A 800MPa grade, uniformly sized, extra-thick steel plate for containers and its manufacturing method.

Abstract

The present invention belongs to the field of metal materials, and particularly relates to an 800 MPa-grade, uniform, and extra-thick steel plate for containers, and its manufacturing method. The chemical composition of the steel, by weight, is as follows: C: 0.18% to 0.23%, Si: 0.15% to 0.37%, Mn: 0.98% to 1.24%, P ≤ 0.01%, S ≤ 0.005%, Ni: 0.11% to 0.32%, Cr: 0.04% to 0.18%, V: 0.02% to 0.04%, with the balance being Fe and unavoidable inclusions. This invention utilizes a novel chemical composition design, a three-stage / two-stage efficient slab heating system, an optimized three-stage rolling process, a two-stage cooling process, a high-temperature, short-time tempering heat treatment, and a unique manufacturing process to produce an extra-thick steel plate for containers with excellent overall performance, high strength, and high uniformity.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and particularly relates to an extra-thick steel plate for containers with 800MPa grade and uniform performance, and its manufacturing method. Background Technology

[0002] With the rapid development of the global economy and the continuous growth in energy demand, industries such as petroleum, chemical, and power plants are increasingly demanding high-strength, corrosion-resistant, and high-temperature-resistant pressure vessel steel plates. These industries require equipment capable of withstanding high-temperature and high-pressure environments, and high-strength pressure vessel steel plates are key materials for manufacturing such equipment. As a crucial material for manufacturing pressure vessels, the uniformity of the microstructure and properties of pressure vessel steel plates directly affects the safe operation of the equipment. When there is inhomogeneity in the internal microstructure of the steel plate, such as uneven grain size or uneven distribution of inclusions, it leads to inconsistent mechanical properties of the material, resulting in stress concentration during stress application and increasing the risk of equipment failure. Therefore, steel plates with uniform microstructure and properties ensure that all parts of the equipment are evenly stressed when subjected to design pressure, avoiding damage caused by excessive local stress. At the same time, uniform microstructure and properties give the steel plate better corrosion resistance and high-temperature resistance, enabling it to resist the erosion of media and high-temperature environments, thereby extending the service life of the equipment. Therefore, the development of extra-thick steel plates for pressure vessels with high strength and uniform properties has become an inevitable trend.

[0003] Patent document CN118497618A discloses "an economical 800MPa grade high-strength steel plate and its production method". The steel plate is composed of the following components by weight percentage: C: 0.14-0.17%, Si: 0.15-0.30%, Mn: 1.30-1.40%, P≤0.015%, S≤0.005%, As≤0.010%, Als: 0.015-0.035%, Nb: 0.030-0.045%, Cr: 0.40-0.55%, Ti: 0.008-0.020%, B: 0.0008-0.0020%, N≤0.0050%, with the balance being Fe and other unavoidable impurities. The contents of the above elements also satisfy the relationship: CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.50%. The steel plates produced by sequentially tempering the above-mentioned components have thicknesses of 15-45mm. However, no process design research was conducted on steel plates with thicknesses greater than 45mm. Furthermore, the impact energy at -20℃ was studied, but the impact toughness at even lower temperatures below -20℃ was not addressed. Therefore, it is not suitable for the production of large-scale high-strength extra-thick container steel.

[0004] Patent document CN114107819A discloses "an 800MPa grade tempering-resistant high-strength steel plate and its preparation method." The steel plate is composed of the following components by weight percentage: C: 0.06–0.13%; Si: 0.30–0.60%; Mn: 1.4–1.8%; P ≤ 0.0010%; S ≤ 0.0005%; As ≤ 0.010%; Als: 0.015–0.045%; Nb: 0.03–0.05%; Cr: 0.20–0.40%; Mo: 0.1–0.40%; Ti: 0.008–0.020%; B: 0.0008–0.0020%; N: ≤ 0.0060%, with the remainder being Fe and unavoidable impurities. Furthermore, the above composition contains high levels of the elements Cr and Mo, and the large amount added increases the production cost of the steel plate. Furthermore, the examples did not specifically study or analyze the production and mechanical properties of steel plates thicker than 50 mm. Also, the above method only investigated impact toughness at -20°C, neglecting low-temperature impact toughness below -20°C, and did not address internal microstructure uniformity. Therefore, this method is not suitable for the large-scale production of high-strength, extra-thick container steel. Summary of the Invention

