Method for producing 120-150mm ultra-thick grade flaw detection steel plate by using 360mm section continuous casting machine without electromagnetic stirring system

Abstract

This invention relates to a method for producing 120-150mm ultra-thick flaw-detecting steel using a 360mm cross-section continuous casting machine without an electromagnetic stirring system. The main improvements are made to the continuous casting process parameters as follows: the casting speed is set to 0.6-0.62 m / min; the surface theoretical straightening temperature is adjusted to 935℃ using the secondary cooling water ratio; simultaneously, the surface theoretical temperature from the bending section of the casting machine to the straightening section outlet is reduced by 15℃; the secondary cooling water ratio is 0.52-0.58 L / kg; and the total reduction is adjusted to 8.4mm for light... In the pressing mode, the reduction amount is redistributed. When the solid fraction is 0-30%, the reduction amount accounts for 20% of the total reduction amount; when it is 30-70%, the reduction amount accounts for 61% of the total reduction amount; and when it is 70-90%, the reduction amount accounts for 14% of the total reduction amount. The center of gravity of the reduction amount in the light pressing mode is shifted forward, so that the low magnification center segregation line position is dispersed into a discontinuous point distribution of individual segregation points. The low magnification center segregation is controlled within C1.5. Combined with the smelting process, rolling process and slow cooling process, 120-150mm ultra-thick steel plates with qualified flaw detection are obtained.

Description

Technical Field

[0001] This invention relates to a method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system. It belongs to the field of ultra-thick flaw-detecting steel manufacturing technology, and the ultra-thick flaw-detecting steel can be used in bridge steel plates, building steel plates and other fields. Background Technology

[0002] In recent years, users have gradually increased their demand for ultra-thick (≥100mm) steel plates for flaw detection. These plates need to meet the requirements of structural strength, safety strength margin, and special functions under extreme working conditions (low temperature impact and fatigue resistance). The thickness requirement has reached up to 150mm to 180mm. Steel plates with a thickness of 120 to 150mm are already considered to be of a relatively conventional thickness. Therefore, the construction of slab casting machines by domestic steel companies is gradually transitioning to the construction of ultra-thick casting machines.

[0003] Currently, the thickest slab casting machine in China is 450-460mm thick, used for rolling steel plates with a thickness of 100mm or more that require flaw detection. The aforementioned casting machine uses a secondary cooling electromagnetic stirring system and a heavy pressure device at the end of solidification, and the flaw detection pass rate of ultra-thick steel plates can reach over 85%.

[0004] However, most steel companies in China still primarily use slab continuous casting machines with standard cross-sectional thicknesses. The mainstream slab continuous casting machines can produce slabs with three cross-sectional thicknesses: 250 / 300 / 360mm. Production and supply are guaranteed according to the principle of a compression ratio of ≥3:1 for the cast slab thickness / rolled thickness. Using a 360mm cross-section, including ensuring the steel plate passes flaw detection, is sufficient for producing steel plates with a specification of less than 100mm. A flaw detection pass rate of over 85% is not a major problem. However, under the current conditions, it is very difficult to ensure the second-level flaw detection pass rate for steel plates with a specification of 120-150mm, with a flaw detection pass rate of only about 20%.

[0005] Some companies also use slab continuous casting machines provided by Pratt & Co. (slab thickness specifications are 200 / 250 / 300mm). These continuous casting machines are equipped with a secondary cooling control system, which can also control the slab quality well. However, the thickness specifications are too small, and it is impossible to produce 120-150mm specification flaw-testing steel plates.

[0006] Therefore, how to produce 120-150mm diameter flaw-tested steel plates using existing 250 / 300 / 360mm cross-section slab continuous casting machines without electromagnetic stirring systems and solidification end-stage heavy pressure equipment, and achieve a flaw-testing pass rate of over 90%, has become an urgent problem to be solved in the industry, in the absence of a 450-460mm thick slab continuous casting machine. Summary of the Invention

[0007] The purpose of this invention is to address the problem that most domestic steel companies currently use slab continuous casting machines without electromagnetic stirring systems. When producing 120-150mm thick steel plates, the flaw detection pass rate is only about 20%, which seriously restricts the delivery of contracts. This invention provides a method for producing 120-150mm ultra-thick steel plates with flaw detection using a 360mm cross-section continuous casting machine without electromagnetic stirring systems. Using the method of this invention, the flaw detection pass rate of 120-150mm ultra-thick steel plates with flaw detection can reach over 90%.

