A production method for improving the resistance to lamellar tearing of a super-thick steel plate

Abstract

The present application relates to the technical field of extra-thick steel plate, and particularly relates to a production method for improving the anti-laminar tearing capacity of an extra-thick steel plate. The production method adopts a 300mm-thick continuous casting billet for one-stage rolling, controls the continuous casting billet to complete rolling in a complete recrystallization zone, and satisfies 5<=T 轧 xξ / H<=10, the unit of ξ is %, T 轧 represents the first-pass rolling temperature of the complete recrystallization zone, H represents the thickness of the finished steel plate, and the sum of the deformation rates of at least one set of adjacent passes is not less than 30%; and the steel plate is subjected to two-stage water cooling after rolling, the surface temperature of the steel plate after the first-stage water cooling is 600-650 DEG C, and the surface temperature of the steel plate after the second-stage water cooling is 500-550 DEG C. The present application has the advantages of simple process, high stability, short production cycle, low cost, great popularization and application prospect, superior low-temperature toughness of the product, -20 DEG C KV2>=110J, and a reduction of area >=38%.

Description

Technical Field

[0001] The present invention relates to the technical field of extra-thick steel plates, and in particular to a production method for improving the lamellar tearing resistance of extra-thick steel plates. Background Art

[0002] Thick, high-strength steel plates are widely used in fields requiring high performance, such as wind power, high-rise buildings, offshore platforms, and large-scale stadium construction. Due to the thickness of the plate, the resistance to lamellar tearing is poor. To improve the steel's resistance to lamellar tearing, the conventional practice is to use steel ingots for forging or composite casting to achieve a compression ratio >3, followed by normalizing. The main disadvantages of this method are: ① The yield rate of steel ingots is low; ② The interface bonding strength of composite castings is poor, and the composite processing of castings is complex and costly, and the metallurgical quality is not as high as that of continuous castings; ③ When using the normalizing process, a large amount of alloying elements needs to be added to ensure strength, resulting in high production costs and complex welding processes; ④ There are many production processes, a long cycle, and high costs.

[0003] Chinese invention patent application CN 109897928 A uses continuous casting slabs with a thickness of 370~450nm, which are produced through high-cost smelting + strong electromagnetic stirring + high-energy heating + high-loss rolling + heat treatment. It has disadvantages such as large rolling mill losses, low yield, high cost, and long production cycle.

[0004] The continuous casting ingot + TMCP process is currently widely used in the production of thin-gauge steel plate. The resulting product offers advantages such as low alloy content, good metallurgical quality, low cost, and excellent weldability. However, its application in the production of thick, high-strength, and lamellar tear-resistant steel plate presents significant challenges. This is particularly true when the continuous casting ingot thickness is fixed and the reduction ratio is low. The TMCP short-flow process presents significant difficulties in producing thick, high-strength, and lamellar tear-resistant steel plate.

[0005] Chinese invention patent application CN 116020867 A discloses a thermomechanical rolling method for improving the core properties of 80-100mm thick, high-strength, tough, and lamellar tear-resistant steel plates. This method uses rapid water flow through the billet in the high-temperature recrystallization zone during each rolling pass to lower the billet's surface temperature. This increases the surface's resistance to rolling deformation and allows deformation to penetrate the core. Repeated water flow and high-reduction rolling in multiple passes results in more complete recrystallization in the core, promoting uniform phase transformation in the extra-thick steel plate and achieving excellent high strength, toughness, and lamellar tear resistance. However, this method has the disadvantage of requiring high mill stiffness and high motor torque, which results in high or overloaded operation of the motor and rolling mill, increasing mill and motor wear and shortening service life. Summary of the Invention

[0006] To address the problems of poor lamellar tear resistance of extra-thick steel plates, high production costs and long production cycles for composite billets or steel ingots, the present invention provides a production method for improving the lamellar tear resistance of extra-thick steel plates. The method is suitable for producing extra-thick steel plates with a thickness of 100-120 mm from 300 mm thick continuous casting billets. The method has simple processes, high stability, a short production cycle, low costs, and great prospects for promotion and application. The product has excellent low-temperature toughness, with a KV2 of ≥110J at -20°C and a cross-sectional shrinkage rate of ≥38%.

