Continuous casting square and round billet and rolled material quality control method
By combining online detection and end-face impact welding with weak oxidation heating and large reduction rolling process, the problem of identifying and repairing central porosity and crack defects in continuously cast square and round billets has been solved, thereby improving yield and product quality.
Patent Information
- Application Number
- CN202511976141.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-02-27
AI Technical Summary
Existing technologies are insufficient to effectively identify and repair central porosity and central crack defects in continuously cast square and round billets, leading to the intrusion of oxidizing gases during rolling, forming oxide bands and microcrack networks, resulting in substandard product performance and economic losses.
By identifying defects in the cast billet through an online detection system, and using an end-face impact device to weld exposed porosity and cracks, combined with a weak oxidizing atmosphere heating and a large reduction rolling process, the defects can be protected and repaired in real time.
It significantly improves the rolling yield of billets with medium to low defects, reduces production losses, and achieves refined processing of billets of different grades and optimized balance of energy, roll consumption, and time costs.
Smart Images
Figure CN121571471A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of continuous casting technology for square and round billets, and more specifically, to a method for quality control of continuously cast square and round billets and rolled products. Background Technology
[0002] Continuous casting is a core process in modern steel production, and the internal quality of the continuously cast billets directly determines the performance, yield, and quality of the final rolled steel. During the continuous casting of square and round billets (including square, rectangular, and round billets), central porosity and central cracks are the most common and extremely harmful internal defects due to factors such as solidification characteristics, process fluctuations, and equipment conditions.
[0003] The essence of central porosity is that during the final stage of solidification of the cast billet, the solidification shrinkage of the remaining molten steel in the core is hindered by the well-developed columnar crystals that have solidified earlier (often forming a "bridging" phenomenon), leading to untimely feeding and the formation of tiny holes or voids. Central cracks, on the other hand, occur in the solidified mushy region (solidity approximately 0.7-0.9), caused by thermal stress, mechanical stress (such as roll misalignment, tensile forces), or both, exceeding the high-temperature strength of the steel at that temperature, resulting in internal cracking. These defects disrupt the continuity of the metal matrix.
[0004] More seriously, these existing internal defects become rapid channels for oxidizing gases (such as O2 and H2O) to diffuse into the billet within the heating furnace during subsequent rolling processes. These oxidizing gases penetrate the defects, forming oxide bands and microcrack networks extending along the rolling direction. Unlike the metal matrix, these oxides cannot undergo plastic deformation and welding during subsequent rolling; as brittle inclusions, they severely hinder defect closure and can even lead to rolling cracks, ultimately resulting in substandard product performance, failure to pass ultrasonic testing, or direct scrapping, causing significant economic losses to the company.
[0005] Currently, industry research and practice largely focus on addressing the root causes of defects in the continuous casting process, such as optimizing steel superheat, adjusting secondary cooling regimes, and employing end-solidation light reduction technology. The aim is to reduce or eliminate defects at their source. However, in actual production, due to fluctuations in equipment condition, changes in production rhythm, and frequent steel grade switching, completely eliminating central defects is extremely difficult. A certain proportion of continuously cast billets will inevitably carry varying degrees of internal defects into the rolling mill process. Summary of the Invention
[0006] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a method for quality control of continuously cast square and round billets and rolled products. The technical problem to be solved by the present invention is: how to systematically identify, protect, and repair square and round billets with central porosity and central crack defects produced by continuous casting online, so as to effectively suppress the oxidation and deterioration of defects during the heating process, and use rolling deformation to achieve the welding of internal defects, thereby significantly improving the rolling yield of billets with medium and lower defects and reducing production losses.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for quality control of continuously cast square and round billets and rolled products, comprising the following steps:
[0008] S1. Establish and operate a billet quality assessment and prediction system:
[0009] In the casting flow area and the post-cutting area of the continuous casting machine, online detection devices are integrated to monitor the temperature and surface quality of the billet in real time. Combined with the continuous casting process control system, data tracking and comprehensive analysis are performed to identify and mark abnormal billets suspected of having internal defects in real time.
[0010] S2. Online processing of identified abnormal billets:
[0011] For the billet that is determined to be abnormal in step S1 and is planned to be sent to the rolling mill, during its hot conveying process, its cut end face is impacted in the roller conveyor area to mechanically weld the exposed central looseness and cracks on the end face in real time, forming a dense surface layer to block the path of oxidizing gas from the end face to enter during subsequent heating.
