An extra-thin wide high-toughness steel slab for coil annealing furnace and its preparation method

Abstract

The present invention discloses an extremely thin wide - specification high - toughness steel plate for coil rolling and its preparation method, which is applicable to steel plates with thickness × width, where the thickness is 4 mm, the width is greater than 2500 mm, or the thickness is greater than 4 - 6 mm, the width is greater than 3000 mm, and the length is less than 80 m, and the yield strength is ≤ 440 MPa. The flatness of the steel plate is 3 - 5 mm / m. The weight percentages are as follows: C: 0.09% - 0.13%, Si: 0.10% - 0.30%, Mn: 0.80% - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.25% - 0.045%, Ti: 0.010% - 0.025%, and the rest is Fe and inevitable impurities. The preparation method is: hot metal pretreatment → BOF steelmaking → LF refining → RH vacuum treatment → continuous casting → slow cooling → heating → rolling. The process of the present invention is simple, with low production cost and is suitable for large - scale industrial stable production; the product has excellent plate shape and low - temperature toughness performance.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a furnace coil of an extremely thin, wide-specification, high-toughness steel plate and a preparation method thereof. Background Art

[0002] Limited thin and wide steel plates are widely used in the fields of ships, bridges, pipeline projects, etc. due to their advantages of fewer welding points and light weight. They can reduce the dead weight of structural parts or equipment, reduce welding points and welding volume, and reduce welding difficulty and engineering costs. At present, the domestic market has a large demand for thin steel plates. Limited by equipment conditions and rolling technology, there are few steel mills in China that can produce thin steel plates below 10mm, and only Nangang can supply narrow tolerance steel plates below 6mm. The market demand for thin and wide steel plates is large, the price is high, and the market competition is small.

[0003] Current domestic production of thin and wide steel plates:

[0004] (1) It is difficult to produce 4mm steel plates in China, especially steel plates with a width of more than 2500mm.

[0005] (2) In order to ensure the control of the extremely thin plate shape, high temperature rolling is adopted, which makes the grain size of the steel plate coarse or mixed crystals appear, which makes it difficult to meet the high performance requirements of steel plates with high requirements for low temperature toughness and crack arrest performance, such as 4-6mmQ370qE.

[0006] (3) In order to ensure the control of the extremely thin plate shape, high temperature heating and high temperature rolling are adopted, while the steel plates with high surface requirements need relatively low temperature heating and multiple descaling. The actual rolling temperature is low, and the conflicting requirements of plate shape and high surface on production process are difficult to control, such as 4-6mm cruise ship steel.

[0007] CN 106544597 A discloses an ultra-thin and ultra-wide steel plate for nuclear power pressure equipment and a manufacturing method thereof, wherein the chemical composition is: C: ≤0.20%; Si: ≤0.10%; Mn: 0.50%-1.80%; P: ≤0.008%; S: ≤0.003%; Ni: 0.20%-1.00%; Cr: 0.30%-0.80%; Cu: 0.10%-0.80%; Mo: ≤0.08%; Alt: ≤0.040%; N: ≤0.008%; the steel plate is rolled by a two-fire process and heat-treated by a normalizing process. The precious alloy has a high content of added elements such as Cr, Cu, and Ni, and the two-fire rolling and normalizing heat treatment have many processes, are complicated, and have high costs.

[0008] CN 113235010 A discloses a preparation method of nuclear power steel plates with thin specifications and uniform properties across the whole plate. By designing low-carbon, low-silicon and a small amount of rare-earth alloy components, and using means such as hot rolls, continuous casting billet heating, and stopping the cooling water of the roller table, the plate shape is controlled. Normalizing and slow cooling in a high-temperature stack are used to improve the properties and plate shape of the steel plates, and the batch production of 5.5 - 10.5 mm steel plates is successfully achieved. Adding rare-earth alloy components and using many technological means such as hot rolls, normalizing, and slow cooling in a high-temperature stack to ensure the plate shape and properties, the processes are numerous and complex, and the production cycle and cost are high.

[0009] Therefore, there is a need for a coil of ultra-thin wide-specification high-toughness steel plate and its preparation method. Summary of the Invention

[0010] The purpose of the present invention is to provide a coil of ultra-thin wide-specification high-toughness steel plate and its preparation method.

[0011] The technical solution adopted by the present invention to solve its technical problems is: a coil of ultra-thin wide-specification high-toughness steel plate, including components with the following percentage contents: C: 0.09% - 0.13%, Si: 0.10% - 0.30%, Mn: 0.80% - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.25% - 0.045%, Ti: 0.010% - 0.025%, and the rest is Fe and inevitable impurities.