[0007] The technical solutions of the present invention are as follows:

[0008] A production method for improving the lamellar tearing resistance of ultra-thick steel plates, using a 300mm thick continuous casting billet for one-stage rolling, controlling the continuous casting billet to complete rolling in the complete recrystallization zone, and the pass deformation rate ξ satisfies 5≤T 轧 ×ξ / H≤10, the unit of ξ is %, where T 轧 Indicates the first rolling temperature in the complete recrystallization zone, that is, the starting rolling temperature, T 轧 =997+463×(%C)+890×(%Ti)+365×(%Al)+6137(%Nb)-641×(%Nb) 1 / 2 +742×(%V)-225×(%V) 1 / 2 , unit is ℃; H represents the thickness of the finished steel plate, 100≤H≤120, unit is mm;

[0009] And the sum of the deformation rates of at least one group of adjacent passes is not less than 30%;

[0010] After rolling, the steel plate is water-cooled in two stages. The surface temperature of the steel plate is 600~650℃ after the first stage of water cooling, and the surface temperature of the steel plate is 500~550℃ after the second stage of water cooling.

[0011] Furthermore, the chemical composition and weight percentage of the continuous casting slab are as follows:

[0012] C 0.10%~0.14%, Si 0.20%~0.30%, Mn 1.70%~2.3%, P≤0.015%, S≤0.003%, Al0.020%~0.035%, 0.030%≤Nb+V+Ti≤0.070%, the balance is Fe and unavoidable impurities, and meets 0.40%≤C+Mn / 6≤0.46%.

[0013] Furthermore, the production method includes molten iron pretreatment → BOF steelmaking → LF refining → RH vacuum treatment → continuous casting → heating → rolling → water cooling → pit cooling.

[0014] Furthermore, after RH calcium treatment, the molten steel satisfies (%Ca)×(%S) 0.22 ≤2.5×10-3 On the one hand, it can further purify the molten steel, and on the other hand, it can modify the sulfides in the steel to make them non-deformable, stable and small spherical sulfides, inhibit the hot brittleness of S, and improve the elongation and Z-direction properties of the rolled piece.

[0015] Furthermore, in order to avoid the harmful effects of white spots and aluminum nitride on the plasticity of the material, it is necessary to reduce the nitrogen and hydrogen content, and the RH vacuum treatment should be controlled to [H] × [N] ≤ 3 × 10 -11 .

[0016] Furthermore, pit cooling involves placing the water-cooled steel plate in a slow cooling pit for slow cooling, controlling the steel plate entry temperature to ≥350°C, the slow cooling time to ≥72h, and the steel plate exit temperature to ≤100°C. After vacuum treatment, the molten steel has a low gas content, but hydrogen is absorbed during the heating of the continuous casting slab. To allow the free hydrogen to fully escape after rolling and to reduce the internal stress generated in the steel plate during the water cooling process, slow cooling in the pit is required to produce a "self-tempering" effect to release the internal stress.

[0017] Furthermore, the finished steel plate has a longitudinal KV2 of ≥110J at -20°C and a cross-sectional shrinkage of ≥38%.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention adopts a fully recrystallized zone rolling process, in which rolling deformation penetrates the interior of the rolled piece, and the internal grain size reaches 10 μm. In addition, the austenite recrystallization is fully utilized to uniformly form grains in the thickness direction of the rolled piece, thereby solving the problem that the internal grains of extra-thick steel plates can only be refined by low temperature and high pressure reduction and the grain uniformity is poor. The losses of the rollers, rolling mills, and motors are reduced, and the one-stage rolling improves production efficiency.

