A thin steel strip and its short-process preparation method

Abstract

This invention relates to the field of iron and steel metallurgy technology, specifically disclosing a thin steel strip and its short-process preparation method. The thin steel strip provided by this invention, through limiting the chemical composition and its content, allows the components to synergistically improve the microstructure of the thin steel strip, refine the grain size, reduce anisotropy, ensure stable performance, and enhance its anti-warping properties and overall mechanical properties. Simultaneously, the short-process preparation method provided by this invention ensures the full dissolution and uniform distribution of alloying elements, avoiding component segregation and oxide doping. Through the action of each preparation step, the microstructure and properties of the thin steel strip are optimized, enhancing its rigidity and toughness, and improving its anti-warping properties and overall mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and specifically discloses a thin steel strip and its short-process preparation method. Background Technology

[0002] In the steel manufacturing industry, hot strip rolling technology has become a key direction for the industry's development due to its high efficiency and high-quality output. Hot strip rolling technology enables continuous production from continuously cast molten steel to finished steel coils, avoiding production interruptions, significantly improving the yield and dimensional accuracy of hot-rolled steel strip products, and creating significant economic benefits for steel companies.

[0003] However, hot-rolled steel strip is highly susceptible to head warping at the pinch rolls during the coiling process, leading to strip head folding. In extreme cases, this can even prevent the strip from being coiled properly, causing steel pile-up accidents and disrupting the production process. Head warping severely damages the surface quality and performance of the steel strip, reduces product qualification rates, and results in significant economic losses.

[0004] Currently, existing technologies primarily address the issue of strip head warping during hot rolling by adjusting equipment, such as improving pinch roll pressure control and adjusting the strip threading speed. However, these measures fail to fundamentally solve the problem. Therefore, resolving the issue of strip head warping during hot rolling has become a pressing technical challenge in this field. Summary of the Invention

[0005] In view of this, the present invention provides a thin steel strip and a short-process preparation method thereof. The thin steel strip provided by the present invention improves the microstructure of the thin steel strip by improving the chemical composition and production process, refines the grains, reduces the anisotropy of the thin steel strip, ensures the stability of overall performance, thereby effectively enhancing the ability of the thin steel strip to resist external deformation and significantly suppressing warping.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a thin steel strip comprising the following chemical composition by weight percentage: C 0.03%-0.08%, Si 0.1%-0.3%, Mn 1.3%-1.6%, Nb 0.03%-0.06%, V 0.06%-0.12%, Ti 0.02%-0.04%, B 0.001%-0.003%, P≤0.010%, S≤0.005%, with the balance being Fe and unavoidable impurity elements.

[0008] The thin steel strip provided by this invention, through the synergistic effect of multiple elements such as niobium, vanadium, manganese, titanium, and boron, possesses excellent anti-warping properties and comprehensive mechanical properties. Specifically:

[0009] During the cooling process of molten steel, niobium combines with carbon and nitrogen to form stable Nb(C,N) compounds, which precipitate as fine particles. These fine particles can hinder dislocation movement through a dispersion strengthening mechanism, thereby improving the strength and hardness of the thin steel strip. During the rolling and threading process, the high hardness and high strength allow the head of the thin steel strip to better resist external deformation, significantly reducing the tendency to warp. Excessive niobium content leads to excessive precipitation and aggregation of carbonitrides, reducing the toughness of the steel strip; conversely, insufficient niobium content results in inadequate dispersion strengthening, making it difficult to effectively improve strength and anti-warping ability. Therefore, this invention selects an Nb content of 0.03%-0.06%.

[0010] During the cooling process of vanadium in molten steel, the resulting V(C,N) compounds precipitate as fine particles. These particles reduce the anisotropy of the thin steel strip, making the strip head more uniform under stress and preventing warping caused by localized stress concentration. Simultaneously, vanadium improves the toughness and plasticity of the thin steel strip, further enhancing the deformation resistance of the strip head. Excessive vanadium content can cause uneven microstructure and reduce overall performance; insufficient vanadium content results in insignificant grain refinement and strengthening effects. Therefore, this invention selects a V content of 0.06%-0.12%.

[0011] Manganese can improve the strength and toughness of thin steel strips while reducing their critical cooling rate, promoting the formation of fine ferrite and pearlite structures during cooling and improving the overall mechanical properties of the strip. The fine ferrite and pearlite structures increase the rigidity of the strip head, effectively suppressing warping during rolling. Simultaneously, manganese can combine with sulfur to form manganese sulfide, preventing the formation of low-melting-point iron sulfide at grain boundaries, thus eliminating sulfur-induced hot brittleness and improving the hot workability of the steel. Therefore, this invention selects a Mn content of 1.3%-1.6%.

