CN110026433B - Method for improving surface quality of P-containing high-strength IF steel continuous annealing plate - Google Patents
Method for improving surface quality of P-containing high-strength IF steel continuous annealing plate Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
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- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
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- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/004—Heating the product
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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Abstract
The invention discloses a method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate, which belongs to the technical field of steel rolling and comprises the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing, wherein the molten steel comprises the following components: c is less than or equal to 0.003 wt%, Si is less than or equal to 0.1 wt%, Cr is less than or equal to 0.1 wt%, Mn is less than or equal to 0.5 wt%, Al is less than or equal to 0.05 wt%, and P is less than or equal to 0.04-0.08 wt%, wherein the slab heating temperature is 1150-1200 ℃, the finish rolling inlet temperature is 980-1000 ℃, the continuous annealing dew point temperature is-40-30 ℃, and the soaking temperature is 780-800 ℃; the method provided by the invention can overcome the defects of hot rolled plate surface pockmarks and continuous annealing plate surface needle points in the preparation process of the P-containing high-strength IF steel continuous annealing plate, and can obviously improve the surface quality of the product without increasing the equipment cost.
Description
Technical Field
The invention relates to a method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate, belonging to the technical field of steel rolling.
Background
In order to meet the requirements of light weight, low energy consumption, low emission and safety performance of automobiles and improve the market competitiveness of automobile steel, research and development of thin-strip high-strength steel are vigorously developed. On one hand: high strength series steel grades are produced on continuous annealing and galvanizing lines which exhibit poor platability and furnace roller ridging problems. This is because the steel sheet contains a large amount of Si, Mn, Cr, Al, P, etcAlloying element whose surface is susceptible to SiO formation2MnO and Mn-Si composite oxides, which seriously deteriorate the surface state of the steel sheet. In the continuous annealing process, the Mn, Si, Cr, P and other alloys have strong affinity with oxygen and are oxidized preferentially to the matrix iron, so that an oxide film is formed on the surface of a matrix material, and the platability of a steel plate and the formation of furnace roller nodules are seriously influenced. On the other hand: the P-containing high-strength IF steel frequently suffers from hot rolling pockmark defects in the hot rolling production process, so that the surface of a product is difficult to meet the requirement of the surface of O5 plate, and the P-containing high-strength IF steel becomes a key for restricting the quality improvement of the product.
The needle point defect of the P-containing high-strength IF steel is essentially that furnace roller nodulation is easy to occur in the production of the steel, low-melting-point substances are formed to damage a furnace roller coating, and the nodulated substances grow up and are pressed into the surface of a steel plate along with the production of strip steel to form needle point-shaped fine defects. The pitting defects of the high-strength steel containing P mainly come from the fact that for the high-strength steel containing alloy elements, under the conditions of different oxygen partial pressures and temperatures, the reaction of oxygen and the alloy elements can be roughly divided into two cases of internal oxidation and external oxidation. When the oxygen diffusion in the steel is sufficient, the oxidation of the alloy element is faster than the diffusion speed of the alloy element to the surface, which shows that the oxidation interface of the alloy element is deep, and the internal oxidation mode is adopted. If the diffusion of oxygen in the steel is insufficient, the alloying elements diffuse towards the surface and oxidation proceeds mainly at the surface, which is an external oxidation regime. Obviously, in order to avoid the occurrence of the accretion of the furnace rolls, it is necessary to suppress the external oxidation of the alloying elements such as Si, Mn, P, etc. In the aspect of improving the process, at present, the commonly adopted methods mainly comprise three methods, namely, firstly, the dew point of the annealing atmosphere is increased to form internal oxidation so as to reduce the deterioration of the wettability caused by external oxidation on the surface of a substrate, but the internal and external oxidation process mechanisms of alloy components are different, and the investigation needs to be carried out by combining the conditions of a production line; secondly, a flash plating method is adopted, namely a layer of pure iron, copper and other alloys are plated on the surface of the base material; thirdly, adopting a pre-oxidation-reduction process, namely, carrying out pre-oxidation treatment to form iron oxides on the surface of the steel, then carrying out reduction treatment to form sponge iron, and covering the oxides of the alloys such as Mn, Si, Cr, P and the like below the sponge iron. Wherein, the second and third devices need to purchase new equipment.
Therefore, in order to solve the above problems, there is a need in the art to develop a method for significantly improving the surface quality of a P-containing high-strength IF steel continuously annealed sheet, which can overcome the defects of hot-rolled sheet surface pockmarks and continuous annealed sheet surface tips in the preparation process of the P-containing high-strength IF steel continuously annealed sheet, without increasing the equipment cost.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate, which can overcome the defects of hot-rolled plate surface pockmarks and continuous annealing plate surface needle points in the preparation process of the P-containing high-strength IF steel continuous annealing plate, and can significantly improve the surface quality of products without increasing the equipment cost.