[0005] The purpose of this invention is to provide an extra-thick steel plate for containers with a strength of 800MPa and uniform performance, as well as its manufacturing method. Through a novel chemical composition design, a three-stage / two-stage efficient slab heating regime, an optimized three-stage rolling process, a two-stage cooling process, and a high-temperature short-time tempering heat treatment, a high-strength, highly uniform extra-thick steel plate for containers with excellent comprehensive performance is obtained. The steel plate exhibits superior strength, low-temperature toughness, high-temperature service performance, and shape, meeting the manufacturing and application requirements for high-performance storage tank steel plates. This invention has a low cost and is suitable for large-scale production.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A type of 800MPa grade, extra-thick container steel plate with uniform performance, wherein the chemical composition of the steel by weight percentage is: C: 0.18%~0.23%, Si: 0.15%~0.37%, Mn: 0.98%~1.24%, P≤0.01%, S≤0.005%, Ni: 0.11%~0.32%, Cr: 0.04%~0.18%, V: 0.02%~0.04%, with the balance being Fe and unavoidable inclusions; and Pcm%=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.30, CE%=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.45.

[0008] The reasons for limiting the amounts of each chemical element (C, Si, Mn, P, S, Ni, Cr, and V) in the steel plate of this invention are detailed below:

[0009] Carbon (C) is a crucial element affecting the properties of steel plates, significantly influencing their strength, toughness, and corrosion resistance. Adding a certain amount of C ensures the strength, hardness, and wear resistance of the steel plate, guaranteeing its service performance. Simultaneously, to ensure that the toughness of the steel plate is not affected and to maintain a good balance of toughness and plasticity under low-temperature conditions, this invention sets the C content range to 0.18%–0.23%.

[0010] Si is an essential element in steel, and because it readily combines with oxygen (O) in steel, it is often used as a deoxidizer. Si can dissolve in ferrite and austenite, playing a role in solid solution strengthening and improving the wear resistance and strength of the material. However, it easily leads to an increase in non-metallic inclusions in steel plates, negatively impacting the low-temperature impact performance of the steel plates. Therefore, this invention sets the Si content range to 0.15%–0.37%.

[0011] Manganese (Mn) is a good deoxidizer and desulfurizer. A certain amount of Mn in steel can eliminate or reduce the hot brittleness caused by sulfur (S), thereby improving the hot working properties of the steel. However, Mn easily combines with sulfur and segregates at grain boundaries, affecting the resistance of steel plates to hydrogen-induced cracking. Therefore, this invention sets the Mn content range to 0.98%–1.24%.

[0012] S and P are harmful elements in steel. To ensure the purity and toughness of steel, they must be strictly controlled. Therefore, this invention limits P to ≤ 0.01% and S to ≤ 0.005%.

[0013] Ni, an important alloying element in steel, can improve steel strength while ensuring its toughness, plasticity, and other processing properties. Adding Ni to steel can lower the pearlite transformation temperature and refine the pearlite microstructure in the steel sheet. Simultaneously, because Ni can lower the carbon content at the eutectoid point and increase the amount of pearlite in the steel sheet, it improves the steel sheet's strength, wear resistance, and corrosion resistance, thus enhancing its service performance. In this invention, the Ni content is set in the range of 0.11% to 0.32%.

[0014] Cr is a strong carbide-forming element, readily combining with C to form fine carbide particles. Chromium carbide particles have a high melting point and, during phase transformation, effectively prevent dislocation movement, increase grain boundary area, reduce austenite grain size, and inhibit grain growth, ensuring a good balance of strength and toughness in the steel plate while maintaining high-temperature performance. Cr also has a high affinity for O, which helps improve the steel plate's oxidation resistance. Cr increases the hardenability of the steel plate, acting as a secondary hardening agent, increasing its hardness, and ensuring good wear resistance and tempering stability. However, adding excessive Cr to steel can easily lead to dendritic segregation, which reduces the steel's plasticity and increases the likelihood of crack formation. This invention sets the Cr content range to 0.04%–0.18%.