[0012] During the cooling process of molten steel, titanium combines with carbon and nitrogen to form Ti(C,N) compound nuclei, promoting grain refinement. Refined grains improve the overall performance of the thin steel strip and also enhance its weldability, ensuring stable overall performance during endless rolling. Excessive titanium content may lead to excessive aggregation of titanium compounds, affecting the performance of the thin steel strip; conversely, insufficient titanium content results in insignificant grain refinement and improved weldability. Therefore, this invention selects a Ti content of 0.02%-0.04%.

[0013] Boron can adsorb at grain boundaries in thin steel strips, reducing grain boundary energy, effectively inhibiting grain growth, and improving the hardenability of the steel. During the hot rolling process of thin steel strips, boron can enhance the strength and toughness of the thin steel strips, thereby improving their resistance to warping. Excessive boron content will lead to increased brittleness; insufficient boron content will hinder its optimizing effects on grain boundaries and hardenability. Therefore, this invention selects a boron content of 0.001%-0.003%.

[0014] A second aspect of the present invention provides a short-process preparation method for the above-mentioned thin steel strip, the short-process preparation method comprising the following steps:

[0015] S1. According to the preset weight percentage of chemical composition, the raw materials are melted and cast to obtain ingots;

[0016] S2. The ingot is subjected to rough rolling and finish rolling in sequence to obtain rough-machined steel strip;

[0017] S3. The rough-machined steel strip is subjected to annealing and tempering treatments in an alternating magnetic field to obtain a thin steel strip.

[0018] The short-process preparation method for thin steel strip provided by this invention involves annealing under an alternating magnetic field, which promotes the full release of internal stress in the thin steel strip. At the same time, the electromagnetic force constrains the deformation of grain boundaries, promotes the uniform diffusion of alloying elements, and effectively inhibits the formation of coarse structures, thereby improving the stability of the internal structure of the thin steel strip. Tempering under an alternating magnetic field further refines the grains, improves the comprehensive mechanical properties, enhances the rigidity and toughness of the thin steel strip, effectively inhibits warping, and achieves simultaneous improvement in anti-warping performance and comprehensive mechanical properties.

[0019] More preferably, in S1, the melting temperature is 1550℃-1650℃ and the time is 2h-3h.

[0020] More preferably, in S1, the casting temperature is 1500℃-1550℃.

[0021] By limiting the melting temperature and time, this invention enables high-melting-point alloying elements to fully dissolve in the iron matrix, avoiding the problem of component segregation. At the same time, it avoids excessive oxidation of iron and silicon due to excessive melting temperature, thereby reducing the amount of oxide doping in the prepared ingot.

[0022] Meanwhile, by limiting the casting temperature, this invention enables the molten metal to form an equiaxed fine-grained structure during the ingot formation process, thereby improving the plastic deformation capacity of the subsequent rolling process and preventing cracks from occurring during rolling.

[0023] More preferably, in S2, the ingot is heated at 1100℃-1200℃ for 30min-60min and then rough rolled.

[0024] More preferably, in S2, the inlet temperature of the roughing mill is 1100℃-1120℃, and the outlet temperature is 980℃-990℃.

[0025] More preferably, in S2, the temperature of the finishing rolling is 870℃-930℃.

[0026] This invention improves the plastic deformation capacity of steel strips and reduces rolling resistance by limiting the rough rolling temperature, thus facilitating rolling. Rough rolling within the aforementioned temperature range inhibits grain growth and improves the overall performance of the steel strip. Simultaneously, by limiting the finish rolling temperature, this invention further refines the grains and enhances the toughness of the steel strip.

[0027] Preferably, in S3, during the annealing process, the frequency of the alternating magnetic field is 60Hz-120Hz and the intensity is 0.6T-1.8T.

[0028] Preferably, in step S3, the annealing temperature is 720℃-780℃ and the time is 2.5h-3.5h.

[0029] Preferably, in S3, the heating rate of the annealing treatment is 12℃ / min-18℃ / min.

[0030] Preferably, in S3, after the annealing treatment, the temperature is reduced to 25℃-35℃ at a rate of 6℃ / min-10℃ / min.

[0031] Preferably, in S3, the alternating magnetic field has a frequency of 30Hz-60Hz and an intensity of 0.4T-1.0T during the tempering process.

[0032] Preferably, in S3, the tempering temperature is 420℃-480℃, and the holding time is 5h-7h.