[0012] S3. Implement comprehensive hierarchical control of the rolling process:
[0013] After the billet enters the rolling area, it is first quickly inspected and classified according to the severity of internal defects. Then, for the defective billets of different grades (e.g., Grade A: slight; Grade B: moderate), the corresponding optimized rolling process is implemented to suppress oxidation and promote welding. The optimized rolling process includes at least weak oxidizing atmosphere heating control and large reduction billet opening system.
[0014] In a preferred embodiment, step S1 specifically includes:
[0015] S11. Online temperature monitoring of billet: A non-contact online temperature measuring device is installed above the casting flow at the end of the straightening machine of the continuous casting machine to monitor the surface temperature of the billet in real time; the actual temperature monitored in real time is compared with the theoretical temperature calculated based on the continuous casting solidification model. If the actual temperature exceeds the preset threshold of the theoretical temperature range, the system will immediately alarm and mark the corresponding section of billet produced in that period as a suspected billet with abnormal temperature.
[0016] S12. Billet Tracking and Positioning: Using the manufacturing execution system or intelligent secondary system in the continuous casting workshop, the suspected billet with abnormal temperature is tracked and precisely positioned throughout the process, and its cutting length position and billet number information are recorded to provide a data basis for subsequent processing.
[0017] S13. Visual monitoring of billet surface quality: A visual monitoring device is set up in the hot billet conveying roller area after the billet cutting equipment to collect and analyze images of the billet surface (especially the cut end face and edge area); the image recognition algorithm is used to detect whether there are obvious surface cracks, depressions or abnormal morphology, further screen and confirm the problematic billets, and integrate the detection results with the information of S11 and S12 to comprehensively determine the final list of problematic billets.
[0018] In a preferred embodiment, step S2 specifically includes:
[0019] S21. Optimize the fixed-length cutting strategy: In the continuous casting process, for steel grades or production conditions that may produce central defects, under the conditions allowed by the process and equipment, appropriately increase the fixed-length cutting of the billet, thereby reducing the number of cut end faces per unit weight of billet and reducing oxidation-sensitive areas from the source.
[0020] S22, Impact Welding Treatment of Cast Billet End Face: On the hot conveyor roller of the cast billet, downstream of the visual monitoring device, an impact device for the end face of the cast billet is set up; when a cast billet that is determined by S1 to need to be treated is transported to this point, it is fixed by a clamping mechanism, and then the impactor is driven to perform a rapid, local impact on the head and / or tail cutting end face of the cast billet with a set energy and frequency; the impact causes the surface metal of the end face to undergo severe plastic deformation, pressing and welding the exposed central loose pores and microcracks together to form a dense metal layer with controllable thickness, sealing the entrance to the internal defects.
[0021] Furthermore, the impact energy, impact frequency, and action time parameters of the impact device can be adaptively calculated and set based on the high-temperature mechanical properties of the steel grade of the billet being processed, the real-time temperature of the billet (which can be provided by the temperature measurement data of S11 or by adding a nearby temperature measurement point), and the estimated level of defects.
[0022] In a preferred embodiment, step S3 specifically includes:
[0023] S31. Rapid classification and management of defective cast billets:
[0024] For defective billets entering the rolling mill, rapid offline or online sampling analysis based on low-magnification acid leaching or sulfur printing is employed. The severity of central porosity and central cracks is quantitatively assessed according to national standards or company internal control standards, and then classified accordingly.
[0025] Grade A (minor defects): The central porosity and crack level are lower than 1.0, and the defects are small and scattered dots; the handling strategy is to roll according to the normal process, but the optimized processes S32 and S33 below need to be implemented.
[0026] Grade B (Medium Defect): Defect level between 1.0 and 3.0, with continuous or discontinuous central dark lines visible on low magnification specimens; the handling strategy is conditional acceptance, and the special rolling procedures S32 and S33 below must be performed, and the final product usually needs to be downgraded for use in standards or applications with lower quality requirements.
[0027] Grade C (Severe Defect): The defect level is higher than 3.0, with obvious macroscopic holes, cracks or severe central segregation bands; the handling strategy is to scrap it directly and return it to the steelmaking process to prevent it from entering the rolling line.
