Method for eliminating color difference defects of stainless steel cold-rolled sheet

Abstract

The invention relates to a method for eliminating color difference type defects of a stainless steel cold-rolled sheet, which comprises the following steps of: controlling the finish rolling temperature in finish rolling of a plate blank and the coiling temperature after finish rolling, so that the thickness of an oxide layer on the surface of the plate blank is within 8-12 microns; in the cold rolling process, the roller roughness of a last roller is adjusted according to the color difference value of the plate blank so as to reduce the edge color difference and the center color difference of the plate blank; and the annealing process after cold rolling is controlled so that the thickness fluctuation of the Cr2O3 film can be smaller than or equal to 5%. By means of the method for eliminating the color difference defects, the color difference defect rate of the 304 stainless steel cold-rolled sheet is reduced to 0.4% from 2.8%, the overall color difference is smaller than or equal to 0.7, the corrosion resistance of a passive film is improved by 40% (salt spray test is larger than or equal to 96 h), and the international leading level is achieved; and the requirement of a high-quality surface is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel, and particularly relates to a method for eliminating color difference defects of cold-rolled stainless steel sheets. Background Art

[0002] With the in-depth promotion of the high-quality development strategy of China's social economy, the performance requirements for key basic materials in the high-end equipment field of the manufacturing industry are becoming increasingly stringent. As one of the core materials for high-end equipment manufacturing, the surface quality of cold-rolled stainless steel sheets directly affects the service performance, service life and appearance quality of the equipment. Especially in typical application scenarios such as liquefied natural gas (LNG) carrier ships, ultra-precision medical devices, and high-end household appliance panels, the surface color difference defects of cold-rolled stainless steel sheets have become the core pain points restricting product upgrading. Taking the LNG ship as an example, the stainless steel used for the inner wall of its liquid cargo tank needs to withstand the low temperature of -163°C and the marine atmospheric corrosion environment for a long time. Surface color difference will not only cause visual defects, but also lead to uneven thickness of the passivation film, accelerating the risk of local corrosion failure; while in the high-end household appliance field, the requirement for the consistency of the surface gloss of the sheet is extremely high. However, at present, domestic austenitic cold-rolled stainless steel sheets generally have a high problem of color difference defect rate, which seriously restricts the improvement of the competitiveness of China's high-end manufacturing industry.

[0003] Color difference defects refer to the situation where there are differences in the color and luster of different regions on the surface of cold-rolled steel sheets. Color differences can be divided into stripe color differences, dot color differences, edge color differences, regional color differences, etc. Their formation mechanism is complex and is essentially the result of the combined action of the surface optical properties and chemical states of the material. For 304 series stainless steel, the work-hardening sensitivity and phase transformation characteristics of its austenitic structure further exacerbate the multi-process coupling effect of color difference formation.

[0004] Specifically, the generation of color difference defects can be traced back to the collaborative out-of-control of the following key processes:

[0005] 1) Oxide layer inheritance effect in the hot rolling process: During hot continuous rolling, if the scale (FeO / Fe3O4 / Fe2O3 composite layer) formed on the surface of the slab is not completely removed in the pickling process, the remaining oxides will enter the cold rolling process as genetic defects, resulting in subsequent surface reflectivity differences. Research shows that when the proportion of Fe3O4 exceeds 40%, its dense structure will significantly increase the pickling difficulty, forming microscopic pits (depth > 2μm), which are magnified into visible color patches during subsequent cold rolling.

[0006] 2) Optical anisotropy induced by texture in the cold rolling process: During the cold rolling plastic deformation process, the 304 stainless steel easily forms a strong {110}<112> rolling texture, resulting in the concentration of grain orientations. This orientation difference is further exacerbated after annealing due to the preferred growth of recrystallized grains, causing differences in the light scattering characteristics of different regions on the surface (glossiness fluctuation > 15%). For wide-width plates (≥1500mm), due to the uneven distribution of rolling force, the texture gradient between the edge and the central region is more significant, forming banded color differences.

