A low-cost low-temperature continuous annealing cold-rolled high-strength steel strip and its production method

Abstract

The present application discloses a low-cost, low-temperature, continuously annealed, cold-rolled, high-strength steel strip and a production method thereof, which relate to the field of metallurgy technology. The casting method of the steel strip slab comprises the following steps: performing post-furnace and argon station treatment after converter smelting, then performing refining, and continuously casting after refining; the casting method of the steel strip slab comprises the following steps: adopting a top-bottom combined blowing mode for converter smelting, raising the steel tapping temperature by 5-10°C, and increasing the desulfurization efficiency during the converter smelting process; in the refining process, adding particle steel when the oxygen content in the molten steel is 20-40ppm and S≤0.040%; during production, after the sulfur content in the molten steel in the smelting process reaches the standard requirement, adding particle steel of different particle sizes in stages to improve the fluidity of the molten steel, improve the stability and fluidity of the molten steel, promote uniform deformation of the steel strip, improve the overall performance of the steel strip, and achieve optimization of the steel structure and improvement of the overall performance.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a low-cost, low-temperature continuous annealing, cold-rolled, high-strength steel strip and a production method thereof. Background Art

[0002] With the rapid development of the country's industry, the demand for steel in fields such as transportation and construction is increasing. Continuously annealed cold-rolled high-strength steel strips are becoming more and more widely used due to their uniform mechanical properties, high dimensional accuracy, and excellent surface quality and plate quality. Low-temperature continuously annealed cold-rolled high-strength steel strips are a type of high-strength steel manufactured using a cold rolling process. After low-temperature continuous annealing treatment, they have excellent mechanical properties and processing properties. The chemical composition of low-temperature continuously annealed cold-rolled high-strength steel strips is precisely controlled to achieve ideal mechanical properties and processing properties. However, with increasing competitive pressure, how to reduce production costs while ensuring product quality is a challenge facing steel companies, especially for different application fields and different processing characteristics. It is better to combine user needs and develop products that meet user performance and other related requirements at low cost.

[0003] For example, the Chinese patent application number CN202110535971.6 discloses a smelting method for improving the fluidity of molten steel after refining and desulfurization of threaded steel. The invention discloses a smelting method for improving the fluidity of molten steel after refining and desulfurization of threaded steel. The threaded steel refining and desulfurization process includes: converter smelting - post-furnace and argon station treatment - LF refining - continuous casting. The LF refining process includes: adding slag-making material lime before refining and power transmission, and adding fluorite to adjust the slag fluidity, and controlling the alkalinity of the refined slag to meet the standard requirements; during power transmission, Diffusion deoxidation is carried out, and the power is turned off after the slag is transparent. Argon is blown from the bottom of the large ladle to control the desulfurization efficiency to meet the standard requirements; particle steel is added to increase the oxygen content in the molten steel and improve the fluidity of the molten steel; the composition of the molten steel is adjusted to ensure that the various components of the molten steel meet the standard requirements, and the ladle is placed for continuous casting after the temperature is qualified; the technical solution provided by this invention is to add an appropriate amount of high-quality oxidizing material particle steel after the sulfur content in the molten steel reaches the standard requirement through the refining process, so as to improve the fluidity of the molten steel, avoid clogging of the pouring nozzle, and make the continuous casting process go smoothly.

[0004] However, the existing production method still has the problem of difficult to control the fluidity of molten steel during the steel strip smelting process, resulting in insufficient uniformity of the steel strip structure and affecting the mechanical properties of the steel strip. Summary of the Invention

[0005] The embodiments of the present application provide a low-cost, low-temperature continuously annealed cold-rolled high-strength steel strip and a production method thereof, thereby solving the problems in the prior art of steel strip smelting production, such as difficulty in controlling the fluidity of molten steel, insufficient uniformity of the produced steel strip structure, and affecting the mechanical properties of the steel strip. During the smelting process, steel particles of different particle sizes are added in steps to improve the stability and fluidity of the molten steel, promote uniform deformation of the steel strip, and achieve optimization of the steel structure and improvement of the overall performance.

[0006] The embodiment of the present application provides a low-cost, low-temperature continuously annealed cold-rolled high-strength steel strip, and the casting method of the steel strip slab is: after converter smelting, post-furnace and argon station treatment, and then refining, and continuous casting after refining.