[0015] Vanadium (V) is a strong carbide / nitride element that forms V(C,N) precipitates in steel, increasing the area of ​​nucleation grain boundaries and subgrain boundaries, strongly refining the grain structure, and playing a precipitation strengthening role, ensuring a good balance of strength and toughness in the steel plate. At high temperatures, vanadium carbides maintain the strength and toughness of the steel while improving its resistance to hydrogen corrosion. However, excessive content increases the brittleness of the steel plate, negatively impacting its weldability; therefore, the V content is set at 0.02–0.04%. Fine, dispersed Cr-C particles precipitated and stably existing at high temperatures ensure the strength and high-temperature service performance of the steel plate, while V(C,N) particles precipitated at low temperatures ensure its toughness. The two work together to ensure a good balance of strength and toughness and good service performance; therefore, the ratio of Cr to V carbides is set at 1.8–3.5 in this paper.

[0016] The microstructure of the steel plate of the present invention is composed of troostite, ferrite and spheroidal bainite in a volume percentage ratio of (1-1.2):1:(1.5-1.8), wherein the size of the spheroidal bainite is not greater than 80 nm and the grain size is grade 7-9. The total inclusion grade of the steel plate is not greater than 1.0 and the ratio of the number of second phase Cr and V carbides in the size range of 35-66 nm is 1.8-3.5.

[0017] The mechanical properties of the steel plate are: tensile strength R at room temperature m 820-840 MPa, yield strength R el With a tensile strength of 770–785 MPa and an elongation A ≥ 22%; and a tensile strength R at -40℃. m With a strength of 860–900 MPa and a yield strength R el With a pressure of 800–890 MPa, an elongation A ≥ 18%, and a transverse impact energy K V2 The average value is ≥185J; the yield strength ratio at T / 2 and T / 4 of the steel plate is in the range of 0.9 to 1.1, and the yield strength of the steel plate can reach 204MPa at a temperature of 450℃.

[0018] According to the hydrogen-induced cracking (HIC) test standards GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", the crack susceptibility (CSR%), crack length ratio (CLR%), and crack width ratio (CTR%) of the steel plate are all 0. According to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Ferric Chloride Pitting Corrosion of Stainless Steel", the corrosion rate of the steel plate is not greater than 0.002 g / m³. 2 .h

[0019] Tests were conducted according to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", and the volumetric wear of the steel plate was no greater than 0.0003 cm. 3 .

[0020] The thickness of the finished steel plate of this invention is 55-100mm.

[0021] A method for manufacturing an extra-thick steel plate for containers with 800MPa grade and uniform properties includes smelting, continuous casting, heating, rolling, cooling, and heat treatment; specifically including:

[0022] 1) Smelting Process: Steelmaking takes place in a converter, using high-quality scrap steel and molten iron as raw materials. The charge size is controlled between 70 and 90 mm, and the iron content is controlled above 78% to ensure steel purity, shorten process time, and reduce the difficulty of subsequent processes. Strict control is maintained over the converter dephosphorization and decarburization parameters. Decarburization oxygen blowing is controlled at 315–400 s; to effectively reduce the harmful element P content, dephosphorization oxygen blowing is controlled at 590–725 s, reducing the phosphorus mass fraction in the molten steel to below 0.01%; further deep desulfurization is performed in an LF refining furnace, with desulfurization oxygen blowing controlled at 575–700 s, reducing the sulfur content to below 0.005%; degassing is completed in an RH furnace, with the initial temperature controlled at 1638–1659℃ and the oxygen blowing rate controlled at 18–28 m³ / s. 3 The net circulation time is 415–700 s, and the pre-casting settling time is 270–390 s. By optimizing the smelting process parameters, steel oxidation is reduced, the content of inclusions in the steel is controlled, internal defects are reduced, and the internal quality of the cast billet is improved.

