9Ni steel plate and production method thereof

Abstract

The invention discloses a 9Ni steel plate and a production method thereof. The steel plate is prepared from chemical components as follows: 0.04%-0.075% of C, 0.15%-0.33% of Si, 0.5%-0.8% of Mn, 8.6%-9.4% of Ni, 0.02%-0.04% of Al and the balance of iron and impurities. The production method comprises the following steps: heating, wherein the soaking temperature is 1150-1200 DEG C; rolling into an intermediate billet at the initial rolling temperature of 1050-1090 DEG C, then holding the temperature, and rolling into a hot-rolled plate at the initial rolling temperature of Tfr + / -10 DEG C and the final rolling temperature of Tfr + / -18 DEG C; water cooling is conducted, the water inlet temperature is Tfc + / -15 DEG C, the final cooling temperature is smaller than or equal to 200 DEG C, and the average cooling speed in the whole process is 25-35 DEG C / s; after discharging water, air-cooling to room temperature; and tempering treatment is conducted, the tempering temperature is 540-580 DEG C, and then air cooling is conducted to the room temperature. The problem of high yield ratio can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation and relates to a 9Ni steel plate and a production method thereof. Background Art

[0002] Compared with traditional energy sources, natural gas has the characteristics of high combustion calorific value and less pollution. In order to facilitate the transportation and storage of natural gas, it is generally liquefied into liquefied natural gas (LNG) at normal pressure of -162℃.

[0003] In view of the flammability and ultra-low temperature of LNG, the structural materials used in storage and transportation equipment must have the characteristics of high strength and excellent low-temperature toughness. Among them, 9Ni steel has become the mainstream structural material in the field of LNG storage and transportation equipment due to its outstanding toughness in deep cold environments.

[0004] However, 9Ni steel usually has a high yield strength ratio, and compared with thick specifications, the yield strength ratio of thin specifications 9Ni steel plates with the same composition is higher. A high yield strength ratio means a great safety hazard in a deep cold environment. Therefore, with the emphasis on safety, in addition to improving strength and low-temperature toughness, how to reduce the yield strength ratio has also become an important research direction for 9Ni steel.

[0005] For example, Chinese patent CN110541110A discloses a thin-gauge 9Ni steel plate and a production method thereof, which is intended to reduce the yield strength ratio, but can only achieve the yield strength ratio below 0.9, for example, within the range of 0.87 to 0.89, and the yield strength ratio is still relatively high. Summary of the invention

[0006] In order to solve the problem of high yield strength ratio of existing 9Ni steel plates, the object of the present invention is to provide a 9Ni steel plate and a production method thereof.

[0007] To achieve the above-mentioned purpose, an embodiment of the present invention provides a method for producing a 9Ni steel plate. The chemical composition of the steel plate includes, by mass percentage: C 0.04-0.075%, Si 0.15-0.33%, Mn 0.5-0.8%, Ni 8.6-9.4%, Al 0.02-0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities; The production method comprises the following steps: Heating process: heating the steel billet, with the soaking temperature at 1150~1200℃; Rolling process: First, the steel billet is rolled into a thickness of t 1 The intermediate billet is then heated and rolled into a thickness of t by the second stage.0 The hot rolled plate; wherein the first stage rolling starting temperature is 1050~1090℃, the second stage rolling starting temperature (T fr -10)~(T fr +10)℃, final rolling temperature (T fr -18)~(T fr +18)℃, 1.3≤t 1 / t 0 ≤12, T fr Obtained by the following formula 1; Cooling process: The hot rolled plate is cooled by water cooling. The water temperature of the hot rolled plate (T fc -15)~(T fc +15)℃,T fc The final cooling temperature is ≤200℃ and the average cooling rate is 25~35℃ / s. After exiting the water, the cooling plate is air-cooled to room temperature to obtain a cooling plate. Heat treatment process: the obtained cooling plate is tempered at a tempering temperature of 540-580°C for more than 30 minutes, and air-cooled to room temperature after tempering. T fr =879-97C+48Si-9.5Mn-5.1Ni-200Al formula 1; T fc =720+116C+27Si-10Mn+6Ni-177Al formula 2; The element symbols in Formula 1 and Formula 2 represent the mass percentage of each element in the steel billet.

[0008] As an optional embodiment, the hot rolled plate has a thickness of t 0 >8mm single-layer steel plate; The production method further comprises a casting step: preparing a continuous casting billet with a thickness of 220-250 mm by steelmaking and continuous casting; Furthermore, in the heating process, the obtained continuous casting billet is heated, the soaking temperature is 1150-1180° C., and the total heating time is 160-220 min.

[0009] Optionally, in the cooling process: the red-returning temperature is ≤300°C.

[0010] Optionally, in the cooling process: The hot rolled plate is water cooled on a post-rolling accelerated cooling control system; The post-rolling accelerated cooling control system has 24 groups of cooling headers, among which the 1st to 6th groups, the 7th to 18th groups, and the 19th to 24th groups constitute the first zone, the second zone, and the third zone respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500~3600L / s, the total cooling water flow of the first partition is 500~530L / s, all cooling manifolds of the first and third partitions are opened, and the cooling manifolds of the second partition are opened alternately.

[0011] Optionally, in the rolling process: the reduction rate of each pass in the first stage of rolling is 10-35%, and the reduction amount of at least three passes in the first five passes is not less than 8 mm.

[0012] Optionally, the heat treatment process: when the thickness t 0 When the thickness is above 10mm, the insulation time is 2t. 0 ~14t 0 min.

[0013] As another optional embodiment, the hot-rolled plate is a composite plate formed by stacking n layers of single plates, n is 2, 3 or 4, and the thickness of at least one layer of single plates is t; The production method further comprises the following steps: Ingot casting process: through steelmaking and continuous casting, a continuous casting ingot with a thickness of 220~250mm is prepared; Billeting process: heating the continuous casting billet, with the soaking temperature at 1200~1240℃ and the total heating time at 200~300min; rolling the heated continuous casting billet into a large slab with a thickness of 4.5t~10t; Composite process: cutting the obtained large slab into a plurality of small slabs, stacking and welding the n small slabs into a composite slab; the composite slab enters the heating process and is heated as the steel slab; Plate separation step: the tempered plate obtained in the heat treatment step is separated into n single-layer 9Ni steel plates by trimming.

