low yield ratio, as well as excellent plate shape, can be obtained by controlling the cooling rate and final cooling temperature; if the cooling rate is too fast or too slow, martensite or pearlite phase will be formed, which is not conducive to improvement; if the final cooling temperature is too high, the bainite phase transformation is incomplete; if the final cooling temperature is too low, the large temperature drop is not conducive to plate shape control.

[0104] After ultra-fast water cooling, air cooling and self-tempering are carried out on the cooling bed to eliminate or weaken internal stress. On the other hand, during the phase change process, pipeline steel plates produce MA hard phase, which is not conducive to the toughness of the steel plates and easily leads to high local hardness of the steel plates. Air cooling and self-tempering cooling can decompose MA, improve toughness and local hard points.

[0105] In summary, the preparation method of one embodiment of the present invention, based on the low alloy composition system, combines the special controlled rolling and cooling process of "continuous casting billet heating → recrystallization zone + water cooling + special controlled rolling in two-phase zone → ultra-fast water cooling + air cooling and self-tempering special controlled cooling". Through the special controlled rolling in the two-phase critical zone, the type and proportion of the finished product structure are adjusted and controlled to obtain a complex phase structure, thereby achieving improvements in the strength, yield strength ratio, hardness, low-temperature toughness and corrosion resistance of the steel plate; and the alloy content is low, and the alloy cost is low; furthermore, no additional heat treatment and other processes are required, the production process is short, the cost is low, and the efficiency is high.

[0106] Furthermore, the chemical composition of the continuous casting billet, in terms of mass percentage, also satisfies:

[0107] CEV = [C] + [Mn] / 6 + ( [Cr] + [Mo]) / 5 + ( [Cu] + [Ni]) / 15 = 0.294 to 0.403; and / or,

[0108] Pcm=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[Mo] / 15=0.118~0.176.

[0109] It should be noted that in the various formulas in this article, [C], [Si], [Mn], [Cr], [Mo], [Cu], [Ni], [Nb], and [Ti] refer to the mass percentages of C, Si, Mn, Cr, Mo, Cu, Ni, Nb, and Ti in the steel, respectively. For example, if the mass percentage of C in a continuous casting billet is 0.050%, then the mass percentage of C [C] is 0.050.

[0110] Preferably, in the second hot rolling process, the rolling temperature of each pass is Ar3-20°C to Ar3+15°C.

[0111] The steel plate prepared by the preparation method of the present invention has excellent structure and performance, which are introduced below.

[0112] The structure of the steel plate is a dual-phase structure of quasi-polygonal ferrite+acicular ferrite+bainite.

[0113] The sum of the volume proportions of the quasi-polygonal ferrite structure and the acicular ferrite structure is greater than 70%, or preferably greater than 80%, and even more preferably greater than 90%.

[0114] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 15-65%, the volume proportion of the acicular ferrite structure is 15-70%, and the volume proportion of the bainite structure is 5-30%.

[0115] The complex phase structure can ensure good matching of various mechanical properties of the steel plate, such as mechanical strength, low-temperature toughness, yield strength ratio, hardness, and drop weight performance.

[0116] Furthermore, the average grain size of the quasi-polygonal ferrite and the acicular ferrite is 3-10 μm, thereby ensuring excellent low-temperature toughness of the steel plate.

[0117] Furthermore, the steel plate has excellent mechanical properties. For example, the yield strength R t0.5 ≥420MPa, tensile strength R m ≥560MPa, elongation A 50mm ≥30%.

[0118] For another example, the yield strength ratio R of the steel plate t0.5 / R m ≤0.82.

[0119] More specifically, the yield strength R t0.5 It is 420~570MPa.

[0120] Tensile strength R m It is 560~680MPa.

[0121] Elongation A 50mm It is 30~60%.

[0122] Yield strength ratio R t0.5 / R m It is 0.65~0.82.

[0123] Here, the steel plate can be sampled and mechanical properties tested in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Location and Specimen Preparation for Mechanical Properties Tests" and GB / T 228.1-2021 "Metallic Materials - Tensile Tests - Part 1: Room Temperature Test Methods".

[0124] The steel plate has excellent low-temperature properties.

[0125] For example, the steel plate has an impact energy KV2 of ≥400J at -20°C.

[0126] The -40°C impact energy KV2 of the steel plate is ≥380J.

[0127] The -60°C impact energy KV2 of the steel plate is ≥320J.

[0128] The -80°C impact energy KV2 of the steel plate is ≥250J.

[0129] The ductile-brittle transition temperature T t50%US ≤-100℃.

[0130] The -10°C DWTT drop weight shear area fraction of the steel plate is 100%.

[0131] The -20°C DWTT drop weight shear area fraction of the steel plate is ≥90%.

[0132] The -30°C DWTT drop weight shear area fraction of the steel plate is ≥80%.

[0133] The -20°C CTOD crack tip opening displacement of the steel plate is ≥1.5 mm.

[0134] Here, the steel plate can be sampled and subjected to low-temperature performance testing in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Location and Specimen Preparation for Mechanical Properties Tests" and GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0135] Furthermore, the steel plate has excellent corrosion resistance, especially excellent corrosion resistance in a carbon dioxide environment.

[0136] For example, under the conditions of 20° C., carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s, the uniform corrosion rate of the steel plate is ≤0.10 mm / year.

[0137] The characteristics of the carbon dioxide used in the corrosion resistance test can be based on the standard GB / T 6052-2011 "Industrial Liquid Carbon Dioxide." For example, the carbon dioxide used in the test is in gaseous form, with a purity (volume fraction) of ≥99.5% and other impurities (water, oxygen, sulfur dioxide, nitrogen, carbon monoxide, etc.) ≤0.5%.

[0138] In addition, the hardness of the steel plate is ≤210HV 10 .

[0139] For example, the hardness is 170~210HV 10 .

