Method for eliminating short linear defects on the surface of cold-rolled sheet

Abstract

The application relates to a cold-rolled plate surface short linear defect elimination method, which comprises the following steps: obtaining a cold-rolled plate analysis sample; determining defect parameters of a defect area on the cold-rolled plate analysis sample; determining a defect abnormality source of the defect area according to the defect parameters; determining a defect cause of the defect area according to the defect abnormality source and the defect parameters; and optimizing a cold-rolled plate production strategy according to the defect cause. The cold-rolled plate surface short linear defect elimination method provided by the application can accurately and quickly lock the defect cause by combining defect macroscopic size characteristics and micro-area component analysis with process and equipment analysis, and the control countermeasures based on the cause are operable and can successfully eliminate the defects.

Description

Technical Field

[0001] This application relates to the field of surface quality analysis and control of steel materials, and in particular to a method for eliminating short linear defects on the surface of cold-rolled steel sheets. Background Technology

[0002] The automotive industry is a crucial pillar of my country's economic development. Steel still constitutes a significant proportion of the raw materials used in automobile manufacturing, with automotive body panels (commonly known as car exterior panels) being the most technically challenging and demanding in terms of quality. Compared to general stamped parts, body panels are characterized by thinner materials, more complex shapes, larger structural dimensions, and higher surface quality requirements. Body panels must not only meet functional structural requirements but also aesthetic requirements for surface decoration; even minor defects on the surface can cause diffuse reflection of light after painting, damaging the appearance. With the development of the automotive industry, the surface quality requirements for car exterior panels are becoming increasingly stringent, demanding "zero defects." The level of surface quality has a significant impact on market share and industry standing. However, the production process for automotive body panels is lengthy, and surface quality issues often exhibit complexity and systemic characteristics, posing a significant challenge to the consistent technical quality management of steel companies.

[0003] In the production of automotive outer panels, linear defects are a major factor causing downgrading. The sources of these defects are complex, hindering accurate identification and control, thus limiting the improvement of automotive outer panel steel quality. How to promptly detect surface defects in steel strips during production, analyze defect information to identify and address their causes, and eliminate these root causes accurately and promptly to control and improve the surface quality of automotive steel products has always been a goal pursued by steel companies. Summary of the Invention

[0004] In order to solve the above-mentioned technical problems, or at least partially solve the above-mentioned technical problems, this application provides a method for eliminating short linear defects on the surface of cold-rolled steel sheets.

[0005] In a first aspect, this application provides a method for eliminating short linear defects on the surface of cold-rolled steel sheets, the method comprising the steps of:

[0006] Obtain analytical samples of cold-rolled steel sheets;

[0007] Determine the defect parameters of the defect region on the cold-rolled steel analytical sample;

[0008] The source of defect anomaly in the defect region is determined based on the defect parameters;

[0009] The cause of the defect in the defect region is determined based on the source of the defect anomaly and the defect parameters.

[0010] Optimize cold-rolled sheet production strategies based on the causes of the defects.

[0011] Preferably, obtaining the cold-rolled steel sheet analytical sample includes the following steps:

[0012] Use a scribing pen to mark the defect areas on the cold-rolled sheet;

[0013] Cut a cold-rolled sheet sample containing the defective area of ​​the predetermined specification for analysis.

[0014] Preferably, determining the defect parameters of the defect region on the cold-rolled steel sheet analytical sample includes the following steps:

[0015] The defective region was observed using a scanning electron microscope;

[0016] The component of the scar tissue in the defect area was analyzed using an energy dispersive spectroscopy (EDS) instrument.

[0017] The length and width of the defect at the location of the scar were measured under a scanning electron microscope;

[0018] Calculate the aspect ratio of the defect.

[0019] Preferably, determining the source of defect anomalies in the defect region based on the defect parameters includes the following steps:

[0020] Obtain the working layer material of the rolls during the hot-rolling to cold-rolling process;

[0021] Obtain the component analysis results of the defect region in the defect parameters;

[0022] The component analysis results are compared with the working layer material to determine the source of the defect anomaly in the defect area. Preferably, determining the cause of the defect in the defect area based on the source of the defect anomaly and the defect parameters includes the following steps:

[0023] Obtain the rolling compression ratio of hot-rolled plate during hot rolling and cold-rolled plate during cold rolling;

[0024] Obtain the aspect ratio of the defect region in the defect parameters;

[0025] The aspect ratio of the defect is compared with the rolling compression ratio to determine the cause of the defect in the defect region.