[0014] Optionally, in the heating process: the steel billet is heated, and the heating process includes preheating, heating and soaking, the preheating temperature is 750~850℃, and the heating rate is 20~30℃ / min; the heating temperature is 1100~1200℃, and the heating rate is 30~50℃ / min; the soaking temperature is 1150~1180℃; and the total heating time is 160~220min.

[0015] Optionally, among the n single-layer 9Ni steel plates, a thickness t of at least one 9Ni steel plate is less than 8 mm.

[0016] Optionally, among the n single-layer 9Ni steel plates, a thickness t of at least one 9Ni steel plate is 3-8 mm.

[0017] Optionally, in the composite process: an antioxidant separator is provided between two adjacent small slabs of the composite blank; The antioxidant isolation agent is a coating composed of 55-65 parts by mass of blast furnace slag hydrothermal leaching material, 7-15 parts by mass of corn starch, 12-33 parts by mass of polyvinyl alcohol, 5-8 parts by mass of sodium tripolyphosphate and water.

[0018] Optionally, the method for preparing the antioxidant isolation agent comprises the following steps: After crushing the blast furnace slag, slag of the required particle size is screened out, the slag, hydrochloric acid and water are put into a reaction container, and then reacted at a temperature of 130-150° C. for 8-10 hours; Separating solid slag from the system after the reaction, and then washing, grinding and screening the solid slag to obtain blast furnace slag hydrothermal leaching material; Using blast furnace slag hydrothermal leaching material, corn starch, polyvinyl alcohol, and sodium tripolyphosphate as powders, and preparing the materials according to a mass ratio of water to the powders of 1:2 to 3:4; After heating the water to 90-95° C., polyvinyl alcohol is added and stirred, and the mixture is allowed to stand until it is cooled to 60-70° C., corn starch is added and stirred for 0.8-1.5 hours under constant temperature conditions, and then the leached material and sodium tripolyphosphate are added and stirred to obtain the antioxidant isolation agent.

[0019] Optionally, in the step of “crushing the blast furnace slag, screening out slag of a desired particle size, adding the slag, hydrochloric acid and water into a reaction container, and then reacting at a temperature of 130-150° C. for 8-10 hours”: The particle size of the slag is r mm, the concentration of hydrochloric acid is C mol / L, the volume ratio of the slag to hydrochloric acid is 0.2~0.8, the volume ratio of water to hydrochloric acid is 0.45~0.7, and C is in the range of (ln(r*60)-0.7)~(ln(r*60)+0.7).

[0020] Optionally, in the cooling process: the red-returning temperature is ≤300°C.

[0021] Optionally, in the cooling process: The hot rolled plate is water cooled on a post-rolling accelerated cooling control system; The post-rolling accelerated cooling control system has 24 groups of cooling headers, among which the 1st to 6th groups, the 7th to 18th groups, and the 19th to 24th groups constitute the first zone, the second zone, and the third zone respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500~3600L / s, the total cooling water flow of the first partition is 500~530L / s, all cooling manifolds of the first and third partitions are opened, and the cooling manifolds of the second partition are opened alternately.

[0022] Optionally, in the rolling process: the reduction rate of each pass in the first stage of rolling is 10-35%, and the reduction amount of at least three passes in the first five passes is not less than 8 mm.

[0023] Optionally, the heat treatment process: when the thickness t 0 When the thickness is above 10mm, the insulation time is 2t. 0 ~14t 0 min.

[0024] To achieve the above-mentioned purpose, an embodiment of the present invention provides a 9Ni steel plate. The chemical composition of the steel plate includes, by mass percentage: C 0.04-0.075%, Si 0.15-0.33%, Mn 0.5-0.8%, Ni 8.6-9.4%, Al0.02-0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities; The steel plate has a thickness of less than 8 mm, a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, a yield strength ratio of ≤0.87, an elongation of ≥23%, and an impact energy of ≥210 J at -196°C.

[0025] Furthermore, the thickness of the steel plate is 3-8 mm.

[0026] Compared with the prior art, the beneficial effects of the present invention include: regardless of whether it is thick or thin specifications, the specific technologies of the rolling process and the cooling process can lay the foundation for reducing the yield ratio, while ensuring the excellent low-temperature toughness and high strength of the steel plate, reducing the increase in the yield ratio caused by the heat treatment process, and finally reducing the yield ratio of the steel plate, thereby achieving comprehensive improvement in the strength, low-temperature toughness and yield ratio of the steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a metallographic structure diagram of a steel plate at 1 / 2 thickness of Example 2A in the second embodiment of the present invention; Figure 2 is a metallographic structure diagram at 1 / 2 thickness of a steel plate of Example 2B in the second embodiment of the present invention; Figure 3 is a metallographic structure diagram at 1 / 2 thickness of a steel plate of Example 2C in the second embodiment of the present invention; Figure 4 is a metallographic structure diagram of a steel plate at 1 / 2 thickness of Example 2D in the second embodiment of the present invention; Figure 5 is a metallographic structure diagram of a steel plate at 1 / 2 thickness of Example 2E in the second embodiment of the present invention; Figure 6 This is a metallographic structure diagram at 1 / 2 thickness of the steel plate of Example 2F in the second embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further introduced below in conjunction with specific implementation methods.

[0029] An embodiment of the present invention provides a method for producing a 9Ni steel plate. The produced 9Ni steel plate not only has the advantages of high strength and high and low temperature toughness, but also has a low yield strength ratio.

[0030] In terms of chemical composition, the chemical composition of the steel plate includes, by mass percentage, C 0.04~0.075%, Si0.15~0.33%, Mn 0.5~0.8%, Ni 8.6~9.4%, Al 0.02~0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities.

[0031] The following is an introduction to the role of each element in the above chemical composition.

[0032] C is a strengthening element and also an austenite stabilizing element. If the C content is low, the strength of the steel plate is difficult to ensure. If the C content is high, the toughness-brittleness transition temperature will be increased, affecting the low-temperature toughness of the steel plate. Therefore, under the premise of ensuring strength, the C content should be as low as possible. In the present invention, the C content is controlled at 0.04-0.075%.

[0033] Si is a deoxidizing element and can also inhibit the grain boundary segregation behavior of P; however, when the Si content is high, it affects the low temperature toughness of the steel plate. In the present invention, the Si content is controlled at 0.15-0.33%, and the deoxidation effect is ensured and the oxide inclusions in the steel are reduced without affecting the low temperature toughness.