[0140] The preferred embodiments of the present invention are introduced below, and these embodiments are implemented within the technical scope provided by the present invention.

[0141] [First embodiment]

[0142] The method for preparing a steel plate provided in this embodiment prepares a finished steel plate by subjecting a continuous casting billet to heating, a first hot rolling, water cooling, a second hot rolling, ultra-fast water cooling, and air cooling and self-tempering.

[0143] The chemical composition of the continuous casting billet includes, by mass percentage, C 0.041-0.071%, Si 0.11-0.17%, Mn 0.89-0.97%, P 0.0060-0.0099%, Cr 0.31-0.39%, Ni 0.15-0.23%, Mo 0.08-0.16%, Cu 0.25-0.33%, Nb 0.058-0.066%, Ti 0.010-0.018%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities.

[0144] Furthermore, the carbon content is preferably controlled within a range of 0.045-0.065%, more preferably within a range of 0.045-0.061%.

[0145] The manganese content is preferably controlled at 0.90-0.96%, more preferably at 0.91-0.96%.

[0146] The chromium content is preferably controlled at 0.33~0.37%.

[0147] The nickel content is preferably controlled at 0.17-0.23%, more preferably at 0.17-0.21%.

[0148] The molybdenum content is preferably controlled at 0.08-0.13%, more preferably at 0.11-0.13%.

[0149] The copper content is preferably controlled at 0.27~0.31%.

[0150] The niobium content is preferably controlled within a range of 0.058 to 0.064%, more preferably within a range of 0.060 to 0.064%.

[0151] The titanium content is preferably controlled within the range of 0.010 to 0.016%, more preferably within the range of 0.013 to 0.016%.

[0152] Furthermore, the chemical composition of the continuous casting slab, in mass percentage, satisfies the following conditions: 13 ≤ Mn / C ≤ 36. Thus, while maintaining a low carbon content, the manganese-carbon ratio is controlled within the range of 13-36, significantly reducing segregation and improving the low-temperature toughness of the pipeline steel.

[0153] Furthermore, the chemical composition of the continuous casting billet satisfies, in terms of mass percentage: CEV=0.294~0.380.

[0154] Preferably, CEV=0.294~0.337.

[0155] More preferably, CEV=0.330~0.337.

[0156] Furthermore, the chemical composition of the continuous casting billet satisfies, in terms of mass percentage: Pcm=0.125~0.176.

[0157] Preferably, Pcm=0.142~0.176.

[0158] More preferably, Pcm=0.142~0.153.

[0159] Preferably, the contents of some impurity elements in the chemical composition of the continuous casting billet are described as follows.

[0160] Sulfur (S): Sulfur is an impurity element in steel that not only increases hot brittleness but also easily forms MnS inclusions with manganese, reducing the steel's low-temperature toughness. In one embodiment, S is controlled to below 0.0015%.

[0161] Considering that too low sulfur content will significantly increase steelmaking costs, the sulfur content is preferably controlled at 0.0009~0.0015%.

[0162] O: Oxygen is an impurity element in steel that easily forms various oxide inclusions. In one embodiment, the O content is controlled to be below 0.0025%.

[0163] Too low oxygen will increase steelmaking costs, so the oxygen content is preferably controlled at 0.0011~0.0025%.

[0164] Nitrogen: Nitrogen is an impurity element in steel. It easily forms brittle inclusions with edges and corners with Ti, Al, etc., reducing the plasticity and toughness of the steel plate. The nitrogen content should be controlled below 0.0055%.

[0165] Too low nitrogen content will increase steelmaking costs, so the nitrogen content is preferably controlled at 0.0025~0.0051%.

[0166] H: Hydrogen is an impurity element in steel that can easily cause hydrogen embrittlement in steel, leading to cracking in continuous casting slabs and steel plates. In one embodiment, H is controlled to be below 0.00020%.

[0167] Too low a hydrogen content will increase the cost of steelmaking, therefore, the hydrogen content is preferably controlled between 0.00005 and 0.00018%.

[0168] Furthermore, the center segregation of the continuous casting billet is ≤0.5 level.

[0169] Here, the central segregation can be specifically determined in accordance with GB / T 34474-2017 "Methods for evaluating the microstructure of steel", by using the sulfur print method or electron probe to detect the degree of element segregation in the central area of ​​the ingot.

[0170] Furthermore, the central porosity of the continuous casting billet is ≤ level 0.5.

[0171] The central porosity level can be determined by a macro-acid immersion test in accordance with GB / T 226-2015 "Macrostructure and Defect Acid Etching Test of Steel", or by ultrasonic testing.

[0172] In this way, by controlling the center segregation and center porosity, the organizational structure at the center is made continuous, the impact toughness, fracture toughness, drop hammer performance, etc. of the steel plate are improved, and cracks are avoided.

[0173] Furthermore, the ratings of the A, B, C, and D inclusions of the continuous casting slab are all ≤ level 1, and the sum of the ratings of the four types of inclusions A, B, C, and D is A+B+C+D ≤ level 3.0.

[0174] Here, the rating of A, B, C, and D inclusions can be specifically based on GB / T 10561-2005 "Microscopic inspection method for the determination of the content of non-metallic inclusions in steel - standard rating chart", and the rating can be compared with the standard chart under a microscope.

[0175] Furthermore, the number of inclusions with a size of ≥10 μm on the cross section of the continuous casting billet is ≤10 / cm 2 .

[0176] Research has shown that inclusions are the most sensitive locations for pitting and crack initiation, and large inclusions with an equivalent circular diameter exceeding 20 μm have a significant impact on corrosion resistance and low-temperature toughness. The pipeline steel of this application has fewer large inclusions, which can improve corrosion resistance and low-temperature toughness.

[0177] The following describes the detailed technical solutions for each step of the preparation method of this embodiment.