[0020] (2) The present invention adopts a two-stage water cooling process. In the first stage, water cooling causes phase transformation to occur from the surface of the steel plate to 1 / 6 of the thickness, generating ferrite + pearlite + a very small amount of bainite (5%~8%) structure, and the ferrite grains are small and uniform. In the second stage, water cooling increases the cooling intensity, causing ferrite + pearlite phase transformation to occur from 1 / 6 of the thickness to the core of the steel plate, and the ferrite grains are uniform, and the overall thickness can reach 10μm; achieving high continuity of the full-thickness structure type and high grain uniformity. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0022] The rolling process of the specific embodiment of the present invention is calculated according to the following formula: 轧 :

[0023] T 轧 =997+463×(%C)+890×(%Ti)+365×(%Al)+6137×(%Nb)-641×(%Nb) 1 / 2 +742×(%V)-225×(%V) 1 / 2 ,

[0024] And the rolling process meets the following two conditions:

[0025] ①5≤T 轧 ×ξ / H≤10,

[0026] Where, ξ represents the deformation rate of the complete recrystallization zone, and the unit is %;

[0027] H represents the thickness of the finished steel plate, 100≤H≤120, in mm;

[0028] ② The sum of the deformation rates of at least one group of adjacent passes is not less than 30%, that is, the situation where the sum of the deformation rates of two consecutive passes is not less than 30% occurs at least once. For example, in a rolling process, the sum of the deformation rates of the third pass and the fourth pass is not less than 30%, or, in a rolling process, the sum of the deformation rates of the second pass and the third pass is not less than 30% and the sum of the deformation rates of the third pass and the fourth pass is not less than 30%, etc.

[0029] Example 1

[0030] A production method for improving the lamellar tearing resistance of extra-thick steel plates, comprising smelting (hot metal pretreatment → BOF steelmaking → LF refining → RH vacuum treatment) → continuous casting → heating → rolling → water cooling → pit cooling;

[0031] Among them, the smelting process: using molten iron pretreatment, the end point S content is 0.0025%; the converter adopts top and bottom double blowing, fully dephosphorized, the end point phosphorus content is 0.004%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; the RH vacuum degree is 100pa, the vacuum time is 15min; the molten steel is calmed for 40min before tapping, and the calcium treatment is (%Ca)×(%S) 0.22 =1.8×10 -3 , [H] × [N] = 2.8 × 10 -11 .

[0032] Continuous casting process: A continuous casting billet with a thickness of 300 mm is obtained. The chemical composition and weight percentage of the continuous casting billet are as follows:

[0033] C 0.14%, Si 0.23%, Mn 1.78%, P 0.012%, S 0.001%, Al 0.032%, Nb 0.025%, V 0.021%, Ti 0.018%, and the rest are Fe and inevitable impurities.

[0034] Heating process: Control the temperature of the continuous casting billet out of the furnace to 1087℃.

[0035] Rolling process: The continuous casting billet is removed from the furnace and descaled by 21MPa high-pressure water before rolling. One-stage rolling is adopted to control the continuous casting billet to complete rolling in the complete recrystallization zone. The rolling start temperature T is calculated according to the formula 轧 The rolling temperature is 1050℃, the sum of the deformation rate of the third pass and the fourth pass is 38%, the cumulative deformation rate in the complete recrystallization zone is 60%, the final rolling temperature is 1018℃, and a steel plate with a thickness of 120mm is obtained.

[0036] Water cooling process: After rolling, the steel plate is subjected to two-stage water cooling. After the first stage of water cooling, the surface temperature of the steel plate is 640°C. After 90s, the second stage of water cooling is carried out. After the second stage of water cooling, the surface temperature of the steel plate is 530°C.

[0037] Pit cooling process: After water cooling, the steel plate enters the slow cooling pit for slow cooling. The slow cooling time is 80 hours. The temperature of the steel plate is 466℃ when entering the pit and 83℃ when leaving the pit.

[0038] Example 2

[0039] A production method for improving the lamellar tearing resistance of extra-thick steel plates, comprising smelting (hot metal pretreatment → BOF steelmaking → LF refining → RH vacuum treatment) → continuous casting → heating → rolling → water cooling → pit cooling;

[0040] Among them, the smelting process: using molten iron pretreatment, the end point S content is 0.0023%; the converter adopts top and bottom double blowing, fully dephosphorized, the end point phosphorus content is 0.005%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; the RH vacuum degree is 100pa, the vacuum time is 14min; the molten steel is calmed for 38min before tapping, and the calcium treatment is (%Ca)×(%S) 0.22 =2.0×10 -3 , [H] × [N] = 2.8 × 10 -11 .