[0007] Furthermore, the casting method of the steel strip slab is specifically as follows: the converter smelting adopts a top and bottom combined blowing mode, which increases the tapping temperature by 5-10°C and improves the desulfurization efficiency during the converter smelting process;

[0008] In the refining process, when the oxygen content in the molten steel is 20-40 ppm and S≤0.040%, particle steel is added.

[0009] Furthermore, the addition of particle steel is carried out in two steps:

[0010] First, add 60% of the total amount of particle steel, let it fully melt and mix with the molten steel;

[0011] After the first added particle steel is melted, add the remaining particle steel;

[0012] The particle size of the particle steel is 300μm, and the amount of particle steel added is 1.5%-3% of the weight of the molten steel. The physical and chemical index requirements of the particle steel are: TFe≥85%, and the oxygen content in the molten steel is controlled in the range of 40-80ppm.

[0013] Furthermore, the particle size of the steel particles added first is 5 mm; after the first added steel particles are melted, the remaining steel particles are added; the particle size of the remaining steel particles is 200 μm.

[0014] Furthermore, the thickness of the steel strip is 0.5-1.0 mm, and the width is 1200-1500 mm.

[0015] Furthermore, the chemical composition and mass percentage of the steel strip are: C: 0.035-0.060%, Si≤0.048%, Mn: 0.30-0.55%, P: 0.015-0.025%, S≤0.020%, Als: 0.020-0.060%, N≤0.005%, Cr: 0.03-0.06%, and the rest are Fe and unavoidable impurities.

[0016] A method for producing a low-cost, low-temperature, continuously annealed, cold-rolled high-strength steel strip comprises the following steps:

[0017] S1. Hot rolling the continuously cast slab to obtain hot-rolled steel strip. The hot rolling process is a laminar cooling mode after finishing rolling, with front-stage centralized cooling. The coiling temperature is 635±15°C, and a U-type coiling mode is adopted. That is, the coiling temperature of the steel strip 30 meters from the beginning to the end is 30°C higher than the design value.

[0018] S2. Continuously pickling and cold rolling the hot-rolled steel strip, using a five-stand tandem CVC+six-roller cold rolling mill with a total cold rolling reduction of 72-82%, to obtain a chilled steel strip;

[0019] S3. Continuously anneal the cold-hardened steel strip in a vertical all-radiant tube heating continuous annealing furnace. The annealing furnace area is equipped with a high-precision radar-type correction system. The annealing soaking temperature is 610-640°C, the annealing slow cooling temperature is 560-575°C, and the annealing over-aging temperature is 355-385°C. A six-roller CVC wet leveler is used with a leveler elongation of 0.6-0.8% to obtain the cold-rolled steel strip.

[0020] Furthermore, the coolant for laminar cooling in step S1 is cooling water, and the cooling water adopts a cooling method combining water column and water mist. Specifically, a row of spray nozzles is arranged between every two rows of water nozzles for laminar cooling.

[0021] Furthermore, the water column pressure is 18 MPa, the water column diameter is 5 mm, and the water column spray duration is 0.5 s; the water mist pressure is 10 MPa, the droplet diameter is 100 μm, the water mist spray diameter is 10 mm, and the water mist spray duration is 0.5 s.

[0022] Furthermore, the coolant also includes hydraulic oil, and the ratio of hydraulic oil to cooling water is 1: (9-20).

[0023] Furthermore, the coolant is pre-treated before injection, specifically:

[0024] Mix the hydraulic oil and cooling water in proportion, add them into the ultrasonic emulsification equipment and stir at a stirring speed of 2000-4000 rpm; continue stirring for 5-30 minutes until a uniform and stable emulsion is formed.

[0025] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0026] First, after the steel particles are added to the molten steel, they interact with the molten steel components through the process of dissolution and diffusion, forming a uniform molten steel composition. The step-by-step addition of the steel particles can control the progress of this process, allowing the steel particles to dissolve and diffuse more fully. By adding the steel particles step by step, first adding 60% of the total amount to allow it to fully melt and mix with the molten steel, and then adding the remaining steel particles, the steel particles can be evenly distributed in the molten steel. This uniform distribution can prevent the formation of local aggregation of steel particles in the molten steel, thereby improving the uniformity of the steel strip composition, reducing local concentration differences and temperature gradients in the molten steel, and thus improving the stability and fluidity of the molten steel. The uniform distribution of the steel particles can also reduce local viscosity differences in the molten steel, further improving fluidity.

