Thin gauge 9ni steel sheet and method of producing the same

Abstract

The present application discloses a thin gauge 9Ni steel plate and its production method. The production method comprises: firstly heating continuous casting billet, then opening the billet into a large slab of 4.5t-10t; cutting, stacking and welding the obtained large slab into a composite billet; heating the composite billet, preheating temperature 750-850℃, heating rate 20-30℃ / min; heating temperature 1100-1200℃, heating rate 30-50℃ / min; soaking temperature 1150-1200℃; two-stage rolling, one-stage opening rolling temperature 1050-1090℃, two-stage opening rolling temperature T fr ±10℃, final rolling temperature T fr ±18℃; water cooling, water inlet temperature T fc ±15℃; after tempering, dividing the slab, tempering temperature 540-580℃, obtaining 9Ni steel plate with thickness below 8mm. Not only the high strength and high low temperature toughness are ensured, but also the yield ratio is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel material preparation, and relates to a thin-gauge 9Ni steel plate and a production method thereof. BACKGROUND

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

[0003] In view of the flammability and ultralow temperature of LNG, the structural material for storage and transportation equipment needs to 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 environment.

[0004] The existing research on 9Ni steel plate is mostly concentrated on thick-gauge products, and the research on thin-gauge products is relatively less. The production technology of thick-gauge products is difficult to be applied to the production of thin-gauge products, and one of the main reasons is that the thin-gauge product has a much higher yield ratio due to large compression ratio, and the high yield ratio means a large safety risk in deep cold environment. SUMMARY

[0005] In order to solve the problem of technical defects in thin-gauge 9Ni steel plate, the purpose of the present application is to provide a thin-gauge 9Ni steel plate and a production method thereof.

[0006] In order to achieve the above-mentioned purpose of the application, an embodiment of the present application provides a production method of a thin-gauge 9Ni steel plate. The production method comprises the following steps,

[0007] The casting blank process: a continuous casting blank with a thickness of 220-250mm is prepared by steelmaking and continuous casting; the chemical composition of the continuous casting blank includes, in terms of 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;

[0008] The cogging process: the continuous casting blank is heated first, and the soaking temperature is 1200-1240℃, and then the heated continuous casting blank is rolled into a large plate blank with a thickness of 4.5t-10t;

[0009] The compounding process: the obtained large plate blank is cut into a plurality of small plate blanks, and n small plate blanks are stacked and welded into a composite blank, n=2, 3 or 4;

[0010] Heating process: the obtained composite blank 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 1150-1200℃; the total heating time is 160-220min;

[0011] Rolling process: the composite blank is first made into an intermediate blank with a thickness t1 by first-stage rolling, 7t≤t1≤16t, and then is warmed, and then the intermediate blank is made into a hot-rolled plate with a thickness t0 by second-stage rolling, 0.8×n×t≤t0≤1.2×n×t; wherein, the opening rolling temperature of the first-stage rolling is 1050-1090℃, the opening rolling temperature of the second-stage rolling is (T fr -10)~(T fr +10)℃, the finishing rolling temperature is (T fr -18)~(T fr +18)℃, T fr is obtained from the following formula 1;

[0012] Cooling process: the obtained hot-rolled plate is cooled by water cooling, the water entry temperature of the hot-rolled plate is (T fc -15)~(T fc +15)℃, T fc is obtained from the following formula 2, and the final cooling temperature is ≤200℃; after water exit, air cooling is performed to room temperature to obtain a cooled plate;

[0013] Heat treatment process: the obtained cooled plate is tempered, the tempering temperature is 540-580℃, the holding time is 30min or more, and after the tempering is finished, air cooling is performed to room temperature;

[0014] Plate separating process: the tempered plate is separated into n single-layer 9Ni steel plates by edge cutting, and the thickness t of at least one 9Ni steel plate is ≤8mm;

[0015] T fr =879-97C+48Si-9.5Mn-5.1Ni-200Al Formula 1;

[0016] T fc =720+116C+27Si-10Mn+6Ni-177Al Formula 2;

[0017] In the formula 1 and the formula 2, the element symbols represent the mass percentage of each element in the steel plate.

[0018] Preferably, in the cooling process, the re-red temperature is ≤300℃.