[0007] 3) Passivation film thickness fluctuation in the annealing process: The non-uniformity of the temperature field (±10°C) in the continuous annealing furnace directly leads to spatial differences in the growth rate of the Cr2O3 passivation film. Experimental data shows that when the annealing temperature deviation exceeds 8°C, the passivation film thickness difference can reach more than 10nm, causing interference color differences in the visible light band (380 - 780nm). In addition, the concentration gradient of the traditional pickling process (fluctuation along the tank direction > 5%) will cause inconsistent surface activation degrees, further amplifying the film thickness difference.

[0008] 4) Cumulative effect of quality transfer between processes: The existing production process lacks a surface state feedback mechanism across processes, resulting in the gradual accumulation of defects such as residual hot-rolled oxide layers, cold-rolled roughness deviations, and uneven annealing film thicknesses in the process. For example, too high a hot-rolled coiling temperature (>700°C) will exacerbate the unevenness of the oxide layer thickness (coefficient of variation CV value > 20%), and the subsequent grinding process can only eliminate macroscopic defects and is powerless against the microscopic oxide layer distribution, ultimately evolving into diffuse color differences after cold rolling and annealing.

[0009] Regarding color difference defects, current technical improvements in controlling color differences in the industry mostly focus on local optimizations of single processes, with significant limitations. For example, strengthening the removal of the oxide layer by increasing the pickling concentration or extending the pickling time, but increasing the pickling concentration or extending the pickling time will lead to risks of over-pickling and intergranular corrosion; for example, using fixed roughness rolls (Ra = 0.3 - 0.5μm) to unify the surface topography, but this method cannot adapt to the stress distribution differences of wide-width plates, and edge color differences still occur frequently; for example, introducing hydrogen reduction technology in the annealing process to improve oxidation uniformity, but the hydrogen embrittlement sensitivity increases, and the control accuracy of the passivation film thickness of this method is insufficient (CV value > 8%).

[0010] In addition, existing patented technologies mostly adopt static process parameter settings and lack systematic designs for the dynamic linkage of multiple processes. For example, existing technologies optimize the cold rolling emulsion formula to reduce the friction coefficient, but this technology does not consider the interference effect of residual hot-rolled oxide layers on rolling lubrication; another existing technology uses two-stage annealing to improve tissue uniformity, but this technology ignores the guiding effect of cold rolling texture on recrystallization behavior. This improvement mode of isolated processes in existing technologies is prone to the repeated occurrence of color difference defects and is difficult to meet the stringent requirements of high-end application scenarios.

[0011] In this context, it is urgent to develop a collaborative control method throughout the entire process of hot rolling - cold rolling - annealing, systematically solving the color difference problem from three dimensions: regulating the formation of the oxide layer, optimizing the rolling surface topography, and coordinating the growth of the passivation film, so as to help China's high - end equipment manufacturing industry break through technical barriers. Summary of the Invention

[0012] To solve all or part of the above problems, the object of the present invention is to provide a method for eliminating color - difference - type defects of stainless - steel cold - rolled sheets.

[0013] According to one aspect of the present invention, there is provided a method for eliminating color - difference - type defects of stainless - steel cold - rolled sheets, including:

[0014] Controlling the finish - rolling temperature during the finish - rolling of the slab and the coiling temperature after finish - rolling, so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm;

[0015] During the cold - rolling process, adjusting the roll roughness of the last stand roll according to the color difference value of the slab to reduce the edge color difference and center color difference of the slab;

[0016] Controlling the annealing process after cold - rolling, so that the thickness fluctuation of the Cr2O3 film is ≤5%.

[0017] Furthermore, the method further includes:

[0018] Before the finish - rolling process, spraying a CeO2 - based composite coating on the surface of the slab, and controlling the coating thickness of the coating to be 10μm - 15μm to inhibit the generation ratio of Fe3O4; wherein, the CeO2 - based composite coating includes 60% CeO2, 30% Al2O3, and 10% binder.

