Method for reducing surface microdefects of strip steel

Abstract

The invention relates to the technical field of steel rolling, in particular to a method for reducing strip steel surface microdefects. The method comprises the steps that a casting blank is subjected to surface treatment, and a pretreated casting blank is obtained; heating the pretreated casting blank to obtain a heated plate blank; the heated plate blank is cooled and then subjected to pre-descaling, and a rolled casting blank is obtained; the rolled casting blank is subjected to rough rolling and finish rolling, and a rolled steel coil is obtained; the rolled steel coil is subjected to front-section cooling and then subjected to coiling and acid pickling, and a coiled steel coil is obtained; wherein heating comprises a preheating section, a multi-stage gradient heating section and a soaking section; the multi-stage gradient heating section meets the conditions that the final temperature of the previous-stage heating section is lower than the final temperature of the next-stage heating section, and the air-fuel ratio of the previous-stage heating section is larger than the air-fuel ratio of the next-stage heating section. According to the method, the thickness of the oxidized scale on the surface of the coiled strip steel can be reduced to be 15 microns or below, and the unevenness of the interface between the scale and the matrix can be 5 microns or below, so that the risk that surface micro-defects appear on the rolled steel coil is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of steel rolling, and in particular to a method for reducing surface micro-defects of steel strips. Background Art

[0002] The complex high-temperature oxidation and deformation that occur on the surface of the strip during the hot rolling process is a complex process of temperature-oxidation-deformation coupling, and is also an integrated complex nonlinear production process that "affects the entire body". During this process, the iron oxide scale on the surface of the strip will undergo growth, removal, growth, deformation, regrowth, phase structure transformation and other processes. During these processes of surface iron oxide scale, it will be affected by the coupling of steel grade composition, heating process, rolling process and equipment, resulting in the common dominant "pressed-in" iron oxide scale defects on the surface of the strip. The processes that are prone to "pressed-in" iron oxide scale defects include: primary (furnace-born), secondary (rough rolling), tertiary (finishing rolling) and fourth iron scale pressing (iron scale ash pressing). However, this type of dominant "pressed-in" iron oxide scale defect can be detected by the surface detection system, so that it can be removed in the subsequent processing stage. However, during the hot rolling process, new iron oxide scale will be continuously produced on the surface of the steel strip. When the surface temperature of the steel strip is uneven, the structure and thickness of the surface iron oxide scale at different positions of the steel strip will be different. These differences will cause local micro defects on the surface of the substrate during the rolling deformation of the steel strip, and these micro defects are covered by the surface iron oxide scale. Therefore, such hidden defects cannot be identified by online surface detection systems or manual work, which easily leads to the omission of products with micro defects to downstream users. Therefore, how to control the surface micro defects of the steel strip during the production process, quickly identify the micro defects on the surface of the steel strip and effectively block the surface micro defects is an important technical problem that needs to be solved in hot rolling.

[0003] Although there are preparation methods for controlling surface defects of steel strips in the prior art, these technologies do not effectively control micro defects on the surface of steel strips, resulting in a large number of micro defects on the surface of steel strips.

[0004] At present, the preparation methods for controlling the surface defects of strip steel include: (1) a descaling method after rough rolling of steel slabs, which uses high-pressure water of 35MPa to 48MPa to remove the scale that penetrates into the ferrite and the scale that is generated during rough rolling, so that the method can improve the surface quality of the slab. (2) a method for manufacturing an automobile outer panel with high surface quality and high formability, which includes: pre-treating the cold-rolled steel sheet to process the cold-rolled steel sheet into a cold-hardened plate with a roughness between 0.8μm and 1.7μm, and then galvanizing the cold-hardened plate to form a plating liquid layer on the surface of the cold-hardened plate; after controlling the thickness of the plating liquid layer within a set range, the cold-hardened plate and the plating liquid layer are subjected to post-plating cold zone treatment. The production method mainly controls the morphology of the surface of the raw material, controls the appropriate coating process (setting the composition and temperature of the zinc pot), and controls the post-plating cooling process to ultimately achieve excellent bonding strength and surface quality of the coating. (3) An optimization method for the red iron scale defect on the surface of high silicon hot rolled strip, the optimization method comprising: sequentially performing a heating process, a rough rolling process, a coil box coiling process, and a finishing process on the high silicon hot rolled strip to obtain the high silicon hot rolled strip; wherein, in the heating process when the tensile strength is greater than 590 MPa, the furnace temperature of the high silicon hot rolled strip is controlled to be 1270°C to 1280°C, and the furnace time is 140 min to 200 min; when the tensile strength is less than 590 MPa, the furnace temperature is controlled to be 1150°C to 1180°C, and the furnace time is 110 min to 140 min. At the same time, the rough rolling descaling pressure is controlled to be greater than or equal to 17 MPa, and the finishing rolling descaling pressure is controlled to be greater than or equal to 24 MPa. The pressure of the descaling manifold is 130 MPa. (4) An austenitic high manganese steel for ultra-low temperature use with excellent surface quality and a method for preparing the same, wherein the steel composition of the austenitic high manganese steel mainly includes: C: 0.4% to 0.5%, Mn: 23% to 26%, Si: 0.03% to 0.5%, Cr: 3% to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, and the remainder is Fe and unavoidable impurities, wherein the microstructure of the austenitic high manganese steel comprises more than 95% austenite as the microstructure, and when a cross section of the austenitic high manganese steel is observed using an optical microscope, it can be observed that among the surface defects in the area from the surface to the position t / 8 (t represents the product thickness), the number of surface defects with a depth of more than 10 μm on the surface of the austenitic high manganese steel can be less than 0.0001 per unit area. In addition, the rolling process of the preparation method is as follows: the rough-rolled rod is finish-rolled in the temperature range of 750°C to 1000°C, and the ratio of the slab reheating temperature to the rough rolling reduction is required to be greater than 0.15, and then the hot-rolled material after finish rolling is accelerated cooled to below 600°C at a cooling rate of more than 10°C / s.(5) A 590 MPa grade cold-rolled dual-phase steel without surface streak defects and a production method, the composition of the steel plate is as follows in weight percentage: C: 0.050% to 0.100%, Si: ≤0.25%, Mn: 1.20% to 2.00%, P: ≤0.012%, S: ≤0.008%, Al: 0.05% to 0.10%, Sb: 0.015% to 0.050%, and the balance is Fe and other inevitable impurities. The production method of the steel plate includes smelting, continuous casting, hot charging heating, high-pressure water descaling and rough rolling, finishing rolling, laminar cooling, coiling, hot-rolled plate pickling and cold continuous rolling, continuous annealing, air cooling, and leveling coiling. The specific process parameters are as follows: hot charging heating: the continuous casting billet is directly hot charged and sent to the heating furnace, the billet hot charging temperature is greater than 850°C, the furnace gas temperature in the preheating section is 900°C to 1000°C, the preheating time is 20min to 30min, the heating section temperature is 1230°C to 1270°C, the heating time is 15min to 25min, the soaking section temperature is 1230°C to 1270°C, the soaking section insulation time is 70min to 90min, and the furnace pressure is always in a slightly positive pressure state in the dynamic state; high-pressure water descaling and rough rolling process: After the continuous casting billet is discharged from the furnace, the rolling rhythm is controlled to roll a billet for 1min to 2min, and the high-pressure water descaling is performed for 4 to 6 times, with the nozzle pressure of 19MPa to 21MPa; the front-stage laminar cooling is adopted, the coiling temperature is 600℃ to 650℃, and the thickness of the hot-rolled plate after rolling is 2.5mm to 5.0mm; hot-rolled plate pickling and cold continuous rolling: turbulent hydrochloric acid pickling is adopted, the hydrochloric acid concentration is 15% to 25%, the pickling temperature is 80℃ to 95℃, the strip is stretched and straightened, and the running speed is 50m / min to 70m / min; continuous annealing: the uniform heating temperature of the steel strip in the remote annealing furnace is 770℃ to 830℃, the slow cooling temperature is 650℃ to 700℃, and the temperature after rapid cooling and over-aging is 260℃ to 290℃. The 590MPa grade cold-rolled dual-phase steel produced by this method has a bright surface, no streak defects, good corrosion resistance and coating adhesion, and the mechanical properties of the steel plate are excellent. Summary of the invention

[0005] The present application provides a method for reducing micro defects on the surface of steel strips to solve the following technical problem: how to effectively reduce the risk of micro defects on the surface of steel strips.

