A large-thickness mn-ni-mo quenched and tempered steel plate produced by rolling instead of forging and a production method thereof

Abstract

The application relates to a kind of Mn-Ni-Mo quenching and tempering steel plates of large thickness produced by rolling instead of forging, which comprises the following components with mass percentage: C 0.14%-0.2%, Si 0.1%-0.2%, Mn 1.35%-1.5%, Ni 0.6%-0.9%, Mo 0.4%-0.5%, Al 0.015%-0.03%, P≤0.01%, S≤0.003%, H≤0.6ppm, and the balance is Fe and inevitable impurities.The application also relates to a production method of the steel plate, which comprises the following processes: smelting, electroslag remelting, electroslag ingot heating, rolling, hydrogen annealing and heat treatment.The application ensures the hardenability of the steel plate, ensures the appropriate strength and toughness matching of the steel plate, further removes inclusions in the steel through electroslag secondary remelting, ensures the density of the steel plate, and ensures the internal quality through differential temperature rolling and hydrogen annealing in the subsequent processes.The internal straight and inclined flaw detection of the steel plate meets the first level requirements of JB / T5000.15-2007.

Description

Technical Field

[0001] This invention relates to the field of steel plate technology, specifically to a method for producing thick Mn-Ni-Mo quenched and tempered steel by replacing forging with rolling. Background Technology

[0002] Thick Mn-Ni-Mo quenched and tempered steel plates are widely used in the manufacture of support plates for fourth-generation nuclear power high-temperature gas-cooled reactors, core rings, and turbine bases for hydroelectric power stations. High internal quality is required, with no single-point equivalent defects exceeding 2mm. Forging is generally used to ensure the quality of internal flaw detection. Thick Mn-Ni-Mo quenched and tempered steel plates produced using conventional smelting and rolling methods suffer from unstable flaw detection quality due to porosity and segregation issues, making it difficult to meet the Class I flaw detection requirements of forgings in JB / T5000.15-2007.

[0003] Furthermore, as the thickness of the steel plate increases, the internal penetration deformation during rolling is insufficient, and the quenching and cooling rate is inadequate, making it difficult to meet technical requirements, especially in the nuclear power field where drop hammer RT is required. NDT Furthermore, most of them require a drop hammer test at one-quarter of the plate thickness, which further increases the difficulty of production. Summary of the Invention

[0004] This invention provides a method for producing thick Mn-Ni-Mo quenched and tempered steel plates using rolling instead of forging, in order to solve the problem that existing technologies cannot meet the first-level flaw detection requirements of forgings in JB / T5000.15-2007.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for producing thick Mn-Ni-Mo quenched and tempered steel plates by rolling instead of forging is characterized by comprising the following components by mass percentage: C 0.14%~0.2%, Si 0.1%~0.2%, Mn 1.35%~1.5%, Ni 0.6%~0.9%, Mo 0.4%~0.5%, Al 0.015%~0.03%, P≤0.01%, S≤0.003%, H≤0.6ppm, with the balance being Fe and unavoidable impurities.

[0006] Preferably, the maximum thickness of the steel plate is 300 mm.

[0007] The chemical composition design principle of the steel plate of this invention is as follows: solid solution strengthening with appropriate amounts of carbon and manganese, and the addition of Mo and Ni to improve the low-temperature toughness and hardenability of the steel plate. Furthermore, high-quality scrap steel and molten iron are selected, and the content of residual elements is controlled. The roles of each component and its content in this invention are as follows: C: It has a significant impact on the yield strength, tensile strength and weldability of steel. Carbon can significantly improve the strength of steel plates through interstitial solid solution, but excessive carbon content will affect the weldability and toughness of steel.

[0008] Si: In the steelmaking process, Si acts as a reducing agent and deoxidizer. At the same time, Si can play a role in solid solution strengthening. However, when the content is high, it will cause the steel to lose toughness and reduce the weldability of the steel.

[0009] Mn can increase the toughness, strength and hardness of steel, improve the hardenability of steel, and improve the hot working performance of steel. It is also inexpensive and can reduce the production cost of steel plates. However, when the manganese content is too high, there is a risk of coarse grains when heated, which reduces the weldability.