[0019] Furthermore, the controlling the finish - rolling temperature during the finish - rolling of the slab and the coiling temperature after finish - rolling, so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm specifically is:

[0020] Controlling the finish - rolling temperature during the finish - rolling of the slab to be 1080 - 1100°C, and controlling the coiling temperature of the slab after finish - rolling to be 640 - 670°C, so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm.

[0021] Furthermore, the method further includes:

[0022] During the finish - rolling process, starting the edge - heating device to heat the slab, and controlling the ratio of the heating power of the edge - heating device to the roller - table speed during the finish - rolling process to be between 1300 - 1500kN.

[0023] Further, during the cold rolling process, the roll roughness of the last stand roll is adjusted according to the color difference value of the slab to reduce the edge color difference and center color difference of the slab. Specifically: during the cold rolling process, when the edge color difference value of the slab is greater than 0.8, the roll roughness of the last stand roll is adjusted to 4.0 μm, and the rolling force of the last stand roll is increased by 3% based on the current rolling force; when the edge color difference value of the slab is less than or equal to 0.8, the roll roughness and rolling force of the last stand roll are maintained for rolling.

[0024] Further, the method further includes:

[0025] During the cold rolling process, emulsion with a concentration between 11% - 12% is used for rolling lubrication, and the temperature of the emulsion is controlled between 43°C ± 1°C, the dynamic filtration accuracy of the emulsion is controlled ≤ 5 μm, and the injection pressure of the emulsion is controlled at 1.2 MPa.

[0026] Further, controlling the annealing process after cold rolling to make the thickness fluctuation of the Cr2O3 film ≤ 5% specifically: during the annealing process after cold rolling, the slab is first heated to 1100°C at a heating rate less than 30°C / s, then cooled to 900°C at a cooling rate of 6°C / s, and finally cooled to 650°C at a cooling rate of 3°C / s to make the thickness fluctuation of the Cr2O3 film ≤ 5%.

[0027] Further, the method further includes: during the annealing process after cold rolling, N2 atmosphere containing 0.5% O2 is introduced into the annealing furnace and maintained for 30 s to make the thickness of the Cr2O3 film on the annealed slab between 0.04 μm - 0.05 μm.

[0028] Further, after controlling the annealing process after cold rolling to make the thickness fluctuation of the Cr2O3 film ≤ 5%, the method further includes: electrolytic pickling and plasma activation treatment are performed on the annealed slab to improve the surface optical uniformity of the slab.

[0029] Further, the electrolytic pickling and plasma activation treatment of the annealed slab to improve the surface optical uniformity of the slab specifically are:

[0030] For the annealed slab, electrolytic pickling is performed using a mixed acid solution of 25% HNO3 and 6% HF, and the current density is controlled at 30 A / dm 2 , the electrolytic time is controlled at 20 s - 30 s; and, the slab is subjected to plasma treatment using a mixed gas of Ar and O2, the treatment time is controlled at 10 s - 15 s, the ratio of Ar and O2 is controlled at 8:2, and the treatment power is controlled at 700 W to improve the surface optical uniformity of the slab.

[0031] As can be seen from the above technical solution, a method for eliminating color difference - type defects of a cold - rolled stainless steel sheet provided by the present invention has the following beneficial effects:

[0032] The application of the method for eliminating color difference - type defects of the present invention reduces the color difference defect rate of 304 cold - rolled stainless steel sheets from 2.8% to 0.4%, and the overall color difference ≤ 0.7, reaching the international leading level; each process can be independently adjusted to adapt to different production line equipment (such as bell - type furnace / continuous annealing line); the surface gloss uniformity index of cold - rolled steel sheets is reduced from 2.0 to within 0.5, meeting the requirements of high - quality surfaces; the corrosion resistance of the passivation film is increased by 40% (salt spray test ≥ 96h). Detailed implementation manners

[0033] In order to fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific implementation manners. Except for the following content, the process methods of the present invention all adopt conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0034] When a numerical range is disclosed in this article, the above range is considered continuous and includes the minimum value and the maximum value of the range, as well as each value between such minimum value and maximum value. Further, when the range refers to integers, it includes each integer between the minimum value and the maximum value of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in this article should be understood to include any and all sub - ranges subsumed therein.

