A method for controlling edge cracks of a wide and thick plate with a large spread ratio and application thereof

Abstract

The application discloses a large-expansion-ratio wide-thick-plate edge crack control method and application, and belongs to the technical field of wide-thick-plate rolling production. The method comprises the following steps: selecting a wide-thick-plate continuous casting blank with an expansion ratio greater than or equal to 1.5, adopting flame cleaning to perform 45-degree chamfering treatment on the upper and lower surfaces and two long edges of the blank after plate turning operation, then adopting XBXL or PVPC conventional rolling mode for rolling, without additionally increasing the width allowance of the assembled plate, and finally cutting to a fixed size according to the conventional edge cutting process. The application can reduce the single-edge crack width of the steel plate from 5-6 cm to 0.5-3 cm, and the crack can be completely removed in combination with the conventional 70-100 mm width allowance; the edge crack rate is reduced from 1.15% to 0.66%, and the 2 cm additional width allowance is cancelled, so that the yield is obviously improved, and the length instability and thin plate bevel angle defects existing in the BXL rolling mode are avoided. The application has the advantages of simple process, on-line popularization and obvious economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of wide and thick plate rolling production technology, specifically relating to a method and application for controlling edge cracks in wide and thick plates with a large width ratio. Background Technology

[0002] Heavy plates are widely used in shipbuilding, bridges, construction, and marine engineering. During their rolling process, when the width ratio (the ratio of the rolled width to the width of the continuously cast billet) reaches 1.5 or higher, severe edge cracks are prone to occur when using conventional XBXL or PVPC rolling methods. Actual production shows that the width of a single-sided crack is usually 5-6 cm, and some cracks are quite deep. After grinding, the steel plate thickness may not meet the contract requirements, resulting in the steel plate falling outside the contract and seriously affecting the yield and production efficiency.

[0003] To address the aforementioned issues, existing technologies primarily employ the following control measures: First, increasing the width allowance of the sheet assembly typically requires an additional 2 cm, with subsequent edge trimming to remove cracked areas. However, this method results in high metal loss and low yield. Second, switching to the BXL rolling mode (lateral widening rolling) is employed, but this mode suffers from unstable length control, tendency to produce bevels on thin sheets, and large head and tail radii, making it unsuitable for all products, including long and thin sheets. Third, relying solely on post-processing grinding is not only inefficient and costly but also makes dimensional accuracy difficult to guarantee. Therefore, a stable process is urgently needed to suppress edge cracks at their source without increasing the width allowance or altering the conventional rolling process.

[0004] In recent years, some researchers have attempted to improve edge quality from the perspective of continuous casting or material pretreatment. For example, Chinese patent application CN117139575A discloses a method for controlling the narrow-face morphology and corner transverse cracks of narrow-face concave continuous casting billets. By optimizing the structure of the narrow-face copper plate and the shape of the foot rolls in the crystallizer, the corners of the billet are made smoother, thereby reducing corner transverse cracks in the continuous casting stage. This method mainly targets the solidification morphology control of the continuous casting billet and does not involve the pretreatment of the solidified slab before rolling. Moreover, it solves the corner crack problem of the continuous casting billet itself, which is different from the edge crack mechanism generated during the widening process of rolling thick plates. Chinese patent application CN121428228A discloses a production method for improving the edge peeling defect of high-grade silicon steel. It uses a chamfered crystallizer to produce chamfered slabs and combines furnace temperature control, segmented heating, and restriction of the reduction of the roughing mill vertical rolls to reduce edge peeling. Although this method uses a chamfered slab, the chamfer is formed directly during continuous casting. The size and shape of the chamfer are limited by the crystallizer, and it is mainly applicable to edge peeling defects in silicon steel. It does not address edge crack control in wide and thick plates with a large width ratio (width ratio ≥ 1.5) under conventional rolling conditions. Chinese patent application CN121869860A discloses a method for preparing high-yield titanium alloy thick plates, in which the edges of the slab are chamfered to suppress edge cracks and improve yield. Although this technology proposes the idea of ​​chamfering the edges of the slab, it is aimed at titanium alloy thick plates. Titanium alloys differ significantly from ordinary wide and thick steel plates in thermal conductivity, high-temperature plasticity, and crack sensitivity. Its rolling process involves complex reversing rolling and vertical roll rolling, and cannot be directly applied to the conventional rolling production of wide and thick steel plates with a large width ratio.