[0010] P and S: Under normal circumstances, these are harmful elements in steel. They increase the brittleness of steel, worsen the weldability of steel, reduce plasticity, and reduce the ductility and toughness of steel. They can also cause cracks during rolling. Therefore, the content of P and S in steel should be minimized.

[0011] Ni slightly improves both the strength and plasticity of steel plates, but significantly improves the low-temperature impact toughness. This is because Ni only forms a solid solution in steel, and the strengthening effect of the solid solution is not obvious. Instead, it mainly improves the material's plasticity by increasing the lattice slip plane during plastic deformation. Ni can also improve the hardenability of alloy steel and enhance the toughness of steel at low temperatures, thus lowering the ductile-brittle transition temperature.

[0012] Mo significantly improves the strength, plasticity, and low-temperature impact toughness of steel plates. This is because when Mo dissolves in ferrite and austenite, it shifts the C-curve of steel to the right, thereby significantly improving the hardenability of steel. Moreover, Mo can significantly increase the recrystallization temperature of steel and improve tempering stability. When Mo carbides are formed, they can play a role in dispersion strengthening.

[0013] TAl (All Aluminum): A commonly used deoxidizer in steel; adding a small amount of Al to steel can refine the grains and improve impact toughness; aluminum also has antioxidant and anti-corrosion properties, but excessive content will affect the hot working performance, weldability and machinability of steel.

[0014] H: High hydrogen content in steel can easily cause cracking, which in turn reduces the strength, plasticity, and impact toughness of the steel, a condition known as "hydrogen embrittlement." It also easily produces white spots, resulting in dense defects during flaw detection. Furthermore, it easily causes lamellar fractures, with alloy steels containing chromium-nickel or chromium-nickel-molybdenum exhibiting more severe lamellar fractures than carbon steel.

[0015] A method for producing thick Mn-Ni-Mo quenched and tempered steel plates by replacing forging with rolling is characterized by including the following steps: smelting, electroslag remelting, electroslag ingot heating, rolling, hydrogen diffusion annealing, and heat treatment.

[0016] Preferably, the smelting process includes electric furnace smelting, LF refining and VD vacuum refining and continuous casting to obtain the billet. The specific process is as follows: steel and alloy smelting, the molten steel is first smelted in an electric furnace, then sent to the LF refining furnace for refining, the molten steel temperature reaches 1570℃ and above and is transferred to the VD furnace for vacuum degassing treatment, and the steel is continuously cast to obtain the continuous casting billet. LF refining process: LF refining time shall not be less than 50 minutes, and vacuuming time for vacuum degree below 66.6 Pa shall not be less than 30 minutes; VD vacuum refining process: Scrap steel and molten iron are selected for smelting, and the mass content of residual elements is controlled as follows: B≤0.0005%, As≤0.010%, Sb≤0.002%, Co≤0.02%, V≤0.01%, Nb≤0.01%, Cu≤0.10%.

[0017] After vacuum treatment, continuous casting is carried out to obtain a continuously cast billet.

[0018] Preferred electroslag remelting process: Using continuously cast billets as consumable electrodes, a five-element slag system is employed for remelting. Before remelting, the slag is baked at 300℃ for 10 hours, with the melting rate controlled at ≤22 kg / min. The ingots are 35-40 ton flat electroslag ingots, and a 980mm thick flat crystallizer is used. The crystallizer is internally cooled by water, with a wide-face water flow of 60m³. 3 / h, narrow face 30m 3 / h; Steel plate rolling compression ratio greater than 3; After the electroslag ingot is demolded, it is cleaned under heat using a flame gun at a temperature of not less than 150°C. After cleaning, it is heated in a soaking furnace.

[0019] Preferably, the method for manufacturing the consumable electrode is as follows: after surface peeling, two 200mm thick continuous casting billets are stacked and spot-welded together to serve as the consumable electrode.