[0035] In order to overcome the above deficiencies of the existing methods for eliminating color difference - type defects of austenitic stainless steel cold - rolled sheets, the embodiments of the present invention have developed a method for eliminating color difference - type defects of austenitic stainless steel cold - rolled sheets based on the coordination of microstructure control and dynamic surface. The method of the embodiments of the present invention realizes the adaptive adjustment of process parameters by establishing a dynamic feedback mechanism of the surface state between processes, thereby breaking through the technical bottleneck of single - process optimization. Through such innovative means of multi - disciplinary intersection, without sacrificing production efficiency, color difference - type defects of 304 series stainless steel cold - rolled sheets are avoided and eliminated.

[0036] In the embodiments of the present invention, a surface quality collaborative control system for the entire hot rolling - cold rolling - annealing process is established to eliminate color difference from four dimensions: oxide layer regulation, rolling parameter optimization, surface finishing, and passivation coordination. The overall idea is as follows: 1) Oxide layer gradient control: In the hot rolling stage, an oxide layer regulator (a composite coating containing nano - CeO2) is introduced to reduce the pickling difficulty by inhibiting the imbalance of the Fe3O4 / Fe2O3 ratio. 2) Dynamic rolling parameter coordination: Based on the online surface reflectivity detection data, the roughness of the cold rolling roll and the rolling force are adjusted in real - time. 3) Dual - phase zone atmosphere annealing: The process of "rapid heating + inert gas protection + two - stage slow cooling" is adopted to inhibit the thickness difference of the Cr2O3 film. 4) Composite surface treatment: By combining electrolytic pickling and plasma activation treatment, the uniformity of the passivation film is improved.

[0037] Specifically, a method for eliminating color - difference - type defects of a stainless - steel cold - rolled plate in the embodiments of the present invention includes the following steps:

[0038] Step S001: Control the finish rolling temperature in slab finish rolling and the coiling temperature after finish rolling so that the thickness of the oxide layer on the slab surface is within 8μm - 12μm.

[0039] Among them, controlling the finish rolling temperature in slab finish rolling and the coiling temperature after finish rolling so that the thickness of the oxide layer on the slab surface is within 8μm - 12μm in step S001 specifically means: controlling the finish rolling temperature in slab finish rolling to be 1080 - 1100°C, and controlling the coiling temperature of the slab after finish rolling to be 640 - 670°C so that the thickness of the oxide layer on the slab surface is within 8μm - 12μm.

[0040] Regarding the finish rolling temperature, for example, a temperature control method with head - tail temperature difference compensation is adopted to make the temperature of the head of the slab with a faster temperature drop higher and the temperature of the tail of the slab with a slower temperature drop higher. Specifically in implementation, for example, controlling the temperature of the head of the slab to be 1100°C and controlling the temperature of the tail of the slab to be 1080°C, so that the finish rolling temperature of the slab during finish rolling is controlled within the range of 1080 - 1100°C.

[0041] Regarding the coiling temperature, for example, after finish rolling, laminar cooling is used to reduce the coiling temperature to 640 - 670°C; specifically in implementation, for example, a gradient cooling mode of strong cooling at the head (cooling rate 35°C / s) and weak cooling at the tail (28°C / s) is adopted.

[0042] In the embodiments of the present invention, by controlling the finish rolling temperature and the coiling temperature, the thickness of the oxide layer is controlled within 8 - 12μm.

[0043] Before the finish rolling process, the method of the embodiment of the present invention further includes: pre-treating the slab raw material, that is, spraying a nano-CeO2-based composite coating on the surface of the slab before hot rolling, and controlling the coating thickness of the coating to be 10μm - 15μm to inhibit the generation ratio of Fe3O4. Specifically, in implementation, the CeO2-based composite coating includes 60% CeO2, 30% Al2O3, and 10% binder; the spraying pressure is, for example, 0.4MPa. The pre-treatment of the slab in this embodiment inhibits the generation ratio of Fe3O4 by more than 30%.