[0033] Preferably, in S3, the heating rate of the tempering treatment is 5℃ / min-10℃ / min.

[0034] Preferably, in step S3, the tempering treatment is followed by cooling to 25°C-35°C at a rate of 1°C / min-3°C / min.

[0035] This invention regulates the microstructure and properties of thin steel strips by setting parameters such as the frequency and intensity of the alternating magnetic field during annealing and tempering, as well as the processing temperature, time, and heating / cooling rates, thereby improving the comprehensive mechanical properties and warping resistance of the thin steel strips.

[0036] In summary, the thin steel strip provided by this invention, by limiting the chemical components and their contents, enables the components to work synergistically to improve the microstructure of the thin steel strip, refine the grains of the thin steel strip, reduce anisotropy, ensure the stability of the performance of the thin steel strip, and improve the anti-warping performance and comprehensive mechanical properties of the thin steel strip.

[0037] Meanwhile, the short-process preparation method provided by this invention can ensure that alloying elements are fully dissolved and uniformly distributed, avoiding component segregation and oxide doping. Under the action of each preparation step, the microstructure and properties of the thin steel strip are optimized, enhancing the rigidity and toughness of the thin steel strip, and improving the anti-warping performance and comprehensive mechanical properties of the thin steel strip. Attached Figure Description

[0038] Figure 1 The image shows the metallographic structure of the thin steel strip obtained in Example 1.

[0039] Figure 2 The image shows the metallographic structure of the thin steel strip obtained in Comparative Example 1. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely one embodiment of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.03%, Si 0.1%, Mn 1.3%, Nb 0.03%, V 0.06%, Ti 0.02%, B 0.001%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0043] The short-process preparation method for the thin steel strip includes the following steps:

[0044] S1. The raw materials are melted at 1550℃ for 2 hours, and then cast at 1500℃ to obtain an ingot. The raw materials contain the following components in the following weight percentages: C 0.03%, Si 0.1%, Mn 1.3%, Nb 0.03%, V 0.06%, Ti 0.02%, B 0.001%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0045] S2. The ingot is heated to 1100°C and held for 30 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1100°C and the outlet temperature is 980°C. Then, it is finished rolled in 7 passes at 870°C to obtain a rough-machined steel strip.

[0046] S3. The rough-processed steel strip is heated to 720°C at a heating rate of 12°C / min under an alternating magnetic field with a frequency of 60Hz and an intensity of 0.6T, and held at that temperature for 2.5h. Then, it is cooled to 25°C at a rate of 6°C / min to obtain a primary steel strip. The primary steel strip is heated to 420°C at a heating rate of 5°C / min under an alternating magnetic field with a frequency of 30Hz and an intensity of 0.4T, and held at that temperature for 5h. Then, it is cooled to 25°C at a rate of 1°C / min to obtain a thin steel strip.

[0047] Depend on Figure 1 It can be seen that the thin steel strip provided in Example 1 has fine grains with uniform size distribution, no obvious coarse grains or abnormally grown grain regions, uniform microstructure distribution, no obvious segregation or local coarsening, and uniform dispersion of precipitates with fine size. It can also be seen that the morphology and grain size of the microstructure in different directions are relatively small, and there is no obvious directional segregation or microstructure orientation concentration.

[0048] Example 2

[0049] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.08%, Si 0.3%, Mn 1.6%, Nb 0.06%, V 0.12%, Ti 0.04%, B 0.003%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0050] The short-process preparation method for the thin steel strip includes the following steps:

[0051] S1. The raw materials are melted at 1650℃ for 3 hours, and then cast at 1550℃ to obtain an ingot. The raw materials contain the following components in the following weight percentages: C 0.08%, Si 0.3%, Mn 1.6%, Nb 0.06%, V 0.12%, Ti 0.04%, B 0.003%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0052] S2. The ingot is heated to 1200℃ and held for 60 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1120℃ and the outlet temperature is 990℃. Then, it is finished rolled in 7 passes at 930℃ to obtain a rough-machined steel strip.

[0053] S3. The rough-processed steel strip is heated to 780°C at a heating rate of 18°C / min under an alternating magnetic field with a frequency of 120Hz and an intensity of 1.8T, and held at that temperature for 3.5h. Then, it is cooled to 35°C at a rate of 10°C / min to obtain a primary steel strip. The primary steel strip is heated to 480°C at a heating rate of 10°C / min under an alternating magnetic field with a frequency of 60Hz and an intensity of 1.0T, and held at that temperature for 7h. Then, it is cooled to 35°C at a rate of 3°C / min to obtain a thin steel strip.