[0020] Preferably, the electroslag ingot heating process is as follows: the maximum heating temperature of the electroslag steel ingot is 1260℃, the uniform heating temperature is 1240℃, the heating rate is controlled to be ≤100℃ / h below 950℃, the temperature is raised to 700℃ and 950℃ respectively and held for 2 hours to reduce the thermal stress and structural stress of the steel ingot, and the temperature is held at 1240~1260℃ for ≥15 hours, with a total heating time of not less than 32 hours.

[0021] Preferably, the rolling process adopts a differential temperature rolling process. In the first stage, the rolling temperature is 950~1200℃, the single-pass reduction is 10%~20%, and the cumulative reduction rate is 30%~60%. Then, the steel is dried and the iron oxide scale on the surface of the steel plate is removed by high pressure water. In the second stage, the rolling temperature is 850~880℃, and the cumulative reduction rate is 30%~50%.

[0022] Preferred hydrogen diffusion annealing process: After rolling, the steel plate is promptly placed in a slow cooling pit for hydrogen diffusion annealing. The furnace temperature is not lower than 350℃, and the temperature is increased to 580±10℃ at a rate of 50℃ / h. The temperature is held for 96 hours, and then the temperature is reduced to 300℃ at a rate of ≤50℃ / h before being removed from the furnace.

[0023] Preferably, the heat treatment process involves a two-stage quenching process. The first stage involves heating at 930±10℃ and holding for 2 minutes / mm. The quenching is then performed using a roller-bottom type thick plate quenching machine with a water volume of not less than 5000 ml. 3 / h, water temperature ≤26℃, swing time 1 hour, the red temperature of the steel plate after water removal is not greater than 40℃; the second quenching heating temperature is 780±10℃, the cooling follows the first quenching process, the tempering is done in the car bottom furnace, the heating temperature is 640±10℃, and the holding time is 3min / mm.

[0024] The electroslag remelting process described in this invention further purifies the molten steel, reducing inclusions and segregation. The electroslag remelting crystallization process reduces the anisotropy of the steel plate, making it more compact internally. In addition, the use of a 980mm crystallizer allows for the rolling of steel plates with a maximum thickness of 300mm and a compression ratio greater than 3, enabling the rolling deformation to penetrate into the core of the steel plate, which is beneficial for flaw detection of thick steel plates.

[0025] In the rolling process described in this invention, the electroslag ingot is heated to 700°C and 950°C with heat preservation platforms, which can reduce the thermal stress and structural stress of the electroslag ingot and reduce the risk of cracking. In addition, the rolling adopts differential temperature rolling, which creates a temperature gradient from the surface to the inside of the steel plate. During the II stage rolling, a deformation resistance gradient from the surface to the inside is formed, which allows the rolling deformation of the steel plate to penetrate to the core and press together the porosity and shrinkage defects in the core.

[0026] The hydrogen diffusion annealing process described in this invention uses slow cooling pit hydrogen diffusion annealing treatment to prevent the generation of white spots on the steel plate and avoid dense defects in the flaw detection points.

[0027] The method of this invention, through a reasonable alloy element ratio in the steel plate and a heat treatment process of quenching + quenching + tempering, enables the steel plate to obtain a bainitic structure with a small amount of undissolved ferrite, thus ensuring the mechanical properties of the steel plate.

[0028] The method of the present invention has the following advantages: The steel plate has a reasonable composition design. Through appropriate carbon and manganese solid solution strengthening, as well as elements such as nickel and molybdenum, the steel plate has a certain hardenability and a suitable strength and toughness match. In addition, through electroslag remelting, inclusions in the steel are further removed to ensure the density of the steel plate. Subsequent processes such as differential temperature rolling and hydrogen diffusion annealing ensure internal quality. The internal straight and oblique flaw detection of the steel plate meets the first-level requirements of forging JB / T5000.15-2007, and the total amount of inclusions A+B+C+D is controlled within 2.0 level.

[0029] The steel plate has a maximum thickness of 300mm, and its internal quality meets the first-level standard for forging flaw detection. The steel plate also passes oblique flaw detection and meets the technical requirements.

[0030] The mechanical properties of the steel plate are as follows: transverse impact energy at -20℃ at 1 / 4 of the plate thickness is above 180J; drop hammer test shows no plastic transformation temperature ≤ -20℃; tensile strength of the steel plate in the Z direction shows a shrinkage of more than 40%, meeting the Z35 standard.