[0044] For the finish rolling process, the method of this embodiment further includes: during the finish rolling process, starting the edge heating device to heat the slab, and controlling the ratio of the heating power P of the edge heating device to the roller table speed v during the finish rolling process to be between 1300 - 1500kN, that is, P / v = (1300 - 1500)kN.

[0045] Step S002: During the cold rolling process, adjust the roll roughness of the last stand roll according to the color difference value of the slab to reduce the edge color difference and center color difference of the slab.

[0046] Among them, in step S002, during the cold rolling process, adjusting the roll roughness of the last stand roll according to the color difference value of the slab to reduce the edge color difference and center color difference of the slab is specifically: during the cold rolling process, when the edge color difference value of the slab is greater than 0.8, adjust the roll roughness of the last stand roll to 4.0μm, and increase the rolling force of the last stand roll by 3% based on the current rolling force; when the edge color difference value of the slab is less than or equal to 0.8, keep the roll roughness and rolling force of the last stand roll for rolling.

[0047] Specifically, in implementation, for example, set a detection point every 200mm along the width direction of the slab, and install a high-precision glossiness detector (wavelength 450 - 750nm) at each detection point, so as to detect the color difference value of the corresponding detection point through the high-precision glossiness detector.

[0048] For the rolls in the cold rolling process, for example, use rolls with variable roughness. For another example, configure the roughness of the first stand to be 0.9 - 1.0μm, configure the roughness of the second to fourth stands to be 0.5 - 0.6μm, and configure the roughness of the fifth stand EDT roll to be 3 - 3.5μm, so as to adjust the roughness of the fifth stand EDT roll according to the color difference value detected by the high-precision glossiness detector.

[0049] For the cold rolling process, the method of the embodiment of the present invention further includes: using an emulsion with a concentration between 11% - 12% for rolling lubrication, controlling the temperature of the emulsion to be between 43℃ ± 1℃, controlling the dynamic filtration accuracy of the emulsion to be ≤5μm, and controlling the spraying pressure of the emulsion to be 1.2MPa.

[0050] For the cold rolling process, the embodiment of the present invention solves the problem that the color difference (ΔE) of wide-width plates (1600 mm) is greater than 1.2 by controlling the roll roughness in the cold rolling process and using an emulsion with rolling lubrication effect.

[0051] Step S003: Control the annealing process after cold rolling to make the thickness fluctuation (CV) of the Cr2O3 film ≤ 5%.

[0052] Among them, step S003 controls the annealing process after cold rolling to make the thickness fluctuation of the Cr2O3 film ≤ 5% specifically as follows: In the annealing process after cold rolling, first heat the slab to 1100 °C at a heating rate less than 30 °C / s, then cool the slab to 900 °C at a cooling rate of 6 °C / s, and finally cool the slab to 650 °C at a cooling rate of 3 °C / s to make the thickness fluctuation of the Cr2O3 film ≤ 5%.

[0053] For the annealing process after cold rolling, the method of the embodiment of the present invention further includes: introducing an N2 atmosphere containing 0.5% O2 into the annealing furnace and maintaining it for 30 s to make the thickness of the Cr2O3 film on the annealed slab between 0.04 μm and 0.05 μm.

[0054] The embodiment of the present invention realizes the purpose of making the thickness of the Cr2O3 film on the slab surface between 0.04 μm and 0.05 μm through the control of the annealing process, thus playing a positive role in eliminating color difference defects.

[0055] Among them, after step S003 controls the annealing process after cold rolling to make the thickness fluctuation of the Cr2O3 film ≤ 5%, the method of the embodiment of the present invention further includes: composite surface treatment, that is, electrolytic pickling and plasma activation treatment of the annealed slab to improve the surface optical uniformity of the slab.

[0056] Here, the purpose of electrolytic pickling and plasma activation treatment of the annealed slab is to eliminate the micro convexities and concavities of the slab, thereby improving the surface optical uniformity of the slab.