[0005] Therefore, it is evident that there is currently a lack of a simple and efficient method in the existing technology that is specifically designed for wide and thick steel plates with a width ratio ≥ 1.5, without changing the conventional rolling mode, without adding extra width allowance, and can significantly suppress edge cracks from the source. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and application for controlling edge cracks in thick plates with a large width ratio. This method can significantly reduce edge cracks, significantly lower the rate of delamination, stabilize dimensional accuracy, significantly improve the overall yield, and reduce production costs, making it suitable for widespread application.

[0007] This invention is achieved through the following technical solution:

[0008] A method for controlling edge cracks in a wide and thick plate with a large aspect ratio includes the following steps:

[0009] Step 1) Select a wide and thick plate continuous casting billet with a width ratio ≥ 1.5;

[0010] Step 2) The continuous casting billet is flipped, and the upper surface, lower surface and two long sides of the continuous casting billet are chamfered by flame cleaning. The right-angled edges are processed into 45° chamfers, and the chamfers on the upper and lower surfaces are uniform.

[0011] Step 3) The chamfered continuous casting billet is rolled using the XBXL rolling mode or PVPC rolling mode in a conventional manner, without adding any extra plate width allowance during the rolling process.

[0012] Step 4) Cut the steel plate to the specified length using the standard edge trimming process, ensuring that the width and length of the finished steel plate match the contract dimensions.

[0013] Preferably, the thickness of the continuously cast billet in step 1) is 220~325 mm.

[0014] Preferably, the thickness of the continuously cast billet is 320 mm.

[0015] Preferably, in step 2), the chamfering process is performed by moving a flame cleaning gun along the long side of the slab, maintaining a 45° angle between the flame and the slab surface, and cleaning to a depth of 5-15 mm.

[0016] Preferably, the length of the right-angled side of the chamfer in step 2) is 50~70 mm.

[0017] Preferably, in step 3), no additional width allowance is pre-compensated for the slab before rolling, and edge cracks are suppressed by chamfering.

[0018] Preferably, in step 3), after rolling, the width of the crack on one side of the finished steel plate is controlled to be 0.5~3cm.

[0019] Preferably, the method is used for the production of wide and thick plates of Q235B, Q355B, DH36 or Q420MD steel grades.

[0020] The above-mentioned method for controlling edge cracks in wide and thick plates with large width ratios is applied in the production of wide and thick plates with large width ratios where the BXL rolling mode cannot be used.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) This invention pre-treats 310~325 mm thick slabs with a width ratio ≥1.5 by double-sided, double-sided 45° chamfering (chamfered edge length 50~70 mm), and then rolls them using conventional XBXL or PVPC rolling modes. This significantly reduces the width of the crack on one side of the finished steel plate from 5~6 cm in conventional processes to 0.5~3 cm, greatly reducing the crack depth and expansion range. This provides sufficient allowance for subsequent edge trimming processes and effectively avoids the problem of insufficient thickness caused by crack repair. Furthermore, because the edge cracks are effectively controlled, the rate of deviation from the contract due to edge cracking defects in the steel plate is reduced from 1.15% in the original process to 0.66%, significantly improving the contract size hit rate and product qualification rate, and reducing quality disputes and rework costs.

[0023] (2) The present invention does not require an additional 2 cm of plate width allowance required in conventional processes. It can meet the contract width requirements by relying on the conventional 70~100 mm trimming allowance, which significantly reduces metal loss, improves the overall yield of wide and thick plate rolling, and reduces production costs.

[0024] (3) The present invention can effectively control edge cracks without changing to the BXL rolling mode, thereby avoiding the defects of the BXL mode such as unstable length control, easy oblique angle of thin plate, and large head and tail arc. It is applicable to various products such as long and thin specifications, and broadens the scope of application of the process.

[0025] (4) The present invention only requires the addition of a flipping plate and flame cleaning chamfering pretreatment process before rolling, without changing the existing rolling process and equipment configuration, and without the need to modify the rolling mill. The flame cleaning method is conducive to the modification and implementation of the existing production line crystallizer, and the operation is simple and can be carried out online in batches. Attached Figure Description

[0026] Figure 1 The image shows the single-sided edge crack state of the upper surface (A) and lower surface (B) of the steel plate before treatment in Example 1.

[0027] Figure 2 This refers to the single-sided edge crack state of the upper surface (A) and lower surface (B) of the steel plate after treatment in Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] This invention provides a method for controlling edge cracks in thick plates with a large aspect ratio. The specific steps and optional process parameter ranges are as follows:

[0030] (1) Selection of slab

[0031] A thick slab with a width ratio ≥1.5 is selected for continuous casting. The thickness of the slab can be 310~325 mm, with a typical thickness of 320 mm. It should be noted that the greater the slab thickness, the more prone it is to edge cracks, which is related to the compression ratio. Taking our company's thick plate production line as an example, the slab specifications are 220 mm and 320 mm, with the edge crack problem being more prominent in the 320 mm thick slab. The technical effect of this invention is particularly significant in the 320 mm thick slab.