[0034] Mn is a solid solution strengthening and fine grain strengthening element, and is also an austenite stabilizing element. Adding Mn can significantly improve the hardenability of the material; at the same time, Mn is also an element that is easy to segregate and form inclusions. Excessive addition will affect the fracture toughness and low temperature impact toughness of the steel plate. In the present invention, the Mn content is controlled at 0.5-0.8%.

[0035] Ni is an austenite stabilizing element, and is particularly important for stabilizing reversed austenite, which is the main component that provides deep-cold toughness of steel plates; it can improve the hardenability of steel plates and increase strength through solid solution strengthening. In the present invention, the Ni content is controlled at 8.6-9.4%.

[0036] Al, as a deoxidizing element, can effectively reduce the inclusion content in steel and refine the grains; excessive aluminum can easily make Al in steel 2 O 3 The increase of inclusions affects the low temperature toughness of the steel. In the present invention, Al is controlled within 0.02-0.04%.

[0037] P, S, N, H, O: impurity elements, should be controlled in a low range as much as possible. In the present invention, P≤0.005%, S≤0.002%, N≤0.0035%, H≤0.00015%, O≤0.002%.

[0038] In terms of production process, the production method uses a steel billet that meets the above chemical composition through the following heating process, rolling process, cooling process, and heat treatment process to produce a steel plate.

[0039] Heating process: heating the steel billet, with the soaking temperature at 1150~1200℃; Rolling process: First, the steel billet is rolled into a thickness of t 1 The intermediate billet is then heated and rolled into a thickness of t by the second stage. 0 The hot rolled plate; wherein the first stage rolling starting temperature is 1050~1090℃, the second stage rolling starting temperature (T fr -10)~(T fr +10)℃, final rolling temperature (T fr -18)~(T fr +18)℃, 1.3≤t 1 / t 0 ≤12; Cooling process: The hot rolled plate is cooled by water cooling. The water temperature of the hot rolled plate (T fc -15)~(T fc +15)℃, final cooling temperature ≤200℃, average cooling rate throughout the process 25~35℃ / s; air-cool to room temperature after exiting the water to obtain a cooling plate; Heat treatment process: the obtained cooling plate is tempered at a tempering temperature of 540-580°C for more than 30 minutes, and air-cooled to room temperature after the tempering.

[0040] The T mentioned above fr It can be obtained by the following formula 1, T fc Obtained by the following formula 2: T fr =879-97C+48Si-9.5Mn-5.1Ni-200Al formula 1; T fc =720+116C+27Si-10Mn+6Ni-177Al Formula 2; The element symbols in Formula 1 and Formula 2 represent the mass percentage of each element in the steel billet. For example, if the C content in the steel billet is 0.04% by mass, the element symbol C in Formula 1 and Formula 2 is substituted by the mass percentage of C 0.04.

[0041] Therefore, the production method of the present invention can not only prepare thick-gauge 9Ni steel plates, but also prepare thin-gauge 9Ni steel plates. Regardless of whether it is thick or thin, the specific techniques of the rolling process and the cooling process can be used to reduce the yield strength while stabilizing the tensile strength, thereby ensuring that the steel plate has excellent low-temperature toughness and high strength, and can reduce the increase in the yield ratio caused by the heat treatment process, and finally reduce the yield ratio of the steel plate, thereby achieving all-round improvement in strength, low-temperature toughness and yield ratio of the steel plate; in particular, for thin-gauge 9Ni steel plates, the difficulty of reducing the yield ratio is much greater than that of thick-gauge 9Ni steel plates. The production method of the present invention can solve the problem of high yield ratio of thin-gauge 9Ni steel plates, which is of great significance for thin-gauge 9Ni steel plates.

[0042] An attempt is made to explain the technical solution of the present invention in principle. For the production of 9Ni steel plates, on the one hand, it is necessary to perform fine grain strengthening through tempering heat treatment to improve strength and low-temperature toughness. However, fine grain strengthening in tempering heat treatment will cause a significant increase in yield strength, thereby simultaneously improving tensile strength, low-temperature toughness and yield strength ratio. In the present application, through specific operations in the rolling and cooling processes, the yield strength can be reduced while stabilizing the tensile strength, thereby eliminating the problem of excessive increase in the yield strength ratio during the heat treatment process, and ultimately achieving the effect of reducing the yield strength ratio without causing a decrease in tensile strength or low-temperature toughness.

[0043] Specifically, the 9Ni steel plate of the present invention has a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, and a yield strength ratio of ≤0.87, and has excellent characteristics of high strength and low yield strength ratio.

[0044] Furthermore, the steel sheet according to one embodiment of the present invention has an elongation of 23% or more, an impact energy of 210 J or more at -196°C, and excellent low-temperature toughness.

[0045] In addition, in one embodiment of the present invention, the metallographic structure of the cooling plate obtained in the cooling process is martensite + ferrite + reversed austenite; and further, after tempering, the metallographic structure of the steel plate finally obtained is a multiphase structure of tempered martensite + ferrite + reversed austenite, and wherein: the volume proportion of tempered martensite is 75~85%, the volume proportion of reversed austenite is 10~18%, and the rest is ferrite.

[0046] Furthermore, in one embodiment, the chemical composition of the steel plate further satisfies 68≤Ni / (C+Al)≤173 in terms of mass percentage. Thus, C, as an austenite stabilizing element, can increase the content of reversed austenite without affecting the composition standard, low temperature toughness, and welding. For example, the content of reversed austenite can be increased from 5% to 10% of general 9Ni steel to 10 to 18%.

[0047] Furthermore, in another embodiment, the chemical composition of the steel plate further satisfies Mn=(1.8-2.5)Si+0.17% in terms of mass percentage. In this way, Mn can improve the hardenability of the steel plate, and the cooling treatment by using the accelerated cooling control system after rolling can avoid the off-line quenching treatment in the conventional technology, reduce the complexity of the subsequent processes after the cooling process, reduce the production cost, and improve the production efficiency.

[0048] As mentioned above, the production method of the present invention can be used to prepare thick-gauge 9Ni steel plates and thin-gauge 9Ni steel plates, which are described in detail below.

[0049] First embodiment This embodiment provides implementation details of the production method described above for preparing thick-gauge 9Ni steel plates.