[0028] S32. Optimization and control of heating furnace process:
[0029] When heating Grade A and Grade B billets, the following core control strategies are implemented to suppress oxidation:
[0030] 1) Furnace atmosphere control: The atmosphere in the heating furnace (especially the soaking zone) is adjusted from the traditional strong oxidizing atmosphere to a weak oxidizing atmosphere or even a near-neutral atmosphere; by precisely adjusting the air-fuel ratio and implementing a fuel-rich combustion mode, the residual oxygen content in the furnace is strictly controlled below 2.0% (volume fraction), with the optimal control between 0.5% and 1.5%; this can significantly reduce the partial pressure of oxidizing gases such as O2 and H2O, and greatly weaken the driving force for their diffusion towards the center through the surface of the billet and internal defect channels;
[0031] 2) Low-temperature rapid heating strategy: Under the premise of ensuring that the core temperature of the billet reaches the minimum temperature required for rolling (i.e., fully heated), a lower homogenization temperature within the process allowable range is adopted (for example, the lower limit temperature of the heating process specification for this steel grade), and the residence time of the billet in the high-temperature homogenization section is shortened as much as possible to achieve rapid tapping; this strategy aims to meet the rolling plasticity requirements while minimizing the overall oxidation loss of the billet, especially reducing the oxidation and deepening of internal defects caused by long-term high-temperature heating;
[0032] S33. Rolling procedure optimization and active defect welding:
[0033] During the rolling stage, specific deformation regimes are implemented for Grade A and Grade B billets to achieve the welding of internal defects:
[0034] 1) High reduction billet opening regime: In the first pass of the billet opening mill or the first stand of the roughing mill, a high single-pass reduction rate of not less than 25% should be applied to the billet; for common square and round billet specifications, the absolute value of the single-pass reduction is usually not less than 50mm; the huge single-pass deformation can put the core area of the billet in a state of strong triaxial compressive stress at high temperature, which is the most favorable condition for closing cavities and welding microcracks; in order to ensure that the deformation fully penetrates to the core, it is recommended to maintain a large pass reduction rate (e.g., not less than 15-20%) in the first 3 to 5 rolling passes.
[0035] 2) Rolling temperature assurance: Throughout the roughing stage, especially in the passes with large reduction, it is necessary to ensure that the core temperature of the billet is always in the austenitic single-phase region, that is, higher than the Ar3 phase transformation point of the steel grade; avoid drastic deformation below the Ar3 point or in the two-phase region to prevent the original defects from being torn apart, expanded, or even induced new cracks due to the sharp decrease in the plasticity and toughness of the core material.
[0036] The technical effects and advantages of this invention are as follows:
[0037] 1. This invention organically integrates three originally relatively independent links: online detection at the end of the continuous casting process, real-time physical treatment at the beginning of the rolling process, and process optimization of the rolling process itself, forming a complete quality control chain from defect identification to real-time protection to graded repair. This method does not solve the problem at a single point in isolation, but systematically addresses the quality risks of the entire process from billet production to finished product warehousing. It has a rigorous control logic and strong operability.
[0038] 2. This invention uses online end-face impact welding to proactively seal the most easily oxidized wounds (cut end faces) of the defective billet before it enters the high-temperature heating furnace. This is equivalent to putting a protective coat on the internal defects of the billet, fundamentally cutting off the main channel for the rapid intrusion of oxidizing gases from the end face, minimizing the risk of the defects deteriorating during the heating process, and creating the basic conditions for subsequent rolling repair.
[0039] 3. This invention proposes a graded judgment and management strategy based on the severity of defects, enabling refined and differentiated processing of problematic billets; avoiding the loss of yield caused by indiscriminate rejection, and preventing more serious quality accidents and energy waste caused by misjudging severely defective billets as repairable billets and allowing them to flow into the next process; by implementing different process routes for different grades of billets, the optimal balance between energy, roll consumption, time cost and quality objectives is achieved.