[0027] Secondly, large-particle steel, as the core of heterogeneous nucleation, can promote the crystallization process of molten steel and refine the cast structure. Large-particle steel provides more nucleation sites, allowing the molten steel to form more and finer grains during the solidification process; large-particle steel can pin the austenite grain boundaries, inhibit the growth of grains during subsequent hot working, and maintain the fine state of the grains, thereby improving the plasticity and toughness of the material; small-particle steel, due to its smaller particle size and larger specific surface area, can quickly react with other substances to promote the homogenization of molten steel and the uniform distribution of its composition; larger-particle steel can release more heat during the melting process, promote the temperature rise and fluidity of molten steel, and smaller-particle steel can melt more quickly and mix evenly with molten steel, ensuring the rapid homogenization of the molten steel composition and avoiding composition segregation, thereby obtaining molten steel with more uniform composition;

[0028] Third, by adopting a cooling method combining water column and water mist, the cooling rate of the steel strip can be controlled more accurately. A U-shaped coiling mode is adopted at the head and tail of the steel strip to further ensure the cooling uniformity of the entire length of the steel strip. This uniform cooling can promote the acquisition of fine ferrite grains. The lower coiling temperature can inhibit the growth of ferrite grains and promote the formation of fine ferrite grains. After hot rolling, the austenite structure inside the steel will undergo a phase transformation during the cooling process and transform into ferrite and other structures. The cooling rate will directly affect the phase transformation process and the size of the ferrite grains. A faster cooling rate can inhibit the growth of ferrite grains, while a slower cooling rate can easily lead to coarse grains. The cooling method combining water column and water mist can provide a more uniform and efficient cooling effect, avoid local overheating or overcooling, and thus obtain fine ferrite grains.

[0029] Fourthly, after the cooling water and liquefied oil are mixed, they are stirred vigorously to form an emulsion. The oil droplets in the emulsion are surrounded by water molecules to form a stable dispersion system. This emulsion has better lubricity and cooling performance. After the emulsion is sprayed onto the surface of the steel strip, it will quickly expand and form a uniform film. Since the emulsion contains hydraulic oil components, this film has lubricity and adhesion, and can fit tightly to the surface of the steel strip, playing a heat insulating role on the surface of the steel strip, reducing heat loss, and making the cooling energy more concentrated on the surface of the steel strip, thereby improving cooling efficiency. At the same time, the lubricating properties of the emulsion can reduce the friction resistance during the cooling process, making the cooling process smoother and further shortening the cooling time. The cooling water component will evaporate quickly, taking away the heat from the surface of the steel strip, causing the temperature of the steel strip to drop rapidly. DETAILED DESCRIPTION

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains; the terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0031] Example 1: A low-cost, low-temperature, continuously annealed, cold-rolled, high-strength steel strip, the chemical composition and mass percentage of the steel strip being: C: 0.035-0.060%, Si≤0.048%, Mn: 0.30-0.55%, P: 0.015-0.025%, S≤0.020%, Als: 0.020-0.060%, N≤0.005%, Cr: 0.03-0.06%, and the remainder being Fe and unavoidable impurities;

[0032] The thickness of the steel strip is 0.5-1.0 mm, and the width is 1200-1500 mm;

[0033] The specific casting method of the steel strip slab is as follows: after converter smelting, it is treated at the post-furnace and argon station, and then refined, and then continuously casted;

[0034] The converter smelting adopts a top-bottom combined blowing mode, which increases the tapping temperature by 5-10°C and improves the desulfurization efficiency during the converter smelting process;

[0035] In the refining process, when the oxygen content in the molten steel is 20-40ppm and S≤0.040%, particle steel is added;

[0036] Among them, the addition of particle steel is divided into two steps:

[0037] First, add 60% of the total amount of particle steel, let it fully melt and mix with the molten steel;

[0038] After the first added particle steel is melted, add the remaining particle steel;

[0039] The particle size of the particle steel is 300μm, and the amount of particle steel added is 1.5%-3% of the weight of the molten steel. The physical and chemical index requirements of the particle steel are: TFe ≥ 85%, and the oxygen content in the molten steel is controlled in the range of 40-80ppm;

[0040] A method for producing a low-cost, low-temperature, continuously annealed, cold-rolled high-strength steel strip comprises the following steps:

[0041] S1. Hot rolling the continuously cast slab to obtain hot-rolled steel strip. The hot rolling process is a laminar cooling mode after finishing rolling, with front-stage centralized cooling. The coiling temperature is 635±15°C, and a U-type coiling mode is adopted. That is, the coiling temperature of the steel strip 30 meters from the beginning to the end is 30°C higher than the design value.