[0019] Preferably, in the n single-layer 9Ni steel plates, the thickness t of at least one 9Ni steel plate is 3-8mm.

[0020] Preferably, the thickness of the intermediate blank t1 is 30-80 mm, and 2≤t1 / t0≤8.

[0021] Preferably, in the cooling process:

[0022] The hot-rolled plate is water-cooled on a post-rolling accelerated cooling control system;

[0023] The post-rolling accelerated cooling control system has 24 groups of cooling headers, wherein the first 6 groups, the seventh to eighteenth groups, and the nineteenth to twenty-fourth groups constitute a first sub-zone, a second sub-zone, and a third sub-zone, respectively.

[0024] The total cooling water flow of the post-rolling accelerated cooling control system is 1500-3600 L / s, the total cooling water flow of the first sub-zone is 500-530 L / s, all cooling headers of the first sub-zone and the third sub-zone are opened, and the cooling headers of the second sub-zone are alternately opened.

[0025] Preferably, in the rolling process: the reduction rate of each pass of the first stage rolling is 10-35%, and the reduction amount of at least three passes of the first five passes is not less than 8 mm.

[0026] Preferably, in the heat treatment process: when the thickness t0 is greater than or equal to 10 mm, the holding time is 2t0-5t0 min.

[0027] Preferably, in the compounding process: the adjacent two slab blanks of the compound blank have an oxidation-resistant isolation agent therebetween.

[0028] The oxidation-resistant isolation agent is a coating material composed of 55-65 parts by mass of a 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.

[0029] Preferably, the chemical composition of the continuous casting blank, in terms of mass percentage, further satisfies: 68≤Ni / (C+Al)≤173, and / or, Mn=(1.8-2.5)Si+0.17%.

[0030] To achieve the above object, one embodiment of the present application provides a thin-gauge 9Ni steel plate. The chemical composition of the steel plate includes, in mass percent, 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 being iron and unavoidable impurities; and further satisfies 68≤Ni / (C+Al)≤173 and / or Mn=(1.8-2.5)Si+0.17%.

[0031] The thickness of the steel plate is 8 mm or less, the tensile strength is 730-810 MPa, the yield strength is 590-680 MPa, the yield ratio is ≤0.87, the elongation is ≥23%, and the impact energy at -196 ℃ is ≥210 J.

[0032] Compared with the prior art, the present application has the following beneficial effects: the production method can produce a thin-gauge 9Ni steel plate, for example, the thickness t is 8 mm or less, and the obtained thin-gauge 9Ni steel plate has high strength, high low-temperature toughness, and low yield ratio, specifically including:

[0033] In the first aspect, fine-grain strengthening is performed by tempering heat treatment to improve the strength and low-temperature toughness, but the fine-grain strengthening in the tempering heat treatment can cause a large increase in the yield strength, thereby improving the tensile strength, low-temperature toughness, and yield ratio at the same time. In the present application, through specific operations in the rolling and cooling processes, the yield strength can be reduced while the tensile strength is stabilized, thereby eliminating the problem of excessive increase in the yield ratio during the heat treatment process, and ultimately achieving the effect of reducing the yield ratio without causing a decrease in the tensile strength or low-temperature toughness.

[0034] On the other hand, the rolling of a thin-gauge steel plate inevitably has a large compression ratio, which can produce high-density dislocations and substructures, thereby causing a large increase in the yield strength and leading to a high yield ratio. This is also an important reason why the yield ratio of a thin-gauge steel plate is higher than that of a thick-gauge steel plate. However, the present application unexpectedly greatly eliminates the problem of excessive increase in the yield strength caused by high-density dislocations and substructures through the operation in the heating process, thereby achieving a low yield ratio for the thin-gauge steel plate.

