Method for eliminating surface lenticular defects of ferritic stainless steel cold plate

Abstract

The application discloses a method for eliminating lisdin grain defects on the surface of ferrite stainless steel cold plates, which comprises the following steps: optimizing continuous casting process, controlling the overheating degree of molten steel at 25-40 DEG C; controlling the electromagnetic stirring intensity as follows: current 1400-1600 A, frequency 3.0-4.0 Hz, and commutation time 10-20 s; controlling the wide surface intensity of crystallizer cooling water at 2600-2800 L / (min.m), controlling the narrow surface intensity of crystallizer cooling water at 2400-2700 L / (min.m), and controlling the cooling water intensity of the secondary cooling section at 1.10-1.30 L / kg; controlling the hot rolling temperature, controlling the rough rolling temperature at 1000-1100 DEG C, and controlling the final rolling temperature of the finishing rolling at 780-880 DEG C; for the cold plates with a thickness of less than 2.0 mm, controlling the total cold rolling deformation rate at more than 70%; and for the cold plates with a thickness of more than 2.0 mm, controlling the total cold rolling deformation rate at not less than 60%. According to the method, the equiaxed crystal ratio of the ferrite stainless steel continuous casting billet is increased to more than 55% by optimizing and controlling the continuous casting process parameters, and finally the grain orientation distribution on the surface of the cold plate is uniform, there is no obvious grain cluster, and the lisdin grain defects on the surface of the ferrite stainless steel cold plate are effectively eliminated by controlling the hot rolling temperature and the total cold rolling deformation rate.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel product manufacturing technology, and more specifically relates to a method for eliminating leucine streaks on the surface of ferritic stainless steel cold-rolled sheets. Background Technology

[0002] Ferritic stainless steel has a significant cost advantage due to its low content of alloying elements and the absence of expensive alloying elements such as Ni, as well as its good corrosion resistance. In particular, cold-rolled sheets and strips of medium-low chromium ferritic stainless steel with a Cr content of less than 20% are widely used in the automotive, construction, and home appliance industries.

[0003] The main production process of ferritic stainless steel cold-rolled sheet is: smelting → continuous casting → hot rolling → cold rolling. After hot rolling and cold rolling, the material is work-hardened, and annealing is required to obtain good processing performance. Finally, during subsequent use, ferritic stainless steel cold-rolled sheet is highly susceptible to surface defects such as lacerations after minor deformations, such as straightening and stretching. Figure 1 As shown, the macroscopic morphology of lissing defects on the surface of ferritic stainless steel cold-rolled sheets consists of fine lines along the rolling direction with a certain spacing, exhibiting a noticeably uneven feel to the touch. Lissing defects on the surface of ferritic stainless steel cold-rolled sheets not only affect the surface appearance quality of the material but also its subsequent processing performance.

[0004] Therefore, developing a method to eliminate lissing marks on the surface of ferritic stainless steel cold-rolled sheets to improve the surface quality and processing performance of ferritic stainless steel cold-rolled sheets is of particular importance for their application. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, this invention provides a method for eliminating lissing defects on the surface of ferritic stainless steel cold-rolled sheets, comprising:

[0006] (1) Optimize the continuous casting process to increase the equiaxed grain ratio of ferritic stainless steel continuous casting billets to ≥55%, wherein the superheat of molten steel is controlled at 25~40℃; the electromagnetic stirring intensity is controlled as follows: current 1400~1600A, frequency 3.0~4.0Hz, reversal time 10~20s; and the cooling water intensity of the crystallizer is controlled at 2600~2800L / ( The cooling water intensity of the crystallizer is controlled at 2400~2700 L / ( The cooling water intensity in the secondary cooling section is controlled at 1.10~1.30 L / kg;

[0007] (2) Control the hot rolling temperature, wherein the roughing temperature is controlled at 1000~1100℃ and the finishing temperature is controlled at 780~880℃;

[0008] (3) Controlling the total deformation rate of cold rolling, for the cold plate with thickness not more than 2.0 mm, the total deformation rate of cold rolling is controlled to be greater than 70%; for the cold plate with thickness greater than 2.0 mm, the total deformation rate of cold rolling is controlled to be not less than 60%.