[0006] In a first aspect, the present application provides a method for reducing surface micro-defects of a steel strip, the method comprising:

[0007] Performing surface treatment on the ingot to obtain a pretreated ingot;

[0008] heating the pretreated ingot to obtain a heated slab;

[0009] Cooling the heated slab, and then pre-descaling the cooled heated slab to remove the furnace iron scale on the surface of the heated slab to obtain a rolled cast slab;

[0010] performing rough rolling and finish rolling on the rolled ingot to obtain a rolled steel coil; and

[0011] The rolled steel coil is subjected to front-stage cooling, and then the rolled steel coil after the front-stage cooling is coiled and pickled to obtain a coiled steel coil;

[0012] Wherein, the heating includes a preheating section, a multi-stage gradient heating section and a soaking section;

[0013] The multi-stage gradient heating section satisfies: the end temperature of the previous stage heating section is less than the end temperature of the next stage heating section, and the air-fuel ratio of the previous stage heating section is greater than the air-fuel ratio of the next stage heating section.

[0014] Optionally, the multi-stage gradient heating includes a primary heating section and a secondary heating section; the terminal temperature of the primary heating section is 1050°C to 1100°C, the time of the primary heating section is 40min to 60min, and the air-fuel ratio of the primary heating section is 1.1 to 1.2;

[0015] The terminal temperature of the secondary heating section is 1250° C. to 1290° C., the time of the secondary heating section is 40 min to 50 min, and the air-fuel ratio of the secondary heating section is 1.00 to 1.05.

[0016] Optionally, the temperature of the preheating section is ≤400°C, and the time of the preheating section is 60min to 70min; and / or

[0017] The duration of the soaking section is 30 minutes to 40 minutes, the air-fuel ratio of the soaking section is 0.95 to 1.00, and the terminal temperature of the soaking section is 1260° C. to 1290° C.

[0018] Optionally, the rough rolling temperature is 1180°C to 1200°C, the final rolling temperature is 1040°C to 1060°C, the intermediate billet thickness is 35mm to 40mm, and the rough rolling includes performing rough rolling in 6 to 8 passes.

[0019] Optionally, the rough rolling includes at least two stages of descaling before rough rolling, the last stage of descaling before rough rolling has 5 to 7 passes, the descaling pressure before rough rolling is 18 MPa to 20 MPa, and the sample feeding speed of the descaling before rough rolling is 0.8 m / s to 1.0 m / s.

[0020] Optionally, the method further includes:

[0021] Rough rolling the heated slab to obtain a rough rolled ingot;

[0022] determining the optimum rolling parameters for finishing rolling according to the weight content of silicon in the heated slab;

[0023] The rough rolling ingot is subjected to rough rolling and finish rolling according to the optimum rolling parameters for the finish rolling to obtain a rolled steel coil.

[0024] Optionally, the finishing rolling includes seven groups of finishing rolling, and an intermediate finishing rolling and descaling are included between the first group of finishing rolling and the second group of finishing rolling;

[0025] The method of determining the optimum rolling parameters for finishing rolling according to the silicon content of the heated slab comprises the following steps:

[0026] When the weight content of silicon in the heated slab is greater than 0.1%, the first four groups of rollers for the finishing rolling use first-class high-speed steel rollers, and the last three groups of rollers for the finishing rolling use infinitely cold hardened rollers, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa;

[0027] When the weight content of silicon in the heated slab is 0.08% to 0.10%, the first six groups of rollers for finishing rolling use second-class high-speed steel rollers, and the last group of rollers for finishing rolling use infinitely chilled rolls, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa;

[0028] When the weight content of silicon in the heated slab is less than 0.08%, the seven groups of rollers for the finish rolling respectively use third-type high-speed steel rollers, and the descaling pressure of the intermediate finish rolling descaling is 5MPa to 10MPa.

[0029] Optionally, the entrance descaling of the finishing rolling includes one-stage finishing descaling and two-stage finishing descaling, the descaling pressure of the one-stage finishing descaling is 30MPa-35MPa, and the descaling pressure of the two-stage finishing descaling is 18MPa-20MPa;

[0030] The inlet temperature of the finishing rolling is 1020°C to 1050°C, and the terminal temperature of the finishing rolling is 880°C to 900°C.

[0031] Optionally, the descaling pressure of the pre-descaling is 18 MPa to 20 MPa, and the sample feeding speed of the pre-descaling is 0.8 m / s to 1.0 m / s.

[0032] Optionally, the coiling temperature is 550° C. to 600° C.; and / or

[0033] The pickling temperature is 70° C. to 80° C., and the pickling time is 5s to 10s.

[0034] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0035] A method for reducing surface micro-defects of strip steel provided in an embodiment of the present application uses a heating process including a preheating section, a multi-stage gradient heating section and a soaking section. In these heating processes, the preheating section can cause the microstructure of the pretreated ingot to undergo a preliminary change, and the multi-stage gradient heating section can cause the microstructure of the pretreated ingot to undergo a further change. In addition, the multi-stage gradient heating section satisfies: the end point temperature of the previous stage heating section is less than the end point temperature of the next stage heating section, and the air-fuel ratio of the previous stage heating section is greater than the air-fuel ratio of the next stage heating section, so that the pretreated ingot is rapidly heated up during the previous stage heating section, so that the thickness of the oxide scale on the surface of the ingot is rapidly increased. long, and then the pretreated billet will reduce the heating rate in the latter heating section to slow down the thickness of the iron oxide scale formed on the surface of the billet in the heating section, so that the thickness of the iron oxide generated in the pretreated billet and the internal oxidation of the interface between the iron oxide scale and the steel matrix can be effectively controlled through the multi-stage gradient heating section when the microstructure of the pretreated billet undergoes phase change, so as to reduce the risk of surface micro defects in the subsequent rolled steel coil; in addition, the soaking section can not only promote the complete microstructure phase change of the pretreated billet, but also further reduce the thickness of the iron oxide generated in the pretreated billet, so as to further reduce the risk of surface micro defects in the rolled steel coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0038] Figure 1 A schematic flow chart of a method for reducing micro-defects on the surface of a steel strip provided in an embodiment of the present application;

[0039] Figure 2 A detailed schematic diagram of a method for reducing micro-defects on the surface of a steel strip provided in an embodiment of the present application;

[0040] Figure 3 A comparison diagram of the steel skin and steel matrix cross-section of the coiled strip prepared in Example 1 and Comparative Example 1 of the present application;

[0041] Figure 4 The graphs are the comparison of the scale indentation of the coiled strip steel and the cross-sectional structure of the strip steel prepared in Example 1 and Comparative Example 1 of the present application;

[0042] Figure 5 This is a comparison chart of the microscopic morphology of the surface of the coiled strip prepared in Example 1 of the present application and Comparative Example 1. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0044] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0045] In this document, the terms including "comprising" and the like mean "including but not limited to". Relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; wherein A and B can be singular or plural. Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased on the market or prepared by existing methods.

[0046] It should be noted that, with respect to the prior art (1) described in the background technology, the inventors have found that high-pressure descaling requires the use of high-flow high-pressure water, which not only increases the amount of water required for strip preparation, but also causes a large temperature drop in the slab, thereby requiring an increase in the slab heating temperature or an increase in the main motor power of the rolling mill, which is not conducive to energy conservation in the strip preparation process and the need to reduce production costs.