[0178] <Heating process>

[0179] The continuous casting slab is heated in a heating furnace.

[0180] The soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min.

[0181] Preferably, the heating process includes preheating, first heating, second heating and soaking in sequence.

[0182] The preheating temperature is ≤950°C, the first heating temperature is 1050±15°C, and the second heating temperature is 1150±15°C. In this way, on the one hand, the solid solution effect of the alloy elements can be improved, and on the other hand, the billet can be heated evenly in the heating furnace.

[0183] <First hot rolling process>

[0184] The heated continuous casting slab is hot rolled in multiple passes, and the thickness of the rolled slab is (3.2~4.2)t.

[0185] Here, t represents the thickness of the finished steel plate, which is also equivalent to the thickness of the steel plate obtained in the second hot rolling process.

[0186] The plate thickness is (3.2~4.2)t, that is, in the first hot rolling process, the steel plate is rolled to a thickness of 3.2~4.2 times the thickness t of the final steel plate product.

[0187] Before rolling, the thickness of the continuous casting billet is 300~320mm.

[0188] Rolling temperature T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃.

[0189] Preferably, the first hot rolling process includes several widening passes and several non-widening passes.

[0190] Among them, the reduction of the initial rolling pass without widening pass is ≥42mm.

[0191] The minimum reduction for each pass is ≥31mm.

[0192] In this way, when the total reduction is large, a large reduction is also used in each pass. In the low-temperature section of the recrystallization zone, large reduction rolling is used to fully break up the continuous casting structure and obtain refined recrystallized grains. The refinement effect on the austenite grains is obvious, and because the temperature is low, the grains will not grow excessively.

[0193] <Water cooling process>

[0194] After the steel plate leaves the hot rolling mill of the first hot rolling process, it enters the water cooling device for water cooling.

[0195] Final cooling temperature is Ar3-20℃~Ar3. That is, the water is discharged when the temperature of the steel plate is cooled to Ar3-20℃~Ar3.

[0196] <Second hot rolling process>

[0197] After the steel plate emerges from the water, it is hot rolled in multiple passes from a plate thickness of (3.2~4.2)t to a plate thickness of t.

[0198] Plate thickness t≥38mm. That is, the thickness of the final steel plate product is above 38mm. In this way, the thicker steel plate can improve the structural strength of the finished steel plate when used in the carbon dioxide transportation project.

[0199] The starting rolling temperature and the final rolling temperature are both Ar3-20℃~Ar3.

[0200] Preferably, in the multiple passes of the second hot rolling process, the reduction in the last pass is ≤8 mm, and the reduction in the remaining passes is ≥22 mm.

[0201] Preferably, the rolling temperature of each pass is Ar3-20℃~Ar3.

[0202] The rolling temperature of each pass can be further controlled to be Ar3-20℃~Ar3-10℃, more preferably Ar3-20℃~Ar3-15℃.

[0203] Furthermore, in the second hot rolling process, the steel plate is water-cooled between two adjacent passes, which can achieve more precise control of temperature and thus improve the control of structure and performance.

[0204] <Ultra-fast water cooling process>

[0205] After the steel plate leaves the hot rolling mill of the second hot rolling process, it directly enters the ultra-fast cooling system for ultra-fast water cooling.

[0206] In this way, ultra-fast water cooling can be performed directly without coiling, which not only shortens the process route but also better controls the structure and performance of the steel plate.

[0207] Water inlet temperature ≥A r3 -30℃.

[0208] Final cooling temperature is B s -(460~400)℃. Final cooling temperature is also the water outlet temperature.

[0209] The cooling rate is 9~22℃ / s.

[0210] Preferably, when ultra-fast water cooling is performed on the ultra-fast cooling system, the water pressure can be controlled to be 0.20~0.50MPa, the upper and lower water ratio can be controlled to be 0.91~0.95, and the roller speed can be controlled to be 0.6~1.0m / s.

[0211] <Air cooling and self-tempering process>

[0212] After the steel plate exits the ultra-fast cooling system, it is placed on a cooling bed for natural air cooling and self-tempering until it cools to room temperature to obtain the finished steel plate.

[0213] The temperature of the upper cooling bed shall not be lower than 150℃.

[0214] Preferably, after the steel plate exits the ultra-fast cooling system, that is, after exiting the water and before being placed on the cooling bed, it can be hot straightened. This can further improve the plate shape. Of course, this application is not limited to this.

[0215] Furthermore, the preparation method also includes a continuous casting billet stacking process.

[0216] That is, the continuous casting strands are stacked directly after leaving the continuous casting machine.

[0217] The stacking temperature is ≥500℃, that is, stacking begins after the continuous casting billet leaves the continuous casting machine and before the temperature cools down to 500℃.

[0218] The destacking temperature is 230~280℃.

[0219] In this way, on the one hand, the cooling rate of the billet is reduced, the stress difference between the core and the surface is reduced, and the generation of microcracks is prevented; on the other hand, stack cooling within this temperature range can effectively promote the diffusion and escape of hydrogen.

[0220] In this embodiment, the finished steel plate obtained by the preparation method has a structure of a multiphase structure of quasi-polygonal ferrite+acicular ferrite+bainite.

[0221] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 55-65%, the volume proportion of the acicular ferrite structure is 15-30%, and the volume proportion of the bainite structure is 15-20%.

[0222] Furthermore, the average grain size of quasi-polygonal ferrite and acicular ferrite is 5-10 μm.

[0223] Furthermore, the yield strength R of the finished steel plate t0.5 ≥420MPa, tensile strength R m ≥560MPa, elongation A 50mm ≥32%.

[0224] For example, the yield strength ratio R of the finished steel plate t0.5 / R m ≤0.72.

[0225] More specifically, the yield strength R t0.5 It is 420~500MPa.