[0012] Specifically, the coil steel plate has a thickness × width, where the thickness is 4 mm, the width is greater than 2500 mm, or the thickness is greater than 4 - 6 mm, the width is greater than 3000 mm, the length is less than 80 m, and the yield strength is ≤ 440 MPa. The flatness of the steel plate is 3 - 5 mm / m.

[0013] A preparation method of a coil of ultra-thin wide-specification high-toughness steel plate is characterized by including the following steps:

[0014] 1) Smelting process: During the pretreatment of hot metal, the S content is controlled below 0.003%; argon is blown throughout the BOF and LF processes with weak stirring, the slag surface is slightly turned over without being exposed, and white slag is made using lime and fluorite; the RH vacuum degree reaches 133 Pa, and the vacuum time is not less than 10 min; the molten steel calming time before tapping is not less than 30 min;

[0015] 2) Continuous casting billet heating process: When the thickness of the coil steel plate is 4 mm, the continuous casting billet tapping temperature is 1250 - 1280 °C; when the finished thickness is greater than 4 - 6 mm, the continuous casting billet tapping temperature is 1240 - 1270 °C; the thickness of the continuous casting billet is 150 mm, and the holding time after the continuous casting billet reaches the tapping temperature is 60 - 90 min;

[0016] 3) Rolling process: One-stage rolling is adopted. When the billet thickness reaches 22 - 26 mm, coiling rolling starts. The starting coiling rolling temperature is 980℃ - 1050℃. The coiling rolling pass is controlled within 4 - 6 passes. The reduction rate of the coiling rolling pass gradually decreases. The rolling temperature for the final pass of 4 mm is 740 - 820℃, and the rolling temperature for 6 mm is 790 - 850℃.

[0017] The present invention has the following beneficial effects:

[0018] 1) The present invention involves simple steel composition design, good microstructure uniformity, excellent plasticity and toughness, high flatness, and excellent machining ability.

[0019] 2) The yield strength of the steel plate is ≤440 MPa, and the flatness of the steel plate is 3 - 5 mm / m. It can be applied to equipment and engineering manufacturing fields such as structural part welding and pipe welding with high flatness requirements.

[0020] 3) The steel of the present invention involves simple chemical composition, simple production process, short production cycle, low cost, and is conducive to popularization and application. Specific embodiments

[0021] Now, the present invention will be further described in detail.

[0022] An extremely thin wide-specification high-toughness steel plate for coil rolling furnace, comprising the following components in percentage by mass: C: 0.09% - 0.13%, Si: 0.10% - 0.30%, Mn: 0.80% - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.25% - 0.045%, Ti: 0.010% - 0.025%, and the rest is Fe and unavoidable impurities.

[0023] According to the above composition, the finished steel plate of the present invention has a size of (thickness × width) 4 mm × >2500 mm, (thickness × width) >4 - 6 mm × >3000 mm, a length of less than 80 m, and a yield strength of ≤440 MPa, and the flatness of the steel plate is 3 - 5 mm / m.

[0024] Chemical composition is one of the important factors affecting the comprehensive quality of products, and the chemical composition of the present invention is restricted.

[0025] C: The main solid solution strengthening element in steel, which can significantly improve the strength of the steel plate, is unfavorable for the welding, toughness and plasticity of the steel plate. In order to avoid large deformation and tensile strength of the prepared steel, large rolling pressure, and increased difficulty in flatness control, its mass percentage content is C: 0.09% - 0.13%.

[0026] Si: Silicon is one of the effective deoxidizing and exothermic elements in the steelmaking process. It has a certain solid-solution strengthening effect. At the same time, too high a silicon content will reduce the surface quality, welding performance and low-temperature toughness of the steel. In this invention, the silicon content is controlled at 0.10% - 0.30%.

[0027] Mn: Manganese has a strong solid-solution strengthening effect. It can significantly reduce the phase transformation temperature of the steel, refine the microstructure of the steel. To avoid large tensile strength, large rolling pressure, difficult control of plate shape, segregation of continuous casting billets, formation of banded structure and reduction of plasticity of steel plates during the preparation of steel; in this invention, the manganese content is controlled at 0.80% - 1.40%.

[0028] Al: Aluminum is one of the effective deoxidizing elements in the steelmaking process. It can effectively reduce the inclusion content in the steel and refine the grains. However, if the content is too high, it is easy to cause cracks on the surface of the continuous casting billet and a significant increase in the strength of the fine grains. In this invention, the aluminum content is controlled at 0.015% - 0.045%.