[0047] With respect to the prior arts (2) to (5) described in the background art, the inventors have found that these prior arts have one or two of the following deficiencies: 1) Most preparation methods are mainly based on product development, and high surface quality hot-rolled products of different strength levels are prepared by controlling surface obvious defects such as surface oxide scale indentation defects and surface streak defects. However, these surface obvious defects are macroscopically visible and can be identified by a surface detection system. Then, high surface quality products are obtained by adjusting and optimizing the composition and process. No effective control and improvement measures are proposed for the micro defects on the surface of the strip. 2) Most preparation methods do not involve micro defects on the surface of the strip. However, micro defects on the surface of the strip cannot be identified on the hot rolling surface detection system and there are no obvious defects on the actual surface. Subsequent operation and processing will cause products with surface micro defects to be released to the user end, greatly increasing the risk of product quality objections.

[0048] Figure 1 A schematic flow chart of a method for reducing surface micro-defects of strip steel provided in an embodiment of the present application is exemplarily shown;

[0049] like Figure 1 As shown, the embodiment of the present application provides a method for reducing micro defects on the surface of a steel strip, the method comprising:

[0050] S1. The ingot is surface treated to obtain a pretreated ingot;

[0051] S2. The pretreated slab is heated to obtain a heated slab;

[0052] S3. The heated slab is cooled, and then the cooled heated slab is pre-scaled to remove the cast iron from the surface of the heated slab to obtain a rolled ingot;

[0053] S4. The rolled ingot is subjected to rough rolling and finish rolling to obtain a rolled steel coil; and

[0054] S5. The rolled steel coil is subjected to front-stage cooling, and then the rolled steel coil after the front-stage cooling is coiled and pickled to obtain a coiled strip;

[0055] Wherein, the heating includes a preheating section, a multi-stage gradient heating section and a soaking section;

[0056] The multi-stage gradient heating section satisfies: the end temperature of the previous stage heating section is less than the end temperature of the next stage heating section, and the air-fuel ratio of the previous stage heating section is greater than the air-fuel ratio of the next stage heating section.

[0057] It should be noted that the surface treatment can be achieved by flame cleaning in combination with grinding. The flame cleaning can eliminate shallow surface defects ≤3 mm on the surface of the ingot, and the grinding can improve the surface quality of the ingot after flame cleaning and avoid defects such as grooves and nodules that exist locally on the surface of the ingot during the flame cleaning process.

[0058] In some optional embodiments, the multi-stage gradient heating section includes a primary heating section and a secondary heating section; the terminal temperature of the primary heating section is 1050°C to 1100°C, the time of the primary heating section is 40min to 60min, and the air-fuel ratio of the primary heating section is 1.1 to 1.2;

[0059] The end temperature of the secondary heating section is 1250°C to 1290°C, the time of the secondary heating section is 40min to 50min, and the air-fuel ratio of the secondary heating section is 1.00 to 1.05;

[0060] In these embodiments, the gradient heating section may include a primary heating section; and the terminal temperature of the primary heating section may be 1050°C to 1100°C, and the time of the primary heating section may be 40min to 60min, and the air-fuel ratio of the primary heating section may be 1.1 to 1.2, and a certain thickness of iron oxide may be quickly formed on the surface of the pretreated billet when the microstructure of the pretreated billet undergoes a phase change by means of primary heating, thereby hindering the diffusion of oxygen in the air into the matrix of the pretreated billet; in addition, the gradient heating section may include a secondary heating section, and the terminal temperature of the secondary heating section may be 1250°C to 1290°C, and the time of the secondary heating section may be 40min to 50min, and the air-fuel ratio of the secondary heating section may be 1.00 to 1.05, and when a certain thickness of iron oxide scale is formed on the surface of the pretreated billet during the primary heating process, the total iron oxide thickness on the surface of the pretreated billet and the oxidation condition inside the pretreated billet may be reduced, thereby reducing the risk of surface micro-defects in the subsequent rolled billet.

[0061] The terminal temperature of the primary heating section can be 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C.

[0062] The time of the primary heating stage can be 40 min, 45 min, 50 min, 55 min or 60 min.

[0063] The air-fuel ratio of the primary heating section can be 1.10, 1.15 or 1.20.

[0064] The endpoint temperature of the secondary heating section may be 1250°C, 1260°C, 1270°C, 1280°C or 1290°C.

[0065] The time of the secondary heating section can be 40 min, 41 min, 42 min, 43 min, 44 min, 45 min, 46 min, 47 min, 48 min, 49 min or 50 min.

[0066] The air-fuel ratio of the secondary heating section can be 1.00, 1.01, 1.02, 1.03, 1.04 or 1.05.

[0067] In some optional embodiments, the temperature of the preheating section is ≤400°C, and the time of the preheating section is 60 min to 70 min; and / or

[0068] The duration of the soaking section is 30 to 40 minutes, the air-fuel ratio of the soaking section is 0.95 to 1.00, and the terminal temperature of the soaking section is 1260° C. to 1290° C.;

[0069] In these embodiments, the temperature of the preheating section is ≤400°C, and the time of the preheating section can be 60min~70min, and the time of the soaking section can be 30min~40min, and the air-fuel ratio of the soaking section can be 0.95~1.00, and the terminal temperature of the soaking section can be 1260°C~1290°C. Through different heating processes, the thickness of the oxide scale on the surface of the pretreated ingot and the interface morphology between the matrix and the oxide scale can be effectively controlled to further reduce the risk of surface micro-defects in the rolled ingot.

[0070] The time of the preheating section can be 60 min, 61 min, 62 min, 63 min, 64 min, 65 min, 66 min, 67 min, 68 min, 69 min or 70 min.

[0071] The soaking period may last for 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min.

[0072] It should be noted that the thickness of the iron oxide scale on the surface of the ingot has the characteristics of first rapid growth and then slow growth during the heating stage, which shows that the iron oxide scale follows the parabolic law. The heating process including the preheating section, the multi-stage gradient heating section and the soaking section can reasonably control the thickness of the iron oxide scale on the surface of the ingot, and reduce the internal oxidation of the interface between the iron oxide scale and the steel matrix.

[0073] It should be noted that the preheating section is a non-heating section and does not input mixed coal gas flow. The heat of the preheating section comes from the gas waste heat of the flue gas recovery system of the multi-gradient heating section and the equalizing section.

[0074] It should be noted that the fuel gas used in the multi-stage gradient heating section and the soaking section is a mixture of blast furnace gas, coke oven gas, converter gas and natural gas in a certain proportion, and the combustion calorific value of the fuel gas can be 2300Kcal~2450Kcal.

[0075] In some optional embodiments, the rough rolling temperature is 1180°C to 1200°C, the final rolling temperature is 1040°C to 1060°C, the intermediate billet thickness at the outlet of the rough rolling is 35mm to 40mm, and the rough rolling includes performing rough rolling in 6 to 8 passes;

[0076] In these embodiments, the rough rolling entry temperature can be 1180°C to 1200°C, and the rough rolling final rolling temperature can be 1040°C to 1060°C, and the intermediate billet thickness at the outlet of the rough rolling can be 35mm to 40mm, and the rough rolling includes rough rolling in 6 to 8 passes, which can reduce the thickness of the iron oxide scale on the surface of the rolled ingot when the rough rolling is sufficient, so as to further reduce the risk of surface micro defects in the rolled steel coil.

[0077] The rolling temperature of the rough rolling may be 1180°C, 1185°C, 1190°C, 1195°C or 1200°C.

[0078] The final rolling temperature of the rough rolling may be 1040°C, 1045°C, 1050°C, 1055°C or 1060°C.

[0079] The thickness of the rough-rolled intermediate billet can be 35 mm, 36 mm, 37 mm, 38 mm, 39 mm or 40 mm.