[0031] (3) The steel plate has low H content, low P and S content, high purity, and the total inclusion content is less than 2.0. Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0033] The invention will be further described in detail below with reference to specific examples.

[0034] Example 1 This paper describes the production of thick Mn-Ni-Mo quenched and tempered steel plates with a thickness of 300mm using rolling instead of forging. The chemical composition by mass percentage is: C 0.14%, Si 0.15%, Mn 1.5%, Ni 0.85%, Mo 0.46%, Al 0.02%, P 0.01%, S 0.001%, with the balance being Fe and unavoidable impurities.

[0035] The specific process steps for producing thick Mn-Ni-Mo quenched and tempered steel plates by replacing forging with rolling are as follows: Smelting process: High-quality scrap steel and alloys are selected for smelting. Molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes. When the temperature of the molten steel reaches 1570℃, it is transferred to the VD furnace for vacuum degassing treatment. The vacuum degree is 66.6 Pa and the vacuum holding time is 30 minutes.

[0036] VD vacuum refining process: smelting uses scrap steel and molten iron, and controls the mass content of residual elements: B 0.0005%, As 0.005%, Sb 0.002%, Co 0.01%, V 0.003%, Nb 0.01%, Cu 0.07%.

[0037] After vacuum treatment, continuous casting is carried out to obtain a continuously cast billet.

[0038] (2) Electroslag remelting process: Two 200mm thick continuous casting billets are stacked and spot-welded together as consumable electrodes. A five-element slag system and a 980mm thick crystallizer are used. The melting rate is 21 kg / min. The ingot is a 35-ton flat electroslag ingot. After it comes off the line, it is cleaned in time. The ingot cleaning temperature is 150℃.

[0039] (3) Electroslag ingot heating process: The steel ingot is heated at a rate of 80℃ / h below 950℃, and held at 700℃ and 950℃ for 2 hours respectively. Above 950℃, the heating rate is 120℃ / h, and the ingot is heated to the maximum temperature of 1260℃. The heat is then spread at 1260℃ and held for 15 hours. The total heating time is 32 hours.

[0040] (4) Rolling process: Differential temperature rolling is adopted, which is divided into two stages: Stage I rolling temperature is 950℃~1200℃, of which the initial rolling temperature is 1050℃ and the final rolling temperature is 980℃. The single-pass reduction in this stage is 10%~20%, and the cumulative reduction rate is 51%. Then the steel is air-dried with a thickness of 1.6t, where t is the thickness of the steel plate. High-pressure water is used to reduce the surface temperature of the steel plate, so that a temperature gradient is formed from the surface to the inside of the steel plate. Stage II initial rolling temperature is 860℃ and final rolling temperature is 840℃. The cumulative reduction rate is 37.5%.

[0041] (5) Hydrogen diffusion annealing process: Hydrogen diffusion annealing is carried out in time after the steel plate is rolled. The furnace temperature is 360℃, and the temperature is increased to 590℃ at a rate of 50℃ / h. The temperature is held for 96 hours, and then the temperature is reduced to 300℃ at a rate of 45℃ / h before being taken out of the furnace.

[0042] (6) Heat treatment process: Quenching adopts a two-stage quenching process. The first heating temperature is 920℃, and the holding temperature is 2min / mm. The quenching is cooled in a roller bottom thick plate quenching machine with a water volume of 5100m³. 3 / h, water temperature 18℃, oscillation time 1 hour, steel plate red-hot temperature after exiting water 40℃. Second quenching heating temperature 790℃, cooling water volume 5150m³. 3 / h, water temperature 20℃, oscillation for 1 hour, steel plate turns red at 28℃ after exiting the water. Tempering is carried out in a car bottom furnace, heating temperature 650℃, holding time 3min / mm.