[0050] It can be understood that the chemical composition of the 9Ni steel plate in this embodiment is consistent with the above, for example, including, by mass percentage: C 0.04~0.075%, Si 0.15~0.33%, Mn 0.5~0.8%, Ni 8.6~9.4%, Al 0.02~0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities.

[0051] More preferably, the chemical composition of the steel plate further satisfies 68≤Ni / (C+Al)≤173, and / or further satisfies Mn=(1.8~2.5)Si+0.17%.

[0052] Specifically, the production method includes a process of sequentially performing a casting process, a heating process, a rolling process, a cooling process, and a heat treatment process to prepare a billet having a thickness of t 0 >8mm single layer 9Ni steel plate.

[0053] Ingot casting process: a continuous casting ingot with a thickness of 220-250 mm is prepared by steelmaking and continuous casting. The chemical composition of the continuous casting ingot is consistent with the chemical composition of the final 9Ni steel plate.

[0054] Heating process: heating the continuous casting billet obtained in the billet casting process, with the aquifer temperature at 1150~1200°C; the total heating time is 160~220min.

[0055] Rolling process: First, the steel billet is rolled into a thickness of t 1 The intermediate billet is then heated and rolled into a thickness of t by the second stage. 0 The hot rolled plate; wherein the first stage rolling starting temperature is 1050~1090℃, the second stage rolling starting temperature (T fr -10)~(T fr +10)℃, final rolling temperature (T fr -18)~(T fr +18)℃, 1.3≤t 1 / t 0 ≤12, T fr Obtained by the formula 1.

[0056] Cooling process: The hot rolled plate is cooled by water cooling. The water temperature of the hot rolled plate (T fc -15)~(T fc +15)℃,T fc According to Formula 2, the final cooling temperature is ≤200°C, and the average cooling rate throughout the process is 25-35°C / s; after exiting the water, the cooling plate is air-cooled to room temperature to obtain a cooling plate.

[0057] Heat treatment process: the obtained cooling plate is tempered at a tempering temperature of 540-580°C for more than 30 minutes. After the tempering is completed, it is air-cooled to room temperature to obtain a 9Ni steel plate.

[0058] In this embodiment, the thickness t of the obtained 9Ni steel plate is 0 >8mm, for example, it can be 8~12mm, tensile strength 730~810MPa, yield strength 590~680MPa, yield strength ratio ≤0.87; elongation ≥23%, -196℃ impact energy ≥210J.

[0059] The metallographic structure of the steel plate is a multiphase structure of tempered martensite + ferrite + reversed austenite, wherein: the volume proportion of tempered martensite is 75-85%, the volume proportion of reversed austenite is 10-18%, and the rest is ferrite.

[0060] Among them, in the casting process, the specific steelmaking and continuous casting methods can be implemented by any feasible technology in the technical field. For example, it can be implemented by adopting the process route of molten iron KR desulfurization-converter smelting-LF refining-RH refining-continuous casting. Since it is not the invention design point of this application, it will not be introduced in detail.

[0061] Preferably, in the heating process, the soaking temperature is controlled at 1150-1180°C.

[0062] Preferably, in the rolling process: the reduction rate of each pass in the first stage of rolling is 10-35%, and the reduction amount of at least three passes in the first five passes is not less than 8 mm.

[0063] Furthermore, in the rolling process, the steel billet may be descaled before the first stage rolling. Specifically, the steel billet may be roughly descaled after leaving the heating furnace and finely descaled before entering the rolling mill.

[0064] In one embodiment, 6≤t 1 / t 0 ≤12, further controlled to 7≤t 1 / t 0 ≤12.

[0065] In one embodiment, after the first stage of rolling, the thickness of the intermediate billet is t 1 It is 60~120mm.

[0066] Preferably, in the cooling process: the average cooling rate throughout the entire process is preferably controlled at 28-33°C / s, more preferably controlled at 28-30°C / s.

[0067] Alternatively, the average cooling rate throughout the entire process can be specifically controlled at 28, 29, 30, 31, 32, or 33°C / s.

[0068] Preferably, in the cooling process: the red-returning temperature is ≤300°C.

[0069] In another preferred embodiment, in the cooling process: The hot-rolled plate is water-cooled on an accelerated cooling control system (ACC) after rolling; the accelerated cooling control system after rolling has 24 groups of cooling headers, wherein the 1st to 6th groups, the 7th to 18th groups, and the 19th to 24th groups constitute the first sub-area, the second sub-area, and the third sub-area, respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500~3600L / s, the total cooling water flow of the first partition is 500~530L / s, all cooling manifolds of the first and third partitions are opened, and the cooling manifolds of the second partition are opened alternately.

[0070] In this way, by controlling the cooling of the first partition, the second partition and the third partition, the shape of the steel plate can be improved and the head and tail warping defects of the steel plate can be reduced.

[0071] In addition, preferably, the heat treatment process: when the thickness t 0When the thickness is above 10mm, the insulation time can be further set to 2t. 0 ~14t 0 min. And for thickness t 0 When the thickness is less than 10 mm, the insulation time may be specifically 30 minutes, but is not limited thereto, as long as it is more than 30 minutes.

[0072] Hereinafter, some corresponding examples are provided for the production method of this embodiment. The chemical compositions of the steel plates of these examples are shown in Table 1.

[0073] Table 1

[0074] The specific preparation process of the steel plates of these embodiments is as follows: Heating process: the continuous casting billet prepared by steelmaking and continuous casting is sent into a heating furnace for heating; wherein the thickness, soaking temperature and total heating time of the continuous casting billet are shown in Table 3; Rolling process: After the continuous casting billet leaves the heating furnace, it first goes through the first stage of rolling to a thickness of t 1 The intermediate billet is then heated and rolled in the second stage to a thickness of t 0 Hot rolled plate; where the thickness is t 1 , thickness t 0 , the first stage rolling temperature (i.e. 1 st The rolling temperature of the second stage (i.e., the rolling temperature of the first stage nd Rolling start temperature), final rolling temperature (i.e. 2 nd Final rolling temperature) are shown in Table 2; Table 2

[0075] Cooling process: On the ACC system, the hot-rolled plate is cooled by water cooling; the water inlet temperature, final cooling temperature, average cooling rate throughout the process, and red-return temperature of the hot-rolled plate are shown in Table 3; the steel plate is air-cooled to room temperature after exiting the water to obtain a cooled plate; Heat treatment process: the obtained cooling plate is subjected to tempering treatment; wherein the tempering temperature and the heat preservation time are shown in Table 3; after the tempering is completed, the plate is air-cooled to room temperature, and the 9Ni steel plate is obtained; Table 3

[0076] The obtained 9Ni steel plate was subjected to performance testing, and the test results are shown in Table 4; and the obtained 9Ni steel plate was subjected to metallographic structure testing, and the metallographic structure of the steel plate of each embodiment was a multiphase structure of tempered martensite+ferrite+reverse transformed austenite, as shown in Table 4; Table 4

[0077] It can be seen that when the production method of this embodiment produces 9Ni steel plates with a thickness of 8 mm or more, the resulting steel plates have the characteristics of high strength, high low temperature toughness and low yield strength ratio, and have excellent comprehensive performance.