[0008] The present invention discloses a method for producing ultra-thick steel plates with a cross-section of 120-150mm using a 360mm section continuous casting machine without an electromagnetic stirring system, comprising the following steps:

[0009] (1) The continuous casting speed is set to 0.6~0.62m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.52~0.58L / kg.

[0010] (2) The total reduction of the continuous casting machine was adjusted from 7.9 mm at the time of commissioning to 8.4 mm. The reduction in the light reduction mode was redistributed. During the solidification process of the billet in the continuous casting machine, the liquid core gradually decreased from 100% to 0% and the solid phase gradually increased from 0% to 100% within the billet. Within this liquid-solid mixing zone, the total light reduction was divided into 10 equal parts with a solid phase ratio from 0% to 100%. A reasonable reduction was set for each part. This was achieved through additional reduction during the liquid core solidification process. For pressure, the reduction amount as a percentage of the total reduction is adjusted from 10% to 20% when the solid fraction is 0-30%, from 50% to 61% when the solid fraction is 30-70%, and from 27% to 14% when the solid fraction is 70-90%. The center of gravity of the reduction amount under light pressure is shifted forward, so that the linear position of low magnification center segregation is dispersed into a point distribution of discontinuous individual segregation points, and the low magnification center segregation rating of the billet is controlled within C1.5.

[0011] Furthermore, in this invention, the billet slow cooling requires that after the billet leaves the stacking platform, it be slow cooled in the on-site slow cooling pit for more than 72 hours until the surface temperature of the billet is ≤200℃, and the billet is sent down after passing the inspection.

[0012] Furthermore, in this invention, the billet heating is as follows: the furnace outlet temperature is ≥1170℃, the furnace soaking time is 45~75min, and the total furnace time is 36*(5.5~10)min+soaking time.

[0013] Furthermore, in this invention, the rolling process is as follows: the roughing rolling start temperature is ≥1150℃, the number of roughing rolling passes with a reduction of ≥28mm is ≥4, a large reduction rolling process is used to fully refine the original austenite grains, the intermediate billet thickness is 160~180mm, the second-stage rolling start temperature is 840~850℃, after rolling, any possible internal pores are fully welded, the final rolling temperature is 800~830℃, and the billet is removed from the production line at a roll speed of 0.5~0.6m / min.

[0014] Furthermore, the steel plates in this invention are slow-cooled: the rolled steel plates are stacked and slow-cooled for ≥48 hours, protected from wind, neatly stacked, and the exposed head and / or tail ends are reduced. They can only be laid out for manual flaw detection after being stacked and cooled to below 50°C.

[0015] Furthermore, in the converter smelting of this invention: argon is blown throughout the smelting process, with an argon flow rate of 300–600 m³ / h. 3 / h, smelting until the mass percentage of P reaches the target value range for the corresponding steel grade.

[0016] Furthermore, in the LF refining process of this invention: when energizing the smelting process, bypassing is avoided to improve the smelting submerged arc effect, and the mass percentage of S is ≤0.003%.

[0017] Furthermore, in the RH vacuum refining of this invention: after the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for ≥15min, ≥300m of calcium iron wire is used per furnace, the soft blowing time is ≥8min, the Ca / S ratio is controlled between 0.6 and 3.0, and the mass percentage of H is controlled at ≤2ppm and the mass percentage of [O] is controlled at ≤30ppm during each batch of production.

[0018] Using the method of the present invention, the flaw detection steel plates that can be produced include, but are not limited to, the aforementioned steel types such as Q345qD, Q345R, Q355B, and Q420NCZ35.

[0019] The method of this invention reduces the low-magnification center segregation of the billet to below 1.5 by controlling the production process, especially by changing the continuous casting process parameters. At the same time, combined with smelting, rolling and slow cooling processes, it can obtain 120-150mm ultra-thick steel plates with qualified flaw detection. Detailed Implementation

[0020] To better explain the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any way.