[0032] (2) Double-sided chamfering treatment

[0033] The selected slab is flipped, and flame cleaning is used to chamfer the upper and lower surfaces and both long edges of the slab. The right-angled edges of the slab are machined into 45° chamfers, with a chamfer length of 50-70 mm, ensuring uniform chamfering on both the upper and lower surfaces. During flame cleaning, the flame cleaning gun is moved along the long edge of the slab, maintaining a 45° angle between the flame and the slab surface, and the cleaning depth is controlled to 5-15 mm. The cleaning speed is adjusted according to the surface condition of the slab to ensure uniform and continuous chamfering without slag or pits.

[0034] Regarding the selection of the 45° chamfer angle, a smaller chamfer size is more conducive to improving edge cracks. However, considering the feasibility and ease of operation of flame cleaning and cutting, this invention adopts a 45° edge chamfer. If direct chamfering is subsequently adopted for steelmaking continuous casting, labor can be further saved, but the structural modification of the crystallizer needs to be considered. The flame cleaning method adopted in this invention is more conducive to the modification of the crystallizer in existing production lines and online implementation.

[0035] (3) Rolling

[0036] The chamfered slab is rolled using either the XBXL or PVPC rolling mode, without any additional width allowance during the rolling process. That is, no additional width allowance is pre-compensated for the slab before rolling; edge cracking is suppressed by the chamfering process. Rolling temperature, pass reduction, and other parameters are executed according to the standard process for thick plate production lines, requiring no additional adjustments due to the chamfering.

[0037] (4) Cut to length

[0038] After rolling, the steel plate is cut to length using standard trimming techniques to ensure that the width and length of the finished steel plate match the contract dimensions. The trimming allowance can be adjusted appropriately based on the measured width of edge cracks, but no additional width allowance is required.

[0039] After processing using the above method, the width of the crack on one side of the finished steel plate is controlled within the range of 0.5~3 cm.

[0040] The method is particularly suitable for the production of wide and thick plates with large width ratios that cannot be produced using the BXL rolling pattern.

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] This embodiment provides a method for controlling edge cracks in a thick plate with a large width-to-width ratio. The specific steps are as follows:

[0044] (1) Selection of slab

[0045] A thick plate continuous casting billet of steel grade Q420MD (Q420qD) was selected, with a billet thickness of 320 mm and a width ratio of 1.75~1.85.

[0046] (2) Double-sided chamfering treatment

[0047] The slab is flipped over, and a flame cleaning gun is used to chamfer the upper and lower surfaces and the two long edges of the slab, machining the right-angled edges of the slab into 45° chamfers. During the flame cleaning process, the flame cleaning gun is moved along the long edge of the slab, maintaining a 45° angle between the flame and the slab surface, and the cleaning depth is controlled within the range of 5~15 mm to ensure that the chamfers on the upper and lower surfaces are uniform and the chamfered surfaces are smooth and free of slag.

[0048] (3) Rolling

[0049] The chamfered slab is directly fed into the rolling mill and rolled using the XBXL conventional rolling mode, without adding any extra allowance for the width of the slab during the rolling process.

[0050] (4) Cut to length

[0051] After rolling, the steel plates are cut to length using conventional edge trimming processes to ensure that the contracted width and length dimensions of the finished steel plates are met.

[0052] Before processing in this embodiment, as follows Figure 1 As shown, the edge crack width of steel plates rolled from conventional right-angle slabs is 5-6 cm, requiring an additional 2 cm width allowance to meet contract requirements. After processing using the method described in this embodiment, as follows... Figure 2 As shown, the width of cracks on a single side of the finished steel plate is controlled within the range of 0.5~3 cm, without the need to increase the width allowance, and all cracks are within the contract dimensions.

[0053] The method described in this embodiment was used in a trial production line for heavy plates, producing approximately 40 slabs with a thickness of 320 mm and a width ratio ≥1.5. Statistical results show that after adopting the method of this invention, the width of the crack on one side of the steel plate decreased from 5-6 cm before the improvement to an average of 2.1 cm. Combined with the general plate assembly and the conventional width allowance of 70-100 mm in the production process, this crack width can be completely eliminated without the need for additional width allowance, and all cracks meet the contract dimensions. The process of this invention is stable and reliable, and suitable for large-scale continuous production on heavy plate production lines.