[0078] Second embodiment This embodiment provides implementation details of the production method described above for preparing thin-gauge 9Ni steel plates.

[0079] It can be understood that the chemical composition of the 9Ni steel plate in this embodiment is consistent with the above, for example, including, by mass percentage: C 0.04~0.075%, Si 0.15~0.33%, Mn 0.5~0.8%, Ni 8.6~9.4%, Al 0.02~0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities.

[0080] More preferably, the chemical composition of the steel plate further satisfies 68≤Ni / (C+Al)≤173, and / or further satisfies Mn=(1.8~2.5)Si+0.17%.

[0081] In this embodiment, the production method includes a process of sequentially performing a casting process, a blanking process, a compounding process, a heating process, a rolling process, a cooling process, a heat treatment process and a plate separation process to prepare a single-layer 9Ni steel plate with a thickness of t≤8mm.

[0082] Specifically, the billet casting process: a continuous casting billet with a thickness of 220-250 mm is prepared by steelmaking and continuous casting, and the chemical composition of the continuous casting billet is consistent with the chemical composition of the finally obtained 9Ni steel plate.

[0083] Billeting process: heat the continuous casting billet, the average heating temperature is 1200~1240℃, and the total heating time is 200~300min; the heated continuous casting billet is rolled into a large slab with a thickness of 4.5t~10t.

[0084] Composite process: the obtained large slab is cut into multiple small slabs, n small slabs are stacked and welded into a composite slab, where n=2, 3 or 4.

[0085] Heating process: heating the obtained composite blank, with the soaking temperature at 1150-1200°C and the total heating time at 160-220min.

[0086] Rolling process: First, the steel billet is rolled into a thickness of t 1The intermediate billet is then heated and rolled into a thickness of t by the second stage. 0 The hot rolled plate; wherein the first stage rolling starting temperature is 1050~1090℃, the second stage rolling starting temperature (T fr -10)~(T fr +10)℃, final rolling temperature (T fr -18)~(T fr +18)℃, 1.3≤t 1 / t 0 ≤12, T fr Obtained by the formula 1.

[0087] Cooling process: The hot rolled plate is cooled by water cooling. The water temperature of the hot rolled plate (T fc -15)~(T fc +15)℃,T fc According to Formula 2, the final cooling temperature is ≤200°C, and the average cooling rate throughout the process is 25-35°C / s; after exiting the water, the cooling plate is air-cooled to room temperature to obtain a cooling plate.

[0088] Heat treatment process: the obtained cooling plate is tempered at a tempering temperature of 540-580°C for more than 30 minutes, and air-cooled to room temperature after the tempering.

[0089] Plate separation process: the tempered plate obtained in the heat treatment process is separated into n single-layer 9Ni steel plates by trimming, that is, the required thin-gauge 9Ni steel plates are obtained.

[0090] Preferably, for the production of a single-layer thin-gauge 9Ni steel plate of target thickness t, t 1 Can satisfy 7t≤t 1 ≤16t,t 0 It can satisfy (0.8~1.2)*n*t. Preferably, t 0 =n*t.

[0091] In one embodiment, 2≤t 1 / t 0 ≤8, further controlled to 2≤t 1 / t 0 ≤5, and further controlled at 2.5≤t 1 / t 0 ≤5, further 2.5≤t 1 / t 0 ≤4.

[0092] Optionally, the n 9Ni steel plates finally obtained may have substantially the same thickness of t, or may be implemented with different thicknesses.

[0093] In the present embodiment, among the obtained n single-layer 9Ni steel plates, the thickness t of at least one 9Ni steel plate is less than 8 mm, more preferably 3 to 8 mm, and further preferably 4 to 8 mm.

[0094] In one embodiment, a 9Ni steel plate has a thickness t of less than 8 mm, a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, a yield strength ratio of ≤0.87, an elongation of ≥23%, and an impact energy of ≥210 J at -196°C.

[0095] Among them, in the casting process, the specific steelmaking and continuous casting methods can be implemented by any feasible technology in the technical field. For example, it can be implemented by adopting the process route of molten iron KR desulfurization-converter smelting-LF refining-RH refining-continuous casting. Since it is not the invention design point of this application, it will not be introduced in detail.

[0096] Preferably, in the heating process: the steel billet is heated, and the heating process includes preheating, heating and soaking, the preheating temperature is 750~850℃, and the heating rate is 20~30℃ / min; the heating temperature is 1100~1200℃, and the heating rate is 30~50℃ / min; the soaking temperature is 1150~1200℃; and the total heating time is 160~220min. Through research, it is found that after the billet is opened, the specific operation of the heating process can not only heat the billet for subsequent rolling, but also reduce the yield strength ratio. Specifically, the rolling of thin-gauge steel plates inevitably has a large compression ratio. The corresponding large compression ratio will produce high-density dislocations and substructures, which will lead to a significant increase in yield strength and cause the problem of high yield strength ratio. This is also an important reason why the defect of high yield strength ratio of thin-gauge steel plates is more prominent than that of thick-gauge steel plates. The present application unexpectedly and largely eliminates the problem of excessive increase in yield strength caused by high-density dislocations and substructures through the operation in the heating process, thereby achieving a low yield strength ratio of thin-gauge steel plates.

[0097] Preferably, in the heating process, the heating temperature can be controlled at 1100-1180°C, and the soaking temperature can be controlled at 1150-1180°C.

[0098] Of course, the heating process of this embodiment is not limited to this.

[0099] Preferably, in the rolling process: the reduction rate of each pass in the first stage of rolling is 10-35%, and the reduction amount of at least three passes in the first five passes is not less than 8 mm.