[0035] In summary of the above two aspects, one embodiment of the present application not only ensures high strength and high low-temperature toughness, but also improves the low yield ratio in the production of a thin-gauge 9Ni steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1is a metallographic structure diagram of the steel plate of Example 1 in one embodiment of the present application at 1 / 2 thickness;

[0037] Figure 2 is a metallographic structure diagram of the steel plate of Example 2 in one embodiment of the present application at 1 / 2 thickness;

[0038] Figure 3 is a metallographic structure diagram of the steel plate of Example 3 in one embodiment of the present application at 1 / 2 thickness;

[0039] Figure 4 is a metallographic structure diagram of the steel plate of Example 4 in one embodiment of the present application at 1 / 2 thickness;

[0040] Figure 5 is a metallographic structure diagram of the steel plate of Example 5 in one embodiment of the present application at 1 / 2 thickness;

[0041] Figure 6 is a metallographic structure diagram of the steel plate of Example 6 in one embodiment of the present application at 1 / 2 thickness. DETAILED DESCRIPTION

[0042] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0043] One embodiment of the present application provides a production method of a thin-gauge 9Ni steel plate, that is, the production method can be used to produce a thin-gauge 9Ni steel plate, and the thin-gauge 9Ni steel plate produced by the production method not only has the advantages of high strength and high low-temperature toughness, but also has a lower yield strength ratio.

[0044] In terms of chemical composition, the chemical composition of the steel plate includes, in terms of 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 being iron and unavoidable impurities.

[0045] The effects of each element in the above chemical composition will be introduced below.

[0046] C is a strengthening element and an austenite stabilizing element; if the C content is low, the strength of the steel plate is difficult to guarantee; if the C content is high, the toughness-embrittlement transition temperature will be increased, affecting the low-temperature toughness of the steel plate, so the C content should be as low as possible on the premise of guaranteeing the strength. In the present application, the C content is controlled to be 0.04-0.075%.

[0047] Si, as a deoxidizing element, can inhibit the grain boundary segregation behavior of P; but when the content of Si is high, the low-temperature toughness of the steel plate is affected. In the present application, the content of Si is controlled at 0.15-0.33%, which ensures the deoxidizing effect and reduces the oxide inclusions in the steel without affecting the low-temperature toughness.

[0048] Mn, as a solid solution strengthening and fine-grain strengthening element, is also an austenite stabilizing element. The addition of Mn can significantly improve the hardenability of the material; meanwhile, Mn is an element that is prone to segregation and the formation of inclusions, and excessive addition will affect the fracture toughness and low-temperature impact toughness of the steel plate. In the present application, the content of Mn is controlled at 0.5-0.8%.

[0049] Ni, as an austenite stabilizing element, is particularly important for stabilizing reversed austenite, which is the main component providing deep cold toughness of the steel plate; Ni can improve the hardenability of the steel plate and increase the strength through solid solution strengthening. In the present application, the content of Ni is controlled at 8.6-9.4%.

[0050] Al, as a deoxidizing element, can effectively reduce the content of inclusions in the steel and refine the grains; excessive aluminum can increase the Al2O3 inclusions in the steel, affecting the low-temperature toughness of the steel. In the present application, Al is controlled at 0.02-0.04%.

[0051] P, S, N, H, O: as impurity elements, they should be controlled as low as possible. In the present application, P≤0.005%, S≤0.002%, N≤0.0035%, H≤0.00015%, and O≤0.002%.

[0052] In terms of production process, the production method includes the processes of casting blank process, blooming process, compounding process, heating process, rolling process, cooling process, heat treatment process and plate dividing process in sequence, to prepare a single-layer 9Ni steel plate with a thickness of ≤8mm.

[0053] Specifically, the casting blank process: a continuous casting blank with a thickness of 220-250mm is prepared by steelmaking and continuous casting, and the chemical composition of the continuous casting blank is consistent with that of the finally obtained 9Ni steel plate, and the specific chemical composition is as introduced above.

[0054] The blooming process: the continuous casting blank is heated at a soaking temperature of 1200-1240℃, and the heated continuous casting blank is rolled into a large plate blank with a thickness of 4.5t-10t.

[0055] The compounding process: the obtained large plate blank is cut into multiple small plate blanks, and n small plate blanks are stacked and welded into a composite blank, n=2, 3 or 4.

[0056] Heating process: the obtained composite 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 1150-1200℃; the total heating time is 160-220min.

[0057] Rolling process: first, the steel billet is made into an intermediate billet with a thickness t1 by first-stage rolling, 7t≤t1≤16t, and then is cooled, and then the intermediate billet is made into a hot-rolled plate with a thickness t0 by second-stage rolling, 0.8×n×t≤t0≤1.2×n×t; wherein, the opening rolling temperature of the first-stage rolling is 1050-1090℃, the opening rolling temperature of the second-stage rolling is (T fr -10)~(T fr +10)℃, the finishing rolling temperature is (T fr -18)~(T fr +18)℃, T fr is obtained from the formula 1.