[0029] Nb: Niobium is one of the important elements for fine grain strengthening. It increases the austenite recrystallization temperature, prevents austenite recrystallization and inhibits grain growth, and refines austenite grains; its carbonitrides precipitate on dislocations and segregate at the austenite grain boundaries, improving strength and toughness; for the rolling of thin and wide specification steel plates, good plasticity and good plasticity uniformity of the material are required, and a high heating temperature of the continuous casting billet and good overall uniformity of the continuous casting billet are required. To prevent the growth or coarsening of austenite during heating, the niobium content is controlled at 0.025% - 0.045%.

[0030] A method for preparing a very thin and wide specification high-toughness steel plate by coil rolling includes the following steps: The above components are obtained through hot metal pretreatment, BOF steelmaking, LF refining, RH vacuum treatment, continuous casting, slow cooling, heating, and rolling.

[0031] Among them, the smelting process is: hot metal pretreatment, converter, LF, RH vacuum treatment, continuous casting. The S content in hot metal pretreatment is controlled below 0.003%; argon is blown throughout the converter and LF processes with weak stirring, and the slag surface is slightly turned over without being exposed. Lime and fluorite are used to make white slag; the RH vacuum degree reaches 133 Pa, and the vacuum time is not less than 10 min; the molten steel calming time before tapping is not less than 30 min.

[0032] Control of continuous casting billet heating temperature: For a finished product thickness of 4 mm, the continuous casting billet furnace outlet temperature is 1250 - 1280 °C; for a finished product thickness > 4 - 6 mm, the continuous casting billet furnace outlet temperature is 1240 - 1270 °C; the continuous casting billet thickness is 150 mm, and the holding time after the continuous casting billet reaches the furnace outlet temperature is 60 - 90 min.

[0033] The cast slab starts rolling after descaling with high-pressure water. One-stage rolling is adopted. When the thickness of the billet reaches 22 - 26 mm, coiling rolling begins. The starting coiling rolling temperature is 980℃ - 1050℃. The number of coiling rolling passes is controlled within 4 - 6 passes. The reduction rate of each coiling rolling pass gradually decreases. The rolling temperature for the final 4-mm pass is 740 - 820℃, and for the 6-mm pass is 790 - 850℃.

[0034] Example 1:

[0035] A kind of extremely thin wide-specification high-toughness steel plate for coil rolling, its chemical composition is as follows: C: 0.12%, Si: 0.20%, Mn: 0.85%, P: 0.012%, S: 0.003%, Al: 0.035%, Nb: 0.041%, Ti: 0.018%, and the rest are Fe and inevitable impurities. The steel plate is (thickness × width) 4 mm × 2900 mm, and the length is 79 m.

[0036] The preparation method of the steel in this example: The raw materials are smelted and refined to obtain molten steel, and finally continuous casting is carried out to obtain a cast slab. Specifically, it includes the following steps:

[0037] The smelting process: Molten iron pretreatment is adopted, and the S content at the end point is 0.002%; the top-bottom combined blowing converter is used for full dephosphorization, and the P content at the end point is 0.005%. Argon blowing is carried out throughout the process with weak stirring, and the slag surface is slightly turned over without being exposed. Lime and fluorite are used to make a white slag; the RH vacuum degree is 130 Pa, and the vacuum time is 13 min; the molten steel is statically cast for 36 min before tapping.

[0038] The cast slab heating process: The thickness of the cast slab is 150 mm, the cast slab furnace outlet temperature is 1276℃, and the holding time after the cast slab reaches the furnace outlet temperature is 82 min.

[0039] The cast slab descaling and rolling process: After the cast slab is descaled with 31 MPa high-pressure water, rolling starts. One-stage rolling is adopted. When the thickness of the billet reaches 23 mm, coiling rolling begins. The starting coiling rolling temperature is 1045℃, and it is coiled for 6 passes. The reduction rate of each coiling rolling pass gradually decreases. The average temperatures of the head, middle, and tail of the 4-mm rolled steel plate in the final pass are 758℃, 811℃, and 800℃ respectively.

[0040] After rolling, the steel plate is pre-straightened and cut by a section shear, and then enters the cooling bed for air cooling.

[0041] The comprehensive performance is shown in Tables 1 - 2.