[0054] Example 3

[0055] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.05%, Si 0.2%, Mn 1.4%, Nb 0.04%, V 0.09%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0056] The short-process preparation method for the thin steel strip includes the following steps:

[0057] S1. The raw materials are melted at 1600℃ for 2.5 hours and then cast at 1525℃ to obtain an ingot. The raw materials contain the following components in the following weight percentages: C 0.05%, Si 0.2%, Mn 1.4%, Nb 0.04%, V 0.09%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0058] S2. The ingot is heated to 1150°C and held for 45 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1110°C and the outlet temperature is 985°C. Then, it is finished rolled in 7 passes at 900°C to obtain a rough-machined steel strip.

[0059] S3. The rough-processed steel strip is heated to 750°C at a heating rate of 14°C / min under an alternating magnetic field with a frequency of 90Hz and an intensity of 1.2T, and held at that temperature for 3 hours. Then, it is cooled to 30°C at a rate of 8°C / min to obtain a primary steel strip. The primary steel strip is heated to 450°C at a heating rate of 7°C / min under an alternating magnetic field with a frequency of 45Hz and an intensity of 0.7T, and held at that temperature for 6 hours. Then, it is cooled to 30°C at a rate of 2°C / min to obtain a thin steel strip.

[0060] Example 4

[0061] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.04%, Si 0.2%, Mn 1.5%, Nb 0.05%, V 0.08%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0062] The short-process preparation method for the thin steel strip includes the following steps:

[0063] S1. The raw materials are melted at 1590℃ for 2.5 hours, and then cast at 1530℃ to obtain an ingot. The raw materials contain the following components in the following weight percentages: C 0.04%, Si 0.2%, Mn 1.5%, Nb 0.05%, V 0.08%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0064] S2. The ingot is heated to 1140°C and held for 40 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1105°C and the outlet temperature is 983°C. Then, it is finished rolled in 7 passes at 910°C to obtain a rough-machined steel strip.

[0065] S3. The rough-processed steel strip is heated to 760°C at a heating rate of 15°C / min under an alternating magnetic field with a frequency of 100Hz and an intensity of 1.4T, and held at that temperature for 3 hours. Then, it is cooled to 32°C at a rate of 7°C / min to obtain a primary steel strip. The primary steel strip is heated to 460°C at a heating rate of 8°C / min under an alternating magnetic field with a frequency of 50Hz and an intensity of 0.6T, and held at that temperature for 6.5 hours. Then, it is cooled to 32°C at a rate of 2°C / min to obtain a thin steel strip.

[0066] Comparative Example 1

[0067] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.05%, Si 0.2%, Mn 1.4%, Nb 0.04%, V 0.09%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0068] The short-process preparation method for the thin steel strip includes the following steps:

[0069] S1. The raw materials are melted at 1600℃ for 2.5 hours and then cast at 1525℃ to obtain an ingot. The raw materials contain the following components in the following weight percentages: C 0.05%, Si 0.2%, Mn 1.4%, Nb 0.04%, V 0.09%, Ti 0.03%, B 0.002%, P≤0.005%, S≤0.002%, with the balance being Fe and unavoidable impurity elements.

[0070] S2. The ingot is heated to 1150°C and held for 45 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1110°C and the outlet temperature is 985°C. Then, it is finished rolled in 7 passes at 900°C to obtain a rough-machined steel strip.

[0071] S3. The rough-processed steel strip is heated to 750°C at a heating rate of 14°C / min, held at that temperature for 3 hours, and then cooled to 30°C at a rate of 8°C / min to obtain a primary steel strip; the primary steel strip is heated to 450°C at a heating rate of 7°C / min, held at that temperature for 6 hours, and then cooled to 30°C at a rate of 2°C / min to obtain a thin steel strip.

[0072] Depend on Figure 2 It can be seen that the thin steel strip prepared in Comparative Example 1 has a strong banded structure, indicating that the structure is significantly anisotropic.

[0073] Comparative Example 2

[0074] This embodiment provides a thin steel strip whose chemical composition by weight percentage includes: C 0.05%, Si 0.2%, Mn 1.5%, Cr 2.0%, Ni 1.2%, Mo 0.4%, Ti 0.1%, with the balance being iron and unavoidable impurities, of which P≤0.005% and S≤0.002%.

[0075] The short-process preparation method for the thin steel strip includes the following steps:

[0076] S1. The raw materials are melted at 1600℃ for 2.5 hours, and then cast at 1525℃ to obtain an ingot. The raw materials include the following components in the following weight percentages: C 0.05%, Si 0.2%, Mn 1.5%, Cr 2.0%, Ni 1.2%, Mo 0.4%, Ti 0.1%, with the balance being iron and unavoidable impurities, of which P≤0.005% and S≤0.002%.

