Method for overcoming slab narrow face transverse crack defect and application

Abstract

The invention provides a method for overcoming the slab narrow face transverse crack defect and application. A method for overcoming slab narrow face transverse crack defects comprises the steps that S1, the taper coefficient of a crystallizer is set to be 1.20%-1.40% for positive peritectic steel with the carbon content being 0.08%-0.12%, S2, in the pouring process, the heat flux density of a wide face and the heat flux density of a narrow face are calculated based on the flow of cooling water of the wide face and the narrow face of the crystallizer and the water inlet and outlet temperature difference, and the ratio of the heat flux density to the heat flux density is controlled to be maintained to be 0.8-0.9; s3, the cast slab meeting the taper and the heat flux ratio is subjected to release rolling, the method for solving the slab narrow face transverse crack defect and the application mainly aim to overcome the defects that in the prior art, due to the fact that the defect is high in concealment and difficult to detect, the slab with the defect often flows into the rolling procedure and develops into a hot-rolled coil broken edge, and the defect cannot be detected easily. And the problems that the yield is reduced, the grinding cost is increased, and the hot charging rate is reduced are solved.

Description

Technical Field

[0001] This invention relates to the field of continuous casting slab technology, and in particular to a method and application for solving the defect of transverse cracks on narrow face of slabs. Background Technology

[0002] With increasingly fierce market competition in the steel industry, customers are demanding ever more stringent surface quality requirements for high-end hot-rolled coils. Product surface quality not only directly affects the performance of downstream end products but also profoundly impacts a company's brand image and market competitiveness. Among numerous surface defects, transverse cracks on the narrow face of slabs are a particularly challenging quality issue—manifesting as micro-cracks distributed along the thickness direction of the narrow face of the slab, mostly concentrated at the troughs of vibration marks. Because the slab surface is covered with a thick layer of iron oxide scale during online production, conventional visual inspection or surface testing methods are insufficient for effective identification; furthermore, due to their random location and limited depth on the narrow face, even pickling methods are difficult to reliably detect. Currently, there is a lack of reliable online monitoring technology for this defect, leading to defective slabs often being mistakenly judged as qualified products and flowing into subsequent rolling processes, where they expand into "rotten edge" defects on the coil edges during hot rolling. In severe cases, this can render the entire coil unusable and forced to be scrapped; in milder cases, edge trimming or manual grinding is necessary, significantly reducing yield and production efficiency while also increasing manufacturing costs. Existing literature indicates a lack of research on the formation mechanism and control technology of such narrow transverse cracks, and no systematic and effective solution has yet been developed. Traditionally, remedial treatment mainly relies on slab grinding, but this method has significant limitations: hot slab grinding, due to its high surface temperature, can easily mask minute defects, leading to missed detection; cold slab grinding may induce crack propagation, exacerbating the defect severity. Furthermore, the grinding process itself causes metal loss, reducing steel yield; prolonging the slab's residence time in previous processes leads to material accumulation and decreased turnover efficiency; and the significant heat loss also hinders high-temperature hot charging (hot charging) in subsequent processes, thus affecting the overall hot charging ratio and energy utilization efficiency. Summary of the Invention

[0003] The main objective of this invention is to provide a method and application for solving the problem of transverse cracks on narrow surfaces of slabs. This aims to overcome the problems in the prior art where the defect is highly concealed and difficult to detect, often leading to slabs with defects flowing into the rolling process and developing into hot-rolled coils with rotten edges, resulting in decreased yield, increased grinding costs, and reduced hot charging rate.

[0004] To achieve the above objectives, the present invention provides a method for solving transverse crack defects on narrow faces of slabs, comprising: S1. For positive peritectic steel with a carbon content of 0.06% to 0.18%, the crystallizer taper factor is set to 1.20% to 1.40%. The taper coefficient of the crystallizer is calculated as: (upper opening width - lower opening width) / lower opening width, where the upper opening width is the inner cavity width of the top of the narrow copper plate of the crystallizer, and the lower opening width is the inner cavity width of the bottom of the narrow copper plate of the crystallizer. S2. During the casting process, based on the flow rate of cooling water on the wide and narrow sides of the crystallizer and the temperature difference between the inlet and outlet water, calculate the heat flux density of the wide and narrow sides and control their ratio to be maintained at 0.8 to 0.9. S3. Rolling is carried out on slabs that meet the above taper and heat flow ratio requirements.