A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: less than or equal to 0.003 wt% of C, less than or equal to 0.1 wt% of Si, less than or equal to 0.1 wt% of Cr, less than or equal to 0.5 wt% of Mn, less than or equal to 0.05 wt% of Al, and less than or equal to 0.04-0.08 wt% of P;
the slab heating temperature is 1150-1200 ℃, the finish rolling inlet temperature is 980-1000 ℃, the continuous annealing dew point temperature is-40 ℃ to-30 ℃, and the soaking temperature is 780-800 ℃.
As shown in figure 1, the defects of the needle point mainly occur on the P-containing high-strength IF steel, mainly occur on the lower surface, and are irregularly distributed on the whole plate surface. The macroscopic morphology is silver bright spots or gray dark spots, has slight hand feeling, and bulges appear after stamping. As shown in fig. 2, microscopic analysis and observation by an electron microscope shows that the defect is microscopically in a ring shape or a semicircular ring shape, and the peripheral ring is internally provided with a plurality of gully fluctuation shapes with the diameter of 200-300 μm, and presents a molten foreign matter shape; the visible defect positions have a large number of oxidation dots with the diameter of less than 10 mu m at high magnification. The precision cutting instrument was used to cut the defect to observe the cross-sectional features, and as shown in FIG. 3, it was found that the interface was uneven, the shallow surface layer was covered with a slag-like foreign matter having a diameter of about 20 μm without spreading. The abnormalities mainly include Co, Y, Ta, W, Cr, Si, Mn, and Al.
Analyzing causes of needle point defects: the production line equipment is checked aiming at the rare components such as Co, Y, Ta and the like of the slag-shaped foreign matter wrapped on the shallow surface layer of the defect, and the result shows that: the components of the furnace roller coating in the high-temperature area of the continuous annealing furnace are very close to the components of foreign matters. Further, Mn and Si are typical furnace roller accretion components. The direct causes of needle point defects are thus seen as: oxidizing alloy components, nodulation of a furnace roller and peeling of a furnace roller coating. Because of containing P high-strength IF steel, the addition of P element causes that the internal oxidation of Mn and Si is damaged under the existing process condition of a production line, and an external oxidation granular layer is easy to form on the surface of a steel plate.
Dew point is the saturation temperature corresponding to the partial pressure of water vapor in humid air and can be measured with a dew point meter or hygrometer. The higher the partial pressure of water vapor, the higher the dew point.
MexOy(s)+y*H2(g)＝x*Me(s)+y*H2O(g) (1)
The formula (1) is an equation of a chemical reaction between water vapor and an alloy element in an annealing furnace, and according to the equation, the partial pressure of water vapor is increased, which facilitates the chemical reaction toward the direction of forming an oxide.
Under the dew point condition, all the surfaces of the strip steel can form a selective oxidation film layer, but under the low dew point condition (-60 ℃), the thickness of the selective oxidation film layer is 30-40nm, and no internal oxidation occurs; under the condition of high dew point (+5 ℃), the thickness of external oxidation is 5nm, the thickness of internal oxidation is 1.0-1.2 μm, and the external oxidation is gradually changed into the internal oxidation along with the increase of the dew point.
According to the preparation method provided by the invention, the steel components are limited, the contents of Si, Mn, Cr, Al and P elements in the steel plate are controlled within the content range, the formation of SiO2, MnO and Mn-Si composite oxides on the surface of the steel plate can be obviously reduced on the premise of not influencing the performance of the steel, and the serious deterioration of the surface state of the steel plate caused by the alloy composite oxides is avoided. Meanwhile, because alloys such as Mn, Si, Cr, P and the like have strong affinity with oxygen, the alloys are oxidized preferentially to matrix iron in the continuous annealing process, a layer of oxide film is formed on the surface of a matrix material, and the platability of a steel plate and the formation of furnace roller nodules are seriously influenced, so that the damage can be avoided by adjusting the steel components.
According to the preparation method, the continuous annealing control temperature of the internal and external oxidation of the element P is controlled, and the dew point control temperature of a continuous annealing furnace is controlled to be-40 ℃ to-30 ℃; the soaking temperature of the continuous annealing furnace is controlled to be 780-800 ℃, so that oxide particles on the surface of the strip steel become fine and sparse, and the problem of furnace roller nodulation in the continuous annealing process is solved.