[0080] In some optional embodiments, the rough rolling includes at least two stages of descaling before rough rolling, the last stage of the descaling before rough rolling has 5 to 7 passes, the descaling pressure of the descaling before rough rolling is 18 MPa to 20 MPa, and the sample feeding speed of the descaling before rough rolling is 0.8 m / s to 1.0 m / s;

[0081] In these embodiments, rough rolling may include descaling before rough rolling, and the number of descaling passes before rough rolling may be 5 to 7, and the descaling pressure before rough rolling may be 18 MPa to 20 MPa, and the sample feeding speed before rough rolling is 0.8 m / s to 1.0 m / s, which can effectively reduce the thickness of the iron oxide scale on the surface of the rolled ingot when the rough rolling is fully carried out, so as to further reduce the risk of surface micro-defects in the rolled steel coil.

[0082] The number of descaling passes before roughing can be 5, 6 or 7.

[0083] The descaling pressure before rough rolling can be 18 MPa, 19 MPa or 20 MPa.

[0084] The sample feeding speed for descaling before rough rolling is 0.8m / s, 0.9m / s or 1.0m / s.

[0085] Figure 2 A detailed flow chart of a method for reducing surface micro-defects of strip steel provided in an embodiment of the present application is exemplarily shown;

[0086] In some optional embodiments, such as Figure 2 As shown, the method also includes:

[0087] S401. Rough rolling the heated slab to obtain a rough-rolled ingot;

[0088] S402. Determine the optimum rolling parameters for finishing rolling according to the weight content of silicon in the heated slab;

[0089] S403. According to the optimum rolling parameters for the finish rolling, the rough-rolled ingot is finish-rolled to obtain a rolled steel coil.

[0090] In these embodiments, the material of the rolling rollers required for the finishing process and the optimal rolling parameters such as the descaling pressure during the rolling process can be determined based on the weight content of silicon in the heated slab. Based on these optimal rolling parameters, the thickness of the iron oxide scale on the surface of the rolled ingot can be minimized while the finishing rolling is effectively carried out, and the good micromorphology of the interface between the heated slab matrix and the iron scale can be controlled to further reduce the risk of surface micro defects in the rolled steel coil.

[0091] In some optional embodiments, the finishing rolling includes seven groups of finishing rolling, and the first group of finishing rolling and the second group of finishing rolling include intermediate finishing rolling and descaling;

[0092] The method of determining the optimum rolling parameters for finishing rolling according to the silicon content of the heated slab comprises the following steps:

[0093] When the weight content of silicon in the heated slab is greater than 0.1%, the first four groups of rollers for the finishing rolling use first-class high-speed steel rollers, and the last three groups of rollers for the finishing rolling use infinitely cold hardened rollers, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa;

[0094] When the weight content of silicon in the heated slab is 0.08% to 0.10%, the first six groups of rollers for finishing rolling use second-class high-speed steel rollers, and the last group of rollers for finishing rolling use infinitely chilled rolls, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa;

[0095] When the weight content of silicon in the heated slab is less than 0.08%, the seven groups of rollers for the finish rolling use third-type high-speed steel rollers, and the descaling pressures of the intermediate finish rolling descaling are 5MPa to 10MPa.

[0096] In these embodiments, according to the change in the weight content of silicon in the heated slab, the roller materials for different finishing rolling in the finishing rolling are changed accordingly, so that the integrity of the oxide film on the roller can be ensured when the finishing rolling is fully carried out, and the peeling of the oxide film on the roller can be avoided to deteriorate the surface of the strip.

[0097] The descaling pressure of the intermediate finishing descaling can be 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa respectively.

[0098] It should be noted that the surface rating of the third type of high-speed steel roll can be level 1; the surface rating of the second type of high-speed steel roll can be level 1 or level 2; and the surface rating of the first type of high-speed steel rod can be above level 2. Generally speaking, the surface quality of the third type of high-speed steel roll is better than that of the second type of high-speed steel roll and the first type of high-speed steel roll. The surface quality of the specific high-speed steel rod needs to be adjusted according to the specific components of the heated slab to ensure the integrity of the oxide film on the roll and avoid the oxide film on the roll from peeling off and deteriorating the strip surface.

[0099] It should be noted that the first type of high-speed steel roller, the second type of high-speed steel roller and the third type of high-speed steel roller all have good wear resistance and can effectively ensure the integrity of the oxide film; generally, the first type of high-speed steel roller, the second type of high-speed steel roller and the third type of high-speed steel roller can use the high-speed steel roller produced by Xingtai Rolling Mill or the high-speed steel roller produced by Mitsubishi Heavy Industries.

[0100] It should be noted that the infinitely cold-hardened roll has good hardness and accident resistance, which can ensure that the rolled plate and steel coil have good surface quality. The infinitely cold-hardened roll can use the infinitely cold-hardened roll produced by Shaanxi Rolling Plant or Taiyuan Heavy Machinery Plant.

[0101] It should be noted that during the intermediate descaling process of the seven groups of finishing rolling, the seven groups of finishing rolling need to be in the rolling state at the same time. When the seven groups of finishing rolling are in the rolling state at the same time, the cooling water of the rolls in the frames of the seven groups of finishing rolling needs to be turned on all the time. The continuously turned-on cooling water can not only reduce the temperature of the rolls to the maximum extent, thereby improving the integrity of the oxide film on the surface of the rolls, but also is beneficial to control the roll oxide scale defects on the surface of the rolled ingot in the finishing rolling.

[0102] In some optional embodiments, the entrance descaling of the finishing rolling includes one-stage finishing descaling and two-stage finishing descaling, the descaling pressure of the one-stage finishing descaling is 30MPa to 35MPa, and the descaling pressure of the two-stage finishing descaling is 18MPa to 20MPa;

[0103] The inlet temperature of the finishing rolling is 1020°C to 1050°C, and the terminal temperature of the finishing rolling is 880°C to 900°C;

[0104] In these embodiments, the entrance section of the finishing rolling may include a first-stage finishing rolling descaling and a second-stage finishing rolling descaling, and the descaling pressure of the first-stage finishing rolling descaling may be 30MPa~35MPa, and the descaling pressure of the second-stage finishing rolling descaling may be 18MPa~20MPa, and the first-stage finishing rolling descaling and the second-stage finishing rolling descaling can be effectively removed The iron oxide scale on the surface of the rolled ingot entering the finishing rolling stage can be removed by effectively removing the iron oxide scale on the surface of the rolled ingot entering the finishing rolling stage, so as to reduce the risk of surface micro-defects in the rolled steel coil obtained by subsequent finishing rolling; in addition, the entrance temperature of the finishing rolling can be 1020℃~1050℃, and the terminal temperature of the finishing rolling can be 880℃~900℃, which can reduce the risk of surface micro-defects in the rolled steel coil obtained by subsequent finishing rolling when the finishing rolling is fully carried out.

[0105] The descaling pressure of the one-stage finishing descaling can be 30 MPa, 31 MPa, 32 MPa, 33 MPa, 34 MPa or 35 MPa.

[0106] The descaling pressure of the two-stage finishing descaling can be 18 MPa, 19 MPa or 20 MPa.

[0107] The inlet temperature of the finish rolling may be 1020°C, 1025°C, 1030°C, 1035°C, 1040°C, 1045°C or 1050°C.

[0108] The end point temperature of the finish rolling may be 880°C, 885°C, 890°C, 895°C or 900°C.

[0109] It should be noted that the first-stage finishing descaling and the second-stage finishing descaling can each use one header descaling for descaling treatment.

[0110] In some optional embodiments, the descaling pressure of the pre-descaling is 18 MPa to 20 MPa, and the sample feeding speed of the pre-descaling is 0.8 m / s to 1.0 m / s;

[0111] In these embodiments, the descaling pressure of the pre-descaling can be 18MPa~20MPa, and the sample feeding speed of the pre-descaling can be 0.8m / s~1.0m / s. The iron oxide scale on the surface of the cooled heated slab can be removed by pre-descaling, which is convenient for the descaling operations in the subsequent rough rolling and finishing rolling stages.