[0041] Continuous casting process: A continuous casting billet with a thickness of 300 mm is obtained. The chemical composition and weight percentage of the continuous casting billet are as follows:

[0042] C 0.10%, Si 0.24%, Mn 2.05%, P 0.013%, S 0.002%, Al 0.029%, Nb 0.022%, V 0.023%, Ti 0.018%, and the rest are Fe and inevitable impurities.

[0043] Heating process: Control the temperature of the continuous casting billet out of the furnace to 1067℃.

[0044] Rolling process: The continuous casting billet is removed from the furnace and descaled by 21MPa high-pressure water before rolling. One-stage rolling is adopted to control the continuous casting billet to complete rolling in the complete recrystallization zone. The rolling start temperature T is calculated according to the formula 轧 The steel plate with a thickness of 100 mm was obtained by rolling at a temperature of 958 ° C and a deformation rate of 998 ° C. The sum of the deformation rate of the third pass and the fourth pass was 43%, the cumulative deformation rate in the complete recrystallization zone was 73.33%, and the final rolling temperature was 958 ° C.

[0045] Water cooling process: After rolling, the steel plate is subjected to two-stage water cooling. After the first stage of water cooling, the surface temperature of the steel plate is 628°C. After 67s, the second stage of water cooling is carried out. After the second stage of water cooling, the surface temperature of the steel plate is 542°C.

[0046] Pit cooling process: After water cooling, the steel plate enters the slow cooling pit for slow cooling. The slow cooling time is 73 hours. The temperature of the steel plate is 446℃ when entering the pit and 84℃ when leaving the pit.

[0047] The properties of the steel plates prepared in Example 1 and Example 2 were tested, and the results are shown in Table 1.

[0048] Table 1 Properties of the steel plates of Examples 1 and 2 of the present invention

[0049]

[0050] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and substance of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be readily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A production method for improving the lamellar tearing resistance of extra-thick steel plates, characterized in that: The continuous casting slab with a thickness of 300mm is used for one-stage rolling. The continuous casting slab is controlled to complete rolling in the complete recrystallization zone, and the pass deformation rate ξ satisfies 5≤T 轧 ×ξ / H≤10, the unit of ξ is %, where T 轧 Indicates the first rolling temperature in the complete recrystallization zone, that is, the starting rolling temperature, T 轧 =997+463×(%C)+890×(%Ti)+365×(%Al)+6137×(%Nb)-641×(%Nb) 1 / 2 +742×(%V)-225×(%V) 1 / 2 , unit is ℃; H represents the thickness of the finished steel plate, 100≤H≤120, unit is mm; And the sum of the deformation rates of at least one group of adjacent passes is not less than 30%; After rolling, the steel plate is water-cooled in two stages. The surface temperature of the steel plate is 600~650℃ after the first stage of water cooling, and the surface temperature of the steel plate is 500~550℃ after the second stage of water cooling.

2. The production method according to claim 1, wherein The chemical composition and weight percentage of the continuous casting billet are as follows: C 0.10%~0.14%, Si 0.20%~0.30%, Mn 1.70%~2.3%, P≤0.015%, S≤0.003%, Al 0.020%~0.035%, 0.030%≤Nb+V+Ti≤0.070%, the balance is Fe and unavoidable impurities, and meets the requirement of 0.40%≤C+Mn / 6≤0.46%.

3. The production method according to claim 1, wherein The production method includes molten iron pretreatment → BOF steelmaking → LF refining → RH vacuum treatment → continuous casting → heating → rolling → water cooling → pit cooling.

4. The production method according to claim 3, wherein After RH calcium treatment, the molten steel meets (%Ca)×(%S) 0.22 ≤2.5×10 -3 .

5. The production method according to claim 3, wherein RH vacuum treatment control [H] × [N] ≤ 3 × 10 -11 .

6. The production method according to claim 3, wherein Pit cooling is to put the water-cooled steel plate into a slow cooling pit for slow cooling, control the steel plate entering the pit temperature ≥350℃, slow cooling time ≥72h, and the steel plate exiting the pit temperature ≤100℃.

7. The production method according to claim 1, wherein The longitudinal KV2 of the finished steel plate at -20℃ is ≥110J.

8. The production method according to claim 1, wherein The cross-sectional shrinkage of the finished steel plate is ≥38%.

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