[0023] 2) Continuous casting process: After vacuum breaking, slab continuous casting is used for casting. The key control is the casting temperature. The tundish steel casting temperature is 1560–1578℃, with a superheat of 6–8℃. The billet pulling speed during casting is 17–26 mm / s. High-temperature casting refines the original as-cast microstructure. A light reduction process is used to improve the internal quality of the billet and reduce defects such as segregation and voids. The light reduction rate is controlled at 3%–5%. After casting, the billet is stacked for slow cooling for 24–36 hours, with 3–4 stacked surfaces.

[0024] 3) Heating Process: The continuously cast slab is sent to a heating furnace for heating. The slab undergoes segmented heating before being removed from the furnace. When the slab thickness is in the range of 320-360mm, a three-stage heating process is adopted, with the first heating stage having a temperature range of 986-1023℃, the second heating stage having a temperature range of 1210-1232℃, and the soaking stage having a temperature range of 1085-1118℃. The total time the slab is in the furnace is controlled at 3.3-4.6 hours. When the slab thickness is less than 320mm, a two-stage heating process is adopted, with the first heating stage having a temperature range of 1139-1235℃, the soaking stage having a temperature range of 1065-1120℃, and the total time in the furnace being controlled at 2.3-3.1 hours. By employing segmented heating, the uniformity of the internal structure of the steel billet is further improved, the original size of precipitated phase particles is controlled, and overheating of the steel plate is avoided, thus increasing heating efficiency. This ensures the uniformity of the internal structure and properties of the steel plate and reduces the impact of large inclusions on its service performance. It also fully releases internal stress in the steel plate while ensuring uniform temperature inside and outside the billet, facilitating further processing.

[0025] 4) Rolling process: The rolling process adopts a three-stage controlled rolling method. The rolling temperature at the beginning of the first stage recrystallization zone is 1132-1165℃, and the rolling temperature at the end of the first stage is 1060-1073℃, which fully refines the original austenite structure. The rolling control process adopts a "large-large-small cycle reduction" rolling process, with a rolling speed of 3.6-4.8m / s, a large reduction range of 9%-11%, and a small reduction range of 4%-6%, which reduces the deformation resistance of the steel plate, improves the yield of the steel plate, ensures sufficient recrystallization of grains, and refines the internal structure of the steel plate while ensuring the uniformity of the structure. After the first stage of rolling, the waiting time for the steel plate to reach the set temperature is controlled within the range of 30 to 45 seconds. In the second stage, the rolling temperature in the non-recrystallization zone starts at 940 to 965°C and ends at 850 to 862°C. The single-pass reduction adopts a "small-small-large cycle reduction" rolling control process, with the small reduction ranging from 5% to 8% and the large reduction ranging from 10% to 12%. With the "small-small-large cycle reduction" process, a phase transformation process occurs during rolling, increasing the ferrite content in the steel plate, further refining the internal structure, increasing the grain boundary area, and further flattening and elongating the austenite grains. The third stage, the fine-grained strengthening rolling stage, begins with a rolling temperature of 830–845℃ and ends with a rolling temperature of 810–822℃. A "small reduction" rolling control process is used for each pass, with a reduction range of 3%–5%. After rolling, the plate is leveled using a concave roll leveler, controlling the crown to 45–56 μm and the flatness to 0.16–0.25 mm / m. This further refines the internal structure of the steel plate, resulting in better overall plate shape control.

[0026] 5) Cooling Process: The uniform and fine microstructure further ensures the uniformity of the steel plate's properties and helps optimize the strength-toughness ratio. The fine-grain strengthening mechanism increases the steel plate's strength, thereby further improving its wear resistance and other service performance. Utilizing an online ultra-fast cooling-water-cooling segmented cooling method, combined with mechanisms such as fine-grain strengthening, precipitation strengthening, and phase transformation strengthening, the mechanical properties of the strip steel are significantly improved. Small-angle grain boundaries are introduced during the cooling process to enhance the steel plate's corrosion resistance. The ultra-fast cooling start temperature of the first cooling stage is controlled at 742–750℃, and the cooling rate is controlled at 120–150℃ / s; the water-cooling start temperature of the second cooling stage is controlled at 422–436℃, and the cooling rate is controlled at 32–57℃ / s.