[0057] Electrolytic pickling and plasma activation treatment of the annealed slab to improve the surface optical uniformity of the slab specifically includes: for the annealed slab, electrolytic pickling is carried out with a mixed acid solution of 25% HNO3 and 6% HF. The pickling process can add 0.1% corrosion inhibitor as needed, and the current density is controlled at 30 A / dm 2 , the electrolysis time is controlled at 20 s - 30 s; and, the slab is subjected to plasma treatment with a mixed gas of Ar and O2, the treatment time is controlled at 10 s - 15 s, the ratio of Ar to O2 is controlled at 8:2, and the treatment power is controlled at 700 W to improve the surface optical uniformity of the slab.

[0058] For the steps of electrolytic pickling and plasma activation treatment of the annealed slab, the roughness Ra of the treated slab is less than or equal to 0.14 μm, thereby obtaining a slab with better surface optical consistency.

[0059] For the method for eliminating color difference - type defects of the cold - rolled stainless - steel sheet in the embodiment of the present invention, a closed - loop quality feedback system can also be established. Specifically, for example, realizing the linkage between the color - difference rating system based on machine vision and the MES system to correct rolling / annealing parameters in real time; at the same time, establishing a knowledge graph of color - difference defects of the 304 series, associating 12 key parameters such as the thickness of the hot - rolled oxide layer, cold - rolled roughness, and annealing film thickness.

[0060] The following are 4 embodiments written for the method for eliminating color - difference - type defects of the present invention, covering core innovation links such as hot - rolled regulation, cold - rolled coordination, annealing optimization, and composite treatment, so as to support the technical effects of the method for eliminating color - difference - type defects in the embodiment of the present invention through the specific parameters and test data of the 4 embodiments.

[0061] Embodiment 1:

[0062] This embodiment includes the coordination of three aspects: pretreatment of the slab raw material, hot - rolled process control, and pickling in composite surface treatment. Specifically:

[0063] 1. Raw material pretreatment: Spray a nano - CeO2 - based composite coating (composition: CeO2 60wt%+Al2O3 30wt%+binder 10%) on the surface of a 304 stainless - steel slab (thickness 200 mm). The coating thickness is 12 ± 2 μm, and the spraying pressure is 0.4 MPa.

[0064] 2. Hot - rolled process: Adopt head - tail temperature difference compensation, 1100 °C at the head, 1080 °C at the tail, and the finish - rolling exit temperature is 1090 ± 5 °C; laminar flow cooling: Adopt a gradient cooling mode of strong cooling at the head (cooling rate 35 °C / s) and weak cooling at the tail (28 °C / s) to reduce the coiling temperature to 650 °C.

[0065] 3. Pickling optimization: 25% HNO3 + 6% HF mixed acid solution, temperature 50 °C, pickling time 90 s, adding 0.1% corrosion inhibitor (benzotriazole).

[0066] After the coordination of the above three aspects, the relevant test data of the obtained slab are as follows: Composition of the oxide layer (XRD analysis method): The proportion of Fe3O4 drops from 45% in the conventional process to 28%; CV value of the oxide layer thickness: drops from 18% in the conventional process to 9.5%; Surface roughness Ra after pickling: 1.4 μm (Ra = 2.1 μm in the conventional process).

[0067] Embodiment 2:

[0068] This embodiment is the control of the cold - rolling process. Specifically:

[0069] 1. Roll configuration: The work roll of the first stand is subjected to laser texturing treatment to make the roughness Ra equal to 1.0 μm. The work rolls of the second to fourth stands are subjected to electro-discharge texturing (EDT) treatment to make the roughness Ra equal to 0.6 μm. The work roll of the fifth stand is subjected to EDT treatment to make the roughness Ra equal to 3.4 μm.

[0070] 2. Color difference on-line feedback and work roll roughness adjustment: Install a high-precision glossiness detector (wavelength 450 - 750 nm), and set a detection point every 200 mm along the width direction of the plate. When the edge color difference ΔE value > 0.8, automatically switch the fifth stand roll to Ra = 4.0 μm and increase the rolling force by 3%.