[0005] This invention addresses the narrow-face transverse crack defect in slabs of peritectic steels with a carbon content ranging from 0.06% to 0.18% that is prone to occur during continuous casting. It proposes a process control method based on the regulation of solidification heat transfer uniformity. Due to abrupt volume changes and thermal stress concentration within the peritectic phase transformation range, this type of steel is highly susceptible to forming microcracks distributed along the troughs of the oscillation marks within the crystallizer. Uneven cooling between the wide and narrow faces further exacerbates the obstructed shrinkage of the narrow-face slab shell, inducing localized stress concentration and promoting crack initiation. Traditional production lacks effective online detection methods, and these defects often remain hidden until the hot rolling process, where they expand into "rotten edges" on the steel coil, severely impacting product surface quality and order fulfillment.

[0006] This invention suppresses crack formation at its source by systematically optimizing key process parameters of the crystallizer: First, the crystallizer taper coefficient (defined as (upper inner width - lower inner width) / lower inner width) is set at approximately 1.30% to match the solidification shrinkage characteristics of positive peritectic steel, reduce the air gap thermal resistance between the billet shell and the copper plate, and improve the uniformity of interface heat transfer. Second, the flow rate fluctuation of the cooling water on the narrow face of the crystallizer is strictly monitored before casting to ensure that it remains stable within ±10 m³ / h, avoiding sudden changes in local heat flux due to flow rate fluctuations. Simultaneously, the ratio of heat flux density between the wide and narrow faces is monitored and adjusted in real time during casting, maintaining it in the range of 0.8 to 0.9, thereby achieving a synergistic match between the temperature field and shrinkage behavior at the solidification front of the wide and narrow faces, effectively alleviating the thermo-mechanical stress concentration in the narrow face region, and suppressing the excessive growth of the proeutectoid ferrite film and grain boundary weakening.

[0007] Compared to existing technologies, this method requires no new equipment or changes to the production line process. It successfully solves the long-standing problem of narrow-face transverse cracks in continuous casting production simply by finely adjusting existing process parameters. Practical application shows that this method not only completely eliminates narrow-face cracks in slabs and their resulting hot-rolled edge defects, but also significantly improves product quality stability. More importantly, by achieving direct rolling of high-quality slabs without grinding, it greatly reduces metal loss and manual intervention, increasing slab yield, order fulfillment rate, and the proportion of high-temperature hot delivery (hot charging ratio). Simultaneously, it reduces the rework rate and product downgrade rate in downstream processes due to surface defects. Overall, this method has advantages such as ease of operation, low cost, and strong compatibility. It does not interfere with existing production organization, is easy to promote and apply in industrial settings, and possesses significant technological advancements and economic benefits.

[0008] According to an embodiment of the present invention, before casting the positive peritectic steel, the fluctuation of the cooling water flow rate on the narrow face of the crystallizer is monitored to ensure that the fluctuation range does not exceed ±10m3 / h.

[0009] According to an embodiment of the present invention, before casting the positive peritectic steel, the fluctuation of the cooling water flow rate on the narrow face of the crystallizer is monitored to ensure that the fluctuation range does not exceed ±5m3 / h.

[0010] According to an embodiment of the present invention, in step S3, the slab that does not meet the requirements of the crystallizer taper coefficient and heat flux density ratio is subjected to narrow-face grinding.

[0011] According to an embodiment of the present invention, the heat flux density of the narrow face is not less than 1.8 MW / m2.

[0012] According to an embodiment of the present invention, the positive peritectic steel grade comprises at least one of Nb and V, and the total amount thereof is 0.02% to 0.10%.

[0013] According to an embodiment of the present invention, for slabs that do not meet the said taper or heat flux density ratio, a narrow surface grinding is performed, with a grinding depth of 2 to 4 mm.

[0014] According to an embodiment of the present invention, the taper to heat flux ratio control is carried out at a pulling speed of 1.0 to 1.4 m / min.

[0015] This invention also proposes an application of the method described above for solving the transverse crack defect on a narrow surface of a slab in the engineering field.