[0027] 6) Heat Treatment Process: Due to the addition of elements such as C, Si, Mn, Ni, Cr, and V to the steel, the rolled steel plate immediately yields a ferrite + troostite + spheroidal bainite microstructure with excellent strength and toughness. However, the uneven grain size distribution of the steel plate leads to concentrations of structural and thermal stresses, making it prone to delayed cracking during flame cutting. Therefore, timely heat treatment is necessary to soften and relieve stress. To further control the internal microstructure of the steel plate while ensuring high production efficiency, this invention employs high-temperature short-time tempering heat treatment to ensure that the steel plate's strength is not compromised while giving it suitable ductility, toughness, low-temperature impact toughness, corrosion resistance, and good machinability. Therefore, the high-temperature tempering heat treatment of the steel is controlled at a temperature of 690–720℃, held for 25–35 minutes, and then cooled to room temperature in the furnace at a controlled cooling rate of 10–22℃ / s.

[0028] This invention optimizes the smelting process, employing hot metal treatment combined with full-process protective casting to improve steel purity, ensure the internal quality of the cast billet, strictly control the influence of elements such as P, S, and O, and maintain the original microstructure grain size. It utilizes a segmented, high-efficiency slab heating process (three-stage heating / two-stage heating) to shorten processing time, improve production efficiency, and ensure the heating quality of the cast billet. Through three-stage controlled rolling combined with two-stage cooling technology, the uniformity of the internal microstructure of the steel plate is further optimized, ensuring the uniformity and superior performance of thick steel plates, improving plate shape, and maintaining production efficiency. A high-temperature, short-time tempering heat treatment process improves the strength-toughness ratio while adjusting the material's microstructure, improving the mechanical properties of the steel plate, and ensuring its service performance. This invention provides an 800MPa grade, uniformly performing, extra-thick container steel plate and its manufacturing method, suitable for large-scale, high-efficiency, high-strength, extra-thick container steel production.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1) Based on the strengthening elements C, Si, and Mn, this invention adds appropriate amounts of Ni, Cr, and V alloying elements while strictly controlling the content of harmful elements P and S. Combined with optimized production processes, a uniform and refined ferrite + troostite + spheroidal bainite structure is obtained. The total inclusion grade of the steel plate is ≤1.0, and the grain size is between 7 and 9. The volume percentage ratio of troostite, ferrite, and spheroidal bainite is (1-1.2):1:(1.5-1.8), and the size of the spheroidal bainite is no greater than 80 nm. The ratio of the second phase Cr and V carbides in the size range of 35-66 nm is set at 1.8-3.5. The second phase Cr / V carbide particles in the size range below 66 nm are uniformly dispersed, ensuring the steel plate's strength, plasticity, low-temperature toughness, corrosion resistance, wear resistance, and other service performance.

[0031] 2) The steel plates for storage tanks obtained by this invention through a unique production process exhibit mechanical properties such as 820MPa≤R at room temperature. m ≤840MPa, 770MPa≤R el ≤785Mpa, A≥22%; under -40℃ condition, 860MPa≤R m ≤900MPa, 800MPa≤R el ≤890MPa, A≥18%, average transverse impact energy KV2≥185J; the yield strength ratio at T / 2 and T / 4 of the steel plate is in the range of 0.9 to 1.1, and the yield strength of the steel plate can still reach 204MPa at a temperature of 450℃; that is, the steel plate has uniform performance and good strength and toughness matching and high and low temperature service performance.

[0032] 3) According to the hydrogen-induced cracking (HIC) test standards GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96 hours of testing in solutions A and B, the crack susceptibility rate (CSR) (%), crack length ratio (CLR) (%), and crack width ratio (CTR) of the steel plate were all 0, indicating excellent resistance to hydrogen-induced cracking. According to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride", the corrosion rate of the steel plate in solutions A and B was not greater than 0.002 g / m. 2 The results indicate that the steel plate has good corrosion resistance (resistance to hydrogen-induced cracking and pitting corrosion) across its entire thickness.