[0054] Example 2

[0055] This embodiment provides another method for controlling edge cracks in thick slabs with a large width ratio, applicable to slabs with a width ratio > 1.5 and for which the BXL rolling mode cannot be used. The specific steps are as follows:

[0056] (1) Slab selection: Select a wide and thick plate continuous casting slab with a width ratio ≥1.5. The slab thickness can be selected according to actual production needs, usually 320 mm.

[0057] (2) Double-sided chamfering: The slab is flipped and the upper and lower surfaces and two long sides of the slab are chamfered at 45° using flame cleaning. The process parameters for flame cleaning are: the flame is at a 45° angle to the slab surface, the cleaning depth is 5~15mm, and the cleaning speed is adjusted according to the surface condition of the slab to ensure that the chamfering is uniform and continuous.

[0058] (3) Rolling: The chamfered slab is rolled using the conventional PVPC rolling mode without adding any extra width allowance. During the rolling process, the conventional reduction per pass and rolling speed are maintained, and there is no need to adjust the mill parameters.

[0059] (4) Cutting to length: Cut according to conventional edge cutting process to ensure that the contract width and length dimensions are met.

[0060] After processing using the method described in this embodiment, the width of the cracks on the edge of the steel plate can be controlled within the range of 0.5 to 3 cm, the trimming allowance meets the requirements, there are no problems with insufficient thickness or delamination, and the yield is significantly improved.

[0061] Test Example 1

[0062] To verify the technical effectiveness of this invention, a systematic trial production verification was conducted on a wide and thick plate production line. Edge crack data were measured and statistically analyzed for both chamfered slabs (using the method of this invention) and unchamfered conventional slabs (for comparison). Furthermore, the thicknesses of two commonly used slabs, 220 mm and 320 mm, were compared and verified. Details are as follows:

[0063] Table 1 below shows the measured edge crack data of 320 mm thick slabs under different steel grades and different width ratios. Among them, B6401201000 and B6401202000 (Q420MD), B6421053000 and B6421054000 (Q355B), B6421055000 and B6421056000 (DH36), and B6421057000 (Q235B) are all chamfered materials treated by the method of the present invention (45° flame chamfering on both sides of the flip plate), while B6379015000 and B6380103000 (Q420MD) are control materials that have not undergone chamfering treatment.

[0064] Table 1. Measured data of lower edge cracks in 320 mm slabs with different steel grades and width ratios.

[0065]

[0066] Note in Table 1: Width ratio = Contract width / Slab width (2165 mm), the values ​​in the table are approximations.

[0067] As shown in Table 1, for the chamfered materials produced by the method of this invention, the single-sided crack width of Q420MD steel (B6401201000, B6401202000) is 1~1.5 cm on the upper surface and 1.5~3 cm on the lower surface; the single-sided crack width of Q355B steel (B6421053000, B6421054000) is 2~4 cm on the upper surface and 2~3 cm on the lower surface; the single-sided crack width of DH36 steel (B6421055000, B6421056000) is 0~3 cm on the upper surface and 0.5~3 cm on the lower surface; and the single-sided crack width of Q235B steel (B6421057000) is 2~3 cm on the upper surface and 1.5~3 cm on the lower surface. In the un-beveled comparison materials, the single-sided crack width of B6379015000 was 1.5 cm on the upper surface and as high as 3.5~6 cm on the lower surface, while that of B6380103000 was 4~5 cm on the upper surface and 3~5.5 cm on the lower surface. A comparison shows that, using the method of this invention, under the same steel grade (Q420MD) and thickness conditions, the edge crack width was significantly reduced from 3~6 cm (without beveling) to less than 3 cm, a reduction of over 50%. Furthermore, the data in Table 1 also shows that the method of this invention can achieve stable control of edge crack width ≤3 cm on various commonly used thick plate steel grades such as Q355B, DH36, and Q235B, proving that the method has excellent steel grade adaptability.

[0068] Table 2 below shows the comparison data of edge cracks after being treated with the method of the present invention for different slab thicknesses and different steel grades. All slabs were subjected to double-sided 45° flame chamfering treatment, covering two thicknesses of 220 mm and 320 mm and three steel grades of Q235B, Q355B and DH36.

[0069] Table 2 Comparison of edge crack data for different slab thicknesses and different steel grades

[0070]

[0071] Note in Table 2: Width ratio = Contract width / Slab width (2165 mm), the values ​​in the table are approximations.