[0040] 4. This invention utilizes a combination of heating in a weak oxidizing atmosphere and rolling process with large reduction in billet size to form a combined process for repairing internal defects. The weak oxidizing atmosphere inhibits the further deterioration of defects from an environmental perspective. Meanwhile, the large reduction deformation at high temperature provides the necessary stress, strain, and temperature conditions for the welding of defects from a mechanical perspective, enabling billets that may be downgraded or scrapped to produce qualified products or products that are downgraded for use. This directly and significantly improves the overall yield and results in outstanding economic benefits.
[0041] 5. The quality judgment and prediction system of this invention integrates online temperature measurement, visual inspection and process tracking. The impact treatment device can adaptively adjust parameters according to steel type and temperature. The entire process relies on data-driven and automatic control, which reduces human interference, improves judgment accuracy and processing consistency, and is conducive to deployment and implementation in modern smart factories. Attached Figure Description
[0042] Figure 1 This is a flowchart illustrating the overall process flow of the present invention.
[0043] Figure 2 This is a schematic diagram of the main process of the present invention.
[0044] The attached figures are labeled as follows: 201 Online temperature measurement device for billet, 202 Visual monitoring device for billet quality, 203 End face impact device for billet, 204 Billet, and 205 Hot conveying roller conveyor. Detailed Implementation
[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0046] Example 1:
[0047] This embodiment takes a medium-sized steel production line equipped with an arc-shaped continuous casting machine and a fully continuous bar rolling mill as the application scenario, and produces square billets with a cross section of 200mm×200mm, and the steel grade is high-quality carbon structural steel.
[0048] This invention provides, for example Figure 1-2 The method for quality control of continuously cast square and round billets and rolled products, as shown, includes the following steps:
[0049] S1. Establish and operate a billet quality assessment and prediction system.
[0050] An infrared thermometer is installed above the outlet of the last straightener of the continuous casting machine as an online temperature measurement device 201 for the billet, which measures the surface temperature of the billet in real time at a frequency of 10Hz. The temperature data is transmitted to the process control computer in real time and compared with the theoretical surface temperature at that location calculated based on the solidification heat transfer model. The system is set to an alarm threshold of 30°C lower than the theoretical lower limit or 50°C higher than the theoretical upper limit for 5 consecutive seconds when the actual temperature is lower than the theoretical lower limit. Once the alarm is triggered, the casting flow length range (calculated based on the casting speed) corresponding to the alarm period is marked.
[0051] At the same time, the MES (Manufacturing Execution System) in the continuous casting workshop receives the alarm signal and starts tracking the section of the billet; when the billet moves to the flame cutting machine, the MES system transmits the marking information to the cutting control system.
[0052] After the billet is cut into 12-meter lengths, it is conveyed along the hot conveyor roller 205. About 15 meters above the roller 205, a visual monitoring device 202 consisting of a linear CCD camera and a high-brightness linear light source is installed to perform high-speed scanning imaging on the four sides and two end faces of the billet. The image processing unit executes a defect recognition algorithm, focusing on detecting whether there are features such as central dark areas and radial cracks on the end faces. The judgment result of the vision system is fused with the temperature anomaly marking information from the MES. If one or both of them confirm an anomaly, the billet 204 is finally determined to be a problematic billet, and its information (bill number, location) is recorded and transmitted to the subsequent process.
[0053] S2. Online processing of identified abnormal billets.
[0054] For billets that are determined to be defective, after they continue to be conveyed along the roller conveyor 205, they arrive at the end face impact treatment station; here is a billet end face impact device 203, which mainly includes a hydraulically driven clamping arm and a high-frequency hydraulic impact hammer.
[0055] Once the target 204 billet is in place, the clamping arm securely clamps it on the roller conveyor, ensuring its end face is directly facing the impact hammer head. The impact hammer automatically calculates the required impact energy and number of impacts (e.g., 15kJ per impact, 3 consecutive impacts) based on the high-temperature yield strength model of the steel grade (e.g., 45 steel) at the current billet surface temperature (approximately 800°C) and the preset desired end face compaction depth (e.g., 5mm). The impact hammer then impacts the head and tail ends of the billet sequentially using the calculated parameters. After impact, the end face visibly becomes smoother and denser, and any previously present micro-cracks are compacted and welded together.
[0056] S3. Implement comprehensive hierarchical control of the rolling process.