[0058] Cooling process: the obtained hot-rolled plate is cooled by water cooling, the water entry temperature of the hot-rolled plate is (T fc -15)~(T fc +15)℃, T fc is obtained from the formula 2, and the final cooling temperature is ≤200℃; after water exit, air cooling is performed to room temperature to obtain a cooled plate.

[0059] Heat treatment process: the obtained cooled plate is tempered, the tempering temperature is 540-580℃, the holding time is ≥30min, and after the tempering is finished, air cooling is performed to room temperature.

[0060] Plate separating process: the obtained tempered plate in the heat treatment process is separated into n single-layer 9Ni steel plates by edge cutting, wherein the thickness t of at least one 9Ni steel plate is ≤8mm, that is, the required thin-gauge 9Ni steel plate is prepared.

[0061] The above-mentioned T fr can be obtained from the following formula 1, T fc is obtained from the following formula 2:

[0062] T fr =879-97C+48Si-9.5Mn-5.1Ni-200Al Formula 1;

[0063] T fc =720+116C+27Si-10Mn+6Ni-177Al Formula 2;

[0064] In the formula 1 and the formula 2, the element symbol represents the mass percentage of each element in the billet, for example, if the content of C in the billet is 0.04% in mass percentage, the element symbol C in the formula 1 and the formula 2 is substituted by the mass percentage of C, i.e. 0.04.

[0065] Therefore, the production method of the present application can prepare a thin-gauge 9Ni steel plate, for example, with a thickness t of less than 8 mm, and the obtained thin-gauge 9Ni steel plate simultaneously has high strength, high low-temperature toughness and low yield ratio, specifically as follows:

[0066] In the first aspect, fine-grain strengthening is performed by tempering heat treatment to improve the strength and low-temperature toughness, but the fine-grain strengthening in the tempering heat treatment can cause a large increase in the yield strength, and thus the tensile strength, the low-temperature toughness and the yield ratio are simultaneously improved. In the present application, through specific operations in the rolling and cooling processes, the yield strength can be reduced while the tensile strength is stabilized, thereby eliminating the problem of excessive increase in the yield ratio during the heat treatment process, and finally achieving the effect of reducing the yield ratio without causing a decrease in the tensile strength or the low-temperature toughness.

[0067] On the other hand, the rolling of a thin-gauge steel plate inevitably has a large compression ratio, and the corresponding large compression ratio can generate high-density dislocations and substructures, thereby causing a large increase in the yield strength and leading to a high yield ratio. This is also an important reason why the yield ratio of a thin-gauge steel plate is higher than that of a thick-gauge steel plate. However, the present application unexpectedly and substantially eliminates the problem of excessive increase in the yield strength caused by high-density dislocations and substructures through the operation in the heating process, thereby achieving a low yield ratio for a thin-gauge steel plate.

[0068] In summary of the above two aspects, in the preparation of a thin-gauge 9Ni steel plate, the present application can not only ensure high strength and high low-temperature toughness, but also improve the low yield ratio.

[0069] In an embodiment, the thin-gauge 9Ni steel plate obtained by the production method has a tensile strength of 730-810 MPa, a yield strength of 590-680 MPa, a yield ratio of ≤0.87, an elongation of ≥23%, and an impact energy at -196℃ of ≥210 J.

[0070] Further, in the finally obtained n 9Ni steel plates, at least one 9Ni steel plate has a thickness t of 3-8 mm.

[0071] Further, at least one 9Ni steel plate has a thickness t of 4-8 mm.

[0072] More preferably, in the finally obtained n 9Ni steel plates, each 9Ni steel plate has a thickness t of 3-8 mm or 4-8 mm.

[0073] Preferably, the final n 9Ni steel plates can be of substantially same thickness, all t, or can also be of different thickness.

[0074] For example, the n 9Ni steel plates can all have excellent strength, low-temperature toughness and yield ratio, such as all meeting the tensile strength of 730-810 MPa, yield strength of 590-680 MPa, yield ratio ≤0.87, elongation ≥23%, and impact energy at -196℃ ≥210 J.