[0026] Preferably, the step of optimizing the cold-rolled sheet production strategy based on the cause of the defect includes the following steps:

[0027] It adopts a full-frame high-speed steel roll and 6 rolls of transition material heat-pressing rolls;

[0028] Adjust the temperature of the ironing rollers;

[0029] Adjust the speed of the ironing rollers;

[0030] Adjust the load on the finishing mill stand;

[0031] Adjust the roller temperature.

[0032] Preferably, adjusting the temperature of the ironing roller includes the following steps:

[0033] Adjust the final rolling temperature of the hot rolling material to below 900℃.

[0034] Preferably, adjusting the speed of the ironing roller includes the following steps:

[0035] Adjust the steel output interval of the first 3 rolls of hot rolling to 180 seconds, and adjust the steel output interval of the 4th to 6th rolls of hot rolling to 150 seconds.

[0036] Preferably, adjusting the load on the finishing mill stand includes the following steps:

[0037] Adjust the reduction rate of the F5 stand at the end of the finishing mill to be less than or equal to 25%;

[0038] Adjust the reduction rate of the F6 stand at the end of the finishing mill to be less than or equal to 15%.

[0039] Preferably, the step of adjusting the roller temperature includes:

[0040] Adjust the roller temperature to less than 60℃.

[0041] The technical solutions provided in this application have the following advantages compared with the prior art:

[0042] The method provided in this application accurately and quickly identifies the cause of defects by combining macroscopic size characteristics and micro-area composition analysis with process and equipment analysis, and the control countermeasures proposed based on the cause are highly operable and successfully eliminate the defects. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic diagram of the macroscopic morphology of short linear defects on the surface of cold-rolled steel sheet;

[0046] Figure 2 for Figure 1 A schematic diagram showing the morphology and size of the defect under a scanning electron microscope;

[0047] Figure 3 for Figure 2Schematic diagram of the weight percentage composition of the scar-like material on the surface of the intermediate sample;

[0048] Figure 4 for Figure 2 A schematic diagram of the elemental distribution on the surface of the intermediate sample analyzed by electron probe microanalysis;

[0049] Figure 5 for Figure 2 Schematic diagram of the cross-sectional morphology of the intermediate sample;

[0050] Figure 6 for Figure 2 Schematic diagram of the cross-sectional composition of the intermediate sample;

[0051] Figure 7 Schematic diagram showing the material and composition of the working layer of the rolls in different parts;

[0052] Figure 8 This is a flowchart illustrating a method for eliminating short linear defects on the surface of cold-rolled steel sheets, as provided in an embodiment of this application. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] Figure 8 This is a flowchart illustrating a method for eliminating short linear defects on the surface of cold-rolled steel sheets, as provided in an embodiment of this application.

[0055] This application provides a method for eliminating short linear defects on the surface of cold-rolled steel sheets, the method comprising the following steps:

[0056] S1: Obtain analytical samples of cold-rolled steel sheets;

[0057] In this embodiment of the application, obtaining the cold-rolled steel sheet analytical sample includes the following steps:

[0058] Use a scribing pen to mark the defect areas on the cold-rolled sheet;

[0059] Cut a cold-rolled sheet sample containing the defective area of ​​the predetermined specification for analysis.

[0060] Specifically, in order to facilitate quick location during microscopic analysis, the defect area is marked on the cold-rolled plate with a scribing pen, and then a defect sample with a full thickness of 15*15mm is cut out to obtain a metallographic analysis sample containing the defect area.

[0061] S2: Determine the defect parameters of the defect area on the cold-rolled steel analytical sample;

[0062] In this embodiment of the application, determining the defect parameters of the defect region on the cold-rolled steel sheet analytical sample includes the following steps:

[0063] The defective region was observed using a scanning electron microscope;

[0064] The component of the scar tissue in the defect area was analyzed using an energy dispersive spectroscopy (EDS) instrument.

[0065] The length and width of the defect at the location of the scar were measured under a scanning electron microscope;

[0066] Calculate the aspect ratio of the defect.

[0067] Specifically, electron microscopy was used to observe the morphology and micro-composition of the cold-rolled sheet surface, and the length and width of defects were measured. This included: observing the defect area using a scanning electron microscope (SEM), which revealed a scar-like indentation morphology; energy dispersive spectroscopy (EDS) analysis of the scar location, revealing the presence of elements such as Fe, Cr, Ni, Si, and O, with Cr and Ni being typical constituent elements of rolls and work rolls. The length and width of the defects were measured under the SEM; the width was approximately 0.2-0.5 mm, and the length was approximately 1-3 mm, resulting in a calculated aspect ratio of approximately 4-6.

[0068] S3: Determine the source of defect anomaly in the defect area based on the defect parameters;

[0069] In this embodiment of the application, determining the source of defect anomalies in the defect region based on the defect parameters includes the following steps:

[0070] Obtain the working layer material of the rolls during the hot-rolling to cold-rolling process;

[0071] Obtain the component analysis results of the defect region in the defect parameters;

[0072] The composition analysis results are compared with the working layer material to determine the source of the defect anomaly in the defect area.