[0057] After end-face treatment, the billets are sent to the billet warehouse of the steel rolling workshop. When entering the warehouse or before loading, representative billets are randomly selected from each heat of steel or each batch for rapid sulfur mark inspection. Based on the width, density and continuity of the central sulfur segregation zone on the sulfur mark, the billets are classified into three levels: A, B and C, according to the billet center defect rating.
[0058] Suppose a cast billet is rated as Grade B (medium defect), and its sulfur mark shows a discontinuous dark line in the center with a width of about 2 mm;
[0059] The billet was assigned to a special rolling downgrade application path;
[0060] S32 heating stage:
[0061] The B-grade billet was loaded into a walking beam furnace; the heating regime was adjusted.
[0062] 1) Atmosphere control: The operator lowers the air-fuel ratio setting of the heating furnace soaking section from the normal 1.05 to 0.95 (rich fuel state); by increasing the gas flow rate and reducing the combustion air flow rate, the residual oxygen content in the furnace is reduced from the usual 3%-5% to about 1.2% (confirmed by online monitoring with a zirconia oxygen probe).
[0063] 2) Temperature and time control: The conventional soaking temperature for this steel grade is 1200℃; for this B grade billet, low-temperature rapid firing is performed, and the soaking temperature is set at 1180℃ (the lower limit of the process), which shortens the total furnace time by 10 minutes compared to the normal process.
[0064] S33 rolling stage:
[0065] After the billet exits the furnace, it enters a φ650 billet mill for rolling;
[0066] 1) Large reduction in billet opening: The operator confirms the reduction procedure for the first pass; the original thickness of the billet is 200mm, the target thickness for the first pass is set at 145mm, the single-pass reduction is 55mm, and the reduction rate reaches 27.5%, meeting the requirement of not less than 25%; the huge reduction causes the core of the billet to bear strong triaxial compressive stress at high temperature; the first five passes of the billet opening machine maintain a large reduction rate (27.5%, 22%, 18%, 16%, 15% respectively) to ensure that the deformation penetrates fully and promotes the welding of the central defects;
[0067] 2) Temperature assurance: The temperature measuring instrument equipped on the rolling line detected that the core temperature of the billet at the billet mill exit (calculated from the surface temperature and model) was 1050℃, which is much higher than the Ar3 point of 45 steel (about 780℃), meeting the requirements of high temperature and large deformation.
[0068] After the aforementioned special rolling process, the Grade B billet was rolled into φ60mm round bars. Subsequent metallographic and low-magnification acid leaching tests revealed that the original central area defect traces had largely disappeared and the structure was dense. This batch of round bars was ultimately downgraded for manufacturing products with relatively lower requirements for central porosity, successfully saving billets that might have been scrapped and achieving value enhancement.
[0069] Example 2:
[0070] This example illustrates the treatment of Class A minor defective cast billets;
[0071] Suppose a cast billet is determined to be Grade A (minor defect) by sulfur stamp inspection, with only a few scattered punctate loose spots in the center;
[0072] The billet enters the normal optimized rolling process path; its heating and rolling are carried out according to the normal production plan, but the optimization concept of this invention is also incorporated:
[0073] Heating stage: The atmosphere inside the furnace is still optimized and controlled to keep the residual oxygen content below 1.5% (forming a weakly oxidizing atmosphere zone inside the furnace); although its defects are minor, preventing oxidation is always beneficial;
[0074] Rolling stage: In the first pass of the billet mill, although the 27.5% ultra-high reduction rate is not mandatory, a large reduction is still performed, for example, from 200mm to 160mm (20% reduction rate); combined with an optimized heating atmosphere, it can be ensured that these tiny point-like porosities are completely welded together during the rolling process (defects are welded into a dense structure under the stress applied by the rolls).
[0075] Ultimately, the products produced from this batch of Grade A billets can achieve the optimal internal quality level and are used for high-end applications;
[0076] For C-grade severely defective billets, they are promptly rejected and returned to the furnace to avoid occupying rolling resources and causing potential quality accidents.