[0033] 4) Tests were conducted according to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics". The results showed that the volumetric wear of the steel plate was no greater than 0.0003 cm. 3 Steel plates have good wear resistance. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0035] The production method adopted in this invention is: molten iron pretreatment—ladle refining—vacuum degassing—slab continuous casting—stacking and slow cooling—slab cleaning—three-stage / two-stage high-efficiency slab heating—three-stage rolling—two-stage cooling—high-temperature short-time tempering heat treatment, to produce container steel plates with a thickness of 55-100mm. The produced steel plates have uniform microstructure and properties, good strength and toughness matching, and excellent corrosion resistance and wear resistance.

[0036] Table 1 shows the chemical composition of the embodiments of the present invention; Table 2 shows the steel smelting-continuous casting and heating process parameters of the embodiments; Table 3 shows the steel rolling, cooling and heat treatment process parameters of the embodiments; Table 4 shows the final mechanical properties of the embodiments; Table 5 shows the evaluation test results of microstructure grain size and second phase particles; Table 6 shows the evaluation test results of microstructure inclusion grade of the steel plate of the embodiments; Table 7 shows the service performance test results of the embodiments - corrosion resistance (hydrogen-induced cracking test, pitting test) test, friction and wear test results.

[0037] Table 1 Chemical composition (wt, %) of the examples

[0038]

[0039] Table 2 Smelting-continuous casting and heating process parameters for the examples

[0040]

[0041] Table 3 shows the process parameters for steel rolling, cooling, and heat treatment in the examples.

[0042]

[0043] Table 4. Final Mechanical Properties of Examples

[0044]

[0045] Table 5 shows the results of the microstructure grain size and second-phase particle evaluation tests.

[0046]

[0047] Table 6. Results of the test for evaluating the inclusion grade of the steel plates in the examples.

[0048]

[0049] Table 7 shows the service performance test results of the examples.

[0050]

[0051] Based on the above results, it can be concluded that the tensile strength R at room temperature of the (55-100) mm thickness specification provided by this invention is [missing information]. m 820-840 MPa, yield strength R el With a tensile strength of 770–785 MPa and an elongation A ≥ 22%; and a tensile strength R at -40℃. m With a strength of 860–900 MPa and a yield strength R el The steel plate has a yield strength of 800–890 MPa, an elongation of A ≥ 18%, and an average transverse impact energy KV2 ≥ 185 J. The yield strength ratio at T / 2 and T / 4 is in the range of 0.9–1.1. Under the condition of 450℃, the yield strength of the steel plate can reach 204 MPa. The total inclusion grade of the steel plate is ≤ 1.0. The microstructure consists of ferrite + troostite + spheroidal bainite with a grain size of 7–9. The size of the spheroidal bainite is not greater than 80 nm, and the second phase Cr / V carbide particles with a size of less than 66 nm are uniformly dispersed. The steel plate exhibits excellent corrosion resistance (resistance to hydrogen-induced cracking and pitting corrosion) across its entire thickness. Specifically, according to the hydrogen-induced cracking (HIC) tests in GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96 hours of testing in solutions A and B, the crack susceptibility rate (CSR) (%), crack length ratio (CLR) (%), and crack width ratio (CTR) (%) are all 0, demonstrating excellent resistance to hydrogen-induced cracking. According to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Ferric Chloride Pitting Corrosion of Stainless Steel", the corrosion rate of the steel plate in solutions A and B is not greater than 0.002 g / m. 2 According to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", the test results show that the volumetric wear of the steel plate is no greater than 0.0003 cm. 3 The steel plate has good wear resistance. That is, the steel plate has excellent strength, low temperature toughness, high temperature service performance and excellent plate shape. The thickness specification of (55~100) mm steel plate meets the manufacturing and application requirements of high performance storage tank steel plates.