[0043] The internal quality of the steel plate meets the Class I standard for forging flaw detection, and the oblique flaw detection of the steel plate also passes, meeting the technical requirements. The mechanical properties of the steel plate are as follows: transverse impact energy at -20℃ at 1 / 4 of the plate thickness is 210J; drop hammer test shows no plastic transformation temperature at -20℃; the tensile Z-direction resistance to lamellar tearing has a shrinkage area of ​​50%, meeting the Z35 standard. The steel plate has a low hydrogen content of 0.6ppm, high purity, and the total inclusion content is less than 1.5%. Example 2

[0044] This paper describes the production of thick Mn-Ni-Mo quenched and tempered steel plates with a thickness of 300mm using rolling instead of forging. The chemical composition by mass percentage is as follows: C 0.2%, Si 0.2%, Mn 1.35%, Ni 0.9%, Mo 0.40%, Al 0.03%, P 0.007%, S 0.002%, with the balance being Fe and unavoidable impurities.

[0045] The specific process steps for producing thick Mn-Ni-Mo quenched and tempered steel plates by replacing forging with rolling are as follows: Smelting process: High-quality scrap steel and alloys are selected for smelting. Molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 50 minutes. When the temperature of the molten steel reaches 1573℃, it is transferred to the VD furnace for vacuum degassing treatment. The vacuum degree is 66.6 Pa and the vacuum holding time is 35 minutes.

[0046] VD vacuum refining process: smelting uses scrap steel and molten iron, and controls the mass content of residual elements: B 0.0004%, As 0.03%, Sb 0.001%, Co 0.016%, V 0.01%, Nb 0.003%, Cu 0.03%.

[0047] After vacuum treatment, continuous casting is carried out to obtain a continuously cast billet.

[0048] (2) Electroslag remelting process: Two 200mm thick continuous casting billets are stacked and spot-welded together as consumable electrodes. A five-element slag system and a 980mm thick crystallizer are used. The melting rate is 20 kg / min. The ingot is a 38-ton flat electroslag ingot. After it is taken off the line, it is cleaned in time. The ingot cleaning temperature is 210℃.

[0049] (3) Electroslag ingot heating process: The steel ingot is heated at a rate of 100℃ / h below 950℃, and held at 700℃ and 950℃ for 2 hours respectively. Above 950℃, the heating rate is 110℃ / h, heated to the maximum temperature of 1260℃, the heat-settling temperature is 1240℃, and held (heat-settling) for 15 hours. The total heating time is 32 hours.

[0050] (4) Rolling process: Differential temperature rolling is adopted, which is divided into two stages: Stage I rolling starts at 1200℃ and ends at 990℃. The reduction per pass in this stage is 10%~20%, and the cumulative reduction rate is 60%. Then the steel is air-dried to a thickness of 1.43t, where t is the thickness of the steel plate. High-pressure water is used to reduce the surface temperature of the steel plate, so that a temperature gradient is formed from the surface to the inside of the steel plate. Stage II rolling starts at 850℃ and ends at 830℃. The cumulative reduction rate is 30%.

[0051] (5) Hydrogen diffusion annealing process: Hydrogen diffusion annealing is carried out in time after the steel plate is rolled. The furnace temperature is 350℃, and the temperature is increased to 580℃ at a rate of 50℃ / h. The temperature is held for 96 hours, and then the temperature is reduced to 300℃ at a rate of 50℃ / h before being taken out of the furnace.

[0052] (6) Heat treatment process: Quenching adopts a two-stage quenching process. The first heating temperature is 940℃, and the holding temperature is 2min / mm. The quenching is cooled in a roller bottom thick plate quenching machine with a water volume of 5000m³. 3 / h, water temperature 26℃, oscillation time 1 hour, steel plate red-hot temperature after exiting water 30℃. Second quenching heating temperature 780℃, cooling water volume 5150m³. 3 / h, water temperature 20℃, oscillation for 1 hour, steel plate turns red at 28℃ after exiting the water. Tempering is carried out in a car bottom furnace, heating temperature 630℃, holding time 3min / mm.