[0009] As a specific embodiment, in the above method for eliminating the surface lisdain defect of the ferritic stainless steel cold plate, the smelted ferritic stainless steel is 439M, the thickness of the continuous casting blank is 200 mm, and the target thickness of the cold plate is 0.92 mm, wherein:

[0010] In the optimized continuous casting process, the overheating degree of the molten steel is controlled to be 31-33 ℃; the electromagnetic stirring intensity is controlled to be: current 1460 A, frequency 3.5 Hz, and reversing time 15 s; the wide surface intensity of the mold cooling water is controlled to be 2700 L / (m2·s ), the narrow surface intensity of the mold cooling water is controlled to be 2500 L / (m2·s ), and the cooling water intensity of the secondary cooling section is controlled to be 1.21 L / kg;

[0011] In the control of the hot rolling rolling temperature, the rough rolling temperature is controlled to be 1080 ℃, and the finishing rolling temperature is controlled to be 830 ℃;

[0012] In the control of the total deformation rate of cold rolling, the hot rolling coil thickness is designed to be 3.56 mm according to the target thickness 0.92 mm of the cold plate, and the total deformation rate of cold rolling is controlled to be 74%.

[0013] As a specific embodiment, in the above method for eliminating the surface lisdain defect of the ferritic stainless steel cold plate, the smelted ferritic stainless steel is 441, the thickness of the continuous casting blank is 200 mm, and the target thickness of the cold plate is 1.12 mm, wherein:

[0014] In the optimized continuous casting process, the overheating degree of the molten steel is controlled to be 29-31 ℃; the electromagnetic stirring intensity is controlled to be: current 1600 A, frequency 3.5 Hz, and reversing time 15 s; the wide surface intensity of the mold cooling water is controlled to be 2650 L / (m2·s ), the narrow surface intensity of the mold cooling water is controlled to be 2480 L / (m2·s ), and the cooling water intensity of the secondary cooling section is controlled to be 1.19 L / kg;

[0015] In the control of the hot rolling rolling temperature, the rough rolling temperature is controlled to be 1080 ℃, and the finishing rolling temperature is controlled to be 830 ℃;

[0016] In the control of the total deformation rate of cold rolling, the hot rolling coil thickness is designed to be 4.16 mm according to the target thickness 1.12 mm of the cold plate, and the total deformation rate of cold rolling is controlled to be 73%.

[0017] The method for eliminating Lissin lines on the surface of ferritic stainless steel cold-rolled sheets of the present invention optimizes and strictly controls key process parameters for continuous casting, hot rolling, and cold rolling of ferritic stainless steel, thereby improving the microstructure of the ferritic stainless steel cold-rolled sheets and ultimately eliminating Lissin lines on the surface of the ferritic stainless steel cold-rolled sheets. Specifically, compared with the prior art, the method for eliminating Lissin lines on the surface of ferritic stainless steel cold-rolled sheets of the present invention has the following advantages and beneficial effects:

[0018] By optimizing and controlling continuous casting process parameters such as steel superheat, electromagnetic stirring intensity, and continuous casting cooling intensity, the steel superheat was controlled at 25~40℃, the electromagnetic stirring current at 1400~1600A, the electromagnetic stirring frequency at 3.0~4.0Hz, the electromagnetic stirring reversal time at 10~20s, and the crystallizer cooling water intensity at 2600~2800L / ( The cooling water intensity of the crystallizer should be controlled at 2400~2700 L / ( By controlling the cooling water intensity of the second cooling section to 1.10~1.30L / kg, the equiaxed grain ratio of ferritic stainless steel continuous casting billets can be significantly increased from 30~40% in the existing technology to over 55%. Furthermore, by controlling the rough rolling temperature at 1000~1100℃ and the finishing rolling temperature at 780~880℃, and by controlling the total cold rolling deformation rate to greater than 70% for cold plates with a thickness not exceeding 2.0mm and to not less than 60% for cold plates with a thickness greater than 2.0mm, the grain orientation distribution on the surface of the final cold plate is uniform, with no obvious grain clusters. This effectively eliminates the Lissin marks defect on the surface of the ferritic stainless steel cold plate, thereby effectively improving the surface quality and processing performance of the ferritic stainless steel cold plate and facilitating its application. Attached Figure Description

[0019] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a macroscopic morphology diagram of lissin lines defects on the surface of ferritic stainless steel cold-rolled plates in the prior art;

[0021] Figure 2 This is a grain orientation diagram of a ferritic stainless steel cold-rolled sheet with lixin defects in the prior art.