[0100] Furthermore, in the rolling process, the steel billet may be descaled before the first stage rolling. Specifically, the steel billet may be roughly descaled after leaving the heating furnace and finely descaled before entering the rolling mill.

[0101] Preferably, in the cooling process: the average cooling rate throughout the entire process is preferably controlled at 28-33°C / s.

[0102] Alternatively, the average cooling rate throughout the entire process can be specifically controlled at 28, 29, 30, 31, 32, or 33°C / s.

[0103] Preferably, in the cooling process: the red-returning temperature is ≤300°C.

[0104] In another preferred embodiment, in the cooling process: The hot-rolled plate is water-cooled on an accelerated cooling control system (ACC) after rolling; the accelerated cooling control system after rolling has 24 groups of cooling headers, wherein the 1st to 6th groups, the 7th to 18th groups, and the 19th to 24th groups constitute the first sub-area, the second sub-area, and the third sub-area, respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500~3600L / s, the total cooling water flow of the first partition is 500~530L / s, all cooling manifolds of the first and third partitions are opened, and the cooling manifolds of the second partition are opened alternately.

[0105] In this way, by controlling the cooling of the first partition, the second partition and the third partition, the plate shape of the steel plate can be improved and the head and tail warping defects of the steel plate can be reduced. Especially for the preparation of thin-gauge 9Ni steel plates in this embodiment, the plate shape problem is more difficult to control. Through this cooling method, the plate shape quality can be greatly improved.

[0106] Among them, the "cooling manifolds of the second partition are opened alternately" can specifically be that among the 7th to 18th groups of cooling manifolds, the 7th, 9th, 11th ... 17th groups of cooling manifolds are opened, and the 8th, 10th ... 18th groups of cooling manifolds are closed.

[0107] In addition, preferably, the heat treatment process: when the thickness t 0 When the thickness is above 10mm, the insulation time can be further set to 2t. 0 ~14t 0 min.

[0108] Furthermore, when the thickness t 0 When the thickness is above 10mm, the insulation time can be further set to 2t. 0 ~5t 0 min, and can be preferably 2t 0 ~4t 0 min.

[0109] For the thickness t 0When the thickness is less than 10 mm, the insulation time may be specifically 30 minutes, but is not limited thereto, as long as it is more than 30 minutes.

[0110] Furthermore, in this embodiment, in the composite process, n stacked small plate blanks can be welded into a composite blank by circumference welding, spot welding or other welding methods so as to form a fixed whole. This application does not limit the specific welding form and welding parameters.

[0111] Preferably, in the embodiment, in the composite process, an antioxidant isolating agent is provided between two adjacent small slabs of the composite billet, so that, on the one hand, the final surface quality of each steel plate can be improved, and on the other hand, it is convenient to smoothly separate two adjacent layers of steel plates in the subsequent plate separation process.

[0112] The antioxidant isolating agent can be implemented by using known antioxidant isolating agents in the technical field, and the present application also provides a preferred implementation of the antioxidant isolating agent, which is as follows.

[0113] In a preferred embodiment, the antioxidant isolating agent is a coating composed of 55-65 parts by mass of blast furnace slag hydrothermal leaching material, 7-15 parts by mass of corn starch, 12-33 parts by mass of polyvinyl alcohol, 5-8 parts by mass of sodium tripolyphosphate and water. The oxidation isolating agent of this embodiment can, on the one hand, realize the treatment and reuse of blast furnace slag, and on the other hand, compared with the existing commonly used antioxidant isolating agents, it can greatly improve the surface quality of steel plates and reduce the difficulty of plate separation.

[0114] In one embodiment, the preparation method of the antioxidant isolation agent is: After crushing the blast furnace slag, slag of the required particle size is screened out, the slag, hydrochloric acid and water are put into a reaction container, and then reacted at a temperature of 130-150° C. for 8-10 hours; Separating solid slag from the system after the reaction, and then washing, grinding and screening the solid slag to obtain blast furnace slag hydrothermal leaching material; Using blast furnace slag hydrothermal leaching material, corn starch, polyvinyl alcohol, and sodium tripolyphosphate as powders, and preparing the materials according to a mass ratio of water to the powders of 1:2 to 3:4; After heating the water to 90-95° C., polyvinyl alcohol is added and stirred, and the mixture is allowed to stand until it is cooled to 60-70° C., corn starch is added and stirred for 0.8-1.5 hours under constant temperature conditions, and then the leached material and sodium tripolyphosphate are added and stirred to obtain the antioxidant isolation agent.

[0115] Preferably, in the step of "crushing the blast furnace slag, screening out slag of a desired particle size, adding the slag, hydrochloric acid and water into a reaction container, and then reacting at a temperature of 130-150° C. for 8-10 hours": The particle size of the slag is r mm, the concentration of hydrochloric acid is C mol / L, the volume ratio of the slag to hydrochloric acid is 0.2~0.8, the volume ratio of water to hydrochloric acid is 0.45~0.7, and C is in the range of (ln(r*60)-0.7)~(ln(r*60)+0.7).

[0116] Here, water or hydrochloric acid can be measured by using a container with a volume scale to determine the volume of water or hydrochloric acid.

[0117] The slag material may be measured by taking a container with a volume scale, first pouring liquid (such as measured hydrochloric acid and / or water) into the container, then adding the slag material into the container and making the slag material completely immersed under the liquid surface, and determining the volume of the slag material in the container based on the scale changes of the liquid surface.

[0118] In this embodiment, a thin-gauge 9Ni steel plate is also provided, whose chemical composition, in mass percentage, includes: C0.04~0.075%, Si 0.15~0.33%, Mn 0.5~0.8%, Ni 8.6~9.4%, Al 0.02~0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities.

[0119] More preferably, the chemical composition of the thin gauge 9Ni steel plate further satisfies 68≤Ni / (C+Al)≤173, and / or further satisfies Mn=(1.8~2.5)Si+0.17%.

[0120] Furthermore, the thickness t of the thin gauge 9Ni steel plate is below 8 mm, preferably 3-8 mm or even 4-8 mm, with a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, a yield strength ratio of ≤0.87, an elongation of ≥23%, and an impact energy of ≥210 J at -196°C.