[0226] Tensile strength R m It is 560~650MPa.

[0227] Elongation A 50mm It is 32~60%.

[0228] Yield strength ratio R t0.5 / R m It is 0.65~0.72.

[0229] The impact energy of the finished steel plate at -20℃ KV2≥400J.

[0230] The impact energy of the finished steel plate at -40℃ KV2≥380J.

[0231] The impact energy of the finished steel plate at -60℃ KV2≥320J.

[0232] The impact energy of the finished steel plate at -80℃ KV2≥250J.

[0233] Tough-brittle transition temperature T of finished steel plate t50%US ≤-100℃.

[0234] The -10℃ DWTT drop weight shear area fraction of the finished steel plate is 100%.

[0235] The -20℃ DWTT drop weight shear area fraction of the finished steel plate is ≥90%.

[0236] The -30℃ DWTT drop weight shear area fraction of the finished steel plate is ≥80%.

[0237] The crack tip opening displacement of the finished steel plate at -20℃ CTOD is ≥1.5mm.

[0238] The hardness of the finished steel plate is ≤200HV 10 .

[0239] For example, the hardness is 170~200HV 10 .

[0240] Furthermore, under the conditions of 20° C., carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s, the uniform corrosion rate of the finished steel plate is ≤0.10 mm / year.

[0241] [Second embodiment]

[0242] The method for preparing a steel plate provided in this embodiment prepares a finished steel plate by subjecting a continuous casting billet to heating, a first hot rolling, water cooling, a second hot rolling, ultra-fast water cooling, and air cooling and self-tempering.

[0243] The chemical composition of the continuous casting billet includes, by mass percentage, C 0.034-0.064%, Si 0.11-0.17%, Mn 0.91-0.99%, P 0.0060-0.0099%, Cr 0.37-0.45%, Ni 0.12-0.20%, Mo 0.11-0.19%, Cu 0.20-0.28%, Nb 0.061-0.069%, Ti 0.012-0.020%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities.

[0244] Furthermore, the carbon content is preferably controlled within a range of 0.039-0.064%, more preferably within a range of 0.039-0.055%.

[0245] The manganese content is preferably controlled at 0.91-0.98%, more preferably at 0.93-0.98%.

[0246] The nickel content is preferably controlled at 0.12-0.18%, more preferably at 0.15-0.18%.

[0247] The molybdenum content is preferably controlled at 0.11-0.16%, more preferably at 0.15-0.16%.

[0248] The copper content is preferably controlled at 0.22~0.26%.

[0249] The niobium content is preferably controlled within a range of 0.061 to 0.067%, more preferably within a range of 0.062 to 0.067%.

[0250] The titanium content is preferably controlled within a range of 0.012 to 0.017%, more preferably within a range of 0.013 to 0.015%.

[0251] Furthermore, the chemical composition of the continuous casting billet also satisfies the following relationship in terms of mass percentage: 13≤Mn / C≤36.

[0252] Furthermore, the chemical composition of the continuous casting billet satisfies, in terms of mass percentage: CEV=0.303~0.389.

[0253] Preferably, CEV=0.343~0.350.

[0254] Furthermore, the chemical composition of the continuous casting billet satisfies, in terms of mass percentage: Pcm=0.121~0.172.

[0255] Preferably, Pcm=0.140~0.172.

[0256] More preferably, Pcm=0.142~0.149.

[0257] Preferably, the contents of some impurity elements in the chemical composition of the continuous casting billet are described as follows.

[0258] S is controlled to be below 0.0015%, preferably controlled to be 0.0009~0.0015%.

[0259] O is controlled below 0.0025%, preferably controlled within 0.0011~0.0025%.

[0260] N is controlled below 0.0055%, preferably controlled to 0.0025~0.0051%.

[0261] H is controlled below 0.00020%, preferably controlled within 0.00005~0.00018%.

[0262] Furthermore, the center segregation of the continuous casting billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0263] Furthermore, the ratings of the A, B, C, and D inclusions of the continuous casting slab are all ≤ level 1, and the sum of the ratings of the four types of inclusions A, B, C, and D is A+B+C+D ≤ level 3.0.

[0264] Furthermore, the number of inclusions with a size of ≥10 μm on the cross section of the continuous casting billet is ≤10 / cm 2 .

[0265] The following describes the detailed technical solutions for each step of the preparation method of this embodiment.

[0266] <Heating process>

[0267] The continuous casting slab is heated in a heating furnace.

[0268] The soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min.

[0269] Preferably, the heating process includes preheating, first heating, second heating and soaking in sequence.

[0270] The preheating temperature is ≤950℃, the first heating temperature is 1050±15℃, and the second heating temperature is 1150±15℃.

[0271] <First hot rolling process>

[0272] The heated continuous casting slab is hot rolled in multiple passes from a thickness of 300~320mm to a plate thickness of (3.2~4.2)t.

[0273] Rolling temperature T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃.

[0274] Preferably, the first hot rolling process includes several widening passes and several non-widening passes.

[0275] Among them, the reduction of the initial rolling pass without widening pass is ≥42mm.

[0276] The minimum reduction for each pass is ≥31mm.

[0277] <Water cooling process>

[0278] After the steel plate leaves the hot rolling mill of the first hot rolling process, it enters the water cooling device for water cooling.

[0279] The final cooling temperature is Ar3-15℃~Ar3+5℃. That is, the water is discharged when the temperature of the steel plate is cooled to Ar3-15℃~Ar3+5℃.

[0280] <Second hot rolling process>

[0281] After the steel plate comes out of the water, it is hot rolled in multiple passes, from the plate thickness (3.2~4.2)t to the plate thickness t≥38mm.

[0282] The starting rolling temperature and the finishing rolling temperature are both Ar3-15℃~Ar3+5℃.