[0053] The internal quality of the steel plate meets the Class I standard for forging flaw detection, and the oblique flaw detection of the steel plate also passes, meeting the technical requirements. The mechanical properties of the steel plate are as follows: transverse impact energy at -20℃ at 1 / 4 of the plate thickness is 230J; drop hammer test shows no plastic transformation temperature at -20℃; tensile strength in the Z-direction of the thicker plate exhibits a shrinkage area of ​​55%, meeting the Z35 standard. The steel plate has a low hydrogen content of 0.5ppm, high purity, and a total inclusion content of less than 1.0%. Example 3

[0054] This paper describes the production of thick Mn-Ni-Mo quenched and tempered steel plates with a thickness of 300mm using rolling instead of forging. The chemical composition by mass percentage is: C 0.17%, Si 0.1%, Mn 1.4%, Ni 0.6%, Mo 0.5%, Al 0.015%, P 0.006%, S 0.003%, with the balance being Fe and unavoidable impurities.

[0055] The specific process steps for producing thick Mn-Ni-Mo quenched and tempered steel plates by replacing forging with rolling are as follows: Smelting process: High-quality scrap steel and alloys are selected for smelting. Molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 55 minutes. When the temperature of the molten steel reaches 1575℃, it is transferred to the VD furnace for vacuum degassing treatment. The vacuum degree is 66.6 Pa and the vacuum holding time is 32 minutes.

[0056] VD vacuum refining process: smelting uses scrap steel and molten iron, and controls the mass content of residual elements: B 0.0002%, As 0.010%, Sb 0.001%, Co 0.02%, V 0.006%, Nb 0.005%, Cu 0.10%.

[0057] After vacuum treatment, continuous casting is carried out to obtain a continuously cast billet.

[0058] (2) Electroslag remelting process: Two 200mm thick continuous casting billets are stacked and spot-welded together as consumable electrodes. A five-element slag system and a 980mm thick crystallizer are used. The melting rate is 22 kg / min. The ingot is a 40-ton flat electroslag ingot. After it comes off the line, it is cleaned in time. The ingot cleaning temperature is 230℃.

[0059] (3) Electroslag ingot heating process: The steel ingot is heated at a rate of 50℃ / h below 950℃, and held at 700℃ and 950℃ for 2 hours respectively. Above 950℃, the heating rate is 130℃ / h, heated to the maximum temperature of 1260℃, the heat-settling temperature is 1250℃, and held (heat-settling) for 17 hours. The total heating time is 35 hours.

[0060] (4) Rolling process: Differential temperature rolling process is adopted, which is divided into two stages of rolling: Stage I rolling starts at 950℃ and ends at 920℃. The single-pass reduction in this stage is 10%~20%, and the cumulative reduction rate is 30%. Then the steel is dried with a thickness of 2.0t, where t is the thickness of the steel plate. High-pressure water is used to reduce the surface temperature of the steel plate, so that the steel plate forms a temperature gradient from the surface to the inside. Stage II rolling starts at 880℃ and ends at 845℃, with a cumulative reduction rate of 50%.

[0061] (5) Hydrogen diffusion annealing process: Hydrogen diffusion annealing is carried out in time after the steel plate is rolled. The furnace temperature is 370℃, and the temperature is increased to 570℃ at a rate of 50℃ / h. The temperature is held for 96 hours, and then the temperature is reduced to 300℃ at a rate of 45℃ / h before being taken out of the furnace.

[0062] (6) Heat treatment process: Quenching adopts a two-stage quenching process. The first heating temperature is 930℃, and the holding temperature is 2min / mm. The quenching is cooled in a roller bottom thick plate quenching machine with a water volume of 5250m³. 3 / h, water temperature 25℃, oscillation time 1 hour, steel plate red-hot temperature after exiting water 36℃. Second quenching heating temperature 770℃, cooling water volume 5160m³. 3 / h, water temperature 26℃, oscillation for 1 hour, steel plate turns red at 38℃ after exiting the water. Tempering is carried out in a car bottom furnace, heating temperature 635℃, holding time 3min / mm.