Claims

1. A type of extra-thick steel plate for containers with a strength of 800MPa and uniform properties, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.18%–0.23%, Si: 0.15%–0.37%, Mn: 0.98%–1.24%, P≤0.01%, S≤0.005%, Ni: 0.11%–0.32%, Cr: 0.04%–0.18%, V: 0.02%–0.04%, with the balance being Fe and unavoidable inclusions; and Pcm% = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B ≤ 0.30%. The manufacturing method of the 800MPa grade and uniformly performing extra-thick container steel plate includes smelting, continuous casting, heating, rolling, cooling, and heat treatment; specifically including: The heating process includes: when the billet thickness is in the range of 320-360mm, a three-stage heating process is adopted, wherein the temperature range of the first heating stage is 986-1023℃, the temperature range of the second heating stage is 1210-1232℃, and the temperature range of the soaking stage is 1085-1118℃, and the total time of the billet in the furnace is controlled at 3.3-4.6h; when the billet thickness is less than 320mm, a two-stage heating process is adopted, wherein the temperature range of the first heating stage is 1139-1235℃, the temperature range of the soaking stage is 1065-1120℃, and the total time of the billet in the furnace is controlled at 2.3-3.1h. The rolling process includes: a three-stage controlled rolling method. In the first stage, the rolling temperature begins in the recrystallization zone at 1132–1165℃ and ends at 1060–1073℃. A "large-large-small cycle reduction" rolling control process is used, with a rolling speed of 3.6–4.8 m / s, a large reduction range of 9%–11%, and a small reduction range of 4%–6%. After the first stage of rolling, the steel plate is allowed to heat for 30–45 seconds. The second stage does not involve further rolling. The initial rolling temperature in the crystallization zone is 940–965℃, and the final rolling temperature is 850–862℃. A "small-small-large cycle reduction" rolling process is used to control the reduction per pass, with small reductions ranging from 5% to 8% and large reductions controlled within 10% to 12%. In the third stage, the fine-grain strengthening rolling stage, the initial rolling temperature is 830–845℃, and the final rolling temperature is 810–822℃. A "small reduction" rolling process is used to control the reduction per pass, with a reduction range of 3% to 5%. The cooling process includes: controlling the starting temperature of the first cooling section of the steel plate to be 742-750℃ for ultra-rapid cooling and the cooling rate to be 120-150℃ / s; and controlling the starting temperature of the second cooling section to be 422-436℃ for water cooling and the cooling rate to be 32-57℃ / s. The heat treatment includes: high-temperature tempering heat treatment of steel at a controlled temperature of 690-720℃, holding at that temperature for 25-35 minutes, followed by furnace cooling to room temperature at a controlled cooling rate of 10-22℃ / s.

2. The 800MPa grade, uniformly sized, extra-thick container steel plate according to claim 1, characterized in that, The microstructure of the steel plate consists of troostite, ferrite, and spheroidal bainite, with a volume percentage ratio ranging from (1 to 1.2):1:(1.5 to 1.8). The spheroidal bainite has a size not exceeding 80 nm and a grain size of 7 to 9. The total grade of inclusions in the microstructure of the steel plate is not greater than 1.0, and the ratio of the second phase Cr and V carbides with a size in the range of 35 to 66 nm is 1.8 to 3.

5.

3. The 800MPa grade and uniformly performing extra-thick container steel plate according to claim 1, characterized in that, The mechanical properties of the steel plate are: tensile strength R at room temperature m 820-840 MPa, yield strength R el With a tensile strength of 770–785 MPa and an elongation A ≥ 22%; and a tensile strength R at -40℃. m With a strength of 860–900 MPa and a yield strength R el The yield strength is 800-890 MPa, elongation A ≥ 18%, and average transverse impact energy KV2 ≥ 185 J; the yield strength ratio at T / 2 and T / 4 of the steel plate is in the range of 0.9-1.1, and the yield strength of the steel plate can reach 204 MPa at a temperature of 450℃.

4. The 800MPa grade and uniformly performing extra-thick container steel plate according to claim 1, characterized in that, According to the hydrogen-induced cracking tests GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", the crack susceptibility (CSR%), crack length ratio (CLR%), and crack width ratio (CTR%) of the steel plate are all 0; according to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride", the corrosion rate of the steel plate is not greater than 0.002 g / m. 2 .h 5. The 800MPa grade and uniformly performing extra-thick container steel plate according to claim 1, characterized in that, Tests were conducted according to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", and the volumetric wear of the steel plate was no greater than 0.0003 cm. 3 .