[0042] S2. Continuously pickling and cold rolling the hot-rolled steel strip, using a five-stand tandem CVC+six-roller cold rolling mill with a total cold rolling reduction of 72-82%, to obtain a chilled steel strip;

[0043] S3. Continuously anneal the cold-hardened steel strip in a vertical all-radiant tube heating continuous annealing furnace. The annealing furnace area is equipped with a high-precision radar-type correction system. The annealing soaking temperature is 610-640°C, the annealing slow cooling temperature is 560-575°C, and the annealing over-aging temperature is 355-385°C. A six-roller CVC wet leveler is used with a leveler elongation of 0.6-0.8% to obtain the cold-rolled steel strip.

[0044] A group experiment was conducted for this example. Table 1 below shows the dosage ratios of each group in the group experiment of Example 1.

[0045] Table 1

[0046]

[0047] The main process control parameters are shown in Table 2;

[0048] Table 2

[0049]

[0050] The low-cost, low-temperature, continuous annealing, cold-rolled, high-strength steel strips obtained from the above experiments were stretched according to the tensile test method for metallic materials (GB / T 228.1). The mechanical properties are shown in Table 3:

[0051] Table 3

[0052]

[0053] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages:

[0054] When particle steel is added to molten steel, the iron oxide in it will react with the reducing substances (such as carbon, silicon, etc.) in the molten steel to release oxygen, thereby increasing the oxygen content in the molten steel; an appropriate amount of oxygen content can improve the fluidity of the molten steel; during the solidification process of the molten steel, oxygen can combine with impurity elements (such as sulfur, phosphorus, etc.) in the molten steel to form high-melting-point compounds. These compounds exist in the molten steel in solid form, thereby reducing the viscosity of the molten steel and improving its fluidity. At the same time, oxygen can also promote the floating and removal of inclusions in the molten steel, further improving the purity and fluidity of the molten steel; after the particle steel is added to the molten steel, it reacts with the molten steel components through the process of dissolution and diffusion. The interaction between the steel particles and the molten steel forms a uniform composition. The step-by-step addition of steel particles can control the progress of this process, allowing the steel particles to dissolve and diffuse more fully. By adding the steel particles step by step, first adding 60% of the total amount to allow it to fully melt and mix with the molten steel, and then adding the remaining steel particles, the uniform distribution of the steel particles in the molten steel can be promoted. This uniform distribution can avoid the formation of local aggregation of steel particles in the molten steel, thereby improving the uniformity of the steel strip composition, reducing local concentration differences and temperature gradients in the molten steel, and thus improving the stability and fluidity of the molten steel. The uniform distribution of steel particles can reduce local viscosity differences in the molten steel and further improve fluidity.

[0055] Small-particle steel has a larger specific surface area, so it reacts faster with other substances. After being added to molten steel, they can quickly dissolve and react with other elements, refining the grain structure of the steel, thereby increasing the density of the grain interface and making the microstructure of the steel more uniform and dense; small-particle steel can increase the number of grain interfaces, thereby improving the grain boundary strengthening effect, increasing the density of the grain interface, and increasing the strength and hardness of the material. In addition, small-particle steel can also increase the difficulty of dislocation movement within the crystal, thereby increasing the tensile strength. The grain boundary strengthening and dislocation strengthening mechanisms jointly improve the strength and hardness of the steel; small-particle steel increases the number of grain boundaries by refining the grains, which allows the material to have more grain boundaries to share and absorb energy when subjected to external forces. At the same time, the increase in dislocation density also improves the material's ability to resist plastic deformation, thereby improving the material's plasticity and toughness.