[0022] Figure 3is a macrostructure diagram of a ferritic stainless steel continuous casting billet in the prior art, showing that the equiaxed crystal ratio of the ferritic stainless steel continuous casting billet corresponding to the ferritic stainless steel cold plate with lenticular defects is 30-40%;

[0023] Figure 4 is a macrostructure diagram of a ferritic stainless steel continuous casting billet after the elimination method of the lenticular defects on the surface of the ferritic stainless steel cold plate according to the application, showing that the equiaxed crystal ratio of the ferritic stainless steel continuous casting billet is more than 55%. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0025] Research shows that the lenticular defects on the surface of the ferritic stainless steel cold plate are closely related to the micro-texture orientation of the ferritic stainless steel cold plate. As can be seen from the detection of the ferritic stainless steel cold plate with lenticular defects, there are obvious grain clusters in the distribution of grains of different orientations, as shown in Figure 2 Moreover, according to the macrostructure analysis of the continuous casting billet, the equiaxed crystal ratio of the continuous casting billet corresponding to the ferritic stainless steel cold plate with lenticular defects is only 30-40%, as shown in Figure 3 .

[0026] Therefore, the lenticular defects on the surface of the ferritic stainless steel cold plate are closely related to the micro-texture of the ferritic stainless steel cold plate, and the micro-texture of the ferritic stainless steel cold plate is greatly related to the original as-cast structure and the subsequent hot rolling and cold rolling processes. The present application aims to optimize and strictly control the key process parameters of continuous casting, hot rolling and cold rolling to improve the micro-texture of the ferritic stainless steel cold plate and further eliminate the lenticular defects on the surface of the ferritic stainless steel cold plate. Specifically, the elimination method of the lenticular defects on the surface of the ferritic stainless steel cold plate according to the present application comprises:

[0027] (1) optimizing the continuous casting process to improve the equiaxed crystal ratio of the ferritic stainless steel continuous casting billet to ≥55%, specifically including controlling the superheat of the molten steel, controlling the electromagnetic stirring intensity and controlling the continuous casting cooling intensity, wherein:

[0028] The superheat of the molten steel is the temperature difference between the actual temperature of the molten steel before casting and the melting point of the steel grade. Too low superheat is easy to cause nozzle clogging and casting interruption, and too high superheat will promote the growth of columnar crystals, so the superheat needs to be strictly controlled, as low as possible under the premise of continuous casting. In the present application, the superheat of the molten steel is controlled to be 25-40℃.

[0029] Electromagnetic stirring is the process by which the electromagnetic force induced when a continuously cast billet passes through an external electromagnetic field causes the unsolidified molten steel inside the billet to stir and flow, thereby inhibiting the growth of columnar crystals and promoting the formation of equiaxed crystals. In this invention, the electromagnetic stirring intensity is controlled as follows: current 1400~1600A, frequency 3.0~4.0Hz, and commutation time 10~20s.

[0030] The continuous casting cooling intensity refers to the effect of cooling water flow rate and pressure on the volumetric flow rate inside the cooling pipe. Changes in cooling intensity affect the solidification structure of the steel. Excessive cooling intensity results in a large temperature gradient along the solidification direction of the billet, promoting the growth of columnar crystals. Insufficient cooling intensity leads to slow shell growth, affecting efficiency. Therefore, it is crucial to strictly control the continuous casting cooling intensity. In this invention, the continuous casting cooling intensity is controlled as follows: crystallizer cooling water: 2600~2800 L / (m²) Narrow face 2400~2700L / ( The cooling water intensity of the secondary cooling section is 1.10~1.30L / kg (1.10~1.30 liters of water per kilogram of steel).

[0031] (2) Controlling the hot rolling temperature: Dynamic recrystallization occurs during hot rolling, which directly affects the texture of the hot-rolled coil and, in turn, influences the final texture of the cold-rolled strip through a legacy effect. Therefore, it is essential to strictly control the rolling temperature during hot rolling, especially the roughing and finishing rolling temperatures. Lowering the finishing rolling temperature can enhance the γ-fiber texture in the hot-rolled annealed strip, but if the finishing rolling temperature is too low, it will not only increase the rolling load but also reduce the uniformity of the microstructure due to insufficient recrystallization. Therefore, in this invention, the hot rolling temperature is controlled as follows: roughing temperature 1000~1100℃, finishing rolling temperature 780~880℃.

[0032] (3) Control the total cold rolling deformation rate. A larger total cold rolling deformation rate can refine the cold rolling structure and improve the uniformity of the structure. Therefore, in this invention, the total cold rolling deformation rate is controlled as follows: for cold plates with a thickness not exceeding 2.0 mm, the total cold rolling deformation rate is controlled to be greater than 70%; for cold plates with a thickness greater than 2.0 mm, the total cold rolling deformation rate is controlled to be not less than 60%.