[0016] According to an embodiment of the present invention, the engineering field includes at least one of construction, bridges, and engineering machinery. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0019] To further illustrate the present invention, the following examples are provided: Example 1 This embodiment is applied to a low-alloy high-strength steel (carbon content 0.095%) of grade H600DPD-1 produced by a steel plant in December 2024. During continuous casting, the method described in this invention is used for process control. S1. Set the taper coefficient of the narrow copper plate of the crystallizer to 1.32%. This taper coefficient is calculated as (upper inner width - lower inner width) / lower inner width, where the upper inner width is the width of the inner cavity at the top of the narrow copper plate of the crystallizer, and the lower inner width is the width of the inner cavity at the bottom. Secondly, check and calibrate the cooling system of the crystallizer before pouring to ensure that the fluctuation of the narrow cooling water flow rate is controlled within ±5 m³ / h. S2. During the casting process, the flow rate and inlet / outlet water temperature difference of the cooling water on the wide and narrow sides of the crystallizer are collected in real time. Based on the heat flux density, the heat flux density of the wide and narrow sides is calculated, and the cooling water volume is dynamically adjusted to keep the ratio of the heat flux density of the wide side to that of the narrow side stable at 0.85 (q = wcΔT / S) throughout the entire casting process. Where q is the heat flux density of the crystallizer (unit: MW / m³). 2 w is the cooling water flow rate (unit: kg / s), and c is the specific heat capacity of water (taken as 4186 J / (kg)). . △T is the temperature difference between the inlet and outlet cooling water of the crystallizer (unit: ℃), and S is the effective heat transfer area of ​​the corresponding surface of the crystallizer (unit: m). 2 ). ); S3. After the above process control, the slabs produced in this batch were directly removed from the production line without narrow-face grinding. Subsequently, randomly selected slab samples underwent narrow-face grinding and visual inspection, and no transverse crack defects were found. This batch of slabs was then hot-charged at a high temperature (hot charging temperature of approximately 650℃) into the hot rolling process, and rolled into hot-rolled coils with a thickness of 3.0 mm. Downstream customers reported that the coil shape after rolling was good, and there were no surface defects such as broken edges or peeling. The order was fully fulfilled.

[0020] This embodiment demonstrates that by synergistically controlling the crystallizer taper coefficient, narrow-face cooling stability, and the ratio of wide to narrow-face heat flux density, the formation of transverse cracks in the narrow face of H600DPD-1 steel slabs can be effectively suppressed, achieving high-quality, grinding-free direct rolling and significantly improving yield and product surface quality.

[0021] Example 2 This embodiment is applied to a low-alloy high-strength steel (carbon content of 0.095%) of grade H600DPD-1 produced by a steel mill in January 2025. The difference between this embodiment and Embodiment 1 is that the taper coefficient of the narrow copper plate of the crystallizer is set to 1.20%; the cooling system of the crystallizer is checked and calibrated before casting to ensure that the fluctuation of the cooling water flow rate of the narrow face is controlled within ±5 m³ / h, and the other conditions are the same; the heat flow ratio of the secondary wide face to the narrow face is 0.83.

[0022] Under the conditions of this embodiment, narrow transverse cracks can still be effectively suppressed, and direct rolling without grinding can be achieved, verifying the feasibility and effectiveness of the lower limit of this parameter.

[0023] Example 3 This embodiment is applied to a low-alloy high-strength steel (carbon content of 0.095%) of grade H600DPD-1 produced by a steel mill in January 2025. The difference between this embodiment and Embodiment 1 is that the taper coefficient of the narrow copper plate of the crystallizer is set to 1.40%, and the cooling system of the crystallizer is checked and calibrated before casting to ensure that the fluctuation of the narrow cooling water flow rate is controlled within ±10 m³ / h. The other conditions are the same. The heat flow ratio of the secondary wide face to the narrow face is 0.89, and the other conditions are the same.

[0024] Under the conditions of this embodiment, narrow transverse cracks can still be effectively suppressed, and direct rolling without grinding can be achieved, verifying the feasibility and effectiveness of the lower limit of this parameter.

[0025] Comparative Example 1 In November 2024, a steel mill produced H600DPD-1 low-alloy high-strength steel (carbon content 0.095%). The taper coefficient of the narrow-face copper plate in the crystallizer was set to 1.0%. Before casting, the crystallizer cooling system was inspected and calibrated to ensure that the fluctuation of the narrow-face cooling water flow rate was controlled within ±5 m³ / h, with all other conditions remaining the same. The heat flow ratio of the wide face to the narrow face for the entire casting was 0.85. After the slab was produced from this casting, grinding and inspection revealed severe longitudinal and transverse cracks on the narrow face, and severe edge defects after rolling.

[0026] The difference between this comparative example and Example 1 is that the crystallizer taper coefficient is set to 1.0%, while the other process parameters are exactly the same as in Example 1.

[0027] Under the above conditions, multiple transverse cracks were found after the narrow face of the slab was ground, and discontinuous rotten edges appeared on the hot-rolled edge after rolling.