[0112] The descaling pressure of the pre-descaling may be 18 MPa, 19 MPa or 20 MPa.

[0113] The sample feeding speed for the pre-descaling can be 0.8 m / s, 0.9 m / s or 1.0 m / s.

[0114] In some optional embodiments, the coiling temperature is 550° C. to 600° C.; and / or

[0115] The pickling temperature is 70°C to 80°C, and the pickling time is 5s to 10s;

[0116] In these embodiments, the coiling temperature can be 550°C to 600°C, which can reduce the unevenness and internal oxidation of the interface between the iron oxide scale on the surface of the rolled steel coil and the steel matrix when the rolled steel coil is converted into a steel coil; in addition, the pickling temperature can be 70°C to 80°C, and the pickling time can be 5s to 10s, so that the iron oxide scale on the surface of the steel coil can be removed by pickling.

[0117] The coiling temperature may be 550°C, 560°C, 570°C, 580°C, 590°C or 600°C.

[0118] The temperature of the pickling may be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C.

[0119] The pickling time can be 5s, 6s, 7s, 8s, 9s or 10s.

[0120] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples that do not specify specific conditions are usually measured according to industry standards; if there are no corresponding industry standards, they are carried out according to common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0121] Example 1

[0122] like Figure 1 and Figure 2 As shown, a method for reducing micro defects on the surface of a strip steel comprises:

[0123] S1. The ingot is surface treated to obtain a pretreated ingot;

[0124] S2. The pretreated slab is heated to obtain a heated slab;

[0125] S3. The heated slab is cooled, and then the cooled heated slab is pre-scaled to remove the cast iron from the surface of the heated slab to obtain a rolled ingot;

[0126] S401. Rough rolling the heated slab to obtain a rough-rolled ingot;

[0127] S402. Determine the optimum rolling parameters for finishing rolling according to the weight content of silicon in the heated slab;

[0128] S403. According to the optimum rolling parameters for finishing rolling, the rough-rolled ingot is subjected to rough rolling and finishing rolling to obtain a rolled steel coil; and

[0129] S5. The rolled steel coil is subjected to front cooling, and then the rolled steel coil after the front cooling is coiled, cooled and pickled after coiling to obtain a coiled steel coil;

[0130] The heating includes a preheating section, a multi-stage gradient heating section and a soaking section;

[0131] The multi-stage gradient heating section includes a primary heating section and a secondary heating section; the end temperature of the primary heating section is 1050°C, the time of the primary heating section is 40 minutes, and the air-fuel ratio of the primary heating section is 1.2;

[0132] The end temperature of the secondary heating section is 1250°C, the time of the secondary heating section is 40 minutes, and the air-fuel ratio of the secondary heating section is 1.00.

[0133] The temperature of the preheating section is 100°C and the preheating time is 60 minutes.

[0134] The time of the soaking section is 40 minutes, the air-fuel ratio of the soaking section is 0.95, and the terminal temperature of the soaking section is 1250°C.

[0135] The combustion calorific value of the gas used in the multi-stage gradient heating section and the soaking section is 2300Kcal.

[0136] The entry temperature of the rough rolling is 1180°C, the final rolling temperature of the rough rolling is 1050°C, the thickness of the intermediate billet at the outlet of the rough rolling is 35mm, and the rough rolling includes 6 rolling passes.

[0137] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 5 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 19MPa, and the descaling pressure before rough rolling of the R2 stand is 18MPa.

[0138] The finishing rolling includes seven groups of finishing rolling, and the first group of finishing rolling and the second group of finishing rolling include intermediate finishing rolling and descaling;

[0139] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0140] When the weight content of silicon in the heated slab is 0.15%, the first four groups of finishing rolling rolls use the first type of high-speed steel rolls, and the last three groups of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing rolling is 5 MPa.

[0141] Among them, the surface rating of the first type of high-speed steel roller is level 2.

[0142] The entrance section of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the first-stage finishing rolling descaling is 30MPa, and the descaling pressure of the second-stage finishing rolling descaling is 18MPa.

[0143] The inlet temperature of the finishing rolling is 1020°C, and the terminal temperature of the finishing rolling is 880°C.

[0144] The descaling pressure of pre-descaling is 18MPa, and the sample feeding speed of pre-descaling is 0.8m / s.

[0145] The coiling temperature is 600°C; the cooling rate after coiling is 8°C / h.

[0146] The cooling length of the front cooling section is 20m.

[0147] Example 2

[0148] Based on the contents disclosed in Example 1, the following modifications are further made:

[0149] The end temperature of the first stage heating section is 1055°C, the time of the first stage heating section is 45 minutes, and the air-fuel ratio of the first stage heating section is 1.2;

[0150] The end temperature of the secondary heating section is 1260°C, the time of the secondary heating section is 45 minutes, and the air-fuel ratio of the secondary heating section is 1.02.

[0151] The temperature of the preheating section is 200°C and the time of the preheating section is 65 minutes;

[0152] The time of the soaking section is 40 minutes, the air-fuel ratio of the soaking section is 1.00, and the terminal temperature of the soaking section is 1260°C.

[0153] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2320Kcal.

[0154] The rolling temperature of the rough rolling is 1185°C, the final rolling temperature of the rough rolling is 1055°C, the thickness of the intermediate billet of the rough rolling is 36mm, and the rolling passes of the rough rolling are 6 times.

[0155] The rough rolling includes two stages of descaling before rough rolling, R1 stand and R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling for R1 stand and 5 descaling before rough rolling for R2 stand. The descaling pressure before rough rolling for R1 stand is 18MPa, and the descaling pressure before rough rolling for R2 stand is 19MPa.

[0156] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0157] When the weight content of silicon in the heated slab is 0.20%, the first four groups of finishing rolling rolls use the first type of high-speed steel rolls, and the last three groups of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing descaling is 6MPa.

[0158] Among them, the surface rating of the first type of high-speed steel roller is level 2.

[0159] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 32MPa, and the descaling pressure of the two-stage finishing rolling descaling is 19MPa.

[0160] The inlet temperature of the finishing rolling is 1040°C, and the terminal temperature of the finishing rolling is 885°C.

[0161] The descaling pressure of pre-descaling is 18MPa, and the sample feeding speed of pre-descaling is 0.8m / s.

[0162] The coiling temperature is 600°C; the cooling rate after coiling is 8.5°C / h.

[0163] The cooling length of the front cooling section is 21m.

[0164] Example 3

[0165] Based on the contents disclosed in Example 1, the following modifications are further made:

[0166] The end temperature of the first stage heating section is 1070°C, the time of the first stage heating section is 40 minutes, and the air-fuel ratio of the first stage heating section is 1.15;

[0167] The end temperature of the secondary heating section is 1250°C, the time of the secondary heating section is 48 minutes, and the air-fuel ratio of the secondary heating section is 1.00.

[0168] The temperature of the preheating section is 150°C and the preheating time is 68 minutes;

[0169] The time of the soaking section is 40 minutes, the air-fuel ratio of the soaking section is 1.00, and the terminal temperature of the soaking section is 1260°C.

[0170] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2350Kcal.

[0171] The rough rolling temperature is 1190° C., the rough rolling final temperature is 1045° C., the intermediate billet thickness is 38 mm, and the rough rolling includes six rolling passes.

[0172] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 5 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 18MPa, and the descaling pressure before rough rolling of the R2 stand is 18MPa.

[0173] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0174] When the weight content of silicon in the heated slab is 0.25%, the first four groups of finishing rolling rolls use the first type of high-speed steel rolls, and the last three groups of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing rolling is 10 MPa.

[0175] Among them, the surface rating of the first type of high-speed steel roller is level 3.

[0176] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 30MPa, and the descaling pressure of the two-stage finishing rolling descaling is 18MPa.