[0021] A method for producing ultra-thick steel plates with flaw detection specifications of 120-150mm using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, according to various embodiments of the present invention, includes the following steps:

[0022] (1) Converter smelting: Argon is blown throughout the smelting process, with a flow rate of 300-600 m³ / h. 3 / h, smelting until the mass percentage content of P reaches the target value range for the corresponding steel grade;

[0023] (2) LF refining: Avoid opening the bypass when energizing the smelting process to improve the submerged arc effect, and smelt to a S mass percentage content ≤0.003%;

[0024] (3) RH vacuum refining: After the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for ≥15min, ≥300m of calcium iron wire is used per furnace, the soft blowing time is ≥8min, the Ca / S ratio is controlled at 0.6~3.0, the mass percentage of H is controlled at ≤2ppm and the mass percentage of [O] is controlled at ≤30ppm during each batch of production;

[0025] (4) Continuous casting:

[0026] ① The continuous casting speed is set to 0.6~0.62m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.52~0.58L / kg.

[0027] ② The overall reduction of the continuous casting machine was adjusted from 7.9mm at the time of commissioning to 8.4mm. The reduction in the light reduction mode was redistributed. During the solidification process of the continuous casting billet, the liquid core gradually decreased from 100% to 0%, while the solid content gradually increased from 0% to 100%. Within this liquid-solid mixing zone, the total light reduction was divided into 10 equal parts, with solid fractions ranging from 0% to 100%. A reasonable reduction was set for each part. Through additional pressure during the liquid core solidification process, the reduction percentage of the total reduction was adjusted from 10% to 20% for 0-30% solid fraction, from 50% to 61% for 30-70% solid fraction, and from 27% to 14% for 70-90% solid fraction. This resulted in 360mm billets with a low magnification center segregation rating of C1.5 or lower. See Table 1 below for the correspondence between solid fraction and cumulative reduction.

[0028] Table 1 Correspondence between solid fraction and cumulative reduction

[0029]

[0030] (5) Slow cooling of billet: After the billet leaves the stacking platform, it is required to be slow cooled in the slow cooling pit on site for more than 72 hours until the surface temperature of the billet is ≤200℃. After the billet passes the inspection, it is sent down.

[0031] (6) Heating of billet: The furnace outlet temperature is ≥1170℃, the furnace soaking time is 45~75min, and the total furnace time is 36*(5.5~10)min+soaking time;

[0032] (7) Rolling: The roughing rolling temperature is ≥1150℃, the number of roughing rolling passes with a reduction of ≥28mm is ≥4, the thickness of the intermediate billet is 160~180mm, the second-stage rolling temperature is 840~850℃, the final rolling temperature is 800~830℃, and the billet is removed from the rolling mill at a speed of 0.5~0.6m / min after rolling.

[0033] (8) Slow cooling of steel plates: After rolling, the steel plates are stacked and slow cooled for ≥48 hours, protected from wind, and neatly stacked to reduce the exposure of the head and / or tail. They can be laid out for manual inspection only after they have cooled to below 50°C.

[0034] Example 1

[0035] This embodiment uses a 120mm Q420NCZ35 steel plate produced in March 2025 as an example to explain the present invention in detail.

[0036] A method for producing 120mm ultra-thick flaw-testing steel plates using a 360mm section continuous casting machine without an electromagnetic stirring system includes the following steps:

[0037] (1) Converter smelting: Argon is blown throughout the smelting process at a flow rate of 450 L / min. The smelting process is carried out until the mass percentage of P reaches the target value range of Q420NCZ35 steel.

[0038] (2) LF refining: Avoid opening the bypass when energizing the smelting process to improve the smelting submerged arc effect, and smelt to a S mass percentage content of 0.002%;

[0039] (3) RH vacuum refining: After the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for 18 minutes. 300m of calcium iron wire is used, the soft blowing time is 9 minutes, the Ca / S ratio is controlled at 1.4, the mass percentage of H is controlled at 1.2ppm, and the mass percentage of [O] is controlled at 28ppm.

[0040] (4) Continuous casting:

[0041] ① The continuous casting speed is set to 0.62 m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.58 L / kg.

[0042] ② Adjust the overall reduction of the continuous casting machine to 8.4 mm, and redistribute the reduction in the light reduction mode according to Table 1 below to obtain a 360 mm billet with a low magnification center segregation rating of C1.5 or less; see Table 1 below for the correspondence between solid fraction and cumulative reduction:

[0043] Table 1 Correspondence between solid fraction and cumulative reduction

[0044]

[0045] (5) Slow cooling of billet: After the billet leaves the stacking platform, it is slow cooled in the slow cooling pit on site for 75 hours until the surface temperature of the billet reaches 150°C. After the billet passes inspection, it is sent down.