[0056] When steel particles are first added to molten steel, they will quickly melt and disperse into the molten steel due to the high temperature of the molten steel. Due to gravity, most of the steel particles will settle to the middle and bottom layers of the molten steel. After the first added steel particles have melted and partially settled, additional steel particles are added. At this time, since a certain amount of steel particles already exist in the molten steel, the newly added steel particles are more easily dispersed into the surface and middle layers of the molten steel, making the distribution of the steel particles in the molten steel more uniform.

[0057] As an iron-based alloy, particle steel can increase the liquid fluidity of molten steel and reduce its viscosity after melting. Particle steel has high oxidizing properties and can react with reducing substances in molten steel to form inclusions such as oxides or sulfides. Adding particle steel twice can make these inclusions more evenly distributed in the molten steel, thereby further improving the fluidity of the molten steel and reducing defects and cracks in the steel strip. Particle steel acts as a heterogeneous nucleation core, which can promote grain nucleation and refinement during the solidification process of molten steel. Adding particle steel twice can make the grain refinement effect more obvious and the grain distribution more uniform. The uniform distribution of particle steel can ensure that the grain refinement degree of each part of the steel strip is similar, thereby improving the strength and toughness of the steel strip, thereby improving the overall performance of the steel strip.

[0058] Improved molten steel fluidity promotes uniform deformation and good surface quality of the steel strip during hot rolling, resulting in uniform steel strip thickness and good surface finish, improving hot rolling efficiency and quality. Uniform distribution of steel particles can reduce local stress concentration during hot rolling and reduce the risk of cracks. During laminar cooling, the cooling rate of the steel strip has a significant impact on its structure and performance. The steel strip formed by hot rolling with molten steel with good fluidity has a more uniform internal structure, which promotes uniform control of the cooling rate during laminar cooling. Uniform distribution of steel particles can ensure that the cooling rate of each part of the steel strip is similar during the cooling process, thereby reducing performance differences caused by uneven cooling. During annealing, the steel strip formed by molten steel with good fluidity is easier to achieve uniform structure and optimized performance during annealing. The step-by-step addition of steel particles can refine the grain size of the steel strip and improve the strength and toughness of the steel strip. The steel strip treated with the step-by-step addition of steel particles will have better tensile properties, impact toughness, strength and processing performance.

[0059] Example 2: The above-mentioned Example 1 obtains a steel strip with excellent mechanical properties and uniform composition by adding particle steel in steps during the smelting process to improve the fluidity of the molten steel, thereby improving the stability and fluidity of the molten steel, promoting the uniform deformation of the steel strip, and improving the overall performance of the steel strip. In order to further improve the overall performance of the steel strip, further improvements are made on the basis of Example 1.

[0060] In the refining process, the addition of particle steel is carried out in two steps:

[0061] First, add the particle steel with a particle size of 5mm;

[0062] After the first added steel particles are melted, the remaining steel particles are added; the particle size of the remaining steel particles is 200 μm.

[0063] The experiment for this embodiment was conducted on the basis of Experiment 5 of Example 1. The difference between the experiment for this embodiment and Experiment 5 of Example 1 is that the addition of particle steel is carried out in two steps: first, the particle size of the added particle steel is 5 mm, and the particle size of the remaining particle steel is 200 μm.

[0064] After testing, the steel strip of this embodiment has a thickness of 0.7 mm, a yield strength of 495 MPa, a tensile strength of 569 MPa, and an elongation after fracture of A 50 The hardness is 25.1% and the HRB hardness is 90.3.

[0065] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages:

[0066] Large-size particle steel, as the core of heterogeneous nucleation, can promote the crystallization process of molten steel and refine the cast structure. Large-size particle steel provides more nucleation sites, allowing the molten steel to form more and finer grains during the solidification process; large-size particle steel can pin the austenite grain boundaries, inhibit the growth of grains during subsequent hot working, and maintain the fine state of the grains, thereby improving the plasticity and toughness of the material; small-size particle steel, due to its smaller particle size and larger specific surface area, can react quickly with other substances, promote the homogenization of molten steel and uniform distribution of components, thereby shortening the steelmaking cycle and improving production efficiency; larger-size particle steel can release more heat during the melting process, promote the temperature rise and fluidity of molten steel, and smaller-size particle steel can melt more quickly and mix evenly with molten steel, ensuring rapid homogenization of molten steel components and avoiding component segregation, thereby obtaining molten steel with more uniform components;