[0177] The inlet temperature of the finishing rolling was 1030°C, and the terminal temperature of the finishing rolling was 890°C.

[0178] The descaling pressure of pre-descaling is 19 MPa, and the sample feeding speed of pre-descaling is 0.9 m / s.

[0179] The coiling temperature was 595°C; the cooling rate after coiling was 8.0°C / h.

[0180] The cooling length of the front cooling section is 22m.

[0181] Example 4

[0182] Based on the contents disclosed in Example 1, the following modifications are further made:

[0183] The end temperature of the first stage heating section is 1080°C, the time of the first stage heating section is 50 minutes, and the air-fuel ratio of the first stage heating section is 1.12;

[0184] The end temperature of the secondary heating section is 1270°C, the time of the secondary heating section is 50 minutes, and the air-fuel ratio of the secondary heating section is 1.05.

[0185] The temperature of the preheating section is 180°C and the preheating time is 68 minutes;

[0186] The time of the soaking section is 30 minutes, the air-fuel ratio of the soaking section is 0.98, and the terminal temperature of the soaking section is 1270°C.

[0187] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2380Kcal.

[0188] The rough rolling temperature is 1200° C., the rough rolling final temperature is 1050° C., the intermediate billet thickness is 35 mm, and the rough rolling includes 8 rolling passes.

[0189] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 7 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 20MPa, and the descaling pressure before rough rolling of the R2 stand is 19MPa.

[0190] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0191] When the weight content of silicon in the heated slab is 0.095%, the rollers of the first six stands for finishing rolling use the second type of high-speed steel rollers, and the rollers of the last stand for finishing rolling use infinitely cold hardened rollers, and the descaling pressure of the intermediate finishing rolling descaling is 7MPa;

[0192] Among them, the surface rating of the second type high speed steel roller is level 2.

[0193] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 35MPa, and the descaling pressure of the two-stage finishing rolling descaling is 20MPa.

[0194] The inlet temperature of the finishing rolling is 1020°C, and the terminal temperature of the finishing rolling is 880°C.

[0195] The descaling pressure of pre-descaling is 18MPa, and the sample feeding speed of pre-descaling is 0.8m / s.

[0196] The coiling temperature was 590°C; the cooling rate after coiling was 9.0°C / h.

[0197] The cooling length of the front cooling section is 23m.

[0198] Example 5

[0199] Based on the contents disclosed in Example 1, the following modifications are further made:

[0200] The end temperature of the first stage heating section is 1080°C, the time of the first stage heating section is 50 minutes, and the air-fuel ratio of the first stage heating section is 1.15;

[0201] The end temperature of the secondary heating section is 1280°C, the time of the secondary heating section is 40 minutes, and the air-fuel ratio of the secondary heating section is 1.03.

[0202] The temperature of the preheating section is 250°C and the preheating time is 62 minutes;

[0203] The time of the soaking section is 35 minutes, the air-fuel ratio of the soaking section is 1.00, and the terminal temperature of the soaking section is 1290°C.

[0204] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2400Kcal.

[0205] The rough rolling temperature is 1195° C., the rough rolling final temperature is 1040° C., the intermediate billet thickness is 40 mm, and the rough rolling includes 8 rolling passes.

[0206] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 7 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 20MPa, and the descaling pressure before rough rolling of the R2 stand is 19MPa.

[0207] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0208] When the weight content of silicon in the heated slab is 0.082%, the first six groups of finishing rolling rolls use the second type of high-speed steel rolls, and the last group of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing rolling is 10 MPa.

[0209] Among them, the surface rating of the second type high speed steel roller is level 1.

[0210] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 33MPa, and the descaling pressure of the two-stage finishing rolling descaling is 19MPa.

[0211] The inlet temperature of the finishing rolling is 1040°C, and the terminal temperature of the finishing rolling is 900°C.

[0212] The descaling pressure of pre-descaling is 19 MPa, and the sample feeding speed of pre-descaling is 1.0 m / s.

[0213] The coiling temperature was 585°C; the cooling rate after coiling was 9.5°C / h.

[0214] The cooling length of the front cooling section is 25m.

[0215] Example 6

[0216] Based on the contents disclosed in Example 1, the following modifications are further made:

[0217] The end temperature of the first stage heating section is 1090°C, the time of the first stage heating section is 40 minutes, and the air-fuel ratio of the first stage heating section is 1.10;

[0218] The end temperature of the secondary heating section is 1290°C, the time of the secondary heating section is 42 minutes, and the air-fuel ratio of the secondary heating section is 1.04.

[0219] The temperature of the preheating section is 300°C and the time of the preheating section is 64 minutes;

[0220] The time of the soaking section is 30 minutes, the air-fuel ratio of the soaking section is 0.97, and the terminal temperature of the soaking section is 1290°C.

[0221] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2420Kcal.

[0222] The rough rolling temperature is 1190° C., the rough rolling final temperature is 1040° C., the intermediate billet thickness is 40 mm, and the rough rolling includes 8 rolling passes.

[0223] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 7 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 20MPa, and the descaling pressure before rough rolling of the R2 stand is 18.5MPa.

[0224] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0225] When the weight content of silicon in the heated slab is 0.04%, the rollers of the seven groups of finishing rolling use the third type of high-speed steel rollers, and the descaling pressure of the intermediate finishing rolling is 8MPa;

[0226] Among them, the surface rating of the third type high-speed steel roller is level 1.

[0227] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 34MPa, and the descaling pressure of the two-stage finishing rolling descaling is 18MPa.

[0228] The inlet temperature of the finishing rolling is 1025°C, and the terminal temperature of the finishing rolling is 890°C.

[0229] The descaling pressure of pre-descaling is 20MPa, and the sample feeding speed of pre-descaling is 0.9m / s.

[0230] The coiling temperature was 580°C; the cooling rate after coiling was 9.0°C / h.

[0231] The cooling length of the front cooling section is 30m.

[0232] Example 7

[0233] Based on the contents disclosed in Example 1, the following modifications are further made:

[0234] The end temperature of the first stage heating section is 1100°C, the time of the first stage heating section is 45 minutes, and the air-fuel ratio of the first stage heating section is 1.13;

[0235] The terminal temperature of the secondary heating section is 1260°C, the time of the secondary heating section is 46 minutes, and the air-fuel ratio of the secondary heating section is 1.05.

[0236] The temperature of the preheating section is 260°C and the preheating time is 64 minutes;

[0237] The time of the soaking section is 40 minutes, the air-fuel ratio of the soaking section is 0.96, and the terminal temperature of the soaking section is 1270°C.

[0238] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2450Kcal.

[0239] The rough rolling temperature is 1200° C., the rough rolling final temperature is 1040° C., the intermediate billet thickness is 35 mm, and the rough rolling includes 8 rolling passes.

[0240] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 7 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 19MPa, and the descaling pressure before rough rolling of the R2 stand is 19MPa.

[0241] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0242] When the weight content of silicon in the heated slab is 0.35%, the first four groups of finishing rolling rolls use the first type of high-speed steel rolls, and the last three groups of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing rolling is 9 MPa.

[0243] Among them, the surface rating of the first type high speed steel roller is level 3.

[0244] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 32MPa, and the descaling pressure of the two-stage finishing rolling descaling is 20MPa.

[0245] The inlet temperature of the finishing rolling is 1035°C, and the terminal temperature of the finishing rolling is 895°C.

[0246] The descaling pressure of pre-descaling is 19MPa, and the sample feeding speed of pre-descaling is 0.95m / s.

[0247] The coiling temperature was 575°C; the cooling rate after coiling was 10.0°C / h.

[0248] The cooling length of the front cooling section is 32m.