[0072] As shown in Table 2, the single-sided crack width of 220 mm thick slabs (B6403001-B6403003) is generally in the range of 0.5~2 cm, while that of 320 mm thick slabs (B6403004-B6403009) is generally in the range of 0.5~3 cm. The crack width of all slabs is ≤3 cm. It should be noted that under the same steel grade, the crack width of the 320 mm slab is slightly larger than that of the 220 mm slab. This confirms the understanding that "the thicker the slab, the more prone it is to edge cracks." However, the method of this invention can still stably control the crack width of the 320 mm thick slab to within 3 cm, fully demonstrating the effectiveness of the technology. Furthermore, the crack width of the three slabs B6403007 (Q235B), B6403008 (Q355B), and B6403009 (DH36) with a width ratio of approximately 2.03 to 2.06 in Table 2 is also controlled within 3 cm (1 to 3 cm on the upper surface and 0.5 to 3 cm on the lower surface), proving that the present invention is still effective under extreme conditions with a large width ratio (≥2.0).

[0073] It is worth noting that there are certain differences in the data for the upper and lower surfaces of the same slab in Tables 1 and 2 (e.g., the upper surface of B6401202000 is 1.5 cm / 1.5 cm while the lower surface is 3 cm / 3 cm, and the upper surface of B6403007 is 1 cm / 1 cm while the lower surface is 3 cm / 3 cm). This is precisely why this invention emphasizes the "flipping" operation and "double-sided" chamfering—without flipping and double-sided chamfering, single-sided treatment may not guarantee the consistency of crack control on the upper and lower surfaces, and may even lead to severe cracks remaining on the untreated surface. This invention ensures that both the upper and lower surfaces are chamfered at 45° through the flipping operation, thereby achieving synchronous and effective control of crack width on both sides.

[0074] Based on the above data on chamfered materials (Tables 1 and 2), the maximum width of single-sided cracks does not exceed 4 cm, and the vast majority are within 3 cm, with an average value of 2.1 cm. This is consistent with the statistical results of the batch trial production (about 40 slabs) in Example 1. With the conventional 70-100 mm width allowance, the cracks can be completely removed without the need for an additional 2 cm width allowance, which significantly improves the yield.

[0075] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. The scope of protection of the present invention is determined by the scope claimed in the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for controlling edge cracks in a wide and thick plate with a large aspect ratio, characterized in that, Includes the following steps: Step 1) Select a wide and thick plate continuous casting billet with a width ratio ≥ 1.5; Step 2) The continuous casting billet is flipped, and the upper surface, lower surface and two long sides of the continuous casting billet are chamfered by flame cleaning. The right-angled edges are processed into 45° chamfers, and the chamfers on the upper and lower surfaces are uniform. Step 3) The chamfered continuous casting billet is rolled using the XBXL rolling mode or PVPC rolling mode in a conventional manner, without adding any extra plate width allowance during the rolling process. Step 4) Cut the steel plate to the specified length using the standard edge trimming process, ensuring that the width and length of the finished steel plate match the contract dimensions.

2. The method for controlling edge cracks in a wide and thick plate with a large width-to-width ratio according to claim 1, characterized in that, Step 1) The thickness of the continuously cast billet is 220~325 mm.

3. The method for controlling edge cracks in a wide and thick plate with a large width ratio according to claim 2, characterized in that, The thickness of the continuously cast billet is 320 mm.

4. The method for controlling edge cracks in a wide and thick plate with a large width ratio according to claim 1, characterized in that, Step 2) The chamfering process is performed by moving a flame cleaning gun along the long side of the slab, maintaining a 45° angle between the flame and the slab surface, and cleaning to a depth of 5~15 mm.

5. The method for controlling edge cracks in a wide and thick plate with a large width-to-width ratio according to claim 1, characterized in that, Step 2) The length of the right-angled side of the chamfer is 50~70 mm.

6. The method for controlling edge cracks in a wide and thick plate with a large width-to-width ratio according to claim 1, characterized in that, In step 3), no additional width allowance is pre-compensated for the slab before rolling, and edge cracks are suppressed by chamfering.

7. The method for controlling edge cracks in a wide and thick plate with a large width ratio according to claim 1, characterized in that, In step 3), after rolling, the width of the crack on one side of the finished steel plate is controlled to be 0.5~3 cm.

8. The method for controlling edge cracks in a wide and thick plate with a large width ratio according to claim 1, characterized in that, The method is used for the production of wide and thick plates of Q235B, Q355B, DH36 or Q420MD steel grades.

9. The method for controlling edge cracks in large-width-ratio thick plates as described in any one of claims 1-8, in the production of large-width-ratio thick plates where the BXL rolling mode cannot be used.

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