[0067] The large-particle steel added first acts as a heterogeneous nucleation core to refine the cast structure of the steel. The small-particle steel added subsequently further refines the grains and increases the density of the grain interfaces through rapid reaction. The large-particle steel pins the austenite grain boundaries, inhibits grain growth, and provides heterogeneous nucleation cores, thereby improving the overall strength of the steel. The small-particle steel increases the density of the grain interfaces and the difficulty of dislocation movement, further improving the strength and hardness of the steel. The large-particle steel improves the plasticity of the material by refining the structure and inhibiting grain growth. The small-particle steel further improves the plasticity and toughness of the material by refining the grains, increasing the dislocation density, and increasing the difficulty of dislocation movement.

[0068] By adding steel particles of different particle sizes in stages, the mechanical properties of the steel, such as strength, hardness, plasticity and toughness, are further improved. For products requiring high strength and high wear resistance, the addition of large- and small-particle steel particles can significantly improve product quality and service life. The rapid response of small-particle steel particles can shorten the steelmaking cycle and improve production efficiency. At the same time, due to the improvement in the fluidity and stability of molten steel, the efficiency of the hot rolling and annealing processes is improved. The step-by-step addition of steel particles of different particle sizes can promote the uniform distribution of steel strip composition and the homogenization of the organization. The uniform grain structure and higher grain boundary density make the deformation of the steel strip more uniform during cold rolling. During annealing, the refined grains and uniform composition distribution promote the homogenization of the organization and the optimization of performance, reducing the performance differences caused by uneven composition or organization.

[0069] Example 3: The above-mentioned Example 2 optimizes the steel structure and improves the overall performance by adding particle steels of different particle sizes step by step during the smelting process and utilizing a combination of large-particle-size and small-particle-size particle steels. In order to further improve the overall performance of the steel strip, further improvements are made on the basis of Example 2.

[0070] In step S1, the coolant for laminar cooling is cooling water, and the cooling water adopts a cooling method combining water column and water mist. Specifically, a row of spray nozzles is arranged between every two rows of water nozzles for laminar cooling;

[0071] Among them, the water column pressure is 18MPa, the water column diameter is 5mm, and the water column spray duration is 0.5s; the water mist pressure is 10MPa, the droplet diameter is 100μm, the water mist spray diameter is 10mm, and the water mist spray duration is 0.5s.

[0072] For this embodiment, an experiment was conducted on the basis of Example 2. The difference between the experiment of this embodiment and the experiment of Example 2 is that the cooling water of laminar cooling adopts a cooling method combining water column and water mist, the water column pressure is 18 MPa, the water column diameter is 5 mm, and the water column spray duration is 0.5 s; the water mist pressure is 10 MPa, the droplet diameter is 100 μm, the water mist spray diameter is 10 mm, and the water mist spray duration is 0.5 s.

[0073] After testing, the steel strip of this embodiment has a thickness of 0.7 mm, a yield strength of 514 MPa, a tensile strength of 591 MPa, and an elongation after fracture of A 50 It is 26.2% and the hardness HRB is 93.9.

[0074] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages:

[0075] By adopting a cooling method that combines cooling water and water mist, the cooling rate of the steel strip can be controlled more accurately, especially by adopting a U-shaped coiling mode at the head and tail of the steel strip, which further ensures the cooling uniformity of the entire length of the steel strip. This uniform cooling can promote the acquisition of fine ferrite grains, and the lower coiling temperature can inhibit the growth of ferrite grains and promote the formation of fine ferrite grains. After hot rolling, the austenite structure inside the steel will undergo a phase transformation during the cooling process, transforming into ferrite and other structures. The speed of the cooling rate will directly affect the phase transformation process and the size of the ferrite grains. A faster cooling rate can inhibit the growth of ferrite grains, while a slower cooling rate can easily lead to coarse grains. The cooling method combining water column and water mist can provide a more uniform and efficient cooling effect, avoid local overheating or overcooling, and thus obtain fine ferrite grains. A lower coiling temperature can slow down the transformation rate of austenite to ferrite, giving ferrite grains less time and space to grow, thereby refining the grains.