[0121] In addition, the metallographic structure of the thin-gauge 9Ni steel plate is a multiphase structure of tempered martensite + ferrite + reversed austenite, wherein: the volume proportion of tempered martensite is 75-85%, the volume proportion of reversed austenite is 10-18%, and the rest is ferrite.

[0122] Below, some corresponding examples are provided for the production method and steel plates of this embodiment. The chemical compositions of the steel plates of these examples are shown in Table 5.

[0123] Table 5

[0124] The thickness t and properties of the steel plates of each embodiment are shown in Table 6. In addition to the properties shown in Table 6, the steel plates of each embodiment also have excellent plate shape and surface quality, and the straightness tolerance of the steel plates is less than 0.8 mm / m. In addition, the metallographic structures of the steel plates are shown in Table 6. Figures 1 to 6 As shown in Table 6, they are all multiphase structures of tempered martensite + ferrite + reversed austenite.

[0125] Table 6

[0126] The specific preparation process of the steel plates of these embodiments is as follows: Ingot forming process: the continuous casting ingot prepared by steelmaking and continuous casting is sent to a heating furnace for heating, and the heated continuous casting ingot is rolled into a large slab; wherein the soaking temperature during the heating process and the thickness of the large slab are shown in Table 7; Composite process: cutting the obtained large slab into a plurality of small slabs, stacking n small slabs, and welding them into a composite slab; wherein the number n of small slabs contained in the composite slab of each embodiment is shown in Table 7; Table 7

[0127] Heating process: sending the obtained composite blank into a heating furnace for heating; wherein the soaking temperature and the total heating time are respectively shown in Table 8; Rolling process: After the composite billet leaves the heating furnace, it first goes through the first stage of rolling to a thickness of t 1 The intermediate billet is then heated and rolled in the second stage to a thickness of t 0 Hot rolled plate; where the thickness is t 1 , thickness t 0 , the first stage rolling temperature (i.e. 1 st The rolling temperature of the second stage (i.e., the rolling temperature of the first stage nd Rolling start temperature), final rolling temperature (i.e. 2 nd Final rolling temperature) are shown in Table 8; Table 8

[0128] Cooling process: On the ACC system, the hot-rolled plate is cooled by water cooling; the water inlet temperature, the average cooling rate throughout the process, and the red-return temperature of the hot-rolled plate are shown in Table 9; the steel plate is cooled to below 200°C and then discharged from the water, and then air-cooled to room temperature to obtain a cooled plate; Heat treatment process: the obtained cooling plate is subjected to tempering treatment; wherein the tempering temperature and the heat preservation time are shown in Table 9; after the tempering is completed, the plate is air-cooled to room temperature; Table 9

[0129] Plate separation process: the tempered plate obtained in the heat treatment process is subjected to edge trimming to separate the tempered plate into n single-layer steel plates, that is, the 9Ni steel plates of the respective embodiments shown in the preceding Tables 5 and 6 are obtained.

[0130] It can be seen that the 9Ni steel plate of the present embodiment not only has high strength and high and low temperature toughness, but also has a low yield strength ratio that the prior art does not have, compared with the existing thin-gauge low-temperature steel plate; furthermore, the production method of the present embodiment can be used to prepare thin-gauge 9Ni steel plates, which solves the technical problem of high yield strength ratio that cannot be solved in the prior art, and the obtained steel plate has the characteristics of high strength, high and low temperature toughness and low yield strength ratio, and has excellent comprehensive performance.

[0131] Furthermore, in each embodiment, in the composite process, an antioxidant isolation agent with the components shown in Table 10 is used between two adjacent small slabs to separate the two adjacent small slabs.

[0132] Table 10

[0133] The preparation process of each antioxidant isolation agent is as follows: After crushing the blast furnace slag, slag with a particle size r as shown in Table 10 is screened out, and the slag and hydrochloric acid with a concentration C as shown in Table 10 are put into a reaction container at a volume ratio of 1:5, and then 63% of the volume of hydrochloric acid is added. Then, the mixture is heated to 130-150° C. and kept warm for 8-10 hours; The solid phase slag is separated from the system after the reaction, and then the solid phase slag is cleaned, ground and screened to obtain the blast furnace slag hydrothermal leaching material; the grinding is specifically carried out by ball milling process, the grinding balls are 5 mm SiC balls, and the ball-to-material ratio is 3:1; the screening can be carried out with a 400 mesh screen; As shown in Table 10, a certain mass of blast furnace slag hydrothermal leaching material, corn starch, polyvinyl alcohol, sodium tripolyphosphate and water were prepared; After heating the water to 90-95° C., polyvinyl alcohol is added and stirred for 30 minutes, and the mixture is allowed to stand until it cools to 60-70° C., corn starch is added and stirred for 0.8-1.5 hours under constant temperature conditions, and then the leached material and sodium tripolyphosphate are added and stirred to obtain the antioxidant isolation agent.

[0134] In addition, it should be noted that in the present application, the metallographic structure of the steel plate can be obtained by structural testing according to the GB / T15125-2009 "Specimens and test methods for metallographic examination of metallic materials" standard; the mechanical properties can be tested in accordance with GB / T 228.1-2021 "Tensile test of metallic materials, Part 1: Room temperature test method"; and the low-temperature toughness test can be carried out in accordance with GB / T 229-2007 "Charpy pendulum impact test method for metallic materials".

Claims

1. A method for producing a 9Ni steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C 0.04-0.075%, Si 0.15-0.33%, Mn 0.5-0.8%, Ni 8.6-9.4%, Al 0.02-0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities; The production method comprises the following steps: Heating process: heating the steel billet, with the soaking temperature at 1150~1200℃; Rolling process: First, the steel billet is rolled into an intermediate billet with a thickness of t1 by the first stage rolling, and then the intermediate billet is heated to a temperature, and then the intermediate billet is rolled into a hot-rolled plate with a thickness of t0 by the second stage rolling; wherein, the first stage rolling has a starting rolling temperature of 1050~1090℃, and the second stage rolling has a starting rolling temperature (T fr -10)~(T fr +10)℃, final rolling temperature (T fr -18)~(T fr +18)℃,1.3≤t1 / t0≤12,T fr Obtained by the following formula 1; Cooling process: The hot rolled plate is cooled by water cooling. The water temperature of the hot rolled plate (T fc -15)~(T fc +15)℃,T fc The final cooling temperature is ≤200℃ and the average cooling rate is 25~35℃ / s. After exiting the water, the cooling plate is air-cooled to room temperature to obtain a cooling plate. Heat treatment process: the obtained cooling plate is tempered at a tempering temperature of 540-580°C for more than 30 minutes, and air-cooled to room temperature after tempering. T fr =879-97C+48Si-9.5Mn-5.1Ni-200Al formula 1; T fc =720+116C+27Si-10Mn+6Ni-177Al formula 2; The element symbols in Formula 1 and Formula 2 represent the mass percentage of each element in the steel billet.