[0046] (6) Billet heating: The furnace outlet temperature is 1178℃, the furnace soaking time is 60min, and the total furnace time is 312min;

[0047] (7) Rolling: The roughing rolling temperature is 1154℃, the roughing rolling reduction is 32mm in 5 passes, the intermediate billet thickness is 160mm, the second stage rolling temperature is 846℃, the final rolling temperature is 821℃, and the billet is rolled off the production line at a speed of 0.6m / min.

[0048] (8) Slow cooling of steel plates: After rolling, the steel plates are stacked and slow cooled for 3 days, protected from wind, and neatly stacked to reduce the exposure of the head and / or tail. After cooling to room temperature, they are laid out for manual inspection. Tensile properties and metallographic structure analysis are performed on different positions in the thickness direction of the steel. The results show that the structure of the upper and lower parts of the steel plate is symmetrical and uniform, and the flaw detection is qualified.

[0049] Example 2

[0050] This embodiment uses a 150mm Q355B steel plate produced in March 2025 as an example to explain the present invention in detail.

[0051] A method for producing 150mm ultra-thick flaw-tested steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system includes the following steps:

[0052] (1) Converter smelting: Argon is blown throughout the smelting process, with an argon flow rate of 450 L / min, and the mass percentage of P reaches the target value range of Q355B steel.

[0053] (2) LF refining: Avoid opening the bypass when energizing the smelting process to improve the smelting submerged arc effect, and smelt to a S mass percentage content of 0.0018%;

[0054] (3) RH vacuum refining: After the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for 19 minutes. 350m of calcium iron wire is used, the soft blowing time is 10 minutes, the Ca / S ratio is controlled at 1.8, the mass percentage of H is controlled at 1.3ppm, and the mass percentage of [O] is controlled at 25ppm.

[0055] (4) Continuous casting:

[0056] ① The continuous casting speed is set to 0.62 m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.54 L / kg.

[0057] ② Adjust the overall reduction of the continuous casting machine to 8.4 mm, and redistribute the reduction in the light reduction mode according to Table 1 below to obtain a 360 mm billet with a low magnification center segregation rating of C1.5 or less; see Table 1 below for the correspondence between solid fraction and cumulative reduction:

[0058] Table 1 Correspondence between solid fraction and cumulative reduction

[0059]

[0060] (5) Slow cooling of billet: After the billet leaves the stacking platform, it is slow cooled in the slow cooling pit on site for 78 hours until the surface temperature of the billet reaches 162℃. After the billet passes inspection, it is sent down.

[0061] (6) Billet heating: The furnace outlet temperature is 1175℃, the furnace soaking time is 75min, and the total furnace time is 435min;

[0062] (7) Rolling: The roughing rolling temperature is 1160℃, the roughing rolling reduction is 30mm in 4 passes, the intermediate billet thickness is 180mm, the second stage rolling temperature is 842℃, the final rolling temperature is 825℃, and the billet is removed from the rolling line at a speed of 0.5m / min after rolling.

[0063] (8) Slow cooling of steel plates: After rolling, the steel plates are stacked and slow cooled for 4 days, protected from wind, and neatly stacked to reduce the exposure of the head and / or tail. After cooling to room temperature, they are laid out for manual inspection. Tensile properties and metallographic structure analysis are performed on different positions in the thickness direction of the steel. The results show that the structure of the upper and lower parts of the steel plate is symmetrical and uniform, and the flaw detection is qualified.

[0064] Example 3

[0065] This embodiment uses a 140mm Q345qD steel plate produced in August 2025 as an example to explain the present invention in detail.

[0066] A method for producing 140mm ultra-thick flaw-testing steel plates using a 360mm section continuous casting machine without an electromagnetic stirring system includes the following steps:

[0067] (1) Converter smelting: Argon is blown throughout the smelting process, with an argon flow rate of 450 L / min, and the mass percentage of P reaches the target value range of Q345qD steel.

[0068] (2) LF refining: Avoid opening the bypass when energizing the smelting process to improve the smelting submerged arc effect, and smelt to a S mass percentage content of 0.002%;

[0069] (3) RH vacuum refining: After the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for 17 minutes. 350m of calcium iron wire is used, the soft blowing time is 8 minutes, the Ca / S ratio is controlled at 1.6, the mass percentage of H is controlled at 1.2ppm, and the mass percentage of [O] is controlled at 27ppm.