[0283] Preferably, in the multiple passes of the second hot rolling process, the reduction in the last pass is ≤8 mm, and the reduction in the remaining passes is ≥22 mm.

[0284] Preferably, the rolling temperature of each pass is Ar3-15°C~Ar3+5°C.

[0285] The rolling temperature of each pass can be further controlled to be Ar3-10℃~Ar3+5℃, more preferably Ar3-10℃~Ar3.

[0286] <Ultra-fast water cooling process>

[0287] After the steel plate leaves the hot rolling mill of the second hot rolling process, it directly enters the ultra-fast cooling system for ultra-fast water cooling.

[0288] Water inlet temperature ≥A r3 -30℃.

[0289] Final cooling temperature is B s -(360~320)℃.

[0290] The cooling rate is 9~22℃ / s.

[0291] Preferably, when ultra-fast water cooling is performed on the ultra-fast cooling system, the water pressure can be controlled to be 0.20~0.50MPa, the upper and lower water ratio can be controlled to be 0.91~0.95, and the roller speed can be controlled to be 1.0~1.4m / s.

[0292] <Air cooling and self-tempering process>

[0293] After the steel plate exits the ultra-fast cooling system, it is placed on a cooling bed for natural air cooling and self-tempering until it cools to room temperature to obtain the finished steel plate.

[0294] The temperature of the upper cooling bed shall not be lower than 150℃.

[0295] Preferably, after the steel plate exits the ultra-fast cooling system, that is, after exiting the water and before being placed on the cooling bed, it can be hot straightened. This can further improve the plate shape. Of course, this application is not limited to this.

[0296] Furthermore, the preparation method also includes a continuous casting billet stacking process.

[0297] The stacking temperature is ≥500℃ and the destacking temperature is 230~280℃.

[0298] In this embodiment, the finished steel plate obtained by the preparation method has a structure of a multiphase structure of quasi-polygonal ferrite+acicular ferrite+bainite.

[0299] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 45-55%, the volume proportion of the acicular ferrite structure is 15-35%, and the volume proportion of the bainite structure is 20-30%.

[0300] Furthermore, the average grain size of quasi-polygonal ferrite and acicular ferrite is 4-9 μm.

[0301] Furthermore, the yield strength R of the finished steel plate t0.5 ≥460MPa, tensile strength R m ≥580MPa, elongation A 50mm ≥31%, yield strength ratio R t0.5 / R m ≤0.80.

[0302] Furthermore, the yield strength R t0.5 It is 460~540MPa.

[0303] Tensile strength R m It is 580~660MPa.

[0304] Elongation A 50mm It is 31~58%.

[0305] Yield strength ratio R t0.5 / R m It is 0.70~0.80.

[0306] The impact energy of the finished steel plate at -20℃ KV2≥400J.

[0307] The impact energy of the finished steel plate at -40℃ KV2≥380J.

[0308] The impact energy of the finished steel plate at -60℃ KV2≥320J.

[0309] The impact energy of the finished steel plate at -80℃ KV2≥250J.

[0310] Tough-brittle transition temperature T of finished steel plate t50%US ≤-100℃.

[0311] The -10℃ DWTT drop weight shear area fraction of the finished steel plate is 100%.

[0312] The -20℃ DWTT drop weight shear area fraction of the finished steel plate is ≥90%.

[0313] The -30℃ DWTT drop weight shear area fraction of the finished steel plate is ≥80%.

[0314] The crack tip opening displacement of the finished steel plate at -20℃ CTOD is ≥1.5mm.

[0315] The hardness of the finished steel plate is ≤205HV 10 .

[0316] For example, the hardness is 175~205HV 10 .

[0317] Furthermore, under the conditions of 20° C., carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s, the uniform corrosion rate of the finished steel plate is ≤0.10 mm / year.

[0318] [Third embodiment]

[0319] The method for preparing a steel plate provided in this embodiment prepares a finished steel plate by subjecting a continuous casting billet to heating, a first hot rolling, water cooling, a second hot rolling, ultra-fast water cooling, and air cooling and self-tempering.

[0320] The chemical composition of the continuous casting billet includes, by mass percentage, C 0.026-0.056%, Si 0.11-0.17%, Mn 0.94-1.02%, P 0.0060-0.0099%, Cr 0.45-0.53%, Ni 0.09-0.17%, Mo 0.14-0.22%, Cu 0.15-0.23%, Nb 0.065-0.073%, Ti 0.014-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities.

[0321] Furthermore, the carbon content is preferably controlled within a range of 0.026-0.045%, more preferably within a range of 0.035-0.045%.

[0322] The manganese content is preferably controlled at 0.96-1.02%, more preferably at 0.96-1.01%.

[0323] The chromium content is preferably controlled at 0.47~0.51%.

[0324] The nickel content is preferably controlled at 0.09-0.15%, more preferably at 0.11-0.15%.

[0325] The molybdenum content is preferably controlled at 0.16-0.22%, more preferably at 0.17-0.19%.

[0326] The copper content is preferably controlled at 0.17~0.21%.

[0327] The niobium content is preferably controlled at 0.067~0.070%.

[0328] The titanium content is preferably controlled within the range of 0.015 to 0.022%, more preferably within the range of 0.015 to 0.018%.

[0329] Furthermore, the chemical composition of the continuous casting billet also satisfies the following relationship in terms of mass percentage: 13≤Mn / C≤36.

[0330] Furthermore, the chemical composition of the continuous casting billet satisfies, in terms of mass percentage: CEV=0.317~0.403.

[0331] Preferably, CEV=0.330~0.403.

[0332] More preferably, CEV=0.347~0.361.

[0333] Furthermore, the chemical composition of the continuous casting billet satisfies the following conditions in terms of mass percentage: Pcm=0.118~0.168.

[0334] Preferably, Pcm=0.118~0.150.

[0335] More preferably, Pcm=0.137~0.146.