[0249] Example 8

[0250] Based on the contents disclosed in Example 1, the following modifications are further made:

[0251] The end temperature of the first stage heating section is 1060°C, the time of the first stage heating section is 55 minutes, and the air-fuel ratio of the first stage heating section is 1.18;

[0252] The end temperature of the secondary heating section is 1270°C, the time of the secondary heating section is 45 minutes, and the air-fuel ratio of the secondary heating section is 1.00.

[0253] The temperature of the preheating section is 400°C and the time of the preheating section is 69 minutes;

[0254] The time of the soaking section is 40 minutes, the air-fuel ratio of the soaking section is 0.99, and the terminal temperature of the soaking section is 1280°C.

[0255] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2360Kcal.

[0256] The rough rolling temperature is 1188° C., the rough rolling final temperature is 1055° C., the intermediate billet thickness is 38 mm, and the rough rolling includes 8 rolling passes.

[0257] The rough rolling includes two stages of descaling before rough rolling for R1 stand and R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling for R1 stand and 7 descaling before rough rolling for R2 stand. The descaling pressure before rough rolling for R1 stand is 18MPa, and the descaling pressure before rough rolling for R2 stand is 20MPa.

[0258] Finishing rolling includes seven groups of finishing rolling;

[0259] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0260] When the weight content of silicon in the heated slab is 0.095%, the first six groups of finishing rolling rolls use the second type of high-speed steel rolls, and the last group of finishing rolling rolls use infinite chilled rolls. The descaling pressure of the intermediate finishing rolling is 6MPa.

[0261] Among them, the surface rating of the second type high speed steel roller is level 2.

[0262] The descaling at the entrance of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the one-stage finishing rolling descaling is 30MPa, and the descaling pressure of the two-stage finishing rolling descaling is 20MPa.

[0263] The inlet temperature of the finishing rolling is 1040°C, and the terminal temperature of the finishing rolling is 880°C.

[0264] The descaling pressure of pre-descaling is 18MPa, and the sample feeding speed of pre-descaling is 0.85m / s.

[0265] The coiling temperature was 570°C; the cooling rate after coiling was 8.8°C / h.

[0266] The cooling length of the front cooling section is 34m.

[0267] Example 9

[0268] Based on the contents disclosed in Example 1, the following modifications are further made:

[0269] The end temperature of the first stage heating section is 1060°C, the time of the first stage heating section is 60 minutes, and the air-fuel ratio of the first stage heating section is 1.16;

[0270] The end temperature of the secondary heating section is 1280°C, the time of the secondary heating section is 50 minutes, and the air-fuel ratio of the secondary heating section is 1.02.

[0271] The temperature of the preheating section is 380°C and the time of the preheating section is 69 minutes;

[0272] The time of the soaking section is 30 minutes, the air-fuel ratio of the soaking section is 1.0, and the terminal temperature of the soaking section is 1270°C.

[0273] The combustion calorific value of the gas used in the multi-stage gradient heating section and the soaking section is 2300Kcal.

[0274] The rough rolling temperature is 1200° C., the rough rolling final temperature is 1040° C., the intermediate billet thickness is 36 mm, and the rough rolling includes six rolling passes.

[0275] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 5 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 20MPa, and the descaling pressure before rough rolling of the R2 stand is 19.6MPa.

[0276] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0277] When the weight content of silicon in the heated slab is 0.07%, the rollers of the seven groups of finishing rolling use the third type of high-speed steel rollers, and the descaling pressure of the intermediate finishing rolling is 10MPa;

[0278] Among them, the surface rating of the third type high-speed steel roller is level 1.

[0279] The entrance section of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the first-stage finishing rolling descaling is 32MPa, and the descaling pressure of the second-stage finishing rolling descaling is 19MPa.

[0280] The inlet temperature of the finishing rolling was 1030°C, and the terminal temperature of the finishing rolling was 900°C.

[0281] The descaling pressure of pre-descaling is 19 MPa, and the sample feeding speed of pre-descaling is 0.90 m / s.

[0282] The coiling temperature was 560°C; the cooling rate after coiling was 9.6°C / h.

[0283] The cooling length of the front cooling section is 35m.

[0284] Example 10

[0285] Based on the contents disclosed in Example 1, the following modifications are further made:

[0286] The end temperature of the first stage heating section is 1090°C, the time of the first stage heating section is 50 minutes, and the air-fuel ratio of the first stage heating section is 1.10;

[0287] The end temperature of the secondary heating section is 1290°C, the time of the secondary heating section is 45 minutes, and the air-fuel ratio of the secondary heating section is 1.05.

[0288] The temperature of the preheating section is 270°C and the preheating time is 64 minutes;

[0289] The time of the soaking section is 30 minutes, the air-fuel ratio of the soaking section is 1.0, and the terminal temperature of the soaking section is 1290°C.

[0290] The combustion calorific value of the fuel gas used in the multi-stage gradient heating section and the soaking section is 2410Kcal.

[0291] The rough rolling temperature is 1192° C., the rough rolling final temperature is 1050° C., the intermediate billet thickness is 36 mm, and the rough rolling includes 6 rolling passes.

[0292] The rough rolling includes two stages of descaling before rough rolling of the R1 stand and the R2 stand. The descaling passes before rough rolling are distributed as follows: 1 descaling before rough rolling of the R1 stand and 5 descaling before rough rolling of the R2 stand. The descaling pressure before rough rolling of the R1 stand is 19MPa, and the descaling pressure before rough rolling of the R2 stand is 20MPa.

[0293] According to the silicon content of the heated slab, the optimum rolling parameters for finishing rolling are determined, including the steps of:

[0294] When the weight content of silicon in the heated slab is less than 0.01%, the rollers of the seven groups of finishing rolling use the third type of high-speed steel rollers, and the descaling pressure of the intermediate finishing rolling is 9MPa;

[0295] Among them, the surface rating of the third type high-speed steel roller is level 1.

[0296] The entrance section of finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling. The descaling pressure of the first-stage finishing rolling descaling is 35MPa, and the descaling pressure of the second-stage finishing rolling descaling is 20MPa.

[0297] The inlet temperature of the finishing rolling is 1035°C, and the terminal temperature of the finishing rolling is 890°C.

[0298] The descaling pressure of the pre-descaling is 20 MPa, the sample feeding speed of the pre-descaling is 0.9 m / s, the coiling temperature is 550°C; and the cooling rate after coiling is 10.0°C / h.

[0299] The cooling length of the front cooling section is 40m.

[0300] Comparative Example 1

[0301] Based on the contents disclosed in Example 1, the following modifications are further made:

[0302] The heating furnace directly uses low calorific value gas to heat the slab, and the combustion calorific value of the gas used is 2100Kcal.

[0303] Comparative Example 2

[0304] Based on the contents disclosed in Example 1, the following modifications are further made:

[0305] The terminal temperature of the first stage heating section is 1000°C, the time of the first stage heating section is 30 minutes, and the air-fuel ratio of the first stage heating section is 1.0.

[0306] Comparative Example 3

[0307] Based on the contents disclosed in Example 1, the following modifications are further made:

[0308] The terminal temperature of the first stage heating section is 1200°C, the time of the first stage heating section is 70 minutes, and the air-fuel ratio of the first stage heating section is 1.5.

[0309] Comparative Example 4

[0310] Based on the contents disclosed in Example 1, the following modifications are further made:

[0311] The end temperature of the secondary heating section is 1200°C, the time of the secondary heating section is 30 minutes, and the air-fuel ratio of the secondary heating section is 0.90.

[0312] Comparative Example 5

[0313] Based on the contents disclosed in Example 1, the following modifications are further made:

[0314] The end temperature of the secondary heating section is 1350°C, the time of the secondary heating section is 70 minutes, and the air-fuel ratio of the secondary heating section is 1.20.

[0315] Comparative Example 6

[0316] Based on the contents disclosed in Example 1, the following modifications are further made:

[0317] The descaling pressure of the R1 stand before rough rolling is 15MPa, and the descaling pressure of the R2 stand before rough rolling is 15MPa.