[0075] In addition, in an embodiment of the present application, the microstructure of the cooling plate obtained in the cooling process is martensite + ferrite + reversed austenite; and further, after tempering, the microstructure of the final steel plate is a multiphase structure of tempered martensite + ferrite + reversed austenite, and wherein: the volume fraction of the tempered martensite is 75-85%, and the volume fraction of the reversed austenite is 10-18%.

[0076] In addition, it should be noted that in this application, the microstructure of the steel plate can be obtained by microstructure detection according to GB / T15125-2009 "Metallic Materials Microstructure Test Sample and Test Method"; the mechanical properties can be detected according to GB / T228.1-2021 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method"; and the low-temperature toughness can be detected according to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0077] Further, in an embodiment, the chemical composition of the steel plate, in terms of mass percentage, further satisfies 68≤Ni / (C+Al)≤173. In this way, C as a stable austenite 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%-10% of general 9Ni steel to 10-18%.

[0078] Further, in another embodiment, the chemical composition of the steel plate, in terms of mass percentage, further satisfies Mn=(1.8-2.5)Si+0.17%. In this way, Mn can improve the hardenability of the steel plate, and cooling treatment using a post-rolling accelerated cooling control system can eliminate offline quenching treatment in conventional technology, reduce the complexity of subsequent processes after the cooling process, reduce production costs and improve production efficiency.

[0079] In the casting blank process, the specific steelmaking and continuous casting method can be implemented by any feasible technology in the technical field, for example, it can be implemented by adopting the process route of hot metal KR desulfurization-converter smelting-LF refining-RH refining-continuous casting, which is not described further as it is not the design point of the present application.

[0080] Preferably, in the rolling process, the reduction ratio of each pass of the first stage rolling is 10-35%, and the reduction of at least three passes of the first five passes is not less than 8 mm.

[0081] Further, the thickness of the intermediate blank t1 is preferably controlled to be 30-80 mm, more preferably 40-70 mm, and further preferably 45-65 mm.

[0082] In addition, t0 can satisfy (0.8-1.2) x n x t, and preferably t0 = n x t.

[0083] Preferably, 2≤t1 / t0≤8, further controlled to be 2≤t1 / t0≤5, and further controlled to be 2.5≤t1 / t0≤5, and further controlled to be 2.5≤t1 / t0≤4.

[0084] Further, in the rolling process, before the first stage rolling, the billet can be descaled, and specifically, rough descaling can be performed after the billet is discharged from the heating furnace, and fine descaling can be performed before the billet is fed into the rolling mill.

[0085] Preferably, in the cooling process, the average cooling rate is 25-35°C / s. In this way, by controlling the cooling rate, the yield strength can be further stabilized while the tensile strength is reduced, thereby eliminating the problem of excessive increase of the yield ratio in the heat treatment process.

[0086] Preferably, in the cooling process, the average cooling rate is preferably controlled to be 28-33°C / s, and more preferably controlled to be 28-30°C / s.

[0087] Preferably, in the cooling process, the reheat temperature is ≤300°C. In this way, the overall performance of the final obtained steel plate can also be improved.

[0088] In another preferred embodiment, in the cooling process:

[0089] The hot-rolled plate is water-cooled on an accelerated-cooling control system (ACC) after rolling, and the accelerated-cooling control system has 24 cooling headers, wherein the first to sixth groups, the seventh to eighteenth groups, and the nineteenth to twenty-fourth groups form a first subzone, a second subzone, and a third subzone, respectively.

[0090] The total cooling water flow rate of the accelerated-cooling control system after rolling is 1500-3600 L / s, the total cooling water flow rate of the first subzone is 500-530 L / s, all the cooling headers of the first subzone and the third subzone are opened, and the cooling headers of the second subzone are alternately opened.

[0091] Generally, the thin gauge 9Ni steel plate has the problem of head and tail warping, that is, the plate shape is difficult to control, and in the preferred embodiment, the cooling control of the first, second and third sub-zones can improve the plate shape of the thin gauge 9Ni steel plate, reduce the head and tail warping defects of the steel plate, and greatly improve the quality of the steel plate.