[0033] The method for eliminating lissing defects on the surface of ferritic stainless steel cold-cast plates according to the present invention, by optimizing and controlling continuous casting process parameters such as steel superheat, electromagnetic stirring intensity, and continuous casting cooling intensity, can significantly increase the equiaxed grain ratio of ferritic stainless steel continuous casting billets from 30-40% in the prior art to over 55%, and in some cases, exceed 70%. Figure 4 As shown; by controlling the subsequent hot rolling temperature and the total cold rolling deformation rate, the grain orientation distribution on the surface of the cold plate is uniform, with no obvious grain clusters, effectively eliminating the Lissin marks defect on the surface of the ferritic stainless steel cold plate.

[0034] The method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate is described below in combination with specific examples.

[0035] Example 1

[0036] In the method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate in Example 1 of the present application, the ferritic stainless steel with the brand 439M is smelted, the thickness of the continuous casting billet is 200 mm, the target thickness of the cold plate is 0.92 mm, and the method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate in Example 1 specifically comprises:

[0037] (1) optimizing the continuous casting process, wherein the superheat of the molten steel is controlled to be 31-33 ℃, the electromagnetic stirring intensity is controlled to be: the current 1460 A, the frequency 3.5 Hz, and the commutation time 15 s, the mold cooling water is controlled to be: the wide surface 2700 L / (m2·s), the narrow surface 2500 L / (m2·s), and the secondary cooling section cooling water intensity is controlled to be 1.21 L / kg.

[0038] (2) controlling the hot rolling rolling temperature, wherein the rough rolling temperature is controlled to be 1080 ℃, and the finish rolling temperature is controlled to be 830 ℃.

[0039] (3) controlling the total deformation rate of cold rolling, wherein the hot rolling coil thickness is designed to be 3.56 mm according to the target thickness 0.92 mm of the cold plate, and thus the total deformation rate of cold rolling is controlled to be 74%.

[0040] According to the macrostructure of the continuous casting billet, the equiaxed crystal ratio of the ferritic stainless steel continuous casting billet is 58% by using the method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate in Example 1 of the present application, and the surface of the cold plate after annealing and straightening treatment is free of Lissajous defect through the control of the subsequent hot rolling temperature and the total deformation rate of cold rolling.

[0041] Example 2

[0042] In the method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate in Example 2 of the present application, the ferritic stainless steel with the brand 441 is smelted, the thickness of the continuous casting billet is 200 mm, the target thickness of the cold plate is 1.12 mm, and the method for eliminating the surface Lissajous defect of the ferritic stainless steel cold plate in Example 2 specifically comprises:

[0043] (1) optimizing the continuous casting process, wherein the superheat of the molten steel is controlled to be 29-31 ℃, the electromagnetic stirring intensity is controlled to be: the current 1600 A, the frequency 3.5 Hz, and the commutation time 15 s, the mold cooling water is controlled to be: the wide surface 2650 L / (m2·s), the narrow surface 2480 L / (m2·s), and the secondary cooling section cooling water intensity is controlled to be 1.19 L / kg.

[0044] ​​​​(2) Control the hot rolling temperature, wherein the roughing temperature is controlled at 1080℃ and the finishing temperature is controlled at 830℃.

[0045] (3) Control the total cold rolling deformation rate. The thickness of the hot-rolled coil is designed to be 4.16 mm based on the target thickness of 1.12 mm for the cold plate, so the total cold rolling deformation rate is controlled to be 73%.

[0046] Using the method for eliminating leucine defects on the surface of ferritic stainless steel cold-rolled sheet according to Embodiment 2 of the present invention, based on the low-magnification microstructure of the continuously cast billet, the equiaxed crystal ratio of the ferritic stainless steel continuously cast billet is 61%. After controlling the subsequent hot rolling temperature and the total deformation rate of cold rolling, the surface of the cold-rolled sheet after straightening treatment is free of leucine defects.

[0047] In summary, the method for eliminating lissin lines on the surface of ferritic stainless steel cold-rolled sheets of the present invention optimizes and strictly controls the key process parameters of continuous casting, hot rolling and cold rolling of ferritic stainless steel, thereby improving the microstructure of ferritic stainless steel cold-rolled sheets and achieving the goal of eliminating lissin lines on the surface of ferritic stainless steel cold-rolled sheets.