Hot rolling surface pitting problem and oxidation characteristic analysis: the oxidation characteristic curve of the high-strength IF steel is analyzed, and as shown in FIG. 4, the following results are found: the steel is rapidly oxidized for the first time at 880 ℃, and plays a certain role in protecting a sample after an oxide film is formed, so that the subsequent oxidation rate is obviously reduced, and the sample enters a slow oxidation stage; when the temperature is close to 980 ℃, the protective effect of the oxide film of the M3A22 sample is obviously reduced for some reason, and the oxidation rate of the oxide film is rapidly increased again; and in the high-temperature stage, the peak position of the oxidation weight gain rate is about 1210 ℃. As the P content of the steel grade is controlled in the temperature range of 0.04-0.08%, as shown in figure 5, the analysis by an electronic probe shows that the obvious P element enrichment condition exists on the surface of the hot rolled plate, and the P element content at the interface can locally reach 0.7 percent and is more than 10 times of the matrix content. The hot rolling surface quality of the steel is tracked on site, so that pockmark-shaped defects are easy to occur on the surface, as shown in figure 6, the defects are easy to form surface pit appearance in the pickling process, and iron oxide is remained in the pits locally, so that the problems of unclean pickling and the like are caused.
According to the preparation method, the oxidation characteristic and the element enrichment characteristic of the steel grade are combined, hot rolling control is mainly performed on billet heating and temperature control in the finish rolling process, surface enrichment of P element is reduced, iron sheet removal is facilitated, and defects caused by iron sheet pressing in the finish rolling process are prevented.
Further, a billet heating step, wherein the heating is carried out in a heating furnace.
Further, heating the steel billet for 170-180 min.
Further, the heating process comprises an auxiliary heating section, a heating section and a uniform heating section, wherein the time of the uniform heating section is 25-35 min.
And in the step of finish rolling, the finish rolling speed is more than or equal to 8 m/s.
And further, a finish rolling step, wherein the finish rolling adopts a multi-pass descaling process.
Further, the surface temperature of the descaling strip steel is less than 980 ℃.
Due to the characteristic of easy oxidation of the P-containing steel, the descaling temperature point in the finish rolling process is further controlled, the descaling temperature is controlled to be below the peak temperature point of the oxidation weight gain rate, the scale can be removed quickly, and the generation of hot rolled plate noise points is further prevented.
And further, a continuous annealing step, wherein the continuous annealing is carried out in a continuous annealing furnace.
Further, the method comprises the following steps: after continuous annealing, mixing the P-containing high-strength IF steel obtained by continuous annealing and ultra-low carbon IF steel for production discharge, and continuously producing no more than 5 coils of the P-containing high-strength IF steel; and 2-3 coils of the ultra-low carbon IF steel are arranged for transition in the production scheduling plan.
Compared with the prior art, the preparation method has the following advantages:
1) the preparation method reduces the surface enrichment of P element by improving the hot rolling process, and can effectively remove the iron sheet, thereby solving the problem of pockmarks of the hot rolled plate.
2) According to the preparation method, the steel component adjustment and the continuous annealing process are improved, so that the oxidation of alloy components and furnace roller nodulation are avoided, the furnace roller coating is prevented from peeling off, and the problem of the needle point of the continuous annealing plate is solved.
3) The preparation method is simple and easy to operate, and can obviously improve the surface quality of the product under the condition of not increasing the equipment cost.
Drawings
FIG. 1 is a macroscopic view of a needle point defect.
FIG. 2 is an observation picture of the microscopic topography of a needle point defect.
FIG. 3 is a microscopic cross-sectional view of a defect of a needle tip.
FIG. 4 is a graph of oxidation characteristics of high strength IF steel.
FIG. 5 is a diagram showing the enrichment of P element at the interface of a hot rolled plate.
FIG. 6 is a diagram showing the surface roughness of a hot-rolled sheet.
FIG. 7 is a graph showing the oxidation condition of the surface of a continuous annealing plate obtained by the method of the present invention.
FIG. 8 is a graph showing the oxidation of the surface of a continuous annealing plate obtained by a conventional method.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1
A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: 0.0030 wt% of C, 0.05 wt% of Si, 0.07 wt% of Cr, 0.4 wt% of Mn, and 0.05 wt% of P;
heating the plate blank in a heating furnace at 1190 ℃, wherein the heating process comprises an auxiliary heating section, a heating section and a soaking section, the heating time is 180min, and the soaking section time is 30 min; the inlet temperature of the finish rolling is 1000 ℃, the finish rolling speed is 9m/s, the finish rolling adopts a multi-pass descaling process, and the surface temperature of the descaling strip steel is 970 ℃; the continuous annealing is carried out in a continuous annealing furnace, the dew point temperature is-30 ℃, and the soaking temperature is 780 ℃.
Example 2
A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: 0.0022 wt% of C, 0.08 wt% of Si, 0.06 wt% of Cr, 0.3 wt% of Mn, and 0.07 wt% of P;
the slab heating is carried out in a heating furnace, the temperature is 1180 ℃, the heating process comprises an auxiliary heating section, a heating section and a uniform heating section, the heating time is 170min, and the uniform heating section time is 33 min; the inlet temperature of the finish rolling is 990 ℃, the finish rolling speed is 10m/s, the finish rolling adopts a multi-pass descaling process, and the surface temperature of the descaled strip steel is 965 ℃; the continuous annealing is carried out in a continuous annealing furnace, the dew point temperature is minus 40 ℃, and the soaking temperature is 790.