[0077] S2. The ingot is heated to 1150°C and held for 45 minutes. Then, it is rough rolled in 5 passes. The inlet temperature of the rough rolling is 1110°C and the outlet temperature is 985°C. Then, it is finished rolled in 7 passes at 900°C to obtain a rough-machined steel strip.

[0078] S3. The rough-processed steel strip is heated to 750°C at a heating rate of 14°C / min under an alternating magnetic field with a frequency of 90Hz and an intensity of 1.2T, and held at that temperature for 3 hours. Then, it is cooled to 30°C at a rate of 8°C / min to obtain a primary steel strip. The primary steel strip is heated to 450°C at a heating rate of 7°C / min under an alternating magnetic field with a frequency of 45Hz and an intensity of 0.7T, and held at that temperature for 6 hours. Then, it is cooled to 30°C at a rate of 2°C / min to obtain a thin steel strip.

[0079] The thin steel strips obtained in Examples 1-4 and Comparative Examples 1-2 of this invention were subjected to mechanical property tests. Specifically, the mechanical property tests included the following: Sampling of the thin steel strips was performed according to GB / T 2975-1998 "Sampling Location and Specimen Preparation for Mechanical Property Testing of Steel and Steel Products," with the sampling location being one-quarter of the width of the strip in the middle. Mechanical properties were tested according to GB / T 228.1-2010 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method," with the tensile specimen direction being longitudinal. The transverse KU2 impact performance of the steel strip was measured at room temperature by cutting the center of the cross-section according to the method described in GB / T 229 "Metallic Materials - Charpy Pendulum Impact Test Method." The test results are shown in Table 1.

[0080] Table 1. Results of Mechanical Performance Tests

[0081]

[0082] As can be seen from Table 1, the thin steel strips provided in Examples 1-4 of the present invention have good tensile strength and elongation at break, and good mechanical properties.

[0083] The short-process preparation methods provided in Examples 1-4 and Comparative Examples 1-2 of this invention were used in actual production. The number of times the thin steel strip warped in 50 batches produced within 24 hours was detected. The test results are shown in Table 2.

[0084] Table 2 Results of warping frequency test

[0085]

[0086] As can be seen from Table 2, the short-process preparation method for thin steel strip provided in Examples 1-4 of the present invention has a good anti-warping effect.

[0087] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A short flow process for the production of thin steel strip, characterized in that, The method comprises the following steps: S1, according to C 0.03%-0.08%, Si 0.1%-0.3%, Mn 1.3%-1.6%, Nb 0.03%-0.06%, V 0.06%-0.12%, Ti 0.02%-0.04%, B 0.001%-0.003%, P≤0.010%, S≤0.005%, the balance is Fe and inevitable impurity elements, each raw material is smelted, cast, and a cast ingot is obtained; S2, the cast ingot is sequentially subjected to rough rolling and finish rolling, and a rough processing steel strip is obtained; S3, the rough processing steel strip is sequentially subjected to annealing treatment and tempering treatment in an alternating magnetic field, and a thin steel strip is obtained, in the annealing treatment, the frequency of the alternating magnetic field is 60Hz-120Hz, and the strength is 0.6T-1.8T, in the tempering treatment, the frequency of the alternating magnetic field is 30Hz-60Hz, and the strength is 0.4T-1.0T.

2. The short flow process for manufacturing a thin steel strip according to claim 1, characterized in that, In S3, the temperature of the annealing treatment is 720℃-780℃, and the time is 2.5h-3.5h.

3. The short flow process for manufacturing a thin steel strip according to claim 2, characterized in that, In S3, the heating rate of the annealing treatment is 12℃ / min-18℃ / min.

4. The short flow process for manufacturing a thin steel strip according to claim 3, characterized in that, In S3, after the annealing treatment, the temperature is decreased to 25℃-35℃ at a rate of 6℃ / min-10℃ / min.

5. The short flow process for manufacturing a thin steel strip according to claim 1, characterized in that, In S3, the temperature of the tempering treatment is 420℃-480℃, and the holding time is 5h-7h.

6. The short flow process for manufacturing a thin steel strip according to claim 5, characterized in that, In S3, the heating rate of the tempering treatment is 5℃ / min-10℃ / min.

7. The short flow process for manufacturing a thin steel strip according to claim 5, characterized in that, In S3, after the tempering treatment, the temperature is decreased to 25℃-35℃ at a rate of 1℃ / min-3℃ / min.

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