2. The method for producing a 9Ni steel plate according to claim 1, characterized in that: The hot-rolled plate is a single-layer steel plate with a thickness t0>8 mm; The production method further comprises a casting step: preparing a continuous casting billet with a thickness of 220-250 mm by steelmaking and continuous casting; Furthermore, in the heating process, the obtained continuous casting billet is heated, the soaking temperature is 1150-1180° C., and the total heating time is 160-220 min.

3. The method for producing a 9Ni steel plate according to claim 1, characterized in that: The hot-rolled plate is a composite plate formed by stacking n layers of single plates, where n is 2, 3 or 4, and the thickness of at least one layer of single plates is t; The production method further comprises the following steps: Ingot casting process: through steelmaking and continuous casting, a continuous casting ingot with a thickness of 220~250mm is prepared; Billeting process: heating the continuous casting billet, with the soaking temperature at 1200~1240℃ and the total heating time at 200~300min; rolling the heated continuous casting billet into a large slab with a thickness of 4.5t~10t; Composite process: cutting the obtained large slab into a plurality of small slabs, stacking and welding the n small slabs into a composite slab; the composite slab enters the heating process and is heated as the steel slab; Plate separation step: the tempered plate obtained in the heat treatment step is separated into n single-layer 9Ni steel plates by trimming.

4. The method for producing a 9Ni steel plate according to claim 3, characterized in that: In the heating process: the steel billet is heated, and the heating process includes preheating, heating and soaking, the preheating temperature is 750~850℃, the heating rate is 20~30℃ / min; the heating temperature is 1100~1200℃, the heating rate is 30~50℃ / min; the soaking temperature is 1150~1180℃; the total heating time is 160~220min.

5. The method for producing a 9Ni steel plate according to claim 3, characterized in that: Among the n single-layer 9Ni steel plates, at least one 9Ni steel plate has a thickness t of less than 8 mm.

6. The method for producing a 9Ni steel plate according to claim 5, characterized in that: Among the n single-layer 9Ni steel plates, at least one 9Ni steel plate has a thickness t of 3 to 8 mm.

7. The method for producing a 9Ni steel plate according to claim 3, characterized in that: In the composite process: an antioxidant isolating agent is provided between two adjacent small slabs of the composite blank; The antioxidant isolation agent is a coating composed of 55-65 parts by mass of blast furnace slag hydrothermal leaching material, 7-15 parts by mass of corn starch, 12-33 parts by mass of polyvinyl alcohol, 5-8 parts by mass of sodium tripolyphosphate and water.

8. The method for producing a 9Ni steel plate according to claim 7, characterized in that: The preparation method of the antioxidant isolation agent comprises the following steps: After crushing the blast furnace slag, slag of the required particle size is screened out, the slag, hydrochloric acid and water are put into a reaction container, and then reacted at a temperature of 130-150° C. for 8-10 hours; Separating solid slag from the system after the reaction, and then washing, grinding and screening the solid slag to obtain blast furnace slag hydrothermal leaching material; Using blast furnace slag hydrothermal leaching material, corn starch, polyvinyl alcohol, and sodium tripolyphosphate as powders, and preparing the materials according to a mass ratio of water to the powders of 1:2 to 3:4; After heating the water to 90-95° C., polyvinyl alcohol is added and stirred, and the mixture is allowed to stand until it is cooled to 60-70° C., corn starch is added and stirred for 0.8-1.5 hours under constant temperature conditions, and then the leached material and sodium tripolyphosphate are added and stirred to obtain the antioxidant isolation agent.

9. The method for producing a 9Ni steel plate according to claim 8, characterized in that: In the step "crushing the blast furnace slag, screening out slag of a desired particle size, putting the slag, hydrochloric acid and water into a reaction container, and then reacting at a temperature of 130-150° C. for 8-10 hours": The particle size of the slag is r mm, the concentration of hydrochloric acid is C mol / L, the volume ratio of the slag to hydrochloric acid is 0.2~0.8, the volume ratio of water to hydrochloric acid is 0.45~0.7, and C is in the range of (ln(r*60)-0.7)~(ln(r*60)+0.7).

10. The method for producing a 9Ni steel plate according to any one of claims 1 to 9, characterized in that: In the cooling process: the red-returning temperature is ≤300°C.

11. The method for producing a 9Ni steel plate according to any one of claims 1 to 9, characterized in that: In the cooling process: The hot rolled plate is water cooled on a post-rolling accelerated cooling control system; The post-rolling accelerated cooling control system has 24 groups of cooling headers, among which the 1st to 6th groups, the 7th to 18th groups, and the 19th to 24th groups constitute the first zone, the second zone, and the third zone respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500~3600L / s, the total cooling water flow of the first partition is 500~530L / s, all cooling manifolds of the first and third partitions are opened, and the cooling manifolds of the second partition are opened alternately.

12. The method for producing a 9Ni steel plate according to any one of claims 1 to 8, characterized in that: In the rolling process, the reduction rate of each pass in the first stage of rolling is 10-35%, and the reduction of at least three passes in the first five passes is not less than 8 mm.

13. The method for producing a 9Ni steel plate according to any one of claims 1 to 9, characterized in that: The heat treatment process: when the thickness t0 is above 10 mm, the insulation time is between 2t0 and 14t0 min.

14. A 9Ni steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C 0.04-0.075%, Si 0.15-0.33%, Mn 0.5-0.8%, Ni 8.6-9.4%, Al 0.02-0.04%, P≤0.005%, S≤0.002%, O≤0.002%, N≤0.0035%, H≤0.00015%, and the balance is iron and unavoidable impurities; The steel plate has a thickness of less than 8 mm, a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, a yield strength ratio of ≤0.87, an elongation of ≥23%, and an impact energy of ≥210 J at -196°C.

15. The 9Ni steel plate according to claim 14, characterized in that: The thickness of the steel plate is 3-8 mm.

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