[0092] Among them, the "cooling of the second sub-zone is alternately opened", specifically, among the 7th-18th cooling headers, the 7th, 9th, 11th, …, 17th cooling headers are opened, and the 8th, 10th, …, 18th cooling headers are closed.

[0093] In addition, preferably, when the thickness t0 is greater than or equal to 10 mm, the holding time can be further 2t0-5t0 min. For a thickness t0 less than 10 mm, the holding time can be specifically 30 min, but is not limited thereto, as long as it is greater than 30 min.

[0094] Further, when the thickness t0 is greater than or equal to 10 mm, the holding time can be further 2t0-4t0 min.

[0095] Further, in this embodiment, in the compounding process, the n small slabs placed in layers can be welded into a composite slab by surrounding welding, spot welding or other welding methods, so as to form a whole fixed together, and the application does not limit the specific welding form and welding parameters.

[0096] Preferably, in this embodiment, in the compounding process, there is an oxidation-resistant isolation agent between the adjacent two small slabs of the composite slab. In this way, on the one hand, the final surface quality of each steel plate can be improved, and on the other hand, the adjacent two layers of steel plates can be easily separated in the subsequent plate separation process.

[0097] The oxidation-resistant isolation agent can be implemented by using the known oxidation-resistant isolation agent in the technical field, and the application also provides a preferred embodiment of the oxidation-resistant isolation agent, which is specifically as follows.

[0098] In a preferred embodiment, the oxidation-resistant isolation agent is a coating material 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. Using the oxidation-resistant isolation agent of this embodiment, on the one hand, the blast furnace slag can be treated and reused, and on the other hand, compared with the existing commonly used oxidation-resistant isolation agent, the surface quality of the steel plate can be greatly improved, and the plate separation difficulty can be reduced.

[0099] In an embodiment, the preparation method of the oxidation-resistant isolation agent is:

[0100] The blast furnace slag is crushed, and slag of a desired 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 or more.

[0101] The solid-phase slag is separated from the reacted system, and then washed, ground, and screened to obtain a blast furnace slag hydrothermal leaching material.

[0102] The blast furnace slag hydrothermal leaching material, corn starch, polyvinyl alcohol, and sodium tripolyphosphate are used as powders, and the mass ratio of water to the powders is 1:2-3:4.

[0103] The water is heated to 90-95°C, and then the polyvinyl alcohol is added and stirred and allowed to stand until cooled to 60-70°C. The corn starch is added and stirred under constant temperature conditions for 0.8-1.5 hours. Then the leaching material and the sodium tripolyphosphate are added and stirred to obtain the antioxidant release agent.

[0104] Preferably, in the step of "crushing the blast furnace slag, and screening out slag of a desired particle size. 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 or more", the following conditions are satisfied:

[0105] The particle size of the slag is r mm, the concentration of the hydrochloric acid is C mol / L, the volume ratio of the slag to the hydrochloric acid is 0.2-0.8, and the volume ratio of the water to the hydrochloric acid is 0.45-0.7, wherein C is in the range of (ln(r×60)-0.7) to (ln(r×60)+0.7).

[0106] Here, the water or the hydrochloric acid can be measured by using a container with a volume scale to determine the volume of the water or the hydrochloric acid.

[0107] The slag can be measured by using a container with a volume scale. First, the liquid (such as the measured hydrochloric acid and / or water) is poured into the container, and then the slag is put into the container so that the slag is completely submerged under the liquid surface. Based on the change in the scale of the liquid surface, the volume of the slag in the container is determined.

[0108] In the embodiment, a thin-gauge 9Ni steel plate is also provided, which has a chemical composition including, in mass percent, 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 being iron and unavoidable impurities.

[0109] 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%.

[0110] Furthermore, the thin gauge 9Ni steel plate has a thickness t of less than 8mm, preferably 3-8mm, even more preferably 4-8mm, a tensile strength of 730-810MPa, a yield strength of 590-680MPa, a yield / tensile ratio of ≤0.87, an elongation of ≥23%, and a -196℃ impact energy of ≥210J.

[0111] In addition, the thin gauge 9Ni steel plate has a multi-phase microstructure of tempered martensite + ferrite + reversed austenite, and wherein: the volume fraction of the tempered martensite is 75-85%, the volume fraction of the reversed austenite is 10-18%, and the rest is ferrite.