[0070] (4) Continuous casting:

[0071] ① The continuous casting speed is set to 0.60 m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.52 L / kg.

[0072] ② Adjust the overall reduction of the continuous casting machine to 8.4 mm, and redistribute the reduction in the light reduction mode according to Table 1 below to obtain a 360 mm billet with a low magnification center segregation rating of C1.5 or less; see Table 1 below for the correspondence between solid fraction and cumulative reduction:

[0073] Table 1 Correspondence between solid fraction and cumulative reduction

[0074]

[0075] (5) Slow cooling of billet: After the billet leaves the stacking platform, it is slow cooled in the slow cooling pit on site for 75 hours until the surface temperature of the billet reaches 164℃. After the billet passes inspection, it is sent down.

[0076] (6) Billet heating: The furnace outlet temperature is 1178℃, the furnace soaking time is 55min, and the total furnace time is 392min;

[0077] (7) Rolling: The roughing rolling temperature is 1160℃, the roughing rolling reduction is 28mm in 4 passes, the intermediate billet thickness is 180mm, the second stage rolling temperature is 844℃, the final rolling temperature is 815℃, and the billet is rolled off the production line at a speed of 0.6m / min.

[0078] (8) Slow cooling of steel plates: After rolling, the steel plates are stacked and slow cooled for 3 days, protected from wind, and neatly stacked to reduce the exposure of the head and / or tail. After cooling to room temperature, they are laid out for manual inspection. Tensile properties and metallographic structure analysis are performed on different positions in the thickness direction of the steel. The results show that the structure of the upper and lower parts of the steel plate is symmetrical and uniform, and the flaw detection is qualified.

[0079] Example 4

[0080] This embodiment uses a 120mm Q345R steel plate produced in May 2025 as an example to explain the present invention in detail.

[0081] A method for producing 120mm ultra-thick flaw-testing steel plates using a 360mm section continuous casting machine without an electromagnetic stirring system includes the following steps:

[0082] (1) Converter smelting: Argon is blown throughout the smelting process, with an argon flow rate of 400 L / min, and the mass percentage of P reaches the target value range of Q345R steel.

[0083] (2) LF refining: Avoid opening the bypass when energizing the smelting process to improve the smelting submerged arc effect, and smelt to a S mass percentage content of 0.0022%;

[0084] (3) RH vacuum refining: After the pressure of the vacuum furnace reaches the ultimate vacuum pressure, the vacuum circulation time is maintained for 16 minutes. 300m of calcium iron wire is used, the soft blowing time is 9 minutes, the Ca / S ratio is controlled at 1.9, the mass percentage of H is controlled at 1.2ppm, and the mass percentage of [O] is controlled at 29ppm.

[0085] (4) Continuous casting:

[0086] ① The continuous casting speed is set to 0.62 m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.55 L / kg.

[0087] ② Adjust the overall reduction of the continuous casting machine to 8.4 mm, and redistribute the reduction in the light reduction mode according to Table 1 below to obtain a 360 mm billet with a low magnification center segregation rating of C1.5 or less; see Table 1 below for the correspondence between solid fraction and cumulative reduction:

[0088] Table 1 Correspondence between solid fraction and cumulative reduction

[0089]

[0090] (5) Slow cooling of billet: After the billet leaves the stacking platform, it is slow cooled in the slow cooling pit on site for 74 hours until the surface temperature of the billet reaches 153℃. After the billet passes inspection, it is sent down.

[0091] (6) Billet heating: The furnace outlet temperature is 1172℃, the furnace soaking time is 60min, and the total furnace time is 375min;

[0092] (7) Rolling: The roughing rolling temperature is 1160℃, the roughing rolling reduction is 29mm in 5 passes, the intermediate billet thickness is 180mm, the second stage rolling temperature is 848℃, the final rolling temperature is 805℃, and the billet is removed from the rolling line at a speed of 0.5m / min after rolling.

[0093] (8) Slow cooling of steel plates: After rolling, the steel plates are stacked and slow cooled for 3 days, protected from wind, and neatly stacked to reduce the exposure of the head and / or tail. After cooling to room temperature, they are laid out for manual inspection. Tensile properties and metallographic structure analysis are performed on different positions in the thickness direction of the steel. The results show that the structure of the upper and lower parts of the steel plate is symmetrical and uniform, and the flaw detection is qualified.