6. The 800MPa grade and uniformly performing extra-thick container steel plate according to claim 1, characterized in that, The thickness of the finished steel plate is 55-100mm.

7. A method for manufacturing an 800MPa grade, uniformly performing, extra-thick container steel plate as described in any one of claims 1-6, comprising smelting, continuous casting, heating, rolling, cooling, and heat treatment; characterized in that, Specifically, it includes: The heating process includes: when the billet thickness is in the range of 320-360mm, a three-stage heating process is adopted, wherein the temperature range of the first heating stage is 986-1023℃, the temperature range of the second heating stage is 1210-1232℃, and the temperature range of the soaking stage is 1085-1118℃, and the total time of the billet in the furnace is controlled at 3.3-4.6h; when the billet thickness is less than 320mm, a two-stage heating process is adopted, wherein the temperature range of the first heating stage is 1139-1235℃, the temperature range of the soaking stage is 1065-1120℃, and the total time of the billet in the furnace is controlled at 2.3-3.1h. The rolling process includes: a three-stage controlled rolling method. In the first stage, the rolling temperature begins in the recrystallization zone at 1132–1165℃ and ends at 1060–1073℃. A "large-large-small cycle reduction" rolling control process is used, with a rolling speed of 3.6–4.8 m / s, a large reduction range of 9%–11%, and a small reduction range of 4%–6%. After the first stage of rolling, the steel plate is allowed to heat for 30–45 seconds. The second stage does not involve further rolling. The initial rolling temperature in the crystallization zone is 940–965℃, and the final rolling temperature is 850–862℃. A "small-small-large cycle reduction" rolling process is used to control the reduction per pass, with small reductions ranging from 5% to 8% and large reductions controlled within 10% to 12%. In the third stage, the fine-grain strengthening rolling stage, the initial rolling temperature is 830–845℃, and the final rolling temperature is 810–822℃. A "small reduction" rolling process is used to control the reduction per pass, with a reduction range of 3% to 5%. The cooling process includes: controlling the starting temperature of the first cooling section of the steel plate to be 742-750℃ for ultra-rapid cooling and the cooling rate to be 120-150℃ / s; and controlling the starting temperature of the second cooling section to be 422-436℃ for water cooling and the cooling rate to be 32-57℃ / s. The heat treatment includes: high-temperature tempering heat treatment of steel at a controlled temperature of 690-720℃, holding at that temperature for 25-35 minutes, followed by furnace cooling to room temperature at a controlled cooling rate of 10-22℃ / s.

8. The method for manufacturing an extra-thick container steel plate with 800MPa grade and uniform performance according to claim 7, characterized in that, The smelting process includes: controlling the charge size to between 70 and 90 mm, and controlling the molten iron content to above 78%; controlling decarburization oxygen blowing to 315–400 s; controlling dephosphorization oxygen blowing to 590–725 s; performing deep desulfurization treatment in an LF refining furnace, with desulfurization oxygen blowing controlled to 575–700 s; and completing degassing in an RH furnace, with the initial temperature controlled at 1638–1659 °C and the oxygen blowing rate controlled at 18–28 m³ / s. 3 The net circulation time is 415–700 s, and the pre-pouring settling time is 270–390 s.

9. The method for manufacturing an extra-thick container steel plate with 800MPa grade and uniform properties according to claim 7, characterized in that, The continuous casting process includes: a tundish steel pouring temperature of 1560–1578°C, a superheat setting of 6–8°C, and a billet pulling speed of 17–26 mm / s during pouring; a continuous casting billet light reduction process is adopted, wherein the light reduction rate is controlled at 3%–5%, and the billet is placed in a stack for slow cooling after leaving the line, with a stacking and slow cooling time of 24–36 hours and a stacking surface number of 3–4.

10. The method for manufacturing an 800MPa grade, uniformly performing, extra-thick container steel plate according to claim 7, characterized in that, After rolling, the plate is leveled by a concave roll leveler to control the crown to 45-56 μm and the flatness of the steel plate to 0.16-0.25 mm / m.

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