[0071] 3. Rolling lubrication: Use an emulsion with a concentration of 11.5%, a dynamic filtration accuracy of 3 μm, and a spraying pressure of 1.2 MPa.

[0072] After controlling the cold rolling process, the relevant detection data of the slab obtained are as follows: Color difference of the wide-width plate ΔE: 0.3 in the central area and 0.6 in the edge area, and the overall color difference ≤ 0.7; Surface roughness uniformity of the slab obtained: The Ra fluctuation range is 0.58 - 0.62 μm (CV = 3.2%); Rolling force fluctuation during the rolling process is ±2.8% (better than the conventional ±5%).

[0073] Example 3:

[0074] This example is about the control of the annealing process after cold rolling. Specifically:

[0075] 1. Annealing control: Heat up to 1100°C at a rate of 22°C / s, hold at 1100°C for 120 s, cool down from 1100°C to 950°C at a cooling rate of 6°C / s, and cool down from 950°C to 700°C at a cooling rate of 3°C / s.

[0076] 2. Passivation control: After annealing, introduce a N2 atmosphere containing 0.5% O2 and maintain it for 30 s to promote the uniform growth of the passivation film (Cr2O3 film).

[0077] 3. On-line monitoring: The X-ray fluorescence spectrometer (XRF) detects the film thickness in real time and feeds back to adjust the cooling rate.

[0078] After controlling the annealing process, the relevant detection data of the slab obtained are as follows: Thickness of the Cr2O3 film: 0.045 μm (CV = 3.6%); Surface glossiness, color difference is equal to 0.5 (color difference of the conventional process is equal to 1.3); In terms of corrosion resistance (salt spray test): No red rust within 108 h (conventional is 96 h).

[0079] Example 4:

[0080] This embodiment is for composite surface treatment. Specifically:

[0081] 1. Electrochemical pickling: Acid solution formula: 25% HNO3 + 6% HF mixed acid solution + 0.05% sodium dodecyl sulfonate; Process parameters: Current density 30 A / dm 2 , temperature 45°C, time 25 s.

[0082] 2. Plasma activation: Gas ratio: Ar / O2 = 8:2, flow rate 15 L / min; Treatment parameters: Radio frequency power 550 W, treatment time 12 s, electrode plate spacing 50 mm.

[0083] 3. Surface detection: Measure the Ra value with a white light interferometer to ensure ≤0.14 μm.

[0084] Through the control of this embodiment, the relevant detection data of the slab obtained are: Surface roughness Ra: 0.12 μm (Ra = 0.25 μm after electrochemical pickling); Microscopic pit density: ≤3 pits / mm 2 (15 pits / mm for conventional process 2 ); Glossiness reflectance: 85 ± 1% (80 ± 5% for conventional).

[0085] For the above-mentioned Embodiment 1 - Embodiment 4, the oxide layer control of Embodiment 1 provides a uniform substrate for the cold rolling of Embodiment 2, and the passivation film optimization of Embodiment 3 and the microscopic flattening of Embodiment 4 form a double guarantee for surface quality.

[0086] Through the combined application of the four embodiments, the color difference defect rate of 304 stainless steel cold rolled plates has decreased from 2.8% to 0.4%, the overall color difference ≤0.7, reaching the international leading level; the parameters of each embodiment can be independently adjusted to adapt to different production line equipment (such as bell-type furnace / continuous annealing line); the surface glossiness uniformity index of cold rolled steel plates has decreased from 2.0 to within 0.5, meeting the requirements of high-quality surfaces; the corrosion resistance of the passivation film has increased by 40% (salt spray test ≥96 h). The above embodiments have systematically verified the feasibility and innovation of the color difference defect elimination method of the embodiments of the present invention through specific process parameters and implementation effects.

[0087] The present invention has been disclosed in the above with preferred embodiments. However, those skilled in the art should understand that these embodiments are only used to depict the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all equivalent changes and substitutions to these embodiments should be regarded as covered within the scope of the claims of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined in the claims.