[0048] Specifically, compared with the prior art, the method for eliminating lissin marks on the surface of ferritic stainless steel cold-rolled plates of the present invention has the following advantages and beneficial effects:

[0049] By optimizing and controlling continuous casting process parameters such as steel superheat, electromagnetic stirring intensity, and continuous casting cooling intensity, the steel superheat was controlled at 25~40℃, the electromagnetic stirring current at 1400~1600A, the electromagnetic stirring frequency at 3.0~4.0Hz, the electromagnetic stirring reversal time at 10~20s, and the crystallizer cooling water intensity at 2600~2800L / ( The cooling water intensity of the crystallizer should be controlled at 2400~2700 L / ( By controlling the cooling water intensity of the second cooling section to 1.10~1.30L / kg, the equiaxed grain ratio of ferritic stainless steel continuous casting billets can be significantly increased from 30~40% in the existing technology to over 55%. Furthermore, by controlling the rough rolling temperature at 1000~1100℃ and the finishing rolling temperature at 780~880℃, and by controlling the total cold rolling deformation rate to greater than 70% for cold plates with a thickness not exceeding 2.0mm and to not less than 60% for cold plates with a thickness greater than 2.0mm, the grain orientation distribution on the surface of the final cold plate is uniform, with no obvious grain clusters. This effectively eliminates the Lissin marks defect on the surface of the ferritic stainless steel cold plate, thereby effectively improving the surface quality and processing performance of the ferritic stainless steel cold plate and facilitating its application.

[0050] It should be noted that, in this text, the term "comprising" or any other variant is intended to cover non-exclusive inclusion, so that the object or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such object or device.

[0051] It should also be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the present application.

Claims

1. A method for eliminating lissing defects on the surface of ferritic stainless steel cold-rolled sheet, characterized in that, include: (1) Optimize the continuous casting process to increase the equiaxed grain ratio of ferritic stainless steel continuous casting billets to ≥55%, wherein the superheat of molten steel is controlled at 25~40℃; the electromagnetic stirring intensity is controlled as follows: current 1400~1600A, frequency 3.0~4.0Hz, reversal time 10~20s; and the cooling water intensity of the crystallizer is controlled at 2600~2800L / ( The cooling water intensity of the crystallizer is controlled at 2400~2700 L / ( The cooling water intensity in the secondary cooling section is controlled at 1.10~1.30 L / kg; (2) Control the hot rolling temperature, wherein the roughing temperature is controlled at 1000~1100℃ and the finishing temperature is controlled at 780~880℃; (3) Control the total cold rolling deformation rate. For cold-rolled sheets with a thickness not exceeding 2.0 mm, the total cold rolling deformation rate shall be controlled to be greater than 70%; for cold-rolled sheets with a thickness greater than 2.0 mm, the total cold rolling deformation rate shall be controlled to be not less than 60%. The prepared ferritic stainless steel cold plate has a uniform grain orientation distribution on its surface and no obvious grain clusters. After annealing and straightening, the surface of the cold plate is free of laceline defects.

2. The method for eliminating lissing defects on the surface of ferritic stainless steel cold-rolled sheet according to claim 1, wherein, The ferritic stainless steel grade 439M, produced by smelting, has a continuous casting billet thickness of 200 mm and a target cold-rolled plate thickness of 0.92 mm. Its characteristics are as follows: In optimizing the continuous casting process, the superheat of the molten steel is controlled at 31~33℃; the electromagnetic stirring intensity is controlled at: current 1460A, frequency 3.5Hz, and reversal time 15s; the cooling water intensity of the crystallizer is controlled at 2700L / ( The cooling water intensity of the crystallizer is controlled at 2500 L / ( The cooling water intensity of the secondary cooling section is controlled at 1.21 L / kg; In controlling the hot rolling temperature, the roughing temperature is controlled at 1080℃, and the finishing temperature is controlled at 830℃. In controlling the total cold rolling deformation rate, the hot-rolled coil thickness is designed to be 3.56 mm based on the target thickness of 0.92 mm for the cold plate, and the total cold rolling deformation rate is controlled to be 74%.

3. The method for eliminating lissing defects on the surface of ferritic stainless steel cold-rolled sheet according to claim 1, wherein, The ferritic stainless steel grade 441, produced by smelting, has a continuous casting billet thickness of 200 mm and a target cold-rolled plate thickness of 1.12 mm. Its characteristics are: In optimizing the continuous casting process, the superheat of the molten steel is controlled at 29~31℃; the electromagnetic stirring intensity is controlled at: current 1600A, frequency 3.5Hz, and reversal time 15s; the cooling water intensity of the crystallizer is controlled at 2650L / ( The cooling water intensity of the crystallizer is controlled at 2480 L / ( The cooling water intensity of the secondary cooling section is controlled at 1.19 L / kg; In controlling the hot rolling temperature, the roughing temperature is controlled at 1080℃, and the finishing temperature is controlled at 830℃. In controlling the total cold rolling deformation rate, the hot-rolled coil thickness is designed to be 4.16 mm based on the target thickness of 1.12 mm for the cold plate, and the total cold rolling deformation rate is controlled to be 73%.

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