[0094] As can be seen from the above four embodiments, the method of producing 120-150mm ultra-thick steel plates with flaw detection using the electromagnetic stirring system-free 360mm continuous casting machine of the present invention is feasible, and the flaw detection of the produced steel plates all meets the specified requirements. In actual production, starting from March 2025, the method of the present invention has been used to produce 120-150mm ultra-thick steel plates with flaw detection, and the flaw detection pass rate is ≥90%.

[0095] The above embodiments are merely specific examples exemplified to explain the present invention and do not limit the present invention in any way. Any non-substantial changes made by any person based on the above content and form that do not depart from the scope of protection of the claims of the present invention should be considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for producing ultra-thick steel plates with flaw detection specifications of 120-150mm using a 360mm section continuous casting machine without an electromagnetic stirring system, including: Converter smelting—LF refining—RH vacuum refining—continuous casting billet formation—slow cooling of billet—heating of billet—rolling—slow cooling of steel plate; characterized in that the continuous casting process includes the following steps: (1) The continuous casting speed is set to 0.6~0.62m / min, the surface theoretical straightening temperature of the secondary cooling water is reduced from 950℃ to 935℃, and the surface theoretical temperature of all parts from the bending section of the casting machine to the outlet of the straightening section is reduced by 15℃. The secondary cooling water volume is 0.52~0.58L / kg. (2) Adjust the overall reduction of the continuous casting machine to 8.4 mm, redistribute the reduction in the light reduction mode, and gradually reduce the liquid core from 100% to 0% and the solid content from 0 to 100% in the solidification process of the continuous casting machine billet. Within this liquid-solid mixing zone, divide the total light reduction into 10 equal parts. The solid content ranges from 0% to 100%. When the solid content is 0% to 30%, the reduction accounts for 20% of the total reduction. When the solid content is 30% to 70%, the reduction accounts for 61% of the total reduction. When the solid content is 70% to 90%, the reduction accounts for 14% of the total reduction. Obtain a 360 mm cross-section billet with low magnification center segregation rating control within C1.

5.

2. The method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: Slow cooling of billets requires that after the billets leave the stacking platform, they be slow cooled in the on-site slow cooling pit for more than 72 hours until the surface temperature of the billets is ≤200℃. After the billets pass inspection, they are sent out.

3. The method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: Billet heating: The furnace outlet temperature is ≥1170℃, the furnace soaking time is 45~75min, and the total furnace time is 36*(5.5~10)min+soaking time.

4. The method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: Rolling: The roughing rolling temperature is ≥1150℃, the number of roughing rolling passes with a reduction of ≥28mm is ≥4, the thickness of the intermediate billet is 160~180mm, the second-stage rolling temperature is 840~850℃, the final rolling temperature is 800~830℃, and the billet is removed from the rolling mill at a speed of 0.5~0.6m / min after rolling.

5. A method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: Slow cooling of steel plates: After rolling, the steel plates are stacked and slow-cooled for ≥48 hours, protected from wind, neatly stacked, and the head and / or tail exposed is reduced. After cooling to below 50℃, they are laid out for manual flaw detection.

6. A method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: Converter smelting: Argon is blown throughout the smelting process, with an argon flow rate of 300-600 L / min, until the mass percentage of phosphorus reaches the target value range for the corresponding steel grade.

7. A method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: LF refining: Avoid opening the bypass when energizing the smelting process to improve the submerged arc effect and smelt to a S mass percentage content ≤0.003%.

8. A method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in claim 1, is characterized in that: RH vacuum refining: After the vacuum furnace reaches the ultimate vacuum pressure, maintain the vacuum circulation time for ≥15min, use ≥300m of calcium iron wire per furnace, soft blowing time for ≥8min, control the Ca / S ratio between 0.6 and 3.0, control the mass percentage of H to ≤2ppm and the mass percentage of [O] to ≤30ppm for each batch of production.

9. A method for producing 120-150mm ultra-thick flaw-detecting steel plates using a 360mm cross-section continuous casting machine without an electromagnetic stirring system, as described in any one of claims 1 to 8, characterized in that: The steel plates used for flaw detection are of the following types: Q345qD, Q345R, Q355B, and Q420NCZ35.

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