[0336] Preferably, the contents of some impurity elements in the chemical composition of the continuous casting billet are described as follows.

[0337] S is controlled to be below 0.0015%, preferably controlled to be 0.0009~0.0015%.

[0338] O is controlled below 0.0025%, preferably controlled within 0.0011~0.0025%.

[0339] N is controlled below 0.0055%, preferably controlled to 0.0025~0.0051%.

[0340] H is controlled below 0.00020%, preferably controlled within 0.00005~0.00018%.

[0341] Furthermore, the center segregation of the continuous casting billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0342] Furthermore, the ratings of the A, B, C, and D inclusions of the continuous casting slab are all ≤ level 1, and the sum of the ratings of the four types of inclusions A, B, C, and D is A+B+C+D ≤ level 3.0.

[0343] Furthermore, the number of inclusions with a size of ≥10 μm on the cross section of the continuous casting billet is ≤10 / cm 2 .

[0344] The following describes the detailed technical solutions for each step of the preparation method of this embodiment.

[0345] <Heating process>

[0346] The continuous casting slab is heated in a heating furnace.

[0347] The soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min.

[0348] Preferably, the heating process includes preheating, first heating, second heating and soaking in sequence.

[0349] The preheating temperature is ≤950℃, the first heating temperature is 1050±15℃, and the second heating temperature is 1150±15℃.

[0350] <First hot rolling process>

[0351] The heated continuous casting slab is hot rolled in multiple passes from a thickness of 300~320mm to a plate thickness of (3.2~4.2)t.

[0352] Rolling temperature T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃.

[0353] Preferably, the first hot rolling process includes several widening passes and several non-widening passes.

[0354] Among them, the reduction of the initial rolling pass without widening pass is ≥42mm.

[0355] The minimum reduction for each pass is ≥31mm.

[0356] <Water cooling process>

[0357] After the steel plate leaves the hot rolling mill of the first hot rolling process, it enters the water cooling device for water cooling.

[0358] Final cooling temperature is Ar3-5℃~Ar3+15℃.

[0359] <Second hot rolling process>

[0360] After the steel plate comes out of the water, it is hot rolled in multiple passes, from the plate thickness (3.2~4.2)t to the plate thickness t≥38mm.

[0361] The starting rolling temperature and the final rolling temperature are both Ar3-5℃~Ar3+15℃.

[0362] Preferably, in the multiple passes of the second hot rolling process, the reduction in the last pass is ≤8 mm, and the reduction in the remaining passes is ≥22 mm.

[0363] Preferably, the rolling temperature of each pass is Ar3-5°C~Ar3+15°C.

[0364] The rolling temperature of each pass can be further controlled to be Ar3-5℃~Ar3+10℃, more preferably Ar3~Ar3+5℃.

[0365] <Ultra-fast water cooling process>

[0366] After the steel plate leaves the hot rolling mill of the second hot rolling process, it directly enters the ultra-fast cooling system for ultra-fast water cooling.

[0367] Water inlet temperature ≥A r3 -30℃.

[0368] Final cooling temperature is B s -(340~300)℃.

[0369] The cooling rate is 9~22℃ / s.

[0370] Preferably, when ultra-fast water cooling is performed on the ultra-fast cooling system, the water pressure can be controlled to be 0.20~0.50MPa, the upper and lower water ratio can be controlled to be 0.91~0.95, and the roller speed can be controlled to be 0.8~1.2m / s.

[0371] <Air cooling and self-tempering process>

[0372] After the steel plate exits the ultra-fast cooling system, it is placed on a cooling bed for natural air cooling and self-tempering until it cools to room temperature to obtain the finished steel plate.

[0373] The temperature of the upper cooling bed shall not be lower than 150℃.

[0374] Preferably, after the steel plate exits the ultra-fast cooling system, that is, after exiting the water and before being placed on the cooling bed, it can be hot straightened. This can further improve the plate shape. Of course, this application is not limited to this.

[0375] Furthermore, the preparation method also includes a continuous casting billet stacking process.

[0376] The stacking temperature is ≥500℃ and the destacking temperature is 230~280℃.

[0377] In this embodiment, the finished steel plate obtained by the preparation method has a structure of a multiphase structure of quasi-polygonal ferrite+acicular ferrite+bainite.

[0378] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 15-25%, the volume proportion of the acicular ferrite structure is 60-70%, and the volume proportion of the bainite structure is 5-15%.

[0379] Furthermore, the average grain size of quasi-polygonal ferrite and acicular ferrite is 3-6 μm.

[0380] Furthermore, the yield strength R of the finished steel plate t0.5 ≥490MPa, tensile strength R m ≥600MPa, elongation A 50mm ≥30%, yield strength ratio R t0.5 / R m ≤0.82.

[0381] Furthermore, the yield strength R t0.5 It is 490~570MPa.

[0382] Tensile strength R m It is 600~680MPa.

[0383] Elongation A 50mm It is 30~56%.

[0384] Yield strength ratio R t0.5 / R m It is 0.75~0.82.

[0385] The impact energy of the finished steel plate at -20℃ KV2≥400J.

[0386] The impact energy of the finished steel plate at -40℃ KV2≥380J.

[0387] The impact energy of the finished steel plate at -60℃ KV2≥320J.

[0388] The impact energy of the finished steel plate at -80℃ KV2≥250J.

[0389] Tough-brittle transition temperature T of finished steel plate t50%US ≤-100℃.

[0390] The -10℃ DWTT drop weight shear area fraction of the finished steel plate is 100%.

[0391] The -20℃ DWTT drop weight shear area fraction of the finished steel plate is ≥90%.

[0392] The -30℃ DWTT drop weight shear area fraction of the finished steel plate is ≥80%.

[0393] The crack tip opening displacement of the finished steel plate at -20℃ CTOD is ≥1.5mm.