[0073] Specifically, by comparing the composition of the defect area with the working layer material of the rolls in the hot-rolling to cold-rolling process, it was found that the defect area contained iron oxide. The mass fraction of Cr in the defect area was 0.8-2.1%, and the mass fraction of Ni was 4.8-6.7%, which was similar to the composition of the ICDP working layer of the F5-F6 stand. Since the other rolls were composed of high Cr and low Ni, it can be inferred that the defect originated from hot rolling.

[0074] S4: Determine the cause of the defect in the defect region based on the source of the defect anomaly and the defect parameters;

[0075] In this embodiment of the application, determining the cause of the defect in the defect region based on the defect anomaly source and the defect parameters includes the following steps:

[0076] Obtain the rolling compression ratio of hot-rolled plate during hot rolling and cold-rolled plate during cold rolling;

[0077] Obtain the aspect ratio of the defect region in the defect parameters;

[0078] The aspect ratio of the defect is compared with the rolling compression ratio to determine the cause of the defect in the defect region.

[0079] Specifically, due to the breakage and spalling of the oxide film and surface substrate of the ICDP rolls in the finishing mill stand, which is rolled into the workpiece, the aspect ratio of the defect is approximately 4-6, close to the rolling compression ratio from hot-rolled to cold-rolled sheet. This indicates that the defect appears as pinholes before cold rolling, further pinpointing the area to the finishing mill stand. Combined with the compositional analysis results, it can be concluded that the defect is caused by the pinhole-like breakage and spalling of the oxide film and surface substrate of the ICDP rolls in the finishing mill stand, which is rolled into the workpiece.

[0080] S5: Optimize the cold-rolled sheet production strategy based on the causes of the defects.

[0081] In this embodiment of the application, the step of optimizing the cold-rolled steel sheet production strategy based on the cause of the defect includes the following steps:

[0082] It adopts a full-frame high-speed steel roll and 6 rolls of transition material heat-pressing rolls;

[0083] Adjust the temperature of the ironing rollers;

[0084] Adjust the speed of the ironing rollers;

[0085] Adjust the load on the finishing mill stand;

[0086] Adjust the roller temperature.

[0087] In this embodiment of the application, adjusting the temperature of the ironing roller includes the following steps:

[0088] Adjust the final rolling temperature of the hot rolling material to below 900℃.

[0089] In this embodiment of the application, adjusting the speed of the ironing roller includes the following steps:

[0090] Adjust the steel output interval of the first 3 rolls of hot rolling to 180 seconds, and adjust the steel output interval of the 4th to 6th rolls of hot rolling to 150 seconds.

[0091] In this embodiment of the application, adjusting the load on the finishing mill stand includes the following steps:

[0092] Adjust the reduction rate of the F5 stand at the end of the finishing mill to be less than or equal to 25%;

[0093] Adjust the reduction rate of the F6 stand at the end of the finishing mill to be less than or equal to 15%.

[0094] In this embodiment of the application, the step of adjusting the roller temperature includes:

[0095] Adjust the roller temperature to less than 60℃.

[0096] Specifically, all the high-speed steel rolls in the frame, including F1-F6, are made of high-speed steel with better wear resistance and oxide film retention.

[0097] The following specific examples illustrate this.

[0098] The actual morphology of the cold-rolled steel plate sample to be tested is as follows: Figure 1 Macroscopic observation revealed short linear defects on the sample surface. After marking the defect locations, metallographic samples were cut. The samples were then cut into analytical specimens of appropriate dimensions (plate thickness * 15 * 15 mm). The surface contaminants were cleaned using an ultrasonic cleaner, and after drying, the specimens were observed under a scanning electron microscope. Figure 2 The defect was measured to be 0.323 mm wide and 2.24 mm long, with a length:width ratio of 6.7. Careful observation of the defect area revealed a scar-like indentation morphology. Energy dispersive spectroscopy (EDS) was used to analyze the composition of the scar tissue. The results are as follows: Figure 3 It contains elements such as Fe, Cr, Ni, Si, and O, with Cr and Ni being typical constituent elements of rolling mill rolls and work rolls.

[0099] Electron probe microanalysis of the elemental distribution in the defect region is as follows: Figure 4 There is significant foreign matter indentation, and the composition of the foreign matter is consistent with the energy dispersive spectroscopy (EDS) analysis results. The results of a cross-section of the scar taken perpendicular to the defect are as follows: Figure 5 This further indicates that the defect scars are caused by the peeling of roll components, and the presence of iron oxide suggests that they originated from hot rolling.