[0076] Precise control of the cooling rate affects the precipitation of carbides. An appropriate cooling rate can promote the precipitation of fine and uniform carbides, thereby improving the hardness and strength of the steel strip. During the cooling process, the carbon element in the steel combines with other alloying elements to form carbides. The precipitation behavior and distribution of carbides have a significant impact on the performance of the steel strip. The cooling rate affects the precipitation kinetics of carbides. A faster cooling rate can inhibit the growth of carbides and promote the formation of fine carbides. A cooling method combining water column and water mist can provide a more uniform cooling environment and promote uniform precipitation of carbides. Fine ferrite grains and uniform carbide precipitation can significantly improve the mechanical properties of the steel strip, such as yield strength, tensile strength, and hardness.

[0077] When only water columns are used for laminar cooling, excess water in the water column will overflow to both sides, affecting the accuracy of laminar cooling on the temperature control of the steel strip area. After the water column sprays water, a large amount of water vapor is generated in situ. The water vapor will have a morphological impact on the subsequent water column and water mist, thereby interfering with the precise temperature control. By arranging the water nozzles and the mist nozzles at intervals, the impact of overflow on the temperature control of the steel strip is avoided. At the same time, the impact of water vapor on temperature control is reduced, ensuring that the water mist can be sprayed onto the steel strip evenly and stably, thereby improving the accuracy of temperature control and the structural properties of the steel strip.

[0078] The water column has a high impact force and cooling efficiency, which can quickly reduce the temperature of the steel strip surface. The water mist can evenly and finely cover the steel strip surface, filling the blind spots of water column cooling and improving the uniformity of cooling. By setting the spray structure of water column and water mist at intervals, the overflow caused by continuous water column is avoided, which affects the temperature control problem. At the same time, intermittent spraying can control the cooling rate and prevent the steel strip from cracking or deformation due to excessive cooling. The water mist has a larger surface area and can more evenly cover the steel strip surface, improving the uniformity of cooling. At the same time, the water mist can also reduce the water splashing phenomenon caused by the water column cooling process, avoiding damage to the steel strip surface.

[0079] The combined use of water column and water mist makes the cooling effect more uniform and efficient; the water column can quickly take away a large amount of heat from the surface of the steel strip, while the water mist can supplement the insufficient cooling of the water column and improve the uniformity of cooling; the uniform cooling effect can obtain a more delicate steel strip structure and improve the mechanical properties and processing performance of the steel strip. At the same time, the supplementary use of water mist can also reduce the temperature gradient caused by water column cooling and avoid excessive stress concentration inside the steel strip; the use of water mist can reduce the water splashing phenomenon generated during the water column cooling process and avoid damage to the steel strip surface. At the same time, the uniform coverage of water mist can also improve the smoothness of the steel strip surface and reduce the occurrence of surface defects; by adjusting the parameter settings of the water nozzle and the spray nozzle, the cooling effect can be flexibly adjusted to improve the flexibility and adaptability of production.

[0080] Example 4: The above-mentioned Example 3 optimizes the cooling effect by adopting a laminar cooling method combining water columns and water mist, and arranges water nozzles and spray nozzles at intervals, thereby improving the cooling efficiency, improving the structural performance of the steel strip, improving the surface quality of the steel strip, and enhancing production flexibility. In order to further improve the overall performance of the steel strip, further improvements are made on the basis of Example 3.

[0081] The coolant for laminar cooling also includes hydraulic oil, and the ratio of hydraulic oil to cooling water is 1: (9-20);

[0082] The coolant is pre-treated before injection, specifically:

[0083] Mix the hydraulic oil and cooling water in proportion, add them to the ultrasonic emulsification equipment and stir at a stirring speed of 2000-4000 rpm; continue stirring for 5-30 minutes until a uniform and stable emulsion is formed;

[0084] The emulsion is transported to the water nozzle and spray nozzle through the pipeline and sprayed according to the set parameters.

[0085] The experiment of this embodiment was conducted on the basis of the experiment of the third embodiment. The difference between the experiment of this embodiment and the experiment of the third embodiment is that the coolant of the laminar cooling also includes hydraulic oil, and the ratio of hydraulic oil to cooling water is 1:15.

[0086] After testing, the steel strip of this embodiment has a thickness of 0.7 mm, a yield strength of 527 MPa, a tensile strength of 599 MPa, and an elongation after fracture of A 50 The hardness is 27.1% and the HRB hardness is 96.7.