[0042] Example 2

[0043] A coil-wound ultra-thin wide high-toughness steel plate has the following chemical composition: C: 0.11%, Si: 0.23%, Mn: 1.33%, P: 0.013%, S: 0.0025%, Al: 0.033%, Nb: 0.030%, Ti: 0.016%, and the rest is Fe and inevitable impurities. The steel plate has a thickness × width of 6 mm × 3000 mm and a length of 71 m.

[0044] A method for preparing a coil-wound ultra-thin wide high-toughness steel plate, wherein the raw materials are smelted and refined to obtain molten steel, and finally continuous casting is carried out to obtain a slab. The specific steps are as follows:

[0045] The smelting process is as follows: hot metal pretreatment is adopted, and the S content at the end point is 0.0015%; the converter adopts top-bottom combined blowing to fully dephosphorize, and the P content at the end point is 0.0055%. Argon blowing is carried out throughout the process with weak stirring, and the slag surface is slightly turned over without being exposed. Lime and fluorite are used to make white slag; the RH vacuum degree is 130 Pa, and the vacuum time is 12 min; the molten steel is kept calm for 35 min before tapping.

[0046] The slab heating process is as follows: the slab thickness is 150 mm, the slab furnace outlet temperature is 1266 °C, and the holding time after the slab reaches the furnace outlet temperature is 76 min.

[0047] The slab descaling and rolling process is as follows: after the slab is taken out of the furnace and descaled with high-pressure water at 31 MPa, rolling starts. One-stage rolling is adopted. When the billet thickness reaches 26 mm, coiling rolling starts. The coiling rolling temperature is 1020 °C, and coiling rolling is carried out for 6 passes. The reduction rate of each coiling rolling pass gradually decreases. The average temperatures of the head, middle, and tail of the 6-mm rolled steel plate in the final pass are 792 °C, 831 °C, and 826 °C respectively.

[0048] After rolling, the steel plate is pre-straightened and cut by a sectional shear, and then enters the cooling bed for air cooling.

[0049] The comprehensive performance is shown in Tables 1-2.

[0050] Table 1 Tensile properties of the steel plate in the example

[0051] Example Thickness / mm Yield strength / MPa Tensile strength / MPa Elongation after fracture A / % Example 1 4 298 405 30.5 Example 2 6 402 543 28.5

[0052] Table 2 Low-temperature toughness of the steel plate in the example

[0053]

[0054] The present invention is not limited to the above embodiments. Anyone should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, all fall within the protection scope of the present invention.

[0055] The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A coil-wound ultra-thin wide-specification high-toughness steel plate, characterized in that, Comprising components with the following percentage contents: C: 0.11% - 0.13%, Si: 0.10% - 0.30%, Mn: 0.80% - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.025% - 0.045%, Ti: 0.010% - 0.025%, the balance being Fe and unavoidable impurities; the coil plate is thickness × width, where the thickness is 4 mm and the width is greater than 2500 mm or the thickness is 6 mm and the width is greater than 3000 mm, and the length is below 80 m, and the yield strength is ≤ 440 MPa, and the flatness of the steel plate is 3 - 5 mm / m; a method for preparing an extra-thin wide-specification high-toughness coil plate, comprising the following steps: 1) Smelting process: During the hot metal pretreatment, the S content is controlled below 0.003%; argon is blown throughout the BOF and LF processes with weak stirring, the slag surface is slightly turned over without being exposed, and white slag is made using lime and fluorite; the RH vacuum degree reaches 133 Pa, and the vacuum time is not less than 10 min; the molten steel calming time before tapping is not less than 30 min; 2) Slab heating process: When the thickness of the coil plate is 4 mm, the slab tapping temperature is 1250 - 1280 °C, and when the finished product thickness is 6 mm, the slab tapping temperature is 1240 - 1270 °C; the slab thickness is 150 mm, and after the slab reaches the tapping temperature, the holding time is 60 - 90 min; 3) Rolling process: One-stage rolling is adopted. When the blank thickness reaches 22 - 26 mm, coiling rolling starts, the starting coiling rolling temperature is 980 °C - 1050 °C, the coiling rolling passes are controlled within 4 - 6 passes, the reduction rate of the coiling rolling passes gradually decreases, and the rolling temperature for the final pass of 4 mm is 740 - 820 °C, and the rolling temperature for 6 mm is 790 - 850 °C; the low-temperature toughness of the steel plate with a thickness of 4 mm, at a temperature of -40 °C, the impact performance AKV is 166 J, 184 J, 180 J; the low-temperature toughness of the steel plate with a thickness of 6 mm, at a temperature of -40 °C, the impact performance AKV is 210 J, 206 J, 198 J.

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