[0063] The internal quality of the steel plate meets the Class I standard for forging flaw detection, and the oblique flaw detection of the steel plate also passes, meeting the technical requirements. The mechanical properties of the steel plate are as follows: transverse impact energy at -20℃ at 1 / 4 of the plate thickness is 235J; drop hammer test shows no plastic transformation temperature at -20℃; tensile strength in the Z-direction of the thicker plate exhibits a shrinkage of 45%, meeting the Z35 standard. The steel plate has a low hydrogen content of 0.4ppm, high purity, and a total inclusion content of less than 1.0%.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for producing thick Mn-Ni-Mo quenched and tempered steel plates by replacing forging with rolling, characterized in that, The process includes the following steps: smelting, electroslag remelting, electroslag ingot heating, rolling, hydrogen diffusion annealing, and heat treatment; Electroslag remelting process: using continuously cast billets as consumable electrodes, a five-element slag system is used for remelting. Before remelting, the slag is baked, and the melting rate is controlled at ≤22 kg / min. The ingots are 35-40 ton flat electroslag ingots, and a 980mm thick flat crystallizer is used. After demolding, the electroslag ingots are cleaned with a flame gun at a temperature not lower than 150℃. After cleaning, they are heated in a soaking furnace. The method for manufacturing consumable electrodes is as follows: after surface peeling, two 200mm thick continuously cast billets are stacked and spot-welded together to serve as consumable electrodes. Electroslag ingot heating process: The maximum heating temperature of the electroslag steel ingot is 1260℃, the uniform heating temperature is 1240℃, the heating rate is controlled to be ≤100℃ / h below 950℃, and the temperature is raised to 700℃ and 950℃ respectively and held for 2 hours to reduce the thermal stress and structural stress of the steel ingot. The temperature is held at 1240~1260℃ for ≥15 hours, and the total heating time is not less than 32 hours. The rolling process employs a differential temperature rolling process. In Stage I, the rolling temperature is 950~1200℃, with a single-pass reduction rate of 10%~20% and a cumulative reduction rate of 30%~60%. The steel is then air-dried and high-pressure water is used to remove the iron oxide scale from the steel plate surface. In Stage II, the initial rolling temperature is 850~880℃, with a cumulative reduction rate of 30%~50%. Hydrogen diffusion annealing process: After rolling, the steel plate is put into the slow cooling pit for hydrogen diffusion annealing in a timely manner. The furnace temperature is not lower than 350℃, and the temperature is increased to 580±10℃ at a rate of 50℃ / h. The temperature is held for 96 hours, and then the temperature is reduced to 300℃ at a rate of ≤50℃ / h before being taken out of the furnace. Heat treatment process: A two-stage quenching process is adopted. The first heating temperature is 930±10℃, and the holding temperature is 2min / mm. The quenching is carried out in a roller bottom type thick plate quenching machine with a water volume of not less than 5000m³. 3 / h, water temperature ≤26℃, swing time 1 hour, the red temperature of the steel plate after water removal is not greater than 40℃; the second quenching heating temperature is 780±10℃, the cooling follows the first quenching process, the tempering is done in the car bottom furnace, the heating temperature is 640±10℃, and the holding time is 3min / mm. The steel plate comprises the following components by mass percentage: C 0.14%~0.2%, Si 0.1%~0.2%, Mn 1.35%~1.5%, Ni 0.6%~0.9%, Mo 0.4%~0.5%, Al 0.015%~0.03%, P≤0.01%, S≤0.003%, H≤0.6ppm, with the balance being Fe and unavoidable impurities; The maximum thickness of the steel plate is 300mm.

2. The production method according to claim 1, characterized in that, The smelting process includes electric furnace smelting, LF refining and VD vacuum refining and continuous casting to obtain the billet. The specific process is as follows: high-quality scrap steel and alloy smelting are selected. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. When the temperature of the molten steel reaches 1570℃ or above, it is transferred to the VD furnace for vacuum degassing treatment and continuously cast to obtain the continuous casting billet. LF refining process: LF refining time shall not be less than 50 minutes, and vacuuming time for vacuum degree below 66.6 Pa shall not be less than 30 minutes; VD vacuum refining process: Scrap steel and molten iron are used for smelting, and the residual element content is controlled as follows: B≤0.0005%, As≤0.010%, Sb≤0.002%, Co≤0.02%, V≤0.01%, Nb≤0.01%, Cu≤0.10%; After vacuum treatment, continuous casting is carried out to obtain a continuously cast billet.