[0087] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages:

[0088] After the cooling water and liquefied oil are mixed, they are vigorously stirred to form an emulsion. The oil droplets in the emulsion are surrounded by water molecules, forming a stable dispersion system. This emulsion has better lubricity and cooling performance. After the emulsion is sprayed onto the surface of the steel strip, it will quickly spread out and form a uniform film. Because the emulsion contains hydraulic oil components, this film has certain lubricity and adhesion, and can fit tightly to the surface of the steel strip, playing a heat insulation role on the surface of the steel strip, reducing heat loss, and making the cooling energy more concentrated on the surface of the steel strip, thereby improving cooling efficiency. At the same time, the lubricating property of the emulsion can reduce the friction resistance during the cooling process, making the cooling process smoother and further shortening the cooling time. The cooling water component will evaporate quickly, taking away the heat from the surface of the steel strip, causing the temperature of the steel strip to drop rapidly.

[0089] The hydraulic oil component in the emulsion has good lubricating properties. The hydraulic oil component forms a thin and uniform oil film on the surface of the steel strip, reducing the water splashing phenomenon generated during the water column cooling process. The lubricating effect of the oil film can reduce the scratches and wear of the steel strip during the cooling process, avoid damage to the steel strip surface, reduce friction and wear, and improve the surface quality of the steel strip; the lubricating effect can also reduce the heat generated by friction, making the cooling process more efficient; the water in the emulsion can quickly absorb and take away the heat from the steel strip surface, lowering the steel strip temperature and thus achieving rapid cooling. The presence of the oil film can reduce heat loss, allowing the cooling energy to act more concentratedly on the steel strip surface, thereby improving cooling efficiency. The emulsion can cover the steel strip surface more evenly, avoiding stress concentration and uneven structure caused by uneven cooling;

[0090] The uniform cooling effect can obtain a more delicate steel strip structure and improve the mechanical properties and processing performance of the steel strip. At the same time, the hydraulic oil component in the emulsion can also reduce the temperature gradient caused by cooling and avoid excessive stress concentration inside the steel strip; the hydraulic oil component in the emulsion forms an oil film on the surface of the steel strip, reducing friction and wear and improving the surface finish of the steel strip. At the same time, the uniform cooling effect can also reduce the occurrence of surface defects and improve the appearance quality of the steel strip. The uniform cooling effect and good lubricity can obtain a more delicate steel strip structure and improve the mechanical properties of the steel strip such as tensile strength, yield strength and elongation.

[0091] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A low-cost, low-temperature, continuous annealing, cold-rolled, high-strength steel strip, characterized in that: The casting method of the steel strip slab is as follows: after converter smelting, it is treated at the back of the furnace and in the argon station, and then refined, and then continuously casted; The specific casting method of the steel strip slab is as follows: the converter smelting adopts the top and bottom combined blowing mode, which increases the steel tapping temperature by 5-10°C and improves the desulfurization efficiency during the converter smelting process; In the refining process, when the oxygen content in the molten steel is 20-40 ppm and S is ≤ 0.040%, particle steel is added; The addition of particle steel is carried out in two steps: First, add 60% of the total amount of particle steel, let it fully melt and mix with the molten steel; After the first added particle steel is melted, add the remaining particle steel; Among them, the particle size of the first added particle steel is 5mm, and the particle size of the remaining particle steel is 200μm. The amount of particle steel added is 1.5%-3% of the weight of the molten steel. The physical and chemical index requirements of the particle steel are: TFe≥85%, and the oxygen content in the molten steel is controlled in the range of 40-80ppm.

2. The low-cost, low-temperature, continuously annealed, cold-rolled, high-strength steel strip according to claim 1, characterized in that: The thickness specification of the steel strip is 0.5-1.0 mm, and the width specification is 1200-1500 mm.

3. The low-cost, low-temperature, continuous annealing, cold-rolled, high-strength steel strip according to claim 1, characterized in that: The chemical composition and mass percentage of the steel strip are: C: 0.035-0.060%, Si≤0.048%, Mn: 0.30-0.55%, P: 0.015-0.025%, S≤0.020%, Als: 0.020-0.060%, N≤0.005%, Cr: 0.03-0.06%, and the rest are Fe and unavoidable impurities.

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