[0100] The main components of the work rolls collected from hot rolling to cold rolling, such as Figure 6 It can be seen that the composition of the foreign matter is similar to that of the finishing mill stand (F5-F6). Combined with the fact that the length-to-width ratio of the defect is close to the rolling compression ratio from hot-rolled plate to cold-rolled plate, it can be concluded that the defect is pinhole-shaped before cold rolling and does not bear rolling deformation. Combined with the composition analysis results, it can be clearly determined that the defect is caused by the pinhole-shaped breakage and peeling of the oxide film and surface matrix of the ICDP roll of the finishing mill stand and being rolled into the workpiece.

[0101] To address the causes of defects, measures were taken to control the temperature and rhythm of the hot rolling rolls. This included arranging six rolls of transition material for hot rolling, with the final rolling temperature of the hot rolling roll material below 900℃ and gradually transitioning from 870-900℃. The steel output rhythm was maintained with an interval of 180 seconds for the first three rolls and 150 seconds for the fourth to sixth rolls. The load and roll temperature of the finishing mill stand were controlled, including a reduction rate of ≤25% for F5, a reduction rate of ≤15% for F6, and a roll temperature of <60℃. High-speed steel rolls were used throughout the mill, including F1-F6, which were made of high-speed steel with better wear resistance and oxide film retention.

[0102] This application provides a method for eliminating short linear defects on the surface of cold-rolled steel sheets. By combining macroscopic dimensional characteristics and micro-area composition analysis of defects with process and equipment analysis, the method accurately and quickly identifies the cause of defects. Based on the cause, the proposed control measures are highly operable and successfully eliminate the defects.

[0103] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0104] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for eliminating short linear defects on the surface of cold-rolled steel sheet, characterized in that, The method includes the following steps: Obtain analytical samples of cold-rolled steel sheets; Determine the defect parameters of the defect region on the cold-rolled steel analytical sample; The source of defect anomaly in the defect region is determined based on the defect parameters; The cause of the defect in the defect region is determined based on the source of the defect anomaly and the defect parameters. Optimize cold-rolled sheet production strategies based on the causes of the defects; Determining the source of defect anomalies in the defect region based on the defect parameters includes the following steps: Obtain the working layer material of the rolls during the hot-rolling to cold-rolling process; Obtain the component analysis results of the defect region in the defect parameters; The composition analysis results are compared with the working layer material to determine the source of defect anomalies in the defect area; Determining the cause of the defect in the defect region based on the defect anomaly source and the defect parameters includes the following steps: Obtain the rolling compression ratio of hot-rolled plate during hot rolling and cold-rolled plate during cold rolling; Obtain the aspect ratio of the defect region in the defect parameters; The aspect ratio of the defect is compared with the rolling compression ratio to determine the cause of the defect in the defect region; The optimization of cold-rolled sheet production strategy based on the causes of defects includes the following steps: It adopts a full-frame high-speed steel roll and 6 rolls of transition material heat-pressing rolls; Adjust the temperature of the ironing rollers; Adjust the speed of the ironing rollers; Adjust the load on the finishing mill stand; Adjust the roller temperature; The process of adjusting the temperature of the ironing roller includes the following steps: Adjust the final rolling temperature of the hot rolling material to below 900℃; The process of adjusting the speed of the ironing roller includes the following steps: Adjust the steel output interval of the first 3 rolls of hot rolling to 180 seconds, and adjust the steel output interval of the 4th to 6th rolls of hot rolling to 150 seconds. The adjustment of the load on the finishing mill stand includes the following steps: Adjust the reduction rate of the F5 stand at the end of the finishing mill to be less than or equal to 25%; Adjust the reduction rate of the F6 stand at the end of the finishing mill to be less than or equal to 15%; The process of adjusting the roller temperature includes the following steps: Adjust the roller temperature to less than 60℃.

2. The method for eliminating short linear defects on the surface of cold-rolled steel sheet according to claim 1, characterized in that, The steps for obtaining cold-rolled steel analytical samples include: Use a scribing pen to mark the defect areas on the cold-rolled sheet; Cut a cold-rolled sheet sample containing the defective area of ​​the predetermined specification.

3. The method for eliminating short linear defects on the surface of cold-rolled steel sheet according to claim 1, characterized in that, Determining the defect parameters of the defect region on the cold-rolled steel analytical sample includes the following steps: The defective region was observed using a scanning electron microscope; The component of the scar tissue in the defect area was analyzed using an energy dispersive spectroscopy (EDS) instrument. The length and width of the defect at the location of the scar were measured under a scanning electron microscope; Calculate the aspect ratio of the defect.

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