[0394] The hardness of the finished steel plate is ≤210HV 10 .

[0395] For example, the hardness is 180~210HV 10 .

[0396] Furthermore, under the conditions of 20° C., carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s, the uniform corrosion rate of the finished steel plate is ≤0.10 mm / year.

[0397] In each embodiment of the present invention, the continuous casting billet can be prepared by any feasible known technical solution in the art, which is understandable to those skilled in the art and is not limited in this application.

[0398] Of course, the continuous casting billet can also be prepared by a preferred smelting technology, for example, including the processes of KR desulfurization, converter smelting, LF refining, RH vacuum refining and continuous casting.

[0399] Among them, KR desulfurization process: the outgoing molten iron temperature is ≥1300℃, S≤0.0020%.

[0400] In the converter smelting process: the slag basicity is controlled at 1.9~2.1, the total iron in the slag is 13~16%; the final slag basicity is controlled at 3.6~4.2, the final slag total iron is controlled at 14~17%, the temperature is controlled at 1645~1665℃, and P≤0.006%.

[0401] In the LF refining process: first deoxidize with a deoxidizer on the slag surface, then blow argon from the bottom of the ladle for strong stirring, then alloying is carried out, and finally power is turned on to control the tapping temperature at 1624±5℃.

[0402] During the strong stirring of the LF refining process, the flow rate of argon gas is 650~850NL / min and the duration does not exceed 6 minutes.

[0403] During alloying in the LF refining process, the bottom blowing argon flow rate is 620~820NL / min and the duration does not exceed 4 minutes; at other times, the bottom blowing argon flow rate does not exceed 450NL / min.

[0404] During the power-on period of the LF refining process, calcium carbide is added for diffusion deoxidation, and white slag is produced, and the white slag retention time is greater than 15 minutes.

[0405] In the RH vacuum refining process: no oxygen is blown throughout the process, and when the vacuum degree is ≤2.5mbar, degassing takes 18~23min, net circulation takes 7~9min, the steel ladle is left standing on the turntable for 12~16min, and the tapping temperature is regulated so that the temperature of the start-casting furnace is 1587±5℃ and the temperature of the continuous casting furnace is 1577±5℃.

[0406] In the continuous casting process: the superheat is controlled at 26~32℃, secondary cooling electromagnetic stirring and dynamic soft reduction are used, the reduction is 4~7% of the continuous casting billet thickness, the crystallizer water volume of the continuous casting machine is 420~550L / min, the water inlet temperature is 25~40℃, and the water outlet temperature difference is 4~10℃.

[0407] As previously mentioned, this application is not limited to the continuous casting process. The above describes the technical principles of the present invention and the basic details of each embodiment. Several experimental examples of the present invention are described below. Of course, these experimental examples are only a portion of the numerous variations of the present invention, not all of them.

[0408] The chemical compositions of the steel plates of these test examples are shown in Table 1.

[0409] [Table 1]

[0410]

[0411] These test examples were all prepared according to the preparation method introduced in the present invention. Specifically, Test Examples 1 and 2 were prepared according to the first embodiment, Test Examples 3 and 4 were prepared according to the second embodiment, and Test Examples 5 and 6 were prepared according to the third embodiment.

[0412] Among them, some important parameters in the production process are shown in Table 2.

[0413] [Table 2]

[0414]

[0415] [Table 2 continued]

[0416]

[0417] The steel plates of each test case were tested for structure and performance, and the test results are as follows:

[0418] (1) The steel plate is a composite structure of quasi-polygonal ferrite + acicular ferrite + bainite; the metallographic structures of test examples 1, 3, and 5 are respectively Figure 1 、 2 , 3; Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite, the volume proportion of each structure in the complex phase structure, and the banded structure grade are shown in Table 3;

[0419] [Table 3]

[0420]

[0421] (2) For the steel plates of each test case, the impact energy KV2 at -20℃ is ≥400J, the impact energy KV2 at -40℃ is ≥380J, the impact energy KV2 at -60℃ is ≥320J, the impact energy KV2 at -80℃ is ≥250J, and the ductile-brittle transition temperature T t50%US≤-100℃, -10℃ DWTT drop weight shear area fraction 100%, -20℃ DWTT drop weight shear area fraction ≥90%, -30℃ DWTT drop weight shear area fraction ≥80%, -20℃ CTOD crack tip opening displacement ≥1.5mm;

[0422] [Table 4]

[0423]

[0424] (3) The strength, elongation, hardness, etc. of the steel plates of each test example are shown in Table 4. In addition, the uniform corrosion rate of the steel plates under the conditions of 20°C, carbon dioxide pressure of 1.0 MPa, and liquid phase flow rate of 1 m / s is also shown in Table 4.

Claims

1. A method for preparing a steel plate for a carbon dioxide transport pipeline, characterized in that: The preparation method prepares the continuous casting billet into a finished steel plate through heating, first hot rolling, water cooling, second hot rolling, ultra-fast water cooling, air cooling and self-tempering; The chemical composition of the continuous casting billet comprises, by mass percentage, C 0.026-0.071%, Si 0.11-0.17%, Mn 0.89-1.02%, P 0.0060-0.0099%, Cr 0.31-0.53%, Ni 0.09-0.23%, Mo 0.08-0.22%, Cu 0.15-0.33%, Nb 0.058-0.073%, Ti 0.010-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities; During the heating process: the soaking temperature is T NbC +(40~100)℃, soaking time is 30~50min; T NbC is the starting precipitation temperature of NbC; The first hot rolling process includes multiple passes, the plate thickness after rolling is (3.2~4.2)t, and the starting rolling temperature is T nr +(5~25)℃, final rolling temperature T nr +(0~20)℃;T nr is the lowest temperature for austenite recrystallization; In the water cooling process: the final cooling temperature is Ar3-20℃~Ar3+15℃; Ar3 is the temperature at which ferrite begins to precipitate from austenite during cooling; The second hot rolling process includes multiple passes, the plate thickness after rolling is t≥38mm, and the starting and finishing temperatures are both Ar3-20℃~Ar3+15℃; In the ultra-fast water cooling process: water inlet temperature ≥A r3 -30℃, final cooling temperature is B s -(460~300)℃, cooling rate is 9~22℃ / s; B s is the temperature at which the bainite transformation begins; In the air-cooling autotempering process: the steel plate is air-cooled to room temperature on the cooling bed.

2. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The chemical composition of the continuous casting billet further satisfies the following in terms of mass percentage: 13≤Mn / C≤36.

3. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The chemical composition of the continuous casting slab, in terms of mass percentage, further satisfies: CEV = [C] + [Mn] / 6 + ( [Cr] + [Mo]) / 5 + ( [Cu] + [Ni]) / 15 = 0.294 to 0.403; and / or, Pcm=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[Mo] / 15=0.118~0.

176.

4. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: In the first hot rolling process: The reduction of the initial rolling pass of the non-widening pass is ≥42mm, and the minimum reduction of each pass is ≥31mm.

5. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: In the second hot rolling process: The reduction of the last pass is ≤8mm, and the reduction of the remaining passes is ≥22mm.

6. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: During the heating process: It includes preheating, first heating, second heating and soaking in sequence; The preheating temperature is ≤950℃, the first heating temperature is 1050±15℃, and the second heating temperature is 1150±15℃.

7. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: In the second hot rolling process: The rolling temperature of each pass is Ar3-20℃~Ar3+15℃.

8. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The preparation method further comprises: After the continuous casting billets leave the continuous casting machine, they are directly stacked. The stacking temperature is ≥500℃ and the destacking temperature is 230~280℃.

9. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The chemical composition of the continuous casting billet comprises, by mass percentage, C 0.041-0.071%, Si 0.11-0.17%, Mn 0.89-0.97%, P 0.0060-0.0099%, Cr 0.31-0.39%, Ni 0.15-0.23%, Mo 0.08-0.16%, Cu 0.25-0.33%, Nb 0.058-0.066%, Ti 0.010-0.018%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities; In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-20℃~Ar3; In the ultra-fast water cooling process: the final cooling temperature is B s -(460~400)℃.

10. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The chemical composition of the continuous casting billet comprises, by mass percentage, C 0.034-0.064%, Si 0.11-0.17%, Mn 0.91-0.99%, P 0.0060-0.0099%, Cr 0.37-0.45%, Ni 0.12-0.20%, Mo 0.11-0.19%, Cu 0.20-0.28%, Nb 0.061-0.069%, Ti 0.012-0.020%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities; In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-15℃~Ar3+5℃; In the ultra-fast water cooling process: the final cooling temperature is B s -(360~320)℃.

11. The method for preparing a steel plate for a carbon dioxide transportation pipeline according to claim 1, wherein: The chemical composition of the continuous casting billet comprises, by mass percentage, C 0.026-0.056%, Si 0.11-0.17%, Mn 0.94-1.02%, P 0.0060-0.0099%, Cr 0.45-0.53%, Ni 0.09-0.17%, Mo 0.14-0.22%, Cu 0.15-0.23%, Nb 0.065-0.073%, Ti 0.014-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities; In the second hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-5℃~Ar3+15℃; In the ultra-fast water cooling process: the final cooling temperature is B s -(340~300)℃.

12. A steel plate for a carbon dioxide transport pipeline, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C 0.026-0.071%, Si 0.11-0.17%, Mn 0.89-1.02%, P 0.0060-0.0099%, Cr 0.31-0.53%, Ni 0.09-0.23%, Mo 0.08-0.22%, Cu 0.15-0.33%, Nb 0.058-0.073%, Ti 0.010-0.022%, Al 0.022-0.049%, and the remainder is iron and unavoidable impurities; Under the conditions of 20° C., a carbon dioxide pressure of 1.0 MPa, and a liquid phase flow rate of 1 m / s, the uniform corrosion rate of the steel plate is ≤0.10 mm / year.

13. The steel plate for carbon dioxide transportation pipeline according to claim 12, characterized in that: On the cross section of the steel plate, the number of inclusions with a size of ≥10 μm is ≤10 / cm 2 , the maximum size of inclusions does not exceed 15μm, and the average size of inclusions is 0.1~2μm.

14. The steel plate for a carbon dioxide transportation pipeline according to claim 12, characterized in that: The yield strength R of the steel plate t0.5 ≥420MPa, tensile strength R m ≥560MPa, elongation A 50mm ≥30%, yield strength ratio R t0.5 / R m ≤0.

82.

15. The steel plate for carbon dioxide transportation pipeline according to claim 12, characterized in that: The steel plate has an impact energy KV2 of ≥400J at -20°C, an impact energy KV2 of ≥380J at -40°C, an impact energy KV2 of ≥320J at -60°C, and an impact energy KV2 of ≥250J at -80°C; The ductile-brittle transition temperature T t50%US ≤-100℃; The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, a -20°C DWTT drop weight shear area fraction of ≥90%, a -30°C DWTT drop weight shear area fraction of ≥80%, and a -20°C CTOD crack tip opening displacement of ≥1.5 mm; The hardness of the steel plate is ≤210HV 10 .

16. The steel plate for a carbon dioxide transportation pipeline according to claim 12, characterized in that: The structure of the steel plate is a multiphase structure of quasi-polygonal ferrite + acicular ferrite + bainite; The volume proportion of quasi-polygonal ferrite is 15-65%, the volume proportion of acicular ferrite is 15-70%, and the volume proportion of bainite is 5-30%. The average grain size of quasi-polygonal ferrite and acicular ferrite is 3~10μm.

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