[0077] The working principle of this invention is:
[0078] Through the synergistic action of online detection, end-face sealing, and graded rolling, a mechanism for monitoring, isolating, and repairing internal defects in continuously cast billets is formed. The quality judgment and prediction system is responsible for accurately identifying the target. End-face impact treatment provides immediate physical isolation at the defect exposure point to prevent oxidation from deepening. The comprehensive control of grading, weak oxygen heating, and high-reduction rolling in the rolling process implements the most suitable process parameters according to different defect levels, suppressing oxidation while actively welding defects using the plastic deformation capacity of the material. The three links are interlocked and indispensable, jointly achieving efficient and high-quality rescue of defective billets.
[0079] For these existing and unavoidable defective billets, an effective set of detection, judgment, treatment and control methods should be adopted in the steelmaking-rolling interface area and the rolling process itself to prevent the defects from worsening during heating and to repair them as much as possible through the rolling process, thereby saving this part of the billet and improving the overall yield.
[0080] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.
[0081] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.
[0082] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for quality control of continuously cast square and round billets and rolled products, characterized in that: Includes the following steps: S1. Establish and operate a billet quality judgment and prediction system: integrate online detection and tracking devices in the continuous casting area to identify and mark abnormal billets suspected of having central porosity or central cracks in real time (204). S2. Online processing of identified abnormal billets: During the hot conveying of billets (204), impact devices (203) are used to impact the cut end face of the billets in the roller conveyor (205) area to weld the exposed defects and block the oxidation channel. S3. Implement comprehensive graded control of the rolling process: classify the defects of the billets entering the rolling area, and implement corresponding optimized rolling processes for different grades. The optimized rolling processes include at least weak oxidizing atmosphere heating control and large reduction billet opening system.
2. The method for quality control of continuously cast square and round billets and rolled products according to claim 1, characterized in that: Step S1 specifically includes: S11. The surface temperature of the billet is monitored by an online temperature measuring device (201) set above the casting flow and compared with the theoretical temperature. If the temperature exceeds the limit, an alarm is triggered and a mark is made. S12. Use the process control system to track and position the marked billet throughout the entire process; S13. The surface of the billet is image-detected by a visual monitoring device (202) installed on the roller conveyor after cutting, and the problem billet is determined by combining temperature, tracking and visual information.
3. The method for quality control of continuously cast square and round billets and rolled products according to claim 2, characterized in that: The impact treatment in step S2 is as follows: the billet (204) is fixed by a clamping mechanism, and the impactor applies a rapid impact to the head and / or tail end face of the billet, so that the surface metal of the end face is plastically deformed and the central porosity and cracks on the cut end face of the continuous casting billet are welded together; the impact parameters of the impact device (203) can be adaptively set according to the billet steel grade, real-time temperature and defect prediction.
4. The method for quality control of continuously cast square and round billets and rolled products according to claim 1, characterized in that: The defect classification in step S3 is as follows: based on the results of low-magnification acid immersion or sulfur printing inspection, the central defects are classified according to their severity as follows: Grade A: Defect level is lower than 1.0; Grade B: Defect level between 1.0 and 3.0; Grade C: Defect level higher than 3.0; Among them, Grade A and Grade B billets are put into the optimized rolling process, while Grade C billets are scrapped and returned to the furnace.
5. The method for quality control of continuously cast square and round billets and rolled products according to claim 4, characterized in that: The weak oxidizing atmosphere heating control refers to adjusting the air-fuel ratio of the heating furnace to a fuel-rich state and controlling the residual oxygen content in the homogenization zone of the furnace to below 2.0%.
6. The method for quality control of continuously cast square and round billets and rolled products according to claim 5, characterized in that: The weak oxidizing atmosphere heating control also includes a low-temperature rapid firing strategy: under the premise of ensuring that the core of the billet is thoroughly fired, the homogenization temperature at the lower limit of the process is adopted and the furnace time is shortened.
7. The method for quality control of continuously cast square and round billets and rolled products according to claim 1, characterized in that: The large reduction billet opening system refers to the implementation of a single-pass reduction rate of not less than 25% on the billet in the first pass of the billet opening machine or the first roughing mill.
8. The method for quality control of continuously cast square and round billets and rolled products according to claim 7, characterized in that: The large reduction billet opening process requires that the first 3-5 rolling passes maintain a large reduction rate to ensure that the deformation fully penetrates into the core of the billet; and when implementing large reduction deformation, it is necessary to ensure that the temperature of the core of the billet is in the austenitic single-phase region, which is higher than the Ar3 phase transformation point of the steel grade.