[0318] The descaling pressure of the first-stage finishing rolling descaling is 20MPa, and the descaling pressure of the second-stage finishing rolling descaling is 15MPa.

[0319] Comparative Example 7

[0320] Based on the contents disclosed in Example 1, the following modifications are further made:

[0321] The descaling pressure of the R1 stand before rough rolling is 25MPa, and the descaling pressure of the R2 stand before rough rolling is 25MPa.

[0322] The descaling pressure of the first-stage finishing rolling descaling is 40MPa, and the descaling pressure of the second-stage finishing rolling descaling is 30MPa.

[0323] Comparative Example 8

[0324] Based on the contents disclosed in Example 1, the following modifications are further made:

[0325] The descaling pressure of pre-descaling is 15MPa, and the sample feeding speed of pre-descaling is 0.50m / s.

[0326] Comparative Example 9

[0327] Based on the contents disclosed in Example 1, the following modifications are further made:

[0328] The descaling pressure of pre-descaling is 30MPa, and the sample feeding speed of pre-descaling is 2.00m / s.

[0329] Related experiments and effect data:

[0330] The coiled strip steels prepared in Example 1 and Comparative Example 1 were compared and analyzed. The comparison between the steel skin and the steel matrix cross section is shown in FIG. Figure 3 As shown in the figure, the iron oxide scale is pressed into the strip and the cross-sectional structure is compared. Figure 4 As shown in the figure, the microscopic morphology of the strip surface after pickling is as follows Figure 5 shown.

[0331] The surface properties of the coiled strips obtained in each embodiment and comparative example were statistically analyzed, and the results are shown in Table 1.

[0332] Table 1 Surface property data of coiled strip obtained in each embodiment and comparative example

[0333]

[0334]

[0335] It can be seen from Table 1 that the embodiment of the present application provides a method for reducing surface micro-defects of strip steel. The method can reduce the thickness of the oxide scale on the surface of the coiled strip steel to less than 15 μm, and the unevenness of the interface between the scale and the substrate to 5 μm or less, and the strip steel has no surface defects. This shows that the method can reduce the risk of surface micro-defects in rolled steel coils.

[0336] In addition, an embodiment of the present application provides a method for reducing micro-defects on the surface of steel strip. The method is based on the existing hot rolling production line, starts from the formation mechanism of micro-defects in steel strip, and redesigns the key process parameters of each process such as heating, rough rolling, finishing rolling and coiling in the hot rolling process; in addition, the thickness of the iron oxide scale on the surface of the hot-rolled steel strip, the unevenness of the interface between the iron scale and the substrate, and the surface micromorphology are evaluated, and a set of hot rolling full-process strip surface micro-defect control processes are creatively formed to achieve stable manufacturing of hot-rolled products with high surface quality.

[0337] In addition, an embodiment of the present application provides a method for reducing surface micro-defects of strip steel. The method has strong versatility in controlling surface micro-defects of coiled strip steel, and the method has the advantages of flexibility, high efficiency and low cost, so it can be widely promoted and applied in hot rolling production lines.

[0338] In addition, an embodiment of the present application provides a method for reducing micro-defects on the surface of strip steel. This method can effectively control the hidden defects of the coiled strip steel obtained by hot rolling, and can provide users with products with higher surface quality and increase product added value.

[0339] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features applied for by the present application.

Claims

1. A method for reducing micro defects on the surface of a steel strip, characterized in that: The method comprises: Performing surface treatment on the ingot to obtain a pretreated ingot; heating the pretreated ingot to obtain a heated slab; Cooling the heated slab, and then pre-descaling the cooled heated slab to remove the furnace iron scale on the surface of the heated slab to obtain a rolled cast slab; performing rough rolling and finish rolling on the rolled ingot to obtain a rolled steel coil; and The rolled steel coil is subjected to front-stage cooling, and then the rolled steel coil after the front-stage cooling is coiled and pickled to obtain a coiled steel coil; Wherein, the heating includes a preheating section, a multi-stage gradient heating section and a soaking section; The multi-stage gradient heating section satisfies: the end temperature of the previous stage heating section is less than the end temperature of the next stage heating section, and the air-fuel ratio of the previous stage heating section is greater than the air-fuel ratio of the next stage heating section.

2. The method according to claim 1, characterized in that The multi-stage gradient heating section includes a primary heating section and a secondary heating section; the terminal temperature of the primary heating section is 1050°C to 1100°C, the time of the primary heating section is 40min to 60min, and the air-fuel ratio of the primary heating section is 1.1 to 1.2; The terminal temperature of the secondary heating section is 1250° C. to 1290° C., the time of the secondary heating section is 40 min to 50 min, and the air-fuel ratio of the secondary heating section is 1.00 to 1.

05.

3. The method according to claim 1, characterized in that: The temperature of the preheating section is ≤400°C, and the time of the preheating section is 60min to 70min; and / or The duration of the soaking section is 30 minutes to 40 minutes, the air-fuel ratio of the soaking section is 0.95 to 1.00, and the terminal temperature of the soaking section is 1260° C. to 1290° C.

4. The method according to claim 1, characterized in that: The rough rolling temperature is 1180°C to 1200°C, the final rolling temperature is 1040°C to 1060°C, the intermediate billet thickness at the outlet of the rough rolling is 35mm to 40mm, and the rough rolling includes 6 to 8 passes of rough rolling.

5. The method according to claim 4, characterized in that The rough rolling includes at least two stages of descaling before rough rolling, the last stage of the descaling before rough rolling has 5 to 7 passes, the descaling pressure of the descaling before rough rolling is 18 MPa to 20 MPa, and the sample feeding speed of the descaling before rough rolling is 0.8 m / s to 1.0 m / s.

6. The method according to claim 1, characterized in that The method further comprises: Rough rolling the heated slab to obtain a rough rolled ingot; determining the optimum rolling parameters for finishing rolling according to the weight content of silicon in the heated slab; The rough rolled ingot is subjected to finish rolling according to the optimum rolling parameters for the finish rolling to obtain a rolled steel coil.

7. The method according to claim 6, characterized in that The finishing rolling includes seven groups of finishing rolling, and the first group of finishing rolling and the second group of finishing rolling include intermediate finishing rolling and descaling; The method of determining the optimum rolling parameters for finishing rolling according to the silicon content of the heated slab comprises the following steps: When the weight content of silicon in the heated slab is greater than 0.1%, the first four groups of rollers for the finishing rolling use first-class high-speed steel rollers, and the last three groups of rollers for the finishing rolling use infinitely cold hardened rollers, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa; When the weight content of silicon in the heated slab is 0.08% to 0.10%, the first six groups of rollers for finishing rolling use second-class high-speed steel rollers, and the last group of rollers for finishing rolling use infinitely chilled rolls, and the descaling pressure of the intermediate finishing descaling is 5MPa to 10MPa; When the weight content of silicon in the heated slab is less than 0.08%, the seven groups of rollers for the finish rolling respectively use third-type high-speed steel rollers, and the descaling pressure of the intermediate finish rolling descaling is 5MPa to 10MPa.

8. The method according to claim 1 or 6, characterized in that: The descaling at the entrance of the finishing rolling includes one-stage finishing rolling descaling and two-stage finishing rolling descaling, the descaling pressure of the one-stage finishing rolling descaling is 30MPa-35MPa, and the descaling pressure of the two-stage finishing rolling descaling is 18MPa-20MPa; The inlet temperature of the finishing rolling is 1020°C to 1050°C, and the terminal temperature of the finishing rolling is 880°C to 900°C.

9. The method according to claim 1, characterized in that: The descaling pressure of the pre-descaling is 18MPa-20MPa, and the sample feeding speed of the pre-descaling is 0.8m / s-1.0m / s.

10. The method according to claim 1, characterized in that The coiling temperature is 550°C to 600°C; and / or The pickling temperature is 70° C. to 80° C., and the pickling time is 5s to 10s.

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