[0028] Comparative Example 2 The low-alloy high-strength steel (carbon content 0.095%) of grade H600DPD-1 produced in December 2024 had a taper coefficient of 1.2% for the narrow face copper plate of the crystallizer. Before casting, the crystallizer cooling system was inspected and calibrated to ensure that the fluctuation of the narrow face cooling water flow rate was controlled within ±20 m³ / h, with all other conditions remaining the same. The overall wide face heat flow / narrow face heat flow ratio for the entire casting was 1.15. After the slab was produced from this casting, grinding and inspection revealed severe transverse cracks on the narrow face, and severe edge damage was observed after rolling. The difference between this comparative example and Example 1 is that the cooling water volume of the narrow face was not adjusted, resulting in a heat flux ratio of 1.15 between the entire cast-in-place wide face and the narrow face. All other conditions are the same as in Example 1.

[0029] Comparative Example 3 The low-alloy high-strength steel (carbon content 0.095%) of grade H600DPD-1 produced in December 2024 had a taper coefficient of 1.2% for the narrow face copper plate of the crystallizer. Before casting, the crystallizer cooling system was inspected and calibrated to ensure that the narrow face cooling water flow fluctuation was controlled within ±32 m³ / h, with all other conditions remaining the same. The overall wide face heat flow / narrow face heat flow ratio for the entire casting was 1.0. After grinding and inspection of the slab produced in this casting, severe transverse cracks were found on the narrow face, and severe edge damage was observed after rolling. The difference between this comparative example and Example 1 is that the ratio of the heat flux density of the wide face to the heat flux density of the narrow face is controlled at 1.0, while all other conditions are completely consistent with Example 1.

[0030] Under the above conditions, multiple transverse cracks were found after the narrow face of the slab was ground, and discontinuous rotten edges appeared on the hot-rolled edge after rolling.

[0031] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for solving transverse crack defects on narrow faces of slabs, characterized in that, include: S1. For positive peritectic steel with a carbon content of 0.06% to 0.18%, the crystallizer taper factor is set to 1.20% to 1.40%. The taper coefficient of the crystallizer is calculated as: (upper opening width - lower opening width) / lower opening width, where the upper opening width is the inner cavity width of the top of the narrow copper plate of the crystallizer, and the lower opening width is the inner cavity width of the bottom of the narrow copper plate of the crystallizer. S2. During the casting process, based on the flow rate of cooling water on the wide and narrow sides of the crystallizer and the temperature difference between the inlet and outlet water, calculate the heat flux density of the wide and narrow sides and control their ratio to be maintained at 0.8 to 0.

9. S3. Rolling is carried out on slabs that meet the above taper and heat flow ratio requirements.

2. The method for solving the transverse crack defect on a narrow surface of a slab according to claim 1, characterized in that, Before casting the positive peritectic steel, monitor the fluctuations in the cooling water flow rate on the narrow face of the crystallizer to ensure that the fluctuation range does not exceed ±10m. 3 / h.

3. The method for solving the transverse crack defect on a narrow face of a slab according to claim 1, characterized in that, Before casting the positive peritectic steel seed, monitor the fluctuation of the cooling water flow rate on the narrow face of the crystallizer to ensure that the fluctuation range does not exceed ±5m. 3 / h.

4. The method for solving the transverse crack defect on a narrow face of a slab according to claim 1, characterized in that, In step S3, the slab that does not meet the requirements of the crystallizer taper coefficient and heat flux density ratio is subjected to narrow-face grinding.

5. The method for solving the transverse crack defect on a narrow face of a slab according to claim 1, characterized in that, The heat flux density of the narrow facet is not less than 1.8 MW / m. 2 .

6. The method for solving the transverse crack defect on a narrow face of a slab according to claim 1, characterized in that, The positive peritectic steel grade comprises at least one of Nb and V, with a total content of 0.02% to 0.10%.

7. The method for solving the transverse crack defect on a narrow surface of a slab according to claim 4, characterized in that, For slabs that do not meet the required taper or heat flux density ratio, narrow-face grinding is performed to a depth of 2–4 mm.

8. The method for solving the transverse crack defect on a narrow face of a slab according to claim 1, characterized in that, The taper to heat flux ratio control was implemented at a pulling speed of 0.6–1.8 m / min.

9. The application of a method for solving transverse crack defects on narrow surfaces of slabs as described in any one of claims 1 to 8 in the field of engineering.

10. The application according to claim 9, wherein the engineering field includes: At least one of the following: buildings, bridges, and engineering machinery.