Claims

1. A method for eliminating color difference - type defects of cold - rolled stainless steel sheets, characterized in that, Including: Controlling the finish rolling temperature during slab finish rolling and the coiling temperature after finish rolling, so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm; During cold rolling, adjusting the roll roughness of the last stand roll according to the color difference value of the slab to reduce the edge color difference and center color difference of the slab; Controlling the annealing process after cold rolling so that the thickness fluctuation of the Cr2O3 film ≤ 5%; 2. The method according to claim 1, wherein The method further includes: Before the finish rolling process, spraying a CeO2-based composite coating on the surface of the slab, and controlling the coating thickness of the coating to be 10μm - 15μm to inhibit the generation ratio of Fe3O4; wherein, the CeO2-based composite coating includes 60% CeO2, 30% Al2O3, and 10% binder.

3. The method according to claim 1, wherein The controlling the finish rolling temperature during slab finish rolling and the coiling temperature after finish rolling so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm specifically is: Controlling the finish rolling temperature during slab finish rolling to be 1080 - 1100°C, and controlling the coiling temperature of the slab after finish rolling to be 640 - 670°C, so that the thickness of the oxide layer on the surface of the slab is within 8μm - 12μm.

4. The method according to claim 1, wherein The method further includes: During the finish rolling process, starting the edge heating device to heat the slab, and controlling the ratio of the heating power of the edge heating device to the roller table speed during the finish rolling process to be between 1300 - 1500 kN.

5. The method according to claim 1, characterized in that The adjusting the roll roughness of the last stand roll according to the color difference value of the slab during cold rolling to reduce the edge color difference and center color difference of the slab specifically is: During cold rolling, when the edge color difference value of the slab is greater than 0.8, adjusting the roll roughness of the last stand roll to be 4.0μm, and increasing the rolling force of the last stand roll by 3% based on the current rolling force; when the edge color difference value of the slab is less than or equal to 0.8, maintaining the roll roughness and rolling force of the last stand roll for rolling.

6. The method according to claim 1, wherein The method further includes: During cold rolling, using an emulsion with a concentration between 11% - 12% for rolling lubrication, and controlling the temperature of the emulsion to be between 43°C ± 1°C, controlling the dynamic filtration accuracy of the emulsion ≤ 5μm, and controlling the injection pressure of the emulsion to be 1.2 MPa.

7. The method according to claim 1, wherein The controlling the annealing process after cold rolling so that the thickness fluctuation of the Cr2O3 film ≤ 5% specifically is: During the annealing process after cold rolling, first heating the slab to 1100°C at a heating rate less than 30°C / s, then cooling the slab to 900°C at a cooling rate of 6°C / s, and finally cooling the slab to 650°C at a cooling rate of 3°C / s, so that the thickness fluctuation of the Cr2O3 film ≤ 5%.

8. The method according to claim 1, wherein The method further includes: During the annealing process after cold rolling, introducing an N2 atmosphere containing 0.5% O2 into the annealing furnace and maintaining it for 30 s, so that the thickness of the Cr2O3 film on the annealed slab is between 0.04μm - 0.05μm.

9. The method according to claim 1, wherein After the controlling the annealing process after cold rolling so that the thickness fluctuation of the Cr2O3 film ≤ 5%, the method further includes: performing electrolytic pickling and plasma activation treatment on the annealed slab to improve the surface optical consistency of the slab.

10. The method according to claim 9, wherein The electrolytic pickling and plasma activation treatment of the annealed slab to improve the surface optical consistency of the slab are specifically as follows: For the annealed slab, electrolytic pickling is carried out using a mixed acid solution of HNO3 with a concentration of 25% and HF with a concentration of 6%, and the current density is controlled to be 30 A / dm 2 , the electrolysis time is controlled to be 20 s - 30 s; and, the slab is subjected to plasma treatment using a mixed gas of Ar and O2, the treatment time is controlled to be 10 s - 15 s, the ratio of Ar to O2 is controlled to be 8:2, and the treatment power is controlled to be 700 W to improve the surface optical uniformity of the slab.