[0112] Below, some corresponding examples are provided for the production method and steel plate of an embodiment of the present application.

[0113] The specific preparation process of the steel plate of these examples is as follows:

[0114] Casting blank process: a continuous casting blank with a thickness of 220mm is prepared by steelmaking and continuous casting, and the chemical composition of the continuous casting blank is shown in Table 1;

[0115] [Table 1]

[0116]

[0117] Breaking down process: the continuous casting blank prepared by steelmaking and continuous casting is sent to a heating furnace for heating, and the total heating time can be controlled at 200-300min, and the heated continuous casting blank is rolled into a large slab; wherein the soaking temperature during heating and the thickness of the large slab are shown in Table 2;

[0118] Compound process: the obtained large slab is cut into multiple small slabs, and n small slabs are stacked and welded into a composite blank; wherein the number n of small slabs contained in the composite blank of each example is shown in Table 2;

[0119] [Table 2]

[0120] Examples Soaking temperature, °C Thickness of the slab, mm n value 1 1217 60 2 2 1233 47 3 3 1231 32 4 4 1226 58 2 5 1209 44 3 6 1218 30 4

[0121] Heating process: the obtained composite blank is sent to a heating furnace for heating; wherein the soaking temperature and the total heating time are shown in Table 3, respectively;

[0122] Rolling process: after the composite blank leaves the heating furnace, first pass through the first stage rolling to make the intermediate blank with thickness t1, then wait for temperature, and then pass through the second stage rolling to make the hot-rolled plate with thickness t0; wherein the thickness t1, the thickness t0, the opening rolling temperature of the first stage rolling (i.e. 1 st opening rolling temperature), the opening rolling temperature of the second stage rolling (i.e. 2 nd opening rolling temperature), and the final rolling temperature (i.e. 2 nd final rolling temperature) are shown in Table 3 respectively;

[0123] [Table 3]

[0124]

[0125] Cooling process: the obtained hot-rolled plate is cooled by water cooling on the ACC system; wherein the water entry temperature of the hot-rolled plate, the average cooling speed throughout the process, and the red temperature are shown in Table 5; the steel plate is cooled to below 200℃ by water, and then air-cooled to room temperature to obtain the cooled plate;

[0126] Heat treatment process: the obtained cooled plate is tempered; wherein the tempering temperature and the holding time are shown in Table 5; after the tempering is finished, air-cooled to room temperature; [Table 5]

[0127]

[0128] Plate dividing process: the tempered plate obtained in the heat treatment process is cut to separate the tempered plate into n single-layer steel plates.

[0129] One of the n single-layer steel plates obtained in each of the embodiments is detected, and the thickness t and the performance are shown in Table 6; and in addition to the performance shown in Table 6, the steel plate of each embodiment also has excellent plate shape and surface quality, and the flatness tolerance of the steel plate is less than 0.8mm / m; in addition, the metallographic structure of the steel plate is shown in Table 6 respectively, which is a multiphase structure of tempered martensite + ferrite + reverted austenite. Figures 1 to 6

[0130] [Table 6]

[0131]

[0132] As can be seen, the 9Ni steel plate of the present embodiment not only has high strength and high low-temperature toughness, but also has a low yield ratio which is not possessed by the prior art; in addition, the production method of the present embodiment can be used to prepare a thin-gauge 9Ni steel plate, which solves the technical problem of high yield ratio that cannot be solved in the prior art, and the obtained steel plate has the characteristics of high strength, high low-temperature toughness and low yield ratio, and has excellent comprehensive performance.

[0133] ​Furthermore, each of the embodiments also respectively uses an antioxidant separator having the composition as shown in Table 7 to separate the adjacent two small plate blanks in the composite process. The preparation method of the antioxidant separator is as described above.