Example 3
A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: 0.0030 wt% of C, 0.1 wt% of Si, 0.1 wt% of Cr, 0.5 wt% of Mn, and 0.08 wt% of P;
the slab heating is carried out in a heating furnace at 1200 ℃, the heating process comprises an auxiliary heating section, a heating section and a soaking section, the heating time is 180min, and the soaking section time is 35 min; the inlet temperature of the finish rolling is 1005 ℃, the finish rolling speed is 14m/s, the finish rolling adopts a multi-pass descaling process, and the surface temperature of the descaling strip steel is 975 ℃; the continuous annealing is carried out in a continuous annealing furnace, the dew point temperature is-35 ℃, and the soaking temperature is 800 ℃.
Example 4
A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: 0.0030 wt% of C, 0.05 wt% of Si, 0.07 wt% of Cr, 0.4 wt% of Mn, and 0.05 wt% of P;
the slab heating is carried out in a heating furnace at the temperature of 1190 ℃, the heating process comprises an auxiliary heating section, a heating section and a uniform heating section, the heating time is 180min, and the uniform heating section time is 28 min; the inlet temperature of the finish rolling is 1000 ℃, the finish rolling speed is 9m/s, the finish rolling adopts a multi-pass descaling process, and the surface temperature of the descaling strip steel is 970 ℃; the continuous annealing is carried out in a continuous annealing furnace, the dew point temperature is-30 ℃, and the soaking temperature is 780 ℃.
The method further comprises the steps of: after continuous annealing, mixing the P-containing high-strength IF steel obtained by continuous annealing and ultra-low carbon IF steel for production discharge, and continuously producing 4 rolls of the P-containing high-strength IF steel; and 2 coils of the ultra-low carbon IF steel are arranged for transition in the production scheduling plan.
Experimental example 1
The examples 1 to 4 were used as experimental groups, and it was determined that the P-containing high-strength IF steel continuous-annealed sheets obtained in the examples 1 to 4 had no needle points on the surface and no pockmark defects, and had good quality, as shown in fig. 7; the prior art process is used for comparison, and the defects of needle points and pockmarks on the surface of the P-containing high-strength IF steel continuous annealing plate prepared by the prior art are measured, and the quality is poor, as shown in figure 8.
Claims (1)
1. A method for improving the surface quality of a P-containing high-strength IF steel continuous annealing plate is characterized by comprising the following steps: continuously casting molten steel after smelting to obtain a plate blank, heating the plate blank, carrying out rough rolling and finish rolling to obtain a hot rolled plate, carrying out acid pickling, cold rolling and continuous annealing on the hot rolled plate, and coiling the hot rolled plate into a finished product after the continuous annealing;
the molten steel comprises the following components: less than or equal to 0.003 wt% of C, less than or equal to 0.1 wt% of Si, less than or equal to 0.1 wt% of Cr, less than or equal to 0.5 wt% of Mn, P: 0.04-0.08 wt%;
the heating temperature of the plate blank is 1150-1200 ℃, the inlet temperature of the finish rolling is 980-1000 ℃, the finish rolling adopts a multi-pass descaling process, the descaling temperature is less than 980 ℃, the continuous annealing dew point temperature is-40 to-30 ℃, and the soaking temperature is 780 to 800 ℃;
a slab heating step, wherein the heating is carried out in a heating furnace; the heating time is 170-180 min;
the heating process comprises an auxiliary heating section, a heating section and a soaking section, wherein the soaking section is 25-35 min;
a finish rolling step, wherein the finish rolling speed is more than or equal to 8 m/s;
the continuous annealing is carried out in a continuous annealing furnace;
the method further comprises the steps of: after continuous annealing, mixing the P-containing high-strength IF steel obtained by continuous annealing and ultra-low carbon IF steel for production discharge, and continuously producing no more than 5 coils of the P-containing high-strength IF steel; in the scheduling plan, the ultra-low carbon IF steel is arranged in 2-3 coils for transition.
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| CN111636031A (en) * | 2020-06-03 | 2020-09-08 | 北京首钢股份有限公司 | Ultra-low carbon bake-hardening steel and production method thereof |
| CN112048671B (en) * | 2020-09-07 | 2021-10-01 | 北京首钢股份有限公司 | Continuous annealing cold-rolled carbon steel for stamping and preparation method thereof |
| CN113549839B (en) * | 2021-06-22 | 2022-06-21 | 首钢集团有限公司 | High-strength steel with good surface quality and production method thereof |
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