[0134] [Table 7]

[0135]

Claims

1. A method of producing a thin gauge 9Ni steel plate, characterized by, The production method comprises the following steps, The casting blank process: preparing a continuous casting blank with a thickness of 220-250 mm through steelmaking and continuous casting; The chemical composition of the continuous casting blank comprises, in 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 %, 68 ≤Ni / (C+Al) ≤173, Mn=(1.8-2.5)Si+0.17 %, and the balance being iron and inevitable impurities; The cogging process: first heating the continuous casting blank, the soaking temperature being 1200-1240 ℃, and then rolling the heated continuous casting blank into a large slab with a thickness of 4.5-10 t; The compounding process: cutting the obtained large slab into multiple small slabs, and stacking and welding n small slabs to form a composite blank, n=2, 3 or 4; The heating process: heating the obtained composite blank, the heating process comprising preheating, heating and soaking, the preheating temperature being 750-850 ℃, the heating rate being 20-30 ℃ / min, the heating temperature being 1100-1200 ℃, the heating rate being 30-50 ℃ / min, and the soaking temperature being 1150-1200 ℃; the total heating time being 160-220 min; Rolling process: first, the composite blank is made into an intermediate blank with thickness t1 by first-stage rolling, 7t≤t1≤16t, and then is warmed up, and then the intermediate blank is made into a hot-rolled plate with thickness t0 by second-stage rolling, 0.8×n×t≤t0≤1.2×n×t; wherein, the opening rolling temperature of the first-stage rolling is 1050~1090℃, the opening rolling temperature of the second-stage rolling is (T fr -10)~(T fr +10)℃, the finishing rolling temperature is (T fr -18)~(T fr +18)℃, T fr is obtained from the following formula 1; Cooling process: the obtained hot-rolled plate is cooled by water cooling, the water entry temperature (T fc -15)~(T fc +15)℃, T fc The final cooling temperature is obtained by formula 2, ≤200℃; after water exit, air cooling to room temperature to obtain a cooled plate; The heat treatment process: tempering the obtained cooling plate, the tempering temperature being 540-580 ℃, the holding time being more than 30 min, and the cooling plate being air-cooled to room temperature after the tempering is completed; The plate separating process: separating the tempered plate into n single-layer 9Ni steel plates through edge cutting, and the thickness t of at least one 9Ni steel plate being less than 8 mm; T fr = 879 - 97C + 48Si - 9.5Mn - 5.1Ni - 200Al Equation 1; T fc = 720 + 116C + 27Si - 10Mn + 6Ni - 177Al Equation 2; In the formula 1 and the formula 2, the element symbols represent the mass percentage of each element in the steel plate.

2. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the cooling process, the re-red temperature is ≤300 ℃.

3. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the n single-layer 9Ni steel plates, the thickness t of at least one 9Ni steel plate is 3-8 mm.

4. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, The thickness of the intermediate blank t1 is 30-80 mm, and 2 ≤t1 / t0 ≤8.

5. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the cooling process, The hot-rolled plate is cooled on a post-rolling accelerated cooling control system; The post-rolling accelerated cooling control system has 24 groups of cooling headers, wherein the first 6 groups, the seventh 18 groups and the nineteenth 24 groups form a first subzone, a second subzone and a third subzone, respectively; The total cooling water flow of the post-rolling accelerated cooling control system is 1500-3600 L / s, the total cooling water flow of the first subzone is 500-530 L / s, all the cooling headers of the first subzone and the third subzone are opened, and the cooling headers of the second subzone are opened alternately.

6. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the rolling process, the reduction rate of each pass in the first stage rolling is 10-35 %, and the reduction amount of at least three passes in the first five passes is not less than 8 mm.

7. The production method of a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the heat treatment process, when the thickness t0 is more than 10 mm, the holding time is valued in the range of 2t0-5t0 min.

8. The method of producing a thin-gauge 9Ni steel plate according to claim 1, characterized by, In the compounding process, an oxidation-resistant isolation agent is arranged between the adjacent two small slabs of the composite blank. The antioxidant release agent is a coating material composed of 55-65 parts by mass of a water heat leaching material of blast furnace slag, 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.

9. A thin-gauge 9Ni steel plate characterized by, The steel plate is prepared by the production method of the thin-gauge 9Ni steel plate according to any one of claims 1 to 8, and the chemical components of the steel plate include, in percentage by mass, 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 being iron and inevitable impurities; and further satisfy 68≤Ni / (C+Al)≤173 and / or Mn=(1.8-2.5)Si+0.17%. The thickness of the steel plate is 8 mm or less, the tensile strength is 730-810 MPa, the yield strength is 590-680 MPa, the yield ratio is ≤0.87, the elongation is ≥23%, and the impact energy at